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DANA'S 
SERIES  OF  MINERALOGIES 

System  of  Mineralogy 

Sixth  edition,  entirely  rewritten.  With  Appendices  I  and  II, 
completing  the  work  to  1909.  1333  pages,  6f  by  10,  over 
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Third  Appendix  to  the  Sixth  Edition  of  Dana's 
System  of  Mineralogy 

Completing  the  Work  to  1915.  By  William  E.  Ford,  Pro- 
fessor of  Mineralogy,  Sheffield  Scientific  School  of  Yale 
University,  87  pages,  6f  by  10 Cloth,  net  $2.00 

A  Text-book  of  Mineralogy 

With  an  extended  Treatise  on  Crystallography  and  Physical 
Mineralogy.  By  Edward  Salisbury  Dana,  Professor  of 
Physics  and  Curator  of  Mineralogy,  Yale  University.  New 
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(1922).  720  pages,  6  by  9,  nearly  1000  figures .  Cloth,  net  $5.00 

Minerals,  and  How  to  Study  Them 

A  book  for  beginners  in  Mineralogy.  By  Prof.  E.  S.  Dana. 
380  pages,  319  figures. Cloth,  net  $2.00 


BY  DANA  AND  FORD 
Manual  of  Mineralogy 

For  the  Student  of  Elementary  Mineralogy,  the  Mining 
Engineer,  the  Geologist,  the  Prospector,  the  Collector,  etc. 
Thirteenth  edition,  entirely  revised  and  rewritten,  by  Wil- 
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A  TEXT-BOOK 

OF 


MINERALOGY 

WITH  AN  EXTENDED  TREATISE  ON 

CRYSTALLOGRAPHY  AND  PHYSICAL  MINERALOGY 


BY 

EDWARD   SALISBURY  DANA 

ft 

Professor  Emeritus  of  Physics  and  Curator  of  Mineralogy 
Yale  University 


THIRD  EDITION,  REVISED  AND  ENLARGED 


BY 

WILLIAM   E.   FORD 

Professor  of  Mineralogy,  Sheffield  Scientific  School  of 
Yale  University 


TOTAL   ISSUE,    TWENTY-SEVEN   THOUSAND 


NEW  YORK 

JOHN  WILEY  &   SONS,   INC. 

LONDON:   CHAPMAN  &  HALL,   LIMITED 

1922 


COPYRIGHT,  1898 

BY 
EDWARD  S.  DANA. 


COPYRIGHT,  1922 

BY 
EDWARD  S.  DANA 

AND 

WILLIAM  E.  FORD. 


TECHNICAL  COMPOSITION  CO. 
CAMBRIDGE,    MASS.,    U.   S.  A. 


EARTH 

SCIENCES 

LIBRARY 


PREFACE  TO  THE  THIRD  EDITION 


The  first  edition  of  this  book  appeared  in  1877  and  approximately  twenty 
years  later  (1898)  the  second  and  revised  edition  was  published.  Now, 
again  after  more  than  twenty  years,  comes  the  third  edition.  The  changes 
involved  in  the  present  edition  are  chiefly  those  of  addition,  the  general 
character  and  form  of  the  book  having  been  retained  unchanged.  In  the 
section  on  Crystallography  the  important  change  consists  in  the  introduction 
of  the  methods  employed  in  the  use  of  the  stereographic  and  gnomonic  pro- 
jections. A  considerable  portion  of  the  section  on  the  Optical  Characters  of 
Minerals  has  been  rewritten  in  the  endeavor  to  make  this  portion  of  the  book 
simpler  and  more  readily  understood  by  the  student.  In  the  section  on 
Descriptive  Mineralogy  all  species  described  since  the  previous  edition  have 
been  briefly  mentioned  in  their  proper  places.  Numerous  other  changes  and 
corrections  have,  of  course,  been  made  in  order  to  embody  the  results  of 
mineral  investigation  during  the  last  two  decades.  Only  minor  changes  have 
been  made  in  the  order  of  classification  of  the  mineral  species.  It  was  felt 
that  as  this  book  is  so  closely  related  to  the  System  of  Mineralogy  it  was 
unwise  to  attempt  any  revision  of  the  chemical  classification  until  a  new 
edition  of  that  work  should  appear.  The  description  of  the  methods  of 
Crystal  Drawing  given  in  Appendix  A  has  been  largely  rewritten.  A  new 
table  has  been  added  to.  Appendix  B  in  which  the  minerals  have  been  grouped 
into  lists  according  to  their  important  basic  elements.  Throughout  the  book 
the  endeavor  has  been  to  present  in  a  clear  and  concise  way  all  the  information 
needed  by  the  elementary  and  advanced  student  of  the  science. 

The  editor  of  this  edition  is  indebted  especially  to  the  published  and  un- 
published writings  of  the  late  Professor  Samuel  L.  Penfield  for  much  ma- 
terial and  many  figures  that  have  been  used  in  the  sections  of  Crystallog- 
raphy and  The  Optical  Character  of  Minerals.  He  also  acknowledges  the 
cordial  support  and  constant  assistance  given  him  by  Professor  Edward  S. 
Dana. 

WILLIAM  E.  FORD 

NEW  HAVEN,  CONN.,  Dec.  1,  1921. 

469105 

m 


PREFACE  TO  THE  SECOND  EDITION 


THE  remarkable  advance  in  the  Science  of  Mineralogy,  during  the  years 
that  have  elapsed  since  this  Text-Book  was  first  issued  in  1877,  has  made  it 
necessary,  in  the  preparation  of  a  new  edition,  to  rewrite  the  whole  as  well  as 
to  add  much  new  matter  and  many  new  illustrations. 

The  work  being  designed  chiefly  to  meet  the  wants  of  class  or  private 
instruction,  this  object  has  at  once  determined  the  choice  of  topics  discussed, 
the  order  and  fullness  of  treatment  and  the  method  of  presentation. 

In  the  chapter  on  Crystallography,  the  different  types  of  crystal  forms  are 
described  under  the  now  accepted  thirty-two  groups  classed  according  to  their 
symmetry.  The  names  given  to  these  groups  are  based,  so  far  as  possible, 
upon  the  characteristic  form  of  each,  and  are  intended  also  to  suggest  the 
terms  formerly  applied  in  accordance  with  the  principles  of  hemihedrism. 
The  order  adopted  is  that  which  alone  seems  suited  to  the  demands  of  the 
elementary  student,  the  special  and  mathematically  simple  groups  of  the 
isometric  system  being  described  first.  Especial  prominence  is  given  to  the 
" normal  group"  under  the  successive  systems,  that  is,  to  the  group  which  is 
relatively  of  most  common  occurrence  and  which  shows  the  highest  degree  of 
symmetry.  The  methods  of  Miller  are  followed  as  regards  the  indices  of  the 
different  forms  and  the  mathematical  calculations. 

In  the  chapters  on  Physical  and  Chemical  Mineralogy,  the  plan  of  the 
former  edition  is  retained  of  presenting  somewhat  fully  the  elementary  prin- 
ciples of  the  science  upon  which  the  mineral  characters  depend;  this  is  par- 
ticularly true  in  the  department  of  Optics.  The  effort  has  been  made  to  give 
the  student  the  means  of  becoming  practically  familiar  with  all  the  modern 
methods  of  investigation  now  commonly  applied.  Especial  attention  is, 
therefore,  given  to  the  optical  properties  of  crystals  as  revealed  by  the  micro- 
scope. Further,  frequent  references  are  introduced  to  important  papers  on 
the  different  subjects  discussed,  in  order  to  direct  the  student's  attention  to 
the  original  literature. 

The  Descriptive  part  of  the  volume  is  essentially  an  abridgment  of  the 
Sixth  Edition  of  Dana's  System  of  Mineralogy,  prepared  by  the  author  (1892). 
To  this  work  (and  future  Appendices)  the  student  is,  therefore,  referred  for 
fuller  descriptions  of  the  crystallographic  and  optical  properties  of  species,  for 
analyses,  lists  of  localities,  etc.;  also  for  the  authorities  for  data  here  quoted. 
In  certain  directions,  however,  the  work  has  been  expanded  when  the  interests 


VI  PREFACE    TO    THE    SECOND    EDITION 

of  the  student  have  seemed  to  demand  it;  for  example,  in  the  statement  of 
the  characters  of  the  various  isomorphous  groups.  Attention  is  also  called  to 
the  paragraph  headed  "Diff.,"  in  the  description  of  each  common  species,  in 
which  are  given  the  distinguishing  characters,  particularly  those  which  serve 
to  separate  it  from  other  species  with  which  it  might  be  easily  confounded. 

The  list  of  American  localities  of  minerals,  which  appeared  as  an  Appendix 
in  the  earlier  edition,  has  been  omitted,  since  in  its  present  expanded  form 
it  requires  more  space  than  could  well  be  given  to  it;  further,  its  reproduc- 
tion here  is  unnecessary  since  it  is  accessible  to  all  interested  not  only  in  the 
System  of  Mineralogy  but  also  in  separate  form.  A  full  topical  Index  has 
been  added,  besides  the  usual  Index  of  Species. 

The  obligations  of  the  present  volume  to  well-known  works  of  other  au- 
thors —  particularly  to  those  of  Groth  and  Rosenbusch  —  are  too  obvious  to 
require  special  mention.  The  author  must,  however,  express  his  gratitude 
to  his  colleague,  Prof.  L.  V.  Pirsson,  who  has  given  him  material  aid  in  the 
part  of  the  work  dealing  with  the  optical  properties  of  minerals  as  examined 
under  the  microscope.  He  is  also  indebted  to  Prof.  S.  L.  Penfield  of  New 
Haven  and  to  Prof.  H.  A.  Miers  of  Oxford,  England,  for  various  valuable 
suggestions. 

EDWARD  SALISBURY  DANA 

NEW  HAVEN,  CONN.,  Aug.  1,  1898. 


TABLE  OF  CONTENTS 


PAGE 

INTRODUCTION 1 

PART  I.   CRYSTALLOGRAPHY 

GENERAL  MORPHOLOGICAL  RELATIONS  OF  CRYSTALS 7 

GENERAL  MATHEMATICAL  RELATIONS  OF  CRYSTALS 26 

I.   ISOMETRIC  SYSTEM 52 

1.  Normal  Class  (1).     Galena  Type , 52 

2.  Pyritohedral  Class  (2).     Pyrite  Type 63 

3.  Tetrahedral  Class  (3).     Tetrahedrite  Type 66 

4.  Plagiohedral  Class  (4).     Cuprite  Type 71 

5.  Tetartohedral  Class  (5).     Ullmannite  Type 72 

Mathematical  Relations  of  the  Isometric  System 72 

II.   TETRAGONAL   SYSTEM 77 

1.  Normal  Class  (6).     Zircon  Type 77 

2.  Hemimorphic  Class  (7).     lodosuccinimide  Type .  84 

3.  Pyramidal  Class  (8).     Scheelite  Type 85 

4.  Pyramidal-Hemimorphic  Class  (9).     Wulfenite  Type 86 

5.  Sphenoidal  Class  (10).     Chalcopyrite  Type 87 

6.  Trapezohedral  Class  (11).     Nickel  Sulphate  Type 89 

7.  Tetartohedral  Class  (12) 89 

Mathematical  Relations  of  the  Tetragonal  System 90 

III.  HEXAGONAL  SYSTEM 94 

A.  Hexagonal  Division 95 

1.  Normal  Class  (13).     Beryl  Type 95 

2.  Hemimorphic  Class  (14).     Zincite  Type 98 

3.  Pyramidal  Class  (15).     Apatite  Type 100 

4.  Pyramidal-Hemimorphic  Class  (16).     Nephelite  Type 101 

5.  Trapezohedral  Class  (17) 102 

B.  Trigonal  or  Rhombohedral  Division 103 

1.  Trigonal  Class  (18).     Benitoite  Type 103 

2.  Rhombohedral  Class  (19).     Calcite  Type. 104 

3.  Rhombohedral-Hemimorphic  Class  (20).     Tourmaline  Type 109 

4.  Trirhombohedral  Class  (21).     Phenacite  Type 110 

5.  Trapezohedral  Class  (22).     Quartz  Type 112 

6.  7.     Other  Classes  (23)  (24) 114 

Mathematical  Relations  of  the  Hexagonal  System 115 

IV.  ORTHORHOMBIC  SYSTEM • 121 

1.  Normal  Class  (25).     Barite  Type 121 

2.  Hemimorphic  Class  (26).     Calamine  Type 126 

3.  Sphenoidal  Class  (27).     Epsomite  Type 128 

Mathematical  Relations  of  the  Orthorhombic  System 128 

vii 


yiii  TABLE    OF    CONTENTS 

PAGE 

V.   MONOCLINIC  SYSTEM 133 

1.  Normal  Class  (28).     Gypsum  Type 133 

2.  Hemimorphic  Class  (29).     Tartaric  Acid  Type 138 

3.  Clinohedral  Class  (30).     Clinohedrite  Type '138 

Mathematical  Relations  of  the  Monoclinic  System 139 

VI.   TRICLINIC  SYSTEM 143 

1.  Normal  Class  (31).     Axinite  Type 144 

2.  Asymmetric  Class  (32).     Calcium  Thiosulphate  Type 147 

Mathematical  Relations  of  the  Triclinic  System 148 

MEASUREMENT  OP  THE  ANGLES  OF  CRYSTALS 152 

COMPOUND  OR  TWIN  CRYSTALS 160 

Examples  of  Important  Methods  of  Twinning 165 

Regular  Grouping  of  Crystals 172 

IRREGULARITIES  OF  CRYSTALS 174 

1.  Variations  in  the  Forms  and  Dimensions  of  Crystals 174 

2.  Imperfections  of  the  Surfaces  of  Crystals 176 

3.  Variations  in  the  Angles  of  Crystals 178 

4.  Internal  Imperfection  and  Inclusions 178 

CRYSTALLINE  AGGREGATES 182 

PART  II.     PHYSICAL   MINERALOGY 

PHYSICAL  CHARACTERS  OF  MINERALS • 185 

I.   Characters  depending  upon  Cohesion  and  Elasticity  186 

II.   Specific  Gravity,  or  Relative  Density ' 195 

III.  Characters  depending  upon  Light 200 

General  Principles  of  Optics 200 

Optical  Instruments  and  Methods 241 

General  Optical  Characters  of  Minerals .  .  / , 246 

1.  Diaphaneity - 247 

2.  Color 247 

3.  Luster 249 

Special  Optical  Characters  of  Minerals  belonging  to  the  different  Systems 251 

A.  Isometric  Crystals 252 

B.  Uniaxial  Crystals 253 

General  Optical  Relations 253 

Optical  Examination  of  Uniaxial  Crystals 259 

C.  Biaxial  Crystals 270 

General  Optical  Relations 270 

Optical  Examination  of  Biaxial  Crystals 278 

IV.  Characters  depending  upon  Heat 303 

V.    Characters  depending  upon  Electricity  and  Magnetism 306 

VI.   Taste  and  Odor 310 

PART  III.     CHEMICAL   MINERALOGY 

GENERAL  PRINCIPLES  OF  CHEMISTRY  AS  APPLIED  TO  MINERALS 311 

CHEMICAL  EXAMINATION  OF  MINERALS 327 

Examination  in  the  Wet  Way 328 

Examination  by  Means  of  the  Blowpipe 329 


TABLE    OF  CONTENTS  IX 
PART  IV.     DESCRIPTIVE   MINERALOGY 

PAGE 

NATIVE  ELEMENTS 344 

SULPHIDES,  SELENIDES,  TELLURIDES,  ETC 357 

SULPHO-SALTS 383 

CHLORIDES,  BROMIDES,  IODIDES,  FLUORIDES 394 

OXIDES 402 

CARBONATES 436 

SILICATES 454 

TlTANO-SlLICATES,    TlTANATES 583 

NIOBATES,  TANTALATES 587 

PHOSPHATES,  ARSENATES,  VANADATES,  ETC 592 

NITRATES 619 

BORATES 619 

URANATES ' 623 

SULPHATES,  CHROMATES,  ETC 624 

TUNGSTATES,  MoLYBDATES 641 

OXALATES,  MELLATES 644 

HYDROCARBON  COMPOUNDS 645 

APPENDIX  A. 

ON  THE  DRAWING  OF  CRYSTAL  FIGURES 649 

APPENDIX  B. 

TABLES  TO  BE  USED  IN  THE  DETERMINATION  OF  MINERALS 663 

GENERAL  INDEX 695 

INDEX  TO  SPECIES.  .  703 


INTRODUCTION 


1.  THE  SCIENCE  OF  MINERALOGY  treats  of  those  inorganic  species  called 
minerals,  which  together  in  rock  masses  or  in  isolated  form  make  up  the 
material  of  the  crust  of  the  earth,  and  of  other  bodies  in  the  universe  so  far 
as  it  is  possible  to  study  them  in  the  form  of  meteorites. 

2.  Definition  of  a  Mineral.  —  A  Mineral  is  a  body  produced  by  the  proc- 
esses of  inorganic  nature,  having  a  definite  chemical  composition  and,  if  formed 
under  favorable  conditions,  a  certain  characteristic  molecular  structure  which 
is  exhibited  in  its  crystalline  form  and  other  physical  properties. 

This  definition  calls  for  some  further  explanation. 

First  of  all,  a  mineral  must  be  a  homogeneous  substance,  even  when 
minutely  examined  by  the  microscope;  further,  it  must  have  a  definite 
chemical  composition,  capable  of  being  expressed  by  a  chemical  formula. 
Thus,  much  basalt  appears  to  be  homogeneous  to  the  eye,  but  when  examined 
under  the  microscope  in  thin  sections  it  is  seen  to  be  made  up  of  different 
substances,  each  having  characters  of  its  own.  Again,  obsicftan,  or  volcanic 
glass,  though  it  may  be  essentially  homogeneous,  has  not  a  definite  composition 
corresponding  to  a  specific  chemical  formula,  and  is  hence  classed  as  a  rock, 
not  as  a  mineral  species.  Further,  several  substances,  as  tachylyte,  hyalome- 
lane,  etc.,  which  at  one  time  passed  as  minerals,  have  been  relegated  to 
petrology,  because  it  has  been  shown  that  they  are  only  local  forms  of  basalt, 
retaining  an  apparently  homogeneous  form  due  to  rapid  cooling. 

Again,  a  mineral  has  in  all  cases  a  definite  molecular  structure,  unless  the 
conditions  of  formation  have  been  such  as  to  prevent  this,  which  is  rarely  true. 
This  molecular  structure,  as  will  be  shown  later,  manifests  itself  in  the  physical 
characters  and  especially  in  the  external  crystalline  form. 

It  is  customary,  as  a  matter  of  convenience,  to  limit  the  name  mineral  to 
those  compounds  which  have  been  formed  by  the  processes  of  nature  alone, 
while  compounds  made  in  the  laboratory  or  the  smelting-furnace  are  at  most 
called  artificial  minerals.  Further,  mineral  substances  which  have  been  pro- 
duced through  the  agency  of  organic  life  are  not  included  among  minerals, 
as  the  pearl  of  an  oyster,  the  opal-silica  (tabasheer)  secreted  by  the  bamboo, 
etc.  Finally,  mineral  species  are,  as  a  rule,  limited  to  solid  substances;  the 
only  liquids  included  being  metallic  mercury  and  water.  Petroleum,  or 
mineral  oil,  is  not  properly  a  homogeneous  substance,  consisting  rather  of 
several  hydrocarbon  compounds;  it  is  hence  not  a  mineral  species. 

It  is  obvious  from  the  above  that  minerals,  in  the  somewhat  restricted 
sense  usually  adopted,  constitute  only  a  part  of  what  is  often  called  the 
Mineral  Kingdom. 

3.  Scope  of  Mineralogy.  —  In  the  following  pages,  the  general  subject 
of  mineralogy  is  treated  under  the  following  heads : 

(1)  Crystallography.  —  This  comprises  a  discussion  of  crystals  in  general 
and  especially  of  the  crystalline  forms  of  mineral  species. 

1 


INTRODUCTION 


(2)  Physical  Mineralogy.  —  This  includes  a  discussion  of  the  physical 
characters  of  minerals,  that  is,  those  depending  upon  cohesion  and  elasticity, 
density,  light,  heat,  electricity,  and  so  on. 

(3)  Chemical  Mineralogy.  —  Under  this  head  are  presented  briefly  the 
general  principles  of  chemistry  as  applied  to  mineral  species;    their  charac- 
ters as  chemical  compounds  are  described,  also  the  methods  of  investigating 
them  from  the  chemical  side  by  the  blowpipe  and  other  means. 

(4)  Descriptive  Mineralogy.  —  This  includes  the  classification  of  minerals 
and  the  description  of  each  species  with  its  varieties,  especially  in  its  relations 
to  closely  allied  species,  as  regards  crystalline  form,  physical  and  chemical 
characters,  occurrence  in  nature,  and  other  points. 

4.  Literature.  —  Reference  is  made  to  the  Introduction  to  the  Sixth 
Edition  of  Dana's  System  of  Mineralogy,  pp.  xlv-lxi,  for  an  extended  list  of 
independent  works  on  Mineralogy  up  to  1892  and  to  its  Appendices  I,  II 
and  III  for  works  published  up  to  1915;  the  names  are  also  given  of  the 
many  scientific  periodicals  which  contain  original  memoirs  on  mineralogical 
subjects.  For  the  convenience  of  the  student  the  titles  of  a  few  works, 
mostly  of  a  general  character,  are  given  here.  Further  references  to  the 
literature  of  Mineralogy  are  introduced  through  the  first  half  of  this  work, 
particularly  at  the  end  of  the  sections  dealing  with  special  subjects. 

Crystallography  and  Physical  Mineralogy 

EARLY  WORKS  *  include  those  of  Rome  de  Flsle,  1772;  Haiiy,  1822;  Neumann,  Krys- 
tallonomie,  1823,  and  Krystallographie,  1825;  Kupffer,  1825;  Grassmann,  Krystallonomie, 
1829;  Naumann,  1829  and  later;  Quenstedt,  1846  (also  1873);  Miller,  1839  and  1863; 
Grailich,  1856;  Kopp,  1862;  von  Lang,  1866;  Bravais,  Etudes  Crist.,  Paris,  1866  (1849); 
Schrauf,  1866-68;  Rose-Sadebeck,  1873. 

RECENT  WORKS  include  the  following: 

Bayley.     Elementary  Crystallography,  1910. 

Beale.     Introduction  to  Crystallography,  1915. 

Beckenkamp.     Statische  und  kinetische  Kristalltheorien,  1913-. 

Bruhns.     Elemente  der  Krystallographie,  1902. 

Goldschmidt.  Index  der  Krystallformen  der  Mineralien;  3  vols.,  1886-91.  Also 
Anwendung  der  Linearprojection  zum  Berechnen  der  Krystalle,  1887.  Atlas  der  Krystall- 
formen, 1913-. 

Gossner.     Kristallberechnung  Und  Kristallzeichnung,  1914. 

Groth.  Physikalische  Krystallographie  und  Einleitung  in  die  krystallographische 
Kenntniss  der  wichtigeren  Substanzen,  1905. 

Klein.     Einleitung  in  die  Krystallberechnung,  1876 

Lewis.     Crystallography,  1899. 

Liebisch.  Geometrische  Krystallographie,  1881.  Physikalische  Krystallographie, 
1891. 

Mallard.  Traite  de  Cristallographie  geometrique  et  physique;  vol.  1,  1879;  vol.  2, 
1884. 

Moses.     Characters  of  Crystals,  1899. 

Reeks.     Hints  for  Crystal  Drawing,  1908. 

Sadebeck.     Angewandte  Krystallographie  (Rose's  Krystallographie,  II.  Band),  1876. 

Sohncke.     Entwickelung  einer  Theorie  der  Krystallstruktur,  1879. 

Sommerfeldt.     Physikalische  Kristallographie,  1907;  Die  Kristallgruppe,  1911. 

Story-Maskelyne.     Crystallography:  the  Morphology  of  Crystals,  1895. 

Tutton.  Crystalline  Structure  and  Chemical  Constitution,  1910;  Crystallography  and 
Practical  Crystal  Measurement,  1911. 

Viola.     Grundziige  der  Kristallographie,  1904. 

Walker.     Crystallography,  1914. 

*  The  full  titles  of  many  of  these  are  given  in  pp.  li-lxi  of  Dana's  System  of  Miner- 
alogy, 1892. 


INTRODUCTION  3 

Wallerant.     Cristallographie,  1909. 

Websky.  Anwendung  der  Linearprojection  zum  Berechnen  der  Krystalle  (Rose's 
Krystallographie  III.  Band),  1887. 

Williams.     Elements  of  Crystallography,  1890. 

Wulfing.  Die  32  krystallographischen  Symmetrieklassen  und  ihre  einfachen  Formen, 
1914. 

In  PHYSICAL  MINERALOGY  the  most  important  general  works  are  those  of  Schrauf 
(1868),  Mallard  (1884),  Liebisch  (1891),  mentioned  -in  the  above  list;  also  Rosenbusch, 
Mikr.  Physiographic,  etc.  (1892).  Important  later  works  include  the  following. 

Davy-Farnham.     Microscopic  Examination  of  the  Ore  Minerals,  1920. 

Duparc  and  Pearce.     Traite  de  Technique  Mineralogique  et  Petrographique,  1907. 

Groth.     Physikalische  Krystallographie,  1905. 

Groth-  Jackson.     Optical  Properties  of  Crystals,  1910. 

Johannsen.  Determination  of  Rock-Forming  Minerals,  1908.  Manual  of  Petrographic 
Methods,  1914. 

Murdoch.     Microscopical  Determination  of  the  Opaque  Minerals,  1916. 

Nikitin,  translated  into  French  by  Duparc  and  de  Dervies.  La  Methode  Universelle 
de  Fedoroff,  1914. 

Winchell.     Elements  of  Optical  Mineralogy,  1909. 

Wright.     The  Methods  of  Petrographic-Microscopic  Research,  1911. 

General  Mineralogy 

Of  the  many  works,  a  knowledge  of  which  is  needed  by  one  who  wishes  a  full  acquaint- 
ance with  the  historical  development  of  Mineralogy,  the  following  are  particularly  im- 
portant. Very  early  works  include  those  of  Theophrastus,  Pliny,  Linnaeus,  Wallerius, 
Cronstedt,  Werner,  Bergmann,  Klaproth. 

Within  the  nineteenth  century:  Hauy's  Treatise,  1801,  1822;  Jameson,  1816,  1820; 
Werner's  Letztes  Mineral-System,  1817;  Cleaveland's  Mineralogy,  1816,  1822;  Leonhard's 
Handbuch,  1821,  1826;  Mohs's  Min.,  1822;  Haidinger's  translation  of  Mohs,  1824;  Breit- 
haupt's  Charakteristik,  1820,  1823,  1832;  Beudant's  Treatise,  1824,  1832;  Phillips's  Min., 
1823,  1837;  Shepard's  Min.,  1832-35,  and  later  editions;  yon  Kobell's  Grundzuge,  1838; 
Mohs's  Min.,  1839;  Breithaupt's  Min.,  1836-1847;  Haidinger's  Handbuch,  1845;  Nau- 
mann's  Min.,  1846  and  later;  Hausmann's  Handbuch,  1847;  Dufrenoy's  Min.,  1844-1847 
(also  1856-1859);  Brooke  &  Miller,  1852;  J.  D.  Dana's  System  of  1837,  1844,  1850,  1854,. 
1868. 

More  RECENT  WORKS  are  the  following: 

Bauer.     Lehrbuch  der  Mineralogie,  1904. 

Bauerman.     Text-Book  of  Descriptive  Mineralogy,  1884. 

Baumhauer.     Das  Reich  der  Krystalle,  1889. 

Bayley.     Descriptive  Mineralogy,  1917. 

Blum.     Lehrbuch  der  Mineralogie,  4th  ed.,  1873-1874. 

Brauns.     Das  Mineralreich,  1903.     English,  translation  by  Spencer,  1912. 

Clarke.     The  Data  of  Geochemistry,  1916. 

Dana,  E.  S.  Dana's  System  of  Mineralogy,  6th  ed.,  New  York,  1892.  Appendix  I, 
1899;  II,  1909;  III,  1915.  Also  (elementary)  Minerals  and  How  to  study  them,  New 
York,  1895. 

Dana-Ford.     Manual  of  Mineralogy,  1912. 

Des  Cloizeaux.  Manuel  de  Mineralogie;  vol.  1,  1862;  vol.  2,  ler  Fasc.,  1874;  2me. 
1893. 

Groth.     Tabellarische  Uebersicht  der  Mineralien,  1898. 

Hintze.     Handbuch  der  Mineralogie,  1889-1915. 

Iddings.     Rock  Minerals,  1906. 

Kraus.     Descriptive  Mineralogy,  1911. 

Lacroix.     Mineralogie  de  la  France  et  de  ses  Colonies,  5  vols.,  1893-1913. 

Miers.     Mineralogy,  1902. 

Moses  and  Parsons.     Mineralogy,  Crystallography  and  Blowpipe  Analysis,  1916. 

Merrill.     The  Non-metallic  Minerals,  1904. 

Phillios.     Mineralogv,  1912. 

Rogers.     Study  of  Minerals,  1912. 

Schrauf.     Atlas  der  Krystall-Formen  des  Mineralreiches,  4to,  vol.  1,  A-C,  1865-1877. 

Tschermak.     Lehrbuch  der  Mineralogie,  1884;  5th  cd.,  1897. 


4  INTRODUCTION 

Weisbach.     Synopsis  Mineralogica,  systematische  Uebersicht  des  Mineralfeiches,  1875. 
Zirkel.     13th  edition  of  Naumann's  Mineralogy,  Leipzig,  1897. 

Wiilfing.  Die  Meteoriten  in  Sammlungen,  etc.,  1897  (earlier  works  on  related  subjects, 
see  Dana's  System,  p.  32). 

For  a  catalogue  of  localities  of  minerals  in  the  United  States  and  Canada  see  the  volume 
(51  pp.)  reprinted  from  Dana's  System,  6th  ed.  See  also  the  volumes  on  the  Mineral  Re- 
sources of  the  United  States  published  (since  1882)  under  the  auspices  of  the  U.  S.  Geo- 
logical Survey. 

Chemical  and  Determinative  Mineralogy 

Bischoff.  Lehrbuch  der  chemischen  und  physikalischen  Geologic,  1847-54;  2d  ed., 
1863-66.  (Also  an  English  edition.) 

Blum.     Die  Pseudomorphosen  des  Mineralreichs,  1843.     With  4  Nachtrage,  1847-1879. 

Brush-Penfield.  Manual  of  Determinative  Mineralogy,  with  an  Introduction  on  Blow- 
pipe Analysis,  1896. 

Doelter.  Allgemeine  chemische  Mineralogie,  Leipzig,  1890.  Handbuch  der  Mineral- 
chemie,  1912-. 

Duparc  and  Monnier.     Traite  de  Technique  Mineralogique  et  Petrographique,  1913. 

Eakle.  Mineral  Tables  for  the  Determination  of  Minerals  by  their  Physical  Properties, 
1904. 

Endlich.     Manual  of  Qualitative  Blowpipe  Analysis,  New  York,  1892. 

Kobell,  F.  von.  Tafeln  zur  Bestimmung  der  Mineralien  mitteist  einfacher  chemischer 
Versuche  auf  trockenem  und  nassem  Wege,  lite  Auflage,  1878. 

Kraus  and  Hunt.     Tables  for  the  Determination  of  Minerals,  1911. 

Lewis.     Determinative  Mineralogy,  1915. 

Rammelsberg.  Handbuch  der  krystallographisch-physikalischen  Chemie,  Leipzig, 
1881-82.  Handbuch  der  Mineralchemie,  2d  ed.,  1875.  Erganzungsheft,  1,  1886;  2,  1895. 

Roth.  Allgemeine  und  chemische  Geologic;  vol.  1,  Bildung  u.  Umbildung  der  Minera- 
lien, etc.,  1879;  2,  Petrographie,  1887-1890. 

Websky.  Die  Mineral  Species  nach  den  fiir  das  specifische  Gewicht  derselben  ange- 
nommenen  und  gefundenen  Werthen,  Breslau,  1868. 

Weisbach.  Tabellen  zur  Bestimmung  der  Mineralien  nach  ausseren  Kennzeichen, 
3te  Auflage,  1886.  Also  founded  on  Weisbach's  work,  Frazer's  Tables  for  the  determina- 
tion of  minerals,  4th  ed.,  1897. 

Artificial  Formation  of  Minerals 

Dittler.     Mineralsynthetisches  Praktikum,  1915. 

'Gurlt.  Uebersicht  der  pyrogeneten  ktinstlichen  Mineralien,  namentlich  der  krystal- 
lisirten  Hiittenerzeugnisse,  1857. 

Fuchs.     Die.  kiinstlich  dargestellten  Mineralien,  1872. 

Daubree.     Etudes  synthetique  de  Geologic  experimentale,  Paris,  1879. 

Fouque  and  M.  Levy.     Synthese  des  Mineraux  et  des  Roches,  1882. 

Bourgeois.     Reproduction  artificielle  des  Mineraux,  1884. 

Meunier.     Les  methodes  de  synthese  en  Mineralogie. 

Vogt.     Die  Silikatschmelzlozungen,  1903-1904. 

Mineralogical  Journals 

The  following  Journals  are  largely  devoted  to  original  papers  on  Mineralogy: 

Amer.  Min.     The  American  Mineralogist,  1916. 

Bull.  Soc.  Min.     Bulletin  de  la  Societe  Francaise  de  Mineralogie,  1878-. 

Centralbl.  Min.     Centralblatt  fiir  Mineralogie,  Geologie  und  Palseontologie,  1900-. 

Fortschr.  Min.  Fortschritte  der  Mineralogie,  Kristallographie  und  Petrographie, 
1911-  . 

Jb.  Min.     Neues  Jahrbuch  fiir  Mineralogie,  Geologie  und  Palaeontologie,  etc.,  from  1833. 

Min.  Mag.  The  Mineralogical  Magazine  and  Journal  of  the  Mineralogical  Society  of 
Gt.  Britain,  1876-. 

Min.  Mitth.  Mineralogische  und  petrographische  Mittheilungen,  1878- ;  Earlier, 
from  1871,  Mineralogische  Mittheilungen  gesammelt  von  G.  Tschermak. 

Riv.  Min.     Ri  vista  di  Mineralogia  e  Crystallografia,  1887-. 

Zs.  Kr.     Zeitschrift  fiir  Krystallographie  und  Mineralogie.     1877-. 


INTRODUCTION  5 
ABBREVIATIONS 

Ax.  pi.        Plane  of  the  optic  axes.                      H.  Hardness. 

Bx,  Bxa.     Acute  bisectrix  (p.  277).                     Obs.  Observations  on  occurrence,  etc. 

Bxo.            Obtuse  bisectrix  (p.  277).                    O.F.  Oxidizing  Flame  (p.  331). 

B.B.            Before  the  Blowpipe  (p.  330).            Pyr.  Pyrognostics  or  blowpipe  and 

Comp.        Composition.  allied  characters. 

Diff.           Differences,  or  distinctive  char-      R.F.  Reducing  Flame  (p.  331). 

acters.                                              Var.  Varieties. 
G.               Specific  Gravity. 

The  sign  A  is  used  to  indicate  the  angle  between  two  faces  of  a  crystal,  as  am  (100  A  110) 
=  44°  30'. 


PART  I.    CRYSTALLOGRAPHY 


GENERAL  MORPHOLOGICAL   RELATIONS   OF 

CRYSTALS 

5.  Crystallography.  —  The    subject    of    Crystallography   includes    the 
description  of  the  characters  of  crystals  in  general;    of  the  various  forms  of 
crystals  and  their  division  into  classes  and  systems;  of  the  methods  of  study- 
ing crystals,  including  the  determination  of  the  mathematical  relations  of 
their  faces,  and  the  measurement  of  the  angles  between  them;  finally,  a  de- 
scription of  compound  or  twin  crystals,  of  irregularities  in  crystals,  of  crystal- 
line aggregates,  and  of  pseudomorphous  crystals. 

6.  Definition  of  a  Crystal. —  A  crystal  *  is  the  regular  polyhedral  form, 
bounded  by  smooth  surfaces,  which  is  assumed  by  a  chemical  compound,  under 
the  action  of  its  intermodular  forces,  when  passing,  under  suitable  conditions, 
from  the  state  of  a  liquid  or  gas  to  that  of  a  solid. 

As  expressed  in  the  foregoing  definition,  a  crystal  is  characterized,  first,  by 
its  definite  internal  molecular  structure,  and,  second,  by  its  external  form.  A 
crystal  is  the  normal  form  of  a  mineral  species,  as  of  all  solid  chemical  com- 
pounds; but  the  conditions  suitable  for  the  formation  of  a  crystal  of  ideal 
perfection  in  symmetry  of  form  and  smoothness  of  surface  are  never  fully 
realized.  Further,  many  species  usually  occur  not  in  distinct  crystals,  but 
in  massive  form,  and  in  some  exceptional  cases  the  definite  molecular  struc- 
ture is  absent. 

7.  Molecular  Structure  in  General. —  By  definite  molecular  structure 
is  meant  the  special  arrangement  which  the  physical  units,  called  molecules,^ 
assume  under  the  action  of  the  forces  exerted  between  them  during  the  forma- 
tion of  the  solid.     Some  remarks  are  given  in  a  later  article  (p.  22  et  seq.)  in 
regard  to  the  kinds  of  molecular  arrangement  theoretically  possible,  and  their 
relation  to  the  symmetry  of  the  different  systems  and  classes  of  crystals. 

The  definite  molecular  structure  is  the  essential  character  of  a  crystal,  and 
the  external  form  is  only  one  of  the  ways,  although  the  most  important,  in 
which  this  structure  is  manifested.  Thus  it  is  found  that  all  similar  direc- 
tions in  a  crystal,  or  a  fragment  of  a  crystal,  have  like  physical  characters,}: 

*  In  its  original  signification  the  term  crystal  was  applied  only  to  crystals  of  quartz, 
which  the  ancient  philosophers  believed  to  be  water  congealed  by  intense  cold.  Hence  the 
term,  from  KpvaraXXos,  ice. 

t  Recent  studies,  particularly  those  made  by  the  use  of  the  X-ray,  would  indicate  that 
the  unit  of  crystalline  structure  is  the  atom  rather  than  the  molecule.  The  grouping  of 
the  atoms  to  form  a  molecule  is  extended  in  the  analogous  grouping  of  the  molecules  to 
form  a  crystal. 

t  This  subject  is  further  elucidated  in  the  chapter  devoted  to  Physical  Mineralogy, 
where  it  is  also  shown  that,  with  respect  to  many,  but  not  all,  of  the  physical  characters, 
the  r^rrr"T>co  ~-f  t.hi^  prop  nation  is  true,  viz.,  that  unlike  directions  in  a  crystal  have  in 
general  unlike  properties. 

7 


8  CRYSTALLOGRAPHY 

as  of  elasticity,  cohesion,  action  on  light,  etc.  This  is  clearly  shown  by  the 
cleavage,  or  natural  tendency  to  fracture  in  certain  directions,  yielding  more 
or  less  smooth  surfaces;  as  the  cubic  cleavage  of  galena,  or  the  rhombohedral 
cleavage  of  calcite.  It  is  evident,  therefore,  that  a  small  crystal  differs  from 
a  large  one  only  in  size,  and  that  a  fragment  of  a  crystal  is  itself  essentially  a 
crystal  in  all  its  physical  relations,  though  showing  no  crystalline  faces. 

Further,  the  external  form  without  the  corresponding  molecular  structure 
does  not  make  a  crystal  of  a  solid.  A  model  of  glass  or  wood  is  obviously 
not  a  crystal,  though  having  its  external  form,  because  there  is  no  relation 
between  form  and  structure.  Also,  an  octahedron  of  malachite,  having  the 
form  of  the  crystal  of  cuprite  from  which  it  has  been  derived  by  chemical 
alteration,  is  not  a  crystal  of  malachite,  but  what  is  known  as  a  pseudomorph 
(see  Art.  478)  of  malachite  after  cuprite. 

On  the  other  hand,  if  the  natural  external  faces  are  wanting,  the  solid  is 
not  called  a  crystal.  A  cleavage  octahedron  of  fluorite  and  a  cleavage  rhom- 
bohedron  of  calcite  are  not  properly  crystals,  because  the  surfaces  have  been 
yielded  by  fracture  and  not  by  the  natural  molecular  growth  of  the  crystal. 

8.  Crystalline  and  Amorphous.  —  When  a  mineral  shows  no  external 
crystalline  form,  it  is  said  to  be  massive.  It  may,  however,  have  a  definite 
molecular  structure,  and  then  it  is  said  to  be  crystalline.  If  this  structure,  as 
shown  by  the  cleavage,  or  by  optical  means,  is  the  same  in  all  parallel  direc- 
tions through  the  mass,  it  is  described  as  a  single  individual.  If  it  varies  from 
grain  to  grain,  or  fiber  to  fiber,  it  is  said  to  be  a  crystalline  aggregate*  since  it 
is  in  fact  made  up  of  a  multitude  of  individuals. 

Thus  in  a  granular  mass  of  galena  or  calcite,  it  may  be  possible  to  separate 
the  fragments  from  one  another,  each  with  its  characteristic  cubic,  or  rhom- 
bohedral, cleavage.  Even  if  the  individuals  are  so  small  that  they  cannot  be 
separated,  yet  the  cleavage,  and  hence  the  crystalline  structure,  may  be  evi- 
dent from  the  spangling  of  a  freshly  broken  surface,  as  with  fine-grained  statu- 
ary marble.  Or,  again,  this  aggregate  structure  may  be  so  fine  that  the 
crystalline  structure  can  only  be  resolved  by  optical  methods  with  the  aid  of 
the  microscope.  In  all  these  cases,  the  structure  is  said  to  be  crystalline. 

If  optical  means  show  a  more  or  less  distinct  crystalline  structure,  which, 
however,  cannot  be  resolved  into  individuals,  the  mass  is  said  to  be  crypto- 
crystalline;  this  is  true  of  some  massive  varieties  of  quartz. 

If  the  definite  molecular  structure  is  entirely  wanting,  and  all  directions  in 
the  mass  are  sensibly  the  same,  the  substance  is  said  to  be  amorphous.  This 
is  true  of  a  piece  of  glass,  and  nearly  so  of  opal.  The  amorphous  state  is  rare 
among  minerals. 

A  piece  of  feldspar  which  has  been  fused  and  cooled  suddenly  may  be  in  the  glass-like 
amorphous  condition  as  regards  absence  of  definite  molecular  structure.  But  even  in  such 
cases  there  is  a  tendency  to  go  over  into  the  crystalline  condition  by  molecular  rearrange- 
ment. A  transparent  amorphous  mass  of  arsenic  trioxide  (AsaOa),  formed  by  fusion, 
becomes  opaque  and  crystalline  after  a  time.  Similarly  the  steel  beams  of  a  railroad  bridge 
may  gradually  become  crystalline  and  thus  lose  some  of  their  original  strength  because  of 
the  molecular  rearrangement  made  possible  by  the  vibrations  caused  by  the  frequent  jar  of 
passing  trains.  The  microscopic  study  of  rocks  reveals  many  cases  in  which  an  analogous 
change  in  molecular  structure  has  taken  place  in  a  solid  mass,  as  caused,  for  example,  by 
great  pressure. 

*  The  consideration  of  the  various  forms  of  crystalline  aggregates  is  postponed  to  the 
end  of  the  present  chapter. 


GENERAL   MORPHOLOGICAL   RELATIONS   OF    CRYSTALS 


9 


9.  External  Form.  —  A  crystal  -is  bounded  by  smooth  plane  surfaces, 
called  faces  or  planes,*  showing  in  their  arrangement  a  certain  characteristic 
symmetry,  and  related  to  each  other  by  definite  mathematical  laws. 

Thus,  without  inquiring,  at  the  moment,  into  the  exact  meaning  of  the 
term  symmetry  as  applied  to  crystals,  and  the  kinds  of  symmetry  possible, 
which  will  be  explained  in  detail  later,  it  is  apparent  that  the  accompanying 
figures,  1-3,  show  the  external  form  spoken  of.  They  represent,  therefore, 
certain  definite  types. 


Galena 


Vesuvianite 


Chrysolite 


10.  Variation  of  Form  and  Surface.  —  Actual  crystals  deviate,  within 
certain  limits,  from  the  ideal  forms. 

First,  there  may  be  variation  in  the  size  of  like  faces,  thus  producing  what 
are  defined  later  as  distorted  forms.  In  the  second  place,  the  faces  are  rarely 
absolutely  smooth  and  brilliant;  commonly  they  lack  perfect  polish,  and  they 
may  even  be  rough  or  more  or  less  covered  with  fine  parallel  lines  (called 
striations),  or  show  minute  elevations,  depressions  or  other  peculiarities. 
Both  the  above  subjects  are  discussed  in  detail  in  another  place. 

It  may  be  noted  in  passing  that  the  characters  of  natural  faces,  just 
alluded  to,  in  general  make  it  easy  to  distinguish  between  them  and  a  face 
artificially  ground,  on  the  one  hand,  like  the  facet  of  a  cut  gem; 
or,  on  the  other  hand,  the  splintery  uneven  surface  commonly 
yielded  by  cleavage. 

11.  Constancy  of  the  Interfacial  Angles  in  the  Same 
Species.  —  The  angles  of  inclination  between  like  faces  on 
the  crystals  of  any  species  are  essentially  constant,  wherever 
they  are  found,  and  whether  products  of  nature  or  of  the 
laboratory.     These  angles,  therefore,  form  one  of  the  im- 
portant distinguishing  characters  of  a  species. 

Thus,  in  Fig.  4,  of  apatite,  the  angle  between  the  adjacent 
faces  x  and  m  (130°  18')  is  the  same  for  any  two  like  faces, 
similarly  situated  with  reference  to  each  other.  Further,  this 
angle  is  constant  for  the  species  no  matter  what  the  size  of 
the  crystal  may  be  or  from  what  locality  it  may  come.  Moreover,  the  angles 
between  all  the  faces  on  crystals  of  the  same  species  (cf .  Figs.  5-8  of  zircon 
below)  are  more  or  less  closely  connected  together  by  certain  definite 
mathematical  laws. 


m,' 

m 

Apatite 


*  This  latter  word  is  usually  limited  to  cases  where  the  direction,  rather  than  the 
definite  surface  itself,  is  designated. 


10 


CRYSTALLOGRAPHY 


12.  Diversity  of  Form,  or  Habit.  —  While  in  the  crystals  of  a  given 
species  there  is  constancy  of  angle  between  like  faces,  the  forms  of  the  crystals 
may  be  exceedingly  diverse.  The  accompanying  figures  (5-8)  are  examples 
of  a  few  of  the  forms  of  the  species  zircon.  There  is  hardly  any  limit  to  the 
number  of  faces  which  may  occur,  and  as  their  relative  size  changes,  the 
habit,  as  it  is  called,  may  vary  indefinitely. 


Zircon 

13.  Diversity  of  Size.  —  Crystals  occur  of  all  sizes,  from  the  merest 
microscopic  point  to  a  yard  or  more  in  diameter.     It  is  important  to  under- 
stand, however,  that  in  a  minute  crystal  the  development  is  as  complete  as 
with  a  large  one.     Indeed  the  highest  perfection  of  form  and  transparency  is 
found  only  in  crystals  of  small  size. 

A  single  crystal  of  quartz,  now  at  Milan,  is  three  and  a  quarter  feet  long  and  five  and  a 
half  in  circumference,  and  its  weight  is  estimated  at  eight  hundred  and  seventy  pounds. 
A  single  cavity  in  a  vein  of  quartz  near  the  Tiefen  Glacier,  in  Switzerland,  discovered  in 
1867,  afforded  smoky  quartz  crystals,  a  considerable  number  of  which  had  a  weight  of  200 
to  250  pounds.  A  gigantic  beryl  from  Acworth,  New  Hampshire,  measured  four  feet  in 
length  and  two  and  a  half  in  circumference;  another,  from  Graf  ton,  was  over  four  feet  long, 
and  thirty-two  inches  in  one  of  its  diameters,  and  weighed  about  two  and  a  half  tons. 

14.  Symmetry  in   General.  —  The   faces   of   a   crystal   are   arranged 
according  to  certain  laws  of  symmetry,  and  this  symmetry  is  the  natural 
basis  of  the  division  of  crystals  into  systems  and  classes.     The  symmetry 
may  be  defined  in  relation  to  (1)  a  plane  of  symmetry,  (2)  an  axis  of  symmetry, 
and  (3)  a  center  of  symmetry. 

These  different  kinds  of  symmetry  may,  or  may  not,  be  combined  in  the 
same  crystal.  It  will  be  shown  later  that  there  is  one  class,  the  crystals  of 
which  have  neither  center,  axis,  nor  plane  of  symmetry;  another  where  there 
is  only  a  center  of  symmetry.  On  the  other  hand,  some  classes  have  all  these 
elements  of^symmetry  represented. 

15.  Planes  of  Symmetry.  —  A  solid  is  said  to  be  geometrically  *  sym- 
metrical with  reference  to  a  plane  of  symmetry  when  for  each  face,  edge,  or 
solid  angle  there  is  another  similar  face,  edge,  or  angle  which  has  a  like  posi- 
tion with  reference  to  this  plane.     Thus  it  is  obvious  that  the  crystal  of  am- 
phibole,  shown  in  Fig.  9,  is  symmetrical  with  reference  to  the  central  plane 
of  symmetry  indicated  by  the  shading. 


*  The  relation  between  the  ideal  geometrical  symmetry  and  the  actual  crystallographic 
symmetry  is  discussed  in  Art.  18. 


GENERAL   MORPHOLOGICAL   RELATIONS   OF    CRYSTALS 


11 


In  the  ideal  crystal  this  symmetry  is  right  symmetry  in  the  geometrical 
sense,  where  every  point  on  the  one  side  of  the  plane  of  symmetry  has  a  cor- 
responding point  at  equal  distances  on  the  other  side, 
measured  on  a  line  normal  to  it.  In  other  words,  in 
the  ideal  geometrical  symmetry,  one  half  of  the  crystal 
is  the  exact  mirror-image  of  the  other  half. 

A  crystal  may  have  as  many  as  nine  planes  of  sym- 
metry, three  of  one  set  and  six  of  another,  as  is  illustrated 
by  the  cube  *  (Fig.  16).  Here  the  planes  of  the  first  set 
pass  through  the  crystal  parallel  to  the  cubic  faces;  they 
are  shown  in  Fig.  10.  The  planes  of  the  second  set  join 
the  opposite  cubic  edges;  they  are  shown  in  Fig.  11. 

16.  Axes  of  Symmetry.  —  If  a  solid  can  be  revolved 
through  a  certain  number  of  degrees  about  some  line  as 
an  axis,  with  the  result  that  it  again  occupies  precisely 
the  same  position  in  space  as  at  first,  that  axis  is  said 
to  be  an  axis  of  symmetry.  There  are  four  different 
kinds  of  axes  of  symmetry  among  crystals;  they  are  de- 
fined according  to  the  number  of  times  which  the  crystal  repeats  itself  in  ap- 
pearance during  a  complete  revolution  of  360°. 


Amphibole 


Symmetry  Planes  in  the  Cube 

(a)  A  crystal  is  said  to  have  an  axis  of  binary,  or  twofold,  symmetry  when 
a  revolution  of  180°  produces  the  result  named  above;  in  other  words,  when  it 
repeats  itself  twice  in  a  complete  revolution.  This  is  true  of  the  crystal  shown 
in  Fig.  12  with  respect  to  the  vertical  axis  (and  indeed  each  of  the  horizontal 
axes  also). 

(6)  A  crystal  has  an  axis  of  trigonal,  or  threefold,  symmetry  when  a  revo- 
lution of  120°  is  needed;  that  is,  when  it  repeats  itself  three  times  in  a  com- 
plete revolution.  The  vertical  axis  of  the  crystal  shown  in  Fig.  13  is  an  axis 
of  trigonal  symmetry. 

(c)  A  crystal  has  an  axis  of  tetragonal,  or  fourfold,  symmetry  when  a 
revolution  of  90°  is  called  for;    in  other  words,  when  it  repeats  itself  four 
times  in  a  complete  revolution.     The  vertical  axis  in  the  crystal  shown  in 
Fig.  14  is  such  an  axis. 

(d)  Finally,  a  crystal  has  an  axis  of  hexagonal,  or  sixfold,  symmetry  when 
a  revolution  of  60°  is  called  for;   in  other  words,  when  it  repeats  itself  six 
times  in  a  complete  revolution.     This  is  illustrated  by  Fig.  15. 


*  This  is  the  cube  of  the  normal  class  of  the  isometric  system. 


12 


CRYSTALLOGRAPHY 


The  different  kinds  of  symmetry  axes  are  sometimes  known  as  diad,  triad,  tetrad  and 
hexad  axes. 


12 


13 


14 


16 


Chrysolite 


Calcite 


Rutile 


Beryl 


The  cube  *  illustrates  three  of  the  four  possible  kinds  of  symmetry  with  respect  to  axes 
of  symmetry.  It  has  six  axes  of  binary  symmetry  joining  the  middle  points  of  opposite 
edges  (Fig.  16).  It  has  four  axes  of  trigonal  symmetry,  joining  the  opposite  solid  angles 
(Fig.  17).  It  has,  finally,  three  axes  of  tetragonal  symmetry  joining  the  middle  points  of 
opposite  faces  (Fig.  18). 


16 


17 


18 


-v 


Symmetry  Axes  in  the  Cube 

17.  Center  of  Symmetry.  —  Most  crystals,  besides  planes  and  axes  of 
symmetry,  have  also  a  center  of  symmetry.  On  the  other  hand,  a  crystal, 
though  possessing  neither  plane  nor  axis  of  symmetry,  may  yet  be  sym- 


Rhodonite 


Heulandite 


metrical  with  reference  to  a  point,  its  center.  This  last  is  true  of  the  triclinic 
crystal  shown  in  Fig.  19,  in  which  it  follows  that  every  face,  edge,  and  solid 
angle  has  a  face,  edge,  and  angle  similar  to  it  in  the  opposite  half  of  the  crystal. 


This  is  again  the  cube  of  the  normal  class  of  the  isometric  system. 


GENERAL   MORPHOLOGICAL   RELATIONS   OF   CRYSTALS 


13 


18.  Relation  of  Geometrical  to  Crystallographic  Symmetry.  —  Since 
the  symmetry  in  the  arrangement  of  the  faces  of  a  crystal  is  an  expression  of 
the  internal  molecular  structure,  which  in  general  is  alike  in  all  parallel  direc- 
tions, the  relative  size  of  the  faces  and  their  distance  from  the  plane  or  axis  of 
symmetry  are  of  no  moment,  their  angular  position  alone  is  essential.  The 
crystal  represented  in  Fig.  20,  although  its  faces  show  an  unequal  develop- 
ment, has  in  the  crystallographic  sense  as  truly  a  vertical  plane  of  symmetry 
(parallel  to  the  face  6)  as  the  ideally  developed  crystal  shown  in  Fig.  21. 
The  strict  geometrical  definition  of  symmetry  would,  however,  apply  only 
to  the  second  crystal.* 

22  23  24 


Cube 


Distorted  Cubes 


Also  in  a  normal  cube  (Fig.  22)  the  three  central  planes  parallel  to  each 
pair  of  cubic  faces  are  like  planes  of  symmetry,  as  stated  in  Art.  15.  But  a 
crystal  is  still  crystallographically  a  cube,  though  deviating  widely  from  the 
requirements  of  the  strict  geometrical  definition,  as  shown  in  Figs.  23,  24,  if 
only  it  can  be  proved,  e.g.,  by  cleavage,  by  the  physical  nature  of  the  faces, 
or  by  optical  means,  that  the  three  pairs  of  faces  are  like  faces,  independently 
of  their  size,  or,  in  other  words,  that  the  molecular  structure  is  the  same  in 
the  three  directions  normal  to  them. 


25 


26 


Cube  and  Octahedron 

Further,  in  the  case  of  a  normal  cube,  a  face  of  an  octahedron  on  any  solid 
angle  requires,  as  explained  beyond,  similar  faces  on  the  other  angles.  It  is 
not  necessary,  however,  that  these  eight  faces  should  be  of  equal  size,  for  in 
the  crystallographic  sense  Fig.  25  is  as  truly  symmetrical  with  reference  to 
the  planes  named  as  Fig.  26. 

*  It  is  to  be  noted  that  the  perspective  figures  of  crystals  usually  show  the  geometrically 
ideal  form,  in  which  like  faces,  edges,  and  angles  have  the  same  shape,  size,  and  position. 
In  other  words,  the  ideal  crystal  is  uniformly  represented  as  having  the  symmetry  called 
for  by  the  strict  geometrical  definition. 


14  CRYSTALLOGRAPHY 

19.  On  the  other  hand,  the  molecular  and  hence  the  crystallographic 
symmetry  is  not  always  that  which  the  geometrical  form  would  suggest. 
Thus,  deferring  for  the  moment  the  consideration  of  pseudo-symmetry,  an 
illustration  of  the  fact  stated  is  afforded  by  the  cube.     It  has  already  been 
implied  and  will  be  fully  explained  later  that  while  the  cube  of  the  normal 
class  of  the  isometric  system  has  the  symmetry  described  in  Arts.  15,  16,  a 
cube  of  the  same  geometrical  form  but  belonging  molecularly,  for  example, 
to  the  tetrahedral  class,  has  no  planes  of  symmetry  parallel  to  the  faces  but 
only  the  six  diagonal  planes;  further,  though  the  four  axes  shown  in  Fig.  17 
are  still  axes  of  trigonal  symmetry,  the  cubic  axes  (Fig.  18)  are  axes  of  binary 
symmetry  only,  and  there  are  no  axes  of  symmetry  corresponding  to  those 
represented  in  Fig.  16.     Other  more  complex  cases  will  be  described  later. 

Further,  a  crystal  having  interf acial  angles  of  90°  is  not  necessarily  a  cube : 
in  other  words,  the  angular  relations  of  the  faces  do  not  show  in  this  case 
whether  the  figure  is  bounded  by  six  like  faces;  or  whether  only  four  are 
alike  and  the  other  pair  unlike;  or,  finally,  whether  there  are  three  pairs  of 
unlike  faces.  The  question  must  be  decided,  in  such  cases,  by  the  molecular 
structure  as  indicated  by  the  physical  nature  of  the  surfaces,  by  the  cleavage, 
or  by  other  physical  characters,  as  pyro-electricity,  those  connected  with 
light  phenomena,  etc. 

Still,  again,  the  student  will  learn  later  that  the  decision  reached  in  regard 
to  the  symmetry  to  which  a  crystal  belongs,  based  upon  the  distribution  of  the 
faces,  is  only  preliminary  and  approximate,  and  before  being  finally  accepted 
it  must  be  confirmed,  first,  by  accurate  measurements,  and,  second,  by  a 
minute  study  of  the  other  physical  characters. 

The  method  based  upon  the  physical  characters,  which  gives  most  conclusive  results 
and  admits  of  the  widest  application,  is  the  skillful  etching  of  the  surface  of  the  crystal  by 
some  appropriate  solvent.  By  this  means  there  are,  in  general,  produced  upon  it  minute 
depressions  the  shape  of  which  conforms  to  the  symmetry  in  the  arrangement  of  the  mole- 
cules. This  process,  which  is  in  part  essentially  one  involving  the  dissection  of  the  molecu- 
lar structure,  is  more  particularly  discussed  in  the  chapter  on  Physical  Mineralogy. 

20.  Pseudo-symmetry.  —  The  crystals  of  certain  species  approximate 
closely  in  angle,  and  therefore  in  apparent  symmetry,  to  the  requirements 
of  a  system  higher  in  symmetry  than  that  to  which  they  actually  belong: 
they  are  then  said  to  exhibit  pseudo-symmetry.     Numerous  examples  are 
given  under  the  different  systems.     Thus  the  micas  have  been  shown  to  be 
truly  monoclinic  in  crystallization,  though  in  angle  they  seem  to  be  in  some 
cases  rhombohedral,  in  others  orthorhombic. 

It  will  be  shown  later  that  compound,  or  twin,  crystals  may  also  simulate 
by  their  regular  grouping  a  higher  grade  of  symmetry  than  that  which  belongs 
to  the  single  crystal.  Such  crystals  also  exhibit  pseudo-symmetry  and  are 
specifically  called  mimetic.  Thus  aragonite  is  an  example  of  an  orthorhombic 
species,  whose  crystals  often  imitate  by  twinning  those  of  the  hexagonal 
system.*  Again,  a  highly  complex  twinned  crystal  of  the  monoclinic  species, 
phillipsite,  may  have  nearly  the  form  of  a  rhombic  dodecahedron  of  the  iso- 
metric system.  This  kind  of  pseudo-symmetry  also  occurs  among  the 
classes  of  a  single  system,  since  a  crystal  belonging  to  a  class  of  low  sym- 
metry may  by  twinning  gain  the  geometrical  symmetry  of  the  corresponding 

*  The  terms  pseudo-hexagonal,  etc.,  used  in  this  and  similar  cases  explain  themselves. 


GENERAL   MORPHOLOGICAL   RELATIONS    OF   CRYSTALS  15 

form  of  the  normal  class.     This  is  illustrated  by  a  twinned  crystal  of  scheelite 
like  that  figured  (Fig.  416)  in  the  chapter  on  twin  crystals. 

Pseudo-symmetry  of  still  another  kind,  where  there  is  an  imitation  of  the 
symmetry  of  another  system  of  lower  grade,  is  particularly  common  in 
crystals  of  the  isometric  system  (e.g.,  gold,  copper).  The  result  is  reached  in 
such  cases  by  an  abnormal  development  of  "  distortion "  in  the  direction  of 
certain  axes  of  symmetry.  This  subject  is  discussed  and  illustrated  on  a 
later  page. 

21.  Possible  Classes  of  Symmetry.  —  The  theoretical  consideration  of 
the  different  kinds  of  symmetry  possible  among  crystals  built  up  of  like  mole- 
cules, as  explained  in  Arts.  30-32,  has  led  to  the  conclusion  that  there  are 
thirty-two  (32)  types  in  all,  differing  with  respect  to  the  combination  of  the 
different  symmetry  elements  just  described.     Of  these  thirty-two  natural 
classes  among  crystals  based  upon  their  symmetry,  seven  classes  include  by 
far  the  larger  number  of  crystallized  minerals.     Besides  these,  some  thirteen 
or  fourteen  others  are  distinctly  represented,  though  several  of  these  are  of 
rare  occurrence.     The  remaining  classes,  with  possibly  one  or   two   excep- 
tions, are  known  among  the  crystallized  salts  made  in  the  laboratory.     The 
characters  of  each  of  the  thirty-two  classes  are  given  under  the  discussion  of 
the  several  crystalline  systems. 

22.  Crystallographic  Axes.  —  In  the  description  of  a  crystal,  especially 
as  regards  the  position  of  its  faces,  it  is  found  convenient  to  assume,  after 
the  methods  of  analytical  geometry,  certain  lines  passing  through  the  center 
of  the  ideal  crystal,  as  a  basis  of  reference.     (See  further  Art.  34  et  seq.) 

These  lines  are  called  the  Crystallographic  axes.  Their  direction  is  to  a 
greater  or  less  extent  fixed  by  the  symmetry  of  the  crystals,  for  an  axis  of 
symmetry  is  in  almost  all  cases  *  a  possible  Crystallographic  axis.  Further, 
the  unit  lengths  assigned  to  these  axes  are  fixed  sometimes  by  the  symmetry, 
sometimes  by  the  position  of  the  faces  assumed  as  fundamental,  i.e.,  the 
unit  forms  in  the  sense  defined  later.  The  broken  lines  shown  in  Fig.  18  are 
the  Crystallographic  axes  to  which  the  cubic  faces  are  referred. 

23.  Systems  of  Crystallization.  —  The  thirty-two  possible  crystal  classes 
which  are  distinguished  from  one  another  by  their  symmetry,  are  classified 
in  this  work  under  six  systems,  each  characterized  by  the  relative  lengths 
and  inclinations  of  the  assumed  Crystallographic  axes.     These  are  as  follows : 

I.  ISOMETRIC  SYSTEM.     Three  equal  axes  at  right  angles  to  each  other. 

II.  TETRAGONAL  SYSTEM.     Three  axes  at  right  angles  to  each  other,  two 
of  them  —  the  horizontal   axes  —  equal,   the  third  —  the  vertical   axis  — 
longer  or  shorter. 

III.  HEXAGONAL  SYSTEM.     Four  axes,  three  equal  horizontal  axes  in  one 
plane  intersecting  at  angles  of  60°,  and  a  vertical  axis  at  right  angles  to  this 
plane  and  longer  or  shorter. 

IV.  ORTHORHOMBIC  SYSTEM.     Three  axes  at  right  angles  to  each  other, 
but  all  of  different  lengths. 

V.  MONOCLINIC  SYSTEM.     Three  axes  unequal  in  length,  and  having 
one  of  their  intersections  oblique,  the  two  other  intersections  equal  to  90°. 

VI.  TRICLINIC    SYSTEM.     Three   unequal    axes   with   mutually   oblique 
intersections. 

*  Exceptions  are  found  in  the  isometric  system,  where  the  axes  must  necessarily  be  the 
axes  of  tetragonal  symmetry  (Fig.  18),  and  cannot  be  those  of  binary  or  trigonal  symmetry 
(Figs.  16,  17). 


16  CRYSTALLOGRAPH 

24.  Each  one  of  the  six  systems,  as  will  be  understood  from  Art.  21, 
embraces  several  classes  differing  among  themselves  in  their  symmetry. 
One  of  these  classes  is  conveniently  called  the  normal  class,  since  it  is  in 
general  the  common  one,  and  since  further  it  exhibits  the  highest  degree  of 
symmetry  possible  for  the  given  system,  while  the  others  are  lower  in  grade 
of  symmetry. 

It  is  important  to  note  that  the  classes  comprised  within  a  given  system 
are  at  once  essentially  connected  together  by  their  common  optical  characters, 
and  in  general  separated  *  from  those  of  the  other  systems  in  the  same  way. 

Below  is  given  a  list  of  the  six  systems  together  with  their  subordinate 
classes,  thirty-two  in  all.  The  order  and  the  names  given  first  are  those  that 
are  used  in  this  book  while  in  the  following  parentheses  are  given  other 
equivalent  names  that  are  also  in  common  use.  Under  nearly  all  of  the 
classes  it  is  possible  to  give  the  name  of  a  mineral  or  an  artificial  compound 
whose  crystals  serve  to  illustrate  the  characters  of  that  particular  class. 
There  is  some  slight  variation  between  different  authors  in  the  order  in  which 
the  crystal  systems  and  classes  are  considered  but  in  the  main  essentials  all 
modern  discussions  of  crystallography  are  uniform. 

ISOMETRIC  SYSTEM 

(Regular,  Cubic  System) 

1.  NORMAL  CLASS.     (Hexoctahedral.     Holohedral.)     Galena  Type. 

2.  PYRITOHEDRAL  CLASS.     (Dyakisdodecahedral.     Pentagonal  Hemihe- 
dral.)     Pyrite  Type. 

3.  TETRAHEDRAL   CLASS.     (Hextetrahedral.     Tetrahedral   Hemihedral.) 
Tetrahedrite  Type. 

4.  PLAGIOHEDRAL   CLASS.     (Pentagonal    Icositetrahedral.     Plagiohedral 
Hemihedral.)     Cuprite  Type. 

5.  TETARTOHEDRAL    CLASS.     (Tetrahedral    Pentagonal    Dodecahedral.) 
Sodium  Chlorate  Type. 

TETRAGONAL  SYSTEM 

6.  NORMAL  CLASS.     (Ditetragonal  Bipyramidal.     Holohedral.)     Zircon 
Type. 

7.  HEMIMORPHIC  CLASS.     (Ditetragonal  Pyramidal.     Holohedral  Hemi- 
morphic.)     lodosuccinimide  Type. 

8.  TRIPYRAMIDAL  CLASS.     (Tetragonal  Bipyramidal.     Pyramidal  Hemi- 
hedral.)    Scheelite  Type. 

9.  PYRAMIDAL-HEMIMORPHIC  CLASS.     (Tetragonal  Pyramidal.     Hemihe- 
dral Hemimorphic.)     Wulfenite  Type. 

10.  SPHENOIDAL  CLASS.     (Tetragonal  Sphenoidal.     Sphenoidal  Hemihe- 
dral.    Scalenohedral.)     Chalcopyrite  Type. 

11.  TRAPEZOHEDRAL    CLASS.     (Tetragonal    Trapezohedral.     Trapezohe- 
dral  Hemihedral.)     Nickel  Sulphate  Type. 

12.  TETARTOHEDRAL        CLASS.      (Tetragonal        Bisphenoidal.)      Artif. 
2  CaO.Al203.SiO2  Type. 

*  Crystals  of  the  tetragonal  and  hexagonal  systems  are  alike  in  being  optically  unaxial; 
but  the  crystals  of  all  the  other  systems  have  distinguishing  optical  characters, 


GENERAL   MORPHOLOGICAL   RELATIONS   OF   CRYSTALS  17 

HEXAGONAL  SYSTEM 
A.     HEXAGONAL  DIVISION 

13.  NORMAL  CLASS.     (Dihexagonal  Bipyramidal.     Holohedral.)     Beryl 
Type. 

14.  HEMIMORPHIC  CLASS.     (Dihexagonal  Pyramidal.     Holohedral  Hemi- 
morphic.)     Zincite  Type. 

15.  TRIPYRAMIDAL  CLASS.     (Hexagonal  Bipyramidal.     Pyramidal  Hemi- 
hedral.)     Apatite  Type. 

16.  PYRAMIDAL-HEMIMORPHIC  CLASS.     (Hexagonal  Pyramidal.     Pyrami- 
dal Hemihedral  Hemimorphic.)     Nephelite  Type. 

17.  TRAPEZOHEDRAL  CLASS.     (Hexagonal  Trapezohedral.    Trapezohedral 
Hemihedral.)     /3-Quartz  Type. 

B.     TRIGONAL  OR  RHOMBOHEDRAL  DIVISION 

(Trigonal  System) 

18.  TRIGONAL  CLASS.     (Ditrigonal  Bipyramidal.     Trigonal  Hemihedral.) 
Benitoite  Type. 

19.  RHOMBOHEDRAL  CLASS.     (Ditrigonal  Scalenohedral.     Rhombohedral 
Hemihedral.)     Calcite  Type^ 

20.  RHOMBOHEDRAL  HEMIMORPHIC  CLASS.     (Ditrigonal  Pyramidal.     Tri- 
gonal Hemihedral  Hemimorphic.)     Tourmaline  Type. 

21.  TRI-RHOMBOHEDRAL  CLASS.     (Rhombohedral.     Rhombohedral  Te- 
tartohedral.)     Phenacite  Type. 

22.  TRAPEZOHEDRAL  CLASS.     (Trigonal  Trapezohedral.     Trapezohedral 
Tetartohedral.)     Quartz  Type. 

23.'  (Trigonal  Bipyramidal.     Trigonal  Tetar- 
tohedral. 

24.  (Trigonal  Pyramidal.     Trigonal  Tetarto- 
hedral Hemimorphic.)  Sodium  Periodate  Type. 

ORTHORHOMBIC   SYSTEM 
(Rhombic  or  Prismatic  System) 

25.  NORMAL  CLASS.     (Orthorhombic  Bipyramidal.     Holohedral.)     Barite 
Type. 

26.  HEMIMORPHIC  CLASS.     (Orthorhombic  Pyramidal.)     Calamine  Type. 

27.  SPHENOIDAL  CLASS.     (Orthorhombic  Bisphenoidal.)     Epsomite  Type. 

MONOCLINIC   SYSTEM 
(Oblique  System) 

28.  NORMAL  CLASS.     (Prismatic.     Holohedral.)     Gypsum  Type. 

29.  HEMIMORPHIC  CLASS.     (Sphenoidal.)     Tartaric  Acid  Type. 

30.  CLINOHEDRAL  CLASS.     (Domatic.    Hemihedral.)    Clinohedrite  Type. 

TRICLINIC   SYSTEM 
(Anorthic  System) 

31.  NORMAL  CLASS.     (Holohedral.     Pinacoidal.)     Axinite  Type. 

32.  ASYMMETRIC  CLASS.     (Hemihedral.)     Clacium  Thiosulphate  Type. 


18 


CRYSTALLOGRAPHY 


25.  Symmetry  of  the  Systems.  —  In  the  paragraphs  immediately  fol- 
lowing, a  synopsis  is  given  of  the  symmetry  of  the  normal  class  of  each  of  the 
different  systems,  and  also  that  of  one  subordinate  class  of  the  hexagonal 
system,  which  is  of  so  great  importance  that  it  is  also  often  conveniently 
treated  as  a  sub-system  even  when,  as  in  this  work,  the  forms  are  referred  to 
the  same  axes  as  those  of  the  strictly  hexagonal  type  —  a  usage  not  adopted 
by  all  authors. 

I.  ISOMETRIC  SYSTEM.  Three  like  axial  *  planes  of  symmetry  (principal 
planes)  parallel  to  the  cubic  faces,  and  fixing  by  their  intersection  the  crystal- 
lographic axes;  six  like  diagonal  planes  of  symmetry,  passing  through  each 
opposite  pair  of  cubic  edges,  and  hence  parallel  to  the  faces  of  the  rhombic 
dodecahedron. 

Further,  three  like  axes  of  tetragonal  symmetry,  the  crystallographic 
axes  normal  to  the  faces  of  the  cube;  four  like  diagonal  axes  of  trigonal  sym- 
metry, normal  to  the  faces  of  the  octahedron;  and  six  like  diagonal  axes  of 
binary  symmetry,  normal  to  the  faces  of  the  dodecahedron.  There  is  also 
obviously  a  center  of  symmetry.!  These  relations  are  illustrated  by  Fig.  27 
also  by  Fig.  35;  further  by  Figs.  92  to  125. 


27 


28 


29 


\m 


Galena 


Rutile 


a 
Rutile 


II.  TETRAGONAL  SYSTEM.  Three  axial  planes  of  symmetry :  of  these,  two 
are  like  planes  intersecting  at  90°  in  a  line  which  is  the  vertical  crystallo- 
graphie  axis,  and  the  third  plane  (a  principal  plane)  is  normal  to  them  and 
hence  contains  the  horizontal  axes.  There  are  also  two  diagonal  planes  of 
symmetry,  intersecting  in  the  vertical  axis  and  meeting  the  two  axial  planes 
at  angles  of  45°. 

Further,  there  is  one  axis  of  tetragonal  symmetry,  a  principal  axis ;  this  is 
the  vertical  crystallographic  axis.  There  are  also  in  a  plane  normal  to  this 
four  axes  of  binary  symmetry  —  like  two  and  two  —  those  of  each  pair  at  right 
angles  to  each  other.  Fig.  28  shows  a  typical  tetragonal  crystal,  and  Fig.  29 
a  basal  projection  of  it,  that  is,  a  projection  on  the  principal  plane  of  sym- 
metry normal  to  the  vertical  axis.  See  also  Fig.  36  and  Figs.  170-192. 

*  Two  planes  of  symmetry  are  said  to  be  like  when  they  divide  the  ideal  crystal  into 
halves  which  are  identical  to  each  other;  otherwise,  they  are  said  to  be  unlike.  Axes  of 
symmetry  are  also  like  or  unlike.  If  a  plane  of  symmetry  includes  two  of  the  crystallo- 
graphic axes,  it  is  called  an  axial  plane  of  symmetry.  If  the  plane  includes  two  or  more 
like  axes  of  symmetry,  it  is  called  a  principal  plane  of  symmetry ;  also  an  axis  of  symmetry 
in  which  two  or  more  like  planes  of  symmetry  meet  is  a  principal  axis  of  symmetry. 

t  In  describing  the  symmetry  of  the  different  classes,  here  and  later,  the  center  of 
symmetry  is  ordinarily  not  mentioned  when  its  presence  or  absence  is  obvious. 


GENERAL    MORPHOLOGICAL    RELATIONS    OF    CRYSTALS 


19 


III.  HEXAGONAL  SYSTEM.  In  the  Hexagonal  Division  there  are  four 
axial  planes  of  symmetry;  of  these  three  are  like  planes  meeting  at  angles  of 
60°,  their  intersection-line  being  the  vertical  crystallographic  axis;  the  fourth 
plane  (a  principal  plane)  is  at  right  angles  to  these.  There  are  also  three 
other  diagonal  planes  of  symmetry  meeting  the  three  of  the  first  set  in  the 
vertical  axis,  arid  making  with  them  angles  of  30°. 

Further,  there  is  one  principal  axis  of  hexagonal  symmetry;  this  is  the 
vertical  crystallographic  axis;  at  right  angles  to  it  there  are  also  six  binary 
axes.  The  last  are  in  two  sets  of  three  each.  Fig.  30  shows  a  typical  hex- 
agonal crystal,  with  a  basal  projection  of  the  same.  See  also  Fig.  37  and 
Figs.  220-227. 

32 


m 

m 

! 

-L 

,---S 

Miorosoinmite 


Cabito 


Chrysolite 


In  the  Trigonal  or  Rhombohedral  Division  of  this  system  there  are  three 
like  planes  of  symmetry  intersecting  at  angles  of  60°  in  the  vertical  axis. 
Further,  the  forms  belonging  here  have  a  vertical  principal  axis  of  trigonal 
symmetry,  and  three  horizontal  axes  of  binary  symmetry,  coinciding  with 
the  horizontal  crystallographic  axes.  Fig.  31  shows  a  typical  rhombohedral 
crystal,  with  its  basal  projection.  See  also  Figs.  243-269. 

IV.  ORTHORHOMBIC  SYSTEM.     Three  unlike  planes  of  symmetry  meeting 
at  90°,  and  fixing  by  their  intersection-lines  the  position  of  the  crystallo- 
graphic axes.     Further,  three  unlike  axes  of  binary  symmetry  coinciding  with 
the  last-named  axes.     Fig.  32  shows  a  typical  orthorhombic  crystal,  with  its 
basal  projection.     See  also  Fig.  38  and  Figs.  298-320. 

V.  MONOCLINIC  SYSTEM.  •  One  plane  of  symmetry  which  contains  two  of 
the  crystallographic  axes.     Also  one  axis  of  binary  symmetry,  normal  to  this 
plane  and  coinciding  with  the  third  crystallographic  axis.     See  Fig.  33;  also 
Fig.  39  and  Figs.  333-347. 

VI.  TRICLINIC  SYSTEM.     No  plane  and  no  axis  of  symmetry,  but  sym- 
metry solely  with  respect  to  the  central  point.     Figs.  34  and  40  show  typical 
triclinic  crystals.     See  also  Figs.  359-366 


20 


CRYSTALLOGRAPHY 


26.  The  relations  of  the  normal  classes  of  the  different  systems  are  further 
illustrated  both  as  regards  the  crystallographic  axes  and  symmetry  by  the 
accompanying  figures,  35-40.  The  exterior  form  is  here  that  bounded  by 
faces  each  of  which  is  parallel  to  a  plane  through  two  of  the  crystallographic 
axes  indicated  by  the  central  broken  lines.  Further,  there  is  shown,  within 
this,  the  combination  of  faces  each  of  which  joins  the  extremities  of  the  unit 
lengths  of  the  axes. 

34 


Pyroxene 


Axinite 


The  full  understanding  of  the  subject  will  not  be  gained  until  after  a 
study  of  the  forms  of  each  system  in  detail.  Nevertheless  the  student  will  do 
well  to  make  himself  familiar  at  the  outset  with  the  fundamental  relations 
here  illustrated. 


35 


37 


Isometric 


Tetragonal 


Hexagonal 


It  will  be  shown  later  that  the  symmetry  of  the  different  classes  can  be 
most  clearly  and  easily  exhibited  by  the  use  of  the  different  projections  ex- 
plained in  Art.  39  et  seq. 


GENERAL   MORPHOLOGICAL   RELATIONS   OF   CRYSTALS 


21 


27.  Models.  —  Glass  (or  transparent  celluloid)  models  illustrating  the  different  sys- 
tems, having  the  forms  shown  in  Figs.  35-40,  will  be  very  useful  to  the  student,  especially 
in  learning  the  fundamental  relations  as  regards  symmetry.  They  should  show  within,  the 
crystallographic  axes,  and  by  colored  threads  or  wires,  the  outlines  of  one  or  more  simple 
forms.  Models  of  wood  are  also  made  in  great  variety  and  perfection  of  form;  these  are 
indispensable  to  the  student  in  mastering  the  principles  of  crystallography. 


Orthorhombic 


Monoclinic 


Triclinic 


28.  So-called  Holohedral  and  Hemihedral  Forms.  —  It  will  appear 
later  that  each  crystal  form  *  of  the  normal  class  in  a  given  system  embraces 
all  the  faces  which  have  a  like  geometrical  position  with  reference  to  the 
crystallograpfeic  axes;  such  a  form  is  said  to  be  holohedral  (from  bXos,  com- 
plete, and  Mpz,  face).  On  the  other  hand,  under  the  classes  of  lower  sym- 
metry, a  certain  form,  while  necessarily  having  all  the  faces  which  the  sym- 
metry allows,  may  yet  have  but  half  as  many  as  the  corresponding  form  of 
the  normal  class ;  these  half -faced  forms  are  sometimes  called  on  this  account 
hemihedral.  Furthermore,  it  will  be  seen  that,  in  such  cases,  to  the  given 
holohedral  form  there  correspond  two  similar  and  complementary  hemihedral 
forms,  called  respectively  positive  and  negative  (or  right  and  left),  which 
together  embrace  all  of  its  faces. 


41 


43 


Octahedron 


Positive  Tetrahedron 


Negative  Tetrahedron 


A  single  example  will  help  to  make  the  above  statement  intelligible.  In  the  normal 
class  of  the  isometric  system,  the  octahedron  (Fig.  41)  is  a  " holohedral"  form  with  all 
the  possible  faces  —  eight  in  number  —  which  are  alike  in  that  they  meet  the  axes  at  equal 
distances.  In  the  tetrahedral  class  of  the  same  system,  the  forms  are  referred  to  the  same 
crystallographic  axes,  but  the  symmetry  defined  in  Art.  19  (and  more  fully  later)  calls  for 
but  four  similar  faces  having  the  position  described.  These  yield  a  four-faced,  or  "hemi- 
hedral/' form,  the  tetrahedron.  Figures  42  and  43  show  the  positive  and  negative  tetra- 
hedron, which  together,  it  will  be  seen,  embrace  all  the  faces  of  the  octahedron,  Fig.  41. 


*  The  use  of  the  word/orw  is  defined  in  Art.  37 


22 


CRYSTALLOGRAPHY 


' 


In  certain  classes  of  still  lower  symmetry  a  given  crystal  form  may  have 
ut  one-quarter  of  the  faces  belonging  to  the  corresponding  normal  form,  and, 
after  the  same  method,  such  a  form  is  sometimes  called  tetartohedral. 

The  development  of  the  various  possible  kinds  of  hemihedral  (and  tetarto- 
hedral) forms  under  a  given  system  has  played  a  prominent  part  in  the  crystal- 
lography of  the  past,  but  it  leads  to  much  complexity  and  is  distinctly  less 
simple  than  the  direct  statement  of  the  symmetry  in  each  case.  The  latter 
method  is  systematically  followed  in  this  work,  and  the  subject  of  hemihe- 
drism  is  dismissed  with  the  brief  (and  incomplete)  statements  of  this  and  the 
following  paragraphs. 

29.  Hemimorphic  Forms.  —  In  several  of  the  systems,  forms  occur 
under  the  classes  of  lower  symmetry  than  that  of  the  normal  class  which  are 
characterized  by  this :  that  the  faces  present  are  only  those  belonging  to  one 
extremity  of  an  axis  of  symmetry  (and  crystallographic 
axis) .  Such  forms  are  conveniently  called  hemimorphic 
(half-form).  A  simple  example  under  the  hexagonal 
system  is  given  in  Fig.  44.  It  is  obvious  that  hemi- 
morphic forms  have  no  center  of  symmetry. 

30.  Molecular  Networks.  —  Much  light  has  re- 
cently been  thrown  upon  the  relations  existing  between 
the  different  types  of  crystals,  on  the  one  hand,  and  of 
these  to  the  physical  propertied  of  crystals,  on  the  other, 
by  the  consideration  of  the  various  possible  methods  of 
grouping  of  the  molecules  of  which  the  crystals  are 
supposed  to  be  built  up.  This  subject,  very  early 
treated  by  Haiiy  and  others  (including  J.  D.  Dana), 
was  discussed  at  length  by  Frankenheim  and  later  by 

Bravais.     More  recently  it  has  been  extended  and  elaborated  by  Sohncke, 
Wulff,  Schonflies,  Fedorow,  Barlow,  and  others. 

All  solid  bodies,  as  stated  in  Art.  7,  are  believed  to  be  made  up  of  definite 
physical  units,  called  the  physical,  or  crystal,  molecules.  Of  the  form  of  the 
molecules  nothing  is  definitely  known,  and  though  theory  has  something  to  say 
about  their  size,  it  is  enough  here  to  understand  that  they  are  almost  infinitely 
small,  so  small  that  the  surface  of  a  solid  —  e.g.,  of  a  crystal  —  may  appear  to 
the  touch  and  to  the  eye,  even  when  assisted  by  a  powerful  microscope,  as 
perfectly  smooth. 

The  molecules  are  further  believed  to  be  not  in  contact  but  separated  from 
one  another  —  if  in  contact,  it  would  be  impossible  to  explain  the  motion  to 
which  the  sensible  heat  of  the  body  is  due,  or  the  transmission  of  radiation 
(radiant  heat  and  light)  through  the  mass  by  the  wave  motion  of  the  ether, 
which  is  believed  to  penetrate  the  body. 

When  a  body  passes  from  the  state  of  a  liquid  or  a  gas  to  that  of  a  solid, 
under  such  conditions  as  to  allow  perfectly  free  action  to  the  forces  acting 
between  the  molecules,  the  result  is  a  crystal  of  some  definite  type  as  regards 
symmetry.  The  simplest  hypothesis  which  can  be  made  assumes  that  the 
form  of  the  crystal  is  determined  by  the  way  in  which  the  molecules  group 
themselves  together  in  a  position  of  equilibrium  under  the  action  of  the  inter- 
molecular  forces. 

As,  however,  the  forces  between  the  molecules  vary  in  magnitude  and 
direction  from  one  type  of  crystal  to  another,  the  resultant  grouping  of  the 
molecules  must  also  vary,  particularly  as  regards  the  distance  between  them 


Zincite 


GENERAL  MORPHOLOGICAL   RELATIONS   OF   CRYSTALS 


23 


and  the  angles  between  the  planes  in  which  they  lie.  This  may  be  simply 
represented  by  a  series  of  geometrical  diagrams,  showing  the  hypothetical 
groupings  of  points  which  are  strictly  to  be  regarded  as  the  centers  of  gravity 
of  the  molecules  themselves.  Such  a  grouping  is  named  a  network,  or  point- 
system,  and  it  is  said  to  be  regular  when  it  is  the  same  for  all  parallel  lines 
and  planes,  however  they  be  taken.  For  the  fundamental  observed  fact,  true 
in  all  simple  crystals,  that  they  have  like  physical  properties  in  all  parallel 
directions,  leads  to  the  conclusion  that  the  grouping  of  the  molecules  must  be 
the  same  about  each  one  of  them  (or  at  least  about  each  unit  group  of  them), 
and  further  the  same  in  all  parallel  lines  and  planes. 


1 

-  - 

l) 

^^MSra^r" 

;  " 

1 

'ill!           i 

I 

H 

•si: 

-•fe 

H 

: 

.   i 

i 

#Hf 

i      1      r 

H 

u 

Crystal  Networks 

The  subject  may  be  illustrated  by  Figs.  45,  46  for  two  typical  cases,  which 
are  easily  understood.  In  Fig.  45  the  most  special  case  is  represented  where 
the  points  are  grouped  at  equal  distances,  in  planes  at  right  angles  to  each 
other.  The  structure  in  this  case  obviously  corresponds  in  symmetry  to  the 
cube  described  in  Arts.  15  and  16,  or,  in  other  words,  to  the  normal  class  of 
the  isometric  system.  Again,  in  Fig.  46,  the  general  case  is  shown  where  the 
molecules  are  unequally  grouped  in  the  three  directions,  and  further  these 
directions  are  oblique.  The  symmetry  is  here  that  of  the  normal  class  of  the 
triclinic  system. 

If,  in  each  of  these  cases,  the,  figure  be  bounded  by  the  simplest  possible 
arrangement  of  eight  points,  the  result  is  an  elementary  parallelepiped,  which 
obviously  defines  the  molecular  structure  of  the  whole.  In  the  grouping  of 
these  parallelepipeds  together,  as  described,  it  is  obvious  that  in  whatever 
direction  a  line  be  drawn  through  them,  the  points  (molecules)  will  be  spaced 
alike  along  it,  and  the  grouping  nbout  any  one  of  these  points  will  be  the  same 
as  about  any  other. 

31.  Certain  important  conclusions  can  be  deduced  from  a  consideration 
of  such  regular  molecular  networks  as  have  been  spoken  of,  which  will  be 
enumerated  here  though  it  is  impossible  to  attempt  a  full  explanation. 

(1)  The  prominent  crystalline  faces  must  1x3  such  as  include  the  largest 
number  of  points,  that  is,  those  in  which  the  points  are  nearest  together. 

Thus  in  Fig.  47,  which  represents  a  section  of  a  network  conforming  in 
symmetry  to  the  structure  of  a  normal  orthorhombic  crystal,  the  common 
crystalline  faces  would  be  expected  to  be  those  having  the  position  66,  aa,  mm, 


24 


CRYSTALLOGRAPHY 


then  II,  nn,  and  so  on.  This  is  found  to  be  true  in  the  study  of  crystals,  for 
the  common  forms  are,  in  nearly  all  cases,  those  whose  position  bears  some 
simple  relation  to  the  assumed  axes;  forms  whose  position  is  complex  are 
usually  present  only  as  small  faces  on  the  simple  predominating  forms,  that 
is,  as  modifications  of  them-  So-called  vicinal  forms,  that  is,  forms  taking 
the  place  of  the  simple  fundamental  forms  to  which  they  approximate  very 
closely  in  angular  position,  are  exceptional. 


Orthorhombic  Point  System 

(2)  When  a  variety  of  faces  occur  on  the  same  crystal,  the  numerical  rela- 
tion existing  between  them  (that  which  fixes  their  position)  must  be  rational 
and,  as  stated  in  (1),  a  simple  numerical  ratio  is  to  be  expected  in  the  common 
cases.     This,  as  explained  later,  is  found  by  experience  to  be  a  fundamental 
law  of  all  crystals.     Thus,  in  Fig.  47,  starting  with  a  face  meeting  the  section 
in  mm,  II  would  be  a  common  face,  and  for  it  the  ratio  is  1  :  2  in  the  directions 
b  and  a;  nn  would  be  also  common  with  the  ratio  2:1. 

(3)  If  a  crystal  shows  the  natural  easy  fracture,  called  cleavage,  due  to  a 
minimum  of  cohesion,  the  cleavage  surface  must  be  a  surface  of  relatively 
great  molecular  crowding,  that  is,  one  of  the  common  or  fundamental  faces. 
This  follows  (and  thus  gives  a  partial,  though  not  complete,  explanation  of 
cleavage)  since  it  admits  of  easy  proof  that  that  plane  in  which  the  points 
are  closest  together  is  farthest  separated  from  the  next  molecular  plane. 
Thus  in  Fig  47  compare  the  distance  separating  two  adjoining  planes  parallel 
to  bb  or  aa,   then  two  parallel  to  mm,  II,  nn,  etc      Illustrations  of  the  above 
will  be  found  under  the  special  discussion  of  the  subject  of  cleavage. 


GENERAL  MORPHOLOGICAL   RELATIONS   OF   CRYSTALS  25 

32.  Kinds  of  Molecular  Groupings.  —  The  discussion  on  the  basis  just 
described  shows  that  there  are  fourteen  possible  types  of  arrangement  of  the 
molecules.     These  agree  as  to  their  symmetry  with  the  seven  classes  defined 
in  Art.  25  as  representing  respectively  the  normal  classes  of  the  six  systems 
with  also  that  of  the  trigonal  (or  the 

rhombohedral)  division  of  the  hex- 
agonal  system.     Of   the   fourteen, 
three  groupings  belong  to  the  iso- 
metric system  (these  are  shown,  for 
sake  of  illustration,  in  Fig.  48  from 
Groth;    a,    cube   lattice;     &,   cube- 
centered   lattice;    c,   face   centered  Isometric  Lattices 
cube  lattice) ;  two  to  the  tetragonal; 
one  each  to  the  hexagonal  and  the  rhombohedral;   four  to  the  orthorhombic 
system;  two  to  the  monoclinic,  and  one  to  the  triclinic. 

In  its  simplest  form,  as  above  outlined,  the  theory  fails  to  explain  the  ex- 
istence of  the  classes  under  the  several  systems  of  a  symmetry  lower  than  that 
of  the  normal  class.  It  has  been  shown,  however,  by  Sohncke  and  later  by 
Fedorow,  Schonflies  and  Barlow,  that  the  theory  admits  of  extension.  The 
idea  supposed  by  Sohncke  is  this:  that,  instead  of  the  simple  form  shown,  the 
network  may  consist  of  a  double  system,  one  of  which  may  be  conceived  of  as 
having  a  position  relative  to  the  other  (1)  as  if  pushed  to  one  side,  or  (2)  as  if 
rotated  about  an  axis,  or  finally  (3)  as  if  both  rotated  as  in  (2)  and  displaced 
as  in  (1)  The  complexity  of  the  subject  makes  it  impossible  to  develop  it 
here.  It  must  suffice  to  say  that  with  this  extension  Sohncke  concludes  that 
there  are  65  possible  groups.  This  number  has  been  further  extended  to  230 
by  the  other  authors  named,  but  it  still  remains  true  that  these  fall  into  32 
distinct  types  as  regards  symmetry,  and  thus  all  the  observed  groups  of  forms 
among  crystals,  described  under  the  several  systems,  have  a  theoretical 
explanation, 

Literature.  —  A  complete  understanding  of  this  subject  can  only  be  gained 
by  a  careful  study  of  the  many  papers  devoted  to  it.  An  excellent  and  very 
clear  summary  of  the  whole  subject  is  given  by  Groth  in  the  fourth  edition  of 
his  Physikalische  Krystallographie,  1905,  and  by  Sommerfeldt,  in  his  Physi- 
kalische  Kristallographie,  1907. 

33.  X-Rays  and  Crystal  Structure.  —  In   1912,   while  attempting  to 
prove  a  similarity  in  character  between  X-rays  and  light,  Dr.  Laue,  of  the 
University  of  Zurich  conceived  the  idea  of  using  the  ordered  arrangement  of 
the  molecules  or  atoms  of  a  crystal  as  a  "  diffraction  grating  "  for  their  analysis 
By  placing  a  photographic  plate  behind  a  crystal  section  which  in  turn  lay 
in  the  path  of  a  beam  of  X-rays  he  found  that  not  only  did  the  developed 
plate  show  a  dark  spot  in  its  center  where  the  direct  pencil  of  the  X-rays  had 
hit  it  but  it  also  showed  a  large  number  of  smaller  spots  arranged  around  the 
center  in  a  regular  geometrical  pattern.     This  pattern  was  formed  by  the 
interference  of  waves  which  had  been  diffracted  in  different  directions  by  the 
molecular  structure  of  the  crystal.     In  this  way  he  succeeded  in  proving  that 
X-rays  belong  to  the  same  class  of  phenomena  as  light  but  with  a  much 
shorter  wave  length.     The  experiment  showed  indeed  that  the  wave  lengths 
of  the  X-rays  must  be  comparable  to  the  distances  between  the  layers  of 
molecular  particles  of  crystals.     Another,  and,  from  the  crystallographic  point 
of  view,  a  very  important,  result  of  this  investigation  was  the  furnishing  of  a 


26  CRYSTALLOGRAPHY 

method  for  the  study  of  the  internal  structure  of  crystals.  The  position  of 
the  smaller  dark  spots  in  the  Laue  photographs  corresponded  to  that  of 
various  planes  existing  in  the  crystal  network  parallel  to  possible  crystal 
faces  and  their  arrangement  indicated  the  symmetry  of  the  crystal. 

Following  these  investigations  of  Laue  and  his  colleagues  another  fruitful 
method  of  investigation  of  crystal  structure  by  means  of  X-rays  was  devised 
by  W.  H.  and  W.  L.  Bragg.  In  this  method  the  beam  of  X-rays  meets  the 
crystal  section  with  varying  acute  angles  of  incidence  and  the  reflection  of 
the  rays  is  studied.  The  X-rays  are  not  reflected  from  the  surface  of  the 
section  like  light  rays  but  because  of  their  short  wave  lengths  penetrate  the 
crystal  section  and  are  reflected  from  the  successive  layers  of  its  molecular 
structure.  In  studying  the  reflection  phenomena  we  have  to  consider  the 
effect  upon  each  other  of  these  different  wave  trains  originating  from  the 
different  layers  of  the  crystal.  In  general  these  various  reflected  waves 
would  be  in  different  phases  of  vibration  and  so  would  tend  to  interfere  with 
each  other  with  the  consequent  cessation  of  all  vibrations.  But  with  a  cer- 
tain angle  of  incidence  and  reflection  it  would  happen  that  the  different  re- 
flected rays  would  possess  on  emergence  from  the  crystal  the  same  phase  of 
vibration  and  would  therefore  reinforce  each  other.  This  angle  would  vary 
with  the  wave  length  of  the  X-ray  used  (for  it  has  been  found  that  the  wave 
length  of  X-rays  varies  with  the  metal  that  is  used  as  the  anticathode  in  the 
X-ray  bulb)  and  with  the  spacing  between  the  molecular  layers  of  the  mineral 
used.  It  is  also  obvious  that  there  might  be  other  angles  of  incidence  at 
which  the  successive  wave  trains  would  each  differ  in  phase  by  two  or  even 
more  whole  wave  lengths  from  the  preceding  one  and  a  similar  strong  re- 
flected beam  obtained.  By  the  use  of  a  special  X-ray  spectrometer  the  angles 
at  which  these  reflections  take  place  can  be  accurately  measured.  If  the 
character  of  the  X-ray  used  is  therefore  kept  constant  these  angles  of  reflec- 
tion give  the  data  necessary  for  calculating  the  distance  between  the  succes- 
sive molecular  layers  in  the  particular  mineral  used  and  for  the  direction 
perpendicular  to  the  surface  used  for  reflection.  The  spacing  of  the  molec- 
ular layers  was  found  to  vary  with  different  substances  and  in  different 
directions  in  the  same  substance  and  by  making  a  series  of  observations  it 
has  been  possible  to  arrive  at  some  very  interesting  conclusions  as  to  the 
character  of  the  molecular  structure  of  certain  minerals  as  well  as  to  the 
relationship  existing  between  the  structures  of  different  but  related  com- 
pounds. The  possibilities  lying  in  these  methods  of  attack  are  very  great 
and  unquestionably  much  new  information  concerning  crystal  structure  will 
soon  be  available.  An  excellent  summary  of  the  methods  employed  and  the 
results  already  obtained  will  be  found  in  "  X-rays  and  Crystal  Structure  " 
by  W.  H.  and  W.  L.  Bragg,  1915. 


GENERAL  MATHEMATICAL  RELATIONS  OF 

CRYSTALS 

34.  Axial  Ratio,  Axial  Plane.  —  The  crystallographic  axes  have  been 
defined  (Art.  22)  as  certain  lines,  usually  determined  by  the  symmetry,  which 
are  used  in  the  description  of  the  faces  of  crystals,  and  in  the  determination  of 
their  position  and  angular  inclination.  With  these  objects  in  view,  certain 


GENERAL   MATHEMATICAL   RELATIONS   OF   CRYSTALS 


27 


49 


lengths  of  these  axes  are  assumed  as  units  to  which  the  occurring  faces  are 
referred. 

The  axes  are,  in  general,  lettered  a,  b,  c,  to  correspond  to  the  scheme  in 
Fig.  49.  If  two  of  the  axes  are  equal,  they  are  designated  a,  a,  c;  if  the  three 
are  equal,  a,  a,  a.  In  one  system,  the  hexagonal,  there  are 
four  axes,  lettered  a,  a,  a,  c. 

Further,  in  the  systems  other  than  the  isometric,  one 
of  the  horizontal  axes  is  taken  as  the  unit  to  which  the  other 
axes  are  referred;  hence  the  lengths  of  the  axes  express 
strictly  the  axial  ratio.  Thus  for  sulphur  (orthorhombic, 
see  Fig.  49)  the  axial  ratio  is 

a  :  b  :  c  =  0'8131  :  1  :  1'9034. 


For  rutile  (tetragonal)  it  is 

a  :  c  =  1  :  0'64415,     or,  simply,     c  =  0'64415. 

The  plane  of  any  two  of  the  axes  is  called  an  axial  plane, 
and  the  space  included  by  the  three  axial  planes  is  an  octant, 
since  the  total  space  about  the  center  is  thus  divided  by  the 
three  axes  into  eight  parts.  In  the  hexagonal  system,  how- 
ever, where  there  are  three  horizontal  axes,  the  space  about 
the  center  is  divided  into  12  parts,  or  sectants. 

35.   Parameters,  Indices,  Symbol.  —  Parameters.     The  parameters  of 
a  plane  consist  of  a  series  of  numbers  which  express  the  relative  intercepts 

of  that  plane  upon  the  crys- 
tallographic  axes.  They  are 
given  in  terms  of  the  estab- 
lished unit  lengths  of  those 
axes.  For  example,  in  Fig. 
50  let  the  lines  OX,  OY,  OZ 
be  taken  as  the  directions  of 
the  crystallographic  axes,  and 
let  OA,  OB,  OC  represent 
their  unit  lengths,  designated 
(always  in  the  same  order)  by 
the  letters  a,  b,  c.  Then  the 


Orthorhombic 
Crystal  Axes 


intercepts  for  the  plane  (1) 
HKL  are  OH,  OK,  OL;  for 
the  plane  (2)  ANM  they  are 
OA,  ON,  OM.  But  in  terms 
of  the  unit  lengths  of  the 
axes  these  give  the  following 
parameters, 


and 


(1) 
(2) 


la 


2c. 


It  is  to  be  noted  that  since 
the    two    planes   HKL   and 

MNA  are  parallel  to  each  other  and  hence  crystallographically  the  same, 
these  two  sets  of  parameters  are  considered  to  be  identical.  Obviously  each 
of  them  may  be  changed  into  the  other  by  multiplying  (or  dividing)  by  4. 


28  CRYSTALLOGRAPHY 

Indices  and  Symbol.  Simplified  and  abbreviated  expressions  which  have 
been  derived  from  the  parameters  of  a  crystal  form  are  commonly  used  to 
give  its  relations  to  the  crystallographic  axes.  These  are  known  as  indices. 
A  number  of  different  methods  of  deriving  indices  have  been  devised  and 
several  are  in  use  at  present.  The  so-called  Miller  indices  are  most  widely 
employed  and  will  be  exclusively  used  in  this  work.*  Below,  a  description 
of  the  other  important  systems  of  indices  is  given  together  with  the  neces- 
sary directions  for  transforming  one  type  into  another. 

The  Miller  indices  may  be  derived  from  the  parameters  of  any  form  by 
taking  their  reciprocals  and  clearing  of  fractions  if  necessary.  For  instance 
take  the  two  sets  of  parameters  as  given  above. 

(1)     \a  :  |6  :  \c,       and       (2)     la  :  |6  :  2c. 

By  inversion  of  these  expressions  we  obtain 

(1)  4a  :  36  :  2c,       and       (2)     la  :  |6  :  ic. 

In  the  case  of  (2)  it  is  necessary  to  clear  of  fractions,  giving 

(2)  4a  :  36  :  2c. 

The  indices  of  this  form  then  are  4  a  :  3  6  :  2  c.  The  letters  indicating  the 
different  axes  are  commonly  dropped  and  the  indices  in  this  case  would  be 
written  simply  as  432,  the  intercepts  on  the  different  axes  being  indicated  by 
the  order  in  which  the  numbers  are  given. 

A  general  expression  frequently  used  for  the  indices  of  a  form  belonging 
to  any  crystal  system  which  has  three  crystallographic  axes  is  hkl.  In  the 
hexagonal  system,  which  has  four  axes,  this  becomes  hkil.  If  the  parameters 
of  a  form  be  written  so  that  they  are  fractions  with  the  numerators  always 
unity  then  the  denominators  will  become  the  same  as  the  corresponding  in- 
dices. The  general  expression  in  this  case  would  therefore  be  T  r  7  • 

rl  K   L 

The  symbol  of  a  given  form  is  the  indices  of  the  face  of  that  form  which 
has  the  simplest  relations  to  the  crystallographic  axes.  The  symbol  is  com- 
monly used  to  designate  the  whole  form. 

Various  examples  are  given  below  illustrating  the  relations  between  param- 
eters and  indices. 

•      Parameters  Miller's  Symbol 

}   =  %a  :  kb  :  Ic  =  221 


fe 


la 
}a 

la 
la 
la 
la 


16 

16 

26 

006 

GO6 

16 

26 
006 


lcl   = 


2c/ 

ooci 
ooc 


:  %c  =  212 

:  jc  =  201 


)   =  \a  :  &  :fc  =  210 


ooc     =  ja  :  £6  :  £c  =  100 

If  the  axial  intercepts  are  measured  in  behind  on  the  a  axis,  or  to  the 
left  on  the  6  axis,  or  below  on  the  c  axis,  they  are  called  negative,  and  a  minus 
sign  is  placed  over  the  corresponding  number  of  the  indices;  as 

Parameters          Indices 


-\a 
-io 


-\b  :  \c  =         221 
201 


*In  the  hexagonal  system  the  indices  used  are  those  adapted  by  Bravais  after  the 
method  of  Miller. 


GENERAL   MATHEMATICAL   RELATIONS   OF   CRYSTALS 


29 


Different  Systems  of 'Indices.  The  Weiss  indices  are  the  same  as  the  parameters 
described  above.  The  different  axes  are  represented  by  the  letters  a,  b  and  c,  each  being 
preceded  by  a  number  indicating  the  relative  intercept  of  the  face  in  question  upon  that 
particular  axis.  For  instance,  a  possible  orthorhombic  pyramid  face  might  be  represented 
as  la  :  26  :  fc.  The  Weiss  indices  may  be  converted  into  the  Miller  indices  by  inversion 
and  clearing  of  fractions,  the  above  symbol  becoming  then  213.  In  the  Naumann  indices 
the  unit  pyramidal  form  is  indicated  by  O  in  the  isometric  system  where  the  three  crystal 
axes  all  have  the  same  unit  lengths  or  by  P  where  the  axes  differ  in  their  unit  lengths. 
For  other  forms  the  indices  become  mPn  (or  mOn)  in  which  m  gives  the  intercept  upon  the 
vertical  axis,  c,  and  n  the  intercept  upon  one  of  the  horizontal  axes  (a  or  6),  the  intercept 
upon  the  other  horizontal  axis  being  always  at  unity.  To  which  particular  horizontal  axis 
this  number  refers  may  be  indicated  by  a  mark  over  it  as  n  for  the  b  axis,  ft  or  n'  for  the 
a  axis.  If  the  intercept  m  or  n  is  unity  it  is  omitted  from  the  indices.  The  pyramid  face 
used  as  an  example  above  would  therefore  in  the  Naumann  notation  be  represented  by 
|P2.  Other  examples  are  given  in  the  table  below.  J.  D.  Dana  modified  the  Naumann 
indices  by  substituting  a  hyphen  for  the  letter  P  or  O  and  i  for  the  infinity  sign,  oo .  He 
designated  the  fundamental  pyramid  form  simply  by  1.  When  the  only  parameter  differ- 
ing from  unity  was  that  one  which  referred  to  the  intercept  upon  the  vertical  axis,  it  was 
written  alone;  for  example  the  pyramid  face  having  the  parameter  relations  of  la  :  16  :  2c 
would  be  indicated  by  2.  The  Naumann  and  Dana  indices  are  easily  converted  into  the 
Miller  indices  by  arranging  them  in  the  proper  order,  inverting  and  then  clearing  of  frac- 
tions. Goldschmidt  has  proposed  another  method  of  deriving  indices.  This  has  the 
advantage  that  the  indices  for  any  particular  face  can  be  derived  directly  from  the  position 
of  its  pole  on  the  gnomonic  projection.  The  first  number  gives  the  linear  position  of  the 
pole  in  respect  to  the  left  to  right  medial  line  of  the  projection  and  in  terms  of  the  unit 
pace  distance  of  the  projection  (see  Art.  84).  The  second  figure  similarly  gives  the 
position  of  the  pole  in  reference  to  the  front  to  back  medial  line.  These  two  figures  con- 
stitute the  Goldschmidt  indices  of  the  face.  If  the  two  numbers  should  be  the  same  the 
second  is  omitted.  The  Goldschmidt  indices  are  easily  converted  into  the  Miller  indices 
by  adding  1  as  the  third  figure  and  clearing  of  fractions  and  eliminating  any  oo  sign. 

The  relations  between  the  Miller  and  the  Miller-Bravais  indices  for  the  hexagonal 
system  are  given  in  Art.  169. 

EXAMPLES  OF  INDICES  ACCORDING  TO  VARIOUS  SYSTEMS  OF 

NOTATION 


Weiss 

Naumann 

Dana 

Goldschmidt 

Miller 

la 

16 

2c.  . 

2P 

2 

2 

221 

\a 

26 

lc  

OP2 

1-2 

ii 

212 

la 

006 

2c  

2Poo 

2-i 

20 

201 

la 

?,b 

ooc  

oo  P2 

i-2 

2oo 

210 

la 

006 

ooc  

oo  Poo 

i-i 

ooO 

100 

36.  Law  of  Rational  Indices.  —  The  study  of  crystals  has  established 
the  general  law  that  the  ratios  between  the  intercepts  on  the  axes  for  the 
different  faces  on  a  crystal  can  always  be  expressed  by  rational  numbers. 
These  ratios  may  be  1:2,  2:1,  2:3,  1  :  oo,  etc.,  but  never  1  :  V2,  etc. 
Hence  the  values  of  hkl  in  the  Miller  symbols  must  always  be  either  whole 
numbers  or  zero. 

If  the  form  whose  intercepts  on  the  axes  a,  6,  c  determine  their  assumed 
unit  lengths  —  the  unit  form  as  it  is  called  —  is  well  chosen,  these  numerical 
values  of  the  indices  are  in  most  cases  very  simple.  In  the  Miller  symbols, 
0  and  the  numbers  from  1  to  6  are  most  common. 

The  above  law,  which  has  been  established  as  the  result  of  experience,  in 
fact  follows  from  the  consideration  of  the  molecular  structure  as  hinted  at  in 
an  earlier  paragraph  (Art.  31). 


30 


CRYSTALLOGRAPHY 


37.  Form.  —  A  form  in  crystallography  includes  all  the  faces  which 
have  a  like  position  relative  to  the  planes,  or  axes,  of  symmetry.  The  full 
meaning  of  this  will  be  appreciated  after  a  study  of  the  several  systems.  It 
will  be  seen  that  in  the  most  general  case,  that  of  a  form  having  the  symbol 
(hkl),  whose  planes  meet  the  assumed  unit  axes  at  unequal 
lengths,  there  must  be  forty-eight  like  faces  in  the  isometric 
system  *  (see  Fig.  121),  twenty-four  in  the  hexagonal  (Fig.  226), 
sixteen  in  the  tetragonal  (Fig.  187),  eight  in  the  orthorhombic 
(Fig.  51),  four  in  the  monoclinic,  and  two  in  the  triclinic.  In 
the  first  four  systems  the  faces  named  yield  an  enclosed  solid, 
and  hence  the  form  is  called  a  closed  form;  in  the  remaining 
two  systems  this  is  not  true,  and  such  forms  in  these  and 
other  cases  are  called  open  forms.  Fig.  298  shows  a  crystal 
bounded  by  three  pairs  of  unlike  faces;  each  pair  is  hence  an 
open  form.  Figs.  52-55  show  open  forms. 

The  unit  or  fundamental  form  is  one  where  parameters  cor- 
respond to  the  assumed  unit  lengths  of  the  axes.  Fig.  51  shows  the  unit 
pyramid  of  sulphur  whose  symbol  is  (111);  it  has  eight  similar  faces,  the 
position  of  which  determines  the  ratio  of  the  axes  given  in  Art.  34. 


52 


53 


Basal  Pinacoid 
(001) 

54 


Prism 
(110)  (/i/cO) 


Dome 
(101),  (MM) 


Dome 
(Oil),  (OW) 


*  The  normal  cla,ss  is  referred  to  in  each  case. 


GENERAL   MATHEMATICAL   RELATIONS   OF   CRYSTALS 


31 


56 


The  forms  in  the  isometric  system  have  special  individual  names,  given  later.  In  the 
other  systems  certain  general  names  are  employed  in  this  book  which  may  be  briefly  men- 
tioned here.  A  form  whose  faces  are  parallel  to  two  of  the  axes  *  is  called  a  pinacoid  (from 
Trufa^j  a  board).  It  is  shown  in  Fig.  52.  One  whose  faces  are  parallel  to  the  vertical  axis 
but  meet  both  the  horizontal  axes  is  called  a  prism,  as  Fig.  53.  If  the  faces  are  parallel  to 
one  horizontal  axis  only,  it  is  a  dome  (Figs.  54,  55) .  If  the  faces  meet  all  the  axes,  the  form 
is  a  pyramid  (Fig.  51);  this  name  is  given  even  if  there  is  only  one  face  belonging  to  the 
form. 

In  Fig.  56,  a(100),  6(010)  are  pinacoids;  w(110),  s(120)  are  prisms;  d(101)  and  fc(021) 
are  domes;  all  these  are  open  forms.  Finally,  e(lll)  is  a  pyramid,  this  being  a  closed  form. 
The  relation  existing  in  each  of  these  cases  between  the  symbol  and  the  position  of  the 
faces  to  the  axes  should  be  carefully  studied. 

As  shown  in  the  above  cases,  the  symbol  of  a  form  is  usually  included  in  parentheses, 
as  (111),  (100);  or  it  may  be  in  brackets  [111]  or  UH  \. 

38.  Zone.  —  A  zone  includes  a  series  of  faces  on  a  crystal  whose  inter- 
section-lines are  mutually  parallel  to  each  other  and  to  a  common  line  drawn 
through  the  center  of  the  crystal,  called  the  zone-axis.     This 

parallelism  means  simply  that  the  given  faces  are  either  all 
parallel  to  one  of  the  crystallographic  axes  or  that  their 
parameters  have  a  constant  ratio  for  two  of  the  axes.  Some 
simple  numerical  relation  exists,  in  every  case,  between  all 
the  faces  in  a  zone,  which  is  expressed  by  the  zonal  equation 
(see  Art.  45).  The  faces  m,  s,  b  (Fig.  56)  are  in  a  zone; 
also,  b  and  k. 

If  a  face  of  a  crystal  falls  simultaneously  in  two  zones, 
it  follows  that  its  symbol  is  fixed  and  can  be  determined 
from  the  two  zonal  equations,  without  the  measurement  of 
angles.  Further,  it  can  be  proved  that  the  face  correspond- 
ing to  the  intersection  of  two  zones  is  always  a  possible 
crystal  face,  that  is,  one  having  rational  values  for  the  indices 
which  define  its  position. 

In  many  cases  the  zonal  relation  is  obvious  at  sight,  but 
it  can  always  be  determined,  as  shown  in  Arts.  45,  46  by  an 
easy  calculation. 

Illustrations  will  be  given  after  the  methods  of  representing  a 
crystal  by  the  various  projections  have  been  explained.  Chrysolite 

39.  Horizontal  Projections.  —  In  addition  to  the  usual 
perspective  figures  of  crystals,  projections  on  the  basal  plane  (or  more  gener- 
ally the  plane  normal  to  the  prismatic  zone)  are  very  conveniently  used. 
These  give  in  fact  a  map  of  the  crystal  as  viewed  from  above  looking  in  the 
direction  of  the  axis  of  the  prismatic  zone.     Figs.  30-33  give  simple  examples. 
In  these  the  successive  faces  may  be  indicated  by  accents,  as  in  Fig.  56,  passing 
around  in  the  direction  of  the  axes  a,  6,  a,  that  is,  counter-clockwise.     On 
the  construction  of  these  projections  see  the  Appendix  A. 

40.  Spherical  Projection.  —  The  study  of  actual  crystals,  particularly 
as  regards  the  angular  and  zonal  relations  of  their  faces,  is  much  facilitated 
by  the  use  of  various  projections.     The  simplest  of  these  and  the  one  from 
which  the  others  may  be  derived  is  known  as  the  spherical  projection. 

In  making  a  spherical  projection  of  a  crystal  it  is  assumed  that  the  crystal 
lies  within  a  sphere,  the  center  of  which  coincides  with  the  center  of  the 


*  In  the  tetragonal  system  the  form  (100)  is,  however,  called  a  prism  and  (101)  a 
pyramid. 


32 


CRYSTALLOGRAPHY 


crystal  (i.e.  the  point  of  intersection  of  its  crystallographic  axes).  From  this 
common  center  normals  are  drawn  to  the  successive  faces  of  the  crystal  and 
continued  until  they  meet  the  surface  of  the  sphere.  The  points  in  which 
these  normals  touch  that  surface  locate  the  poles  of  the  respective  faces  and 

together  form  the  spherical 
projection  of  the  crystal. 
The  method  of  formation 
and  the  character  of  the 
spherical  projection  is  shown 
in  Fig.  57. 

It  is  to  be  noted  that  all 
the  poles  of  faces  which  lie 
in  the  same  zone  on  the 
crystal,  i.e.  faces  whose  in- 
tersection lines  are  mutually 
parallel,  fall  upon  the  same 
great  circle  on  the  sphere. 
TTulTls  illustrated  in  the 
figure  in  the  case  of  the 
zone  a-d-a  and  a-o-d.  Con- 
versely, of  course,  all  faces 
whose  poles  fall  on  the  same 
great  circle  of  the  spherical 
projection  must  lie  in  the 
same  zone.  A  face  whose 
pole  falls  at  the  intersection 
of  two  or  more  great  circles 
lies  in  two  or  more  inde- 


Spherical  Projection  (after  Penfield) 


pendent  zones,  as  for  instance  o(lll),  in  Fig.  57.  The  angular  relations 
between  the  faces  on  the  crystal  are  of  course  preserved  in  the  angles  exist- 
ing between  their  respective  poles  on  the  spherical  projection.  The  angles 
between  the  poles,  however,  are  the  supplementary  angles  to  those  between 
the  faces  on  the  crystal,  as  shown  in  Fig.  58.  The 
supplementary  angles  are  those  which  are  commonly 
measured  and  recorded  when  studying  a  crystal,  see 
Art.  230. 

The  spherical  projection  is  very  useful  in  getting 
a  mental  picture  of  the  relations  existing  between  the 
various  faces  and  zones  upon  a  crystal  but  because  of 
its  nature  does  not  permit  of  the  close  study  and  ac- 
curate measurements  that  may  be  made  on  the  other 
projections  described  below  which  are  made  on  plane 
surfaces. 

41.  The  Stereographic  Projection.  —  The  stereo- 
graphic  projection  may  be  best  considered  as  derived 
from  the  spherical  projection  in  the  following  man- 


sioij °[ 
projection  * 


ner.  The  plane  of  the  projection  is  commonly  taken  as  the  equatorial 
plane  of  the  sphere.  Imaginary  lines  are  drawn  from  the  poles  of  the  spheri- 
cal projection  to  the  south  pole  of  the  sphere.  The  points  in  which  these 
lines  pierce  the  plane  of  the  equator  locate  the  poles  in  the  stereographic  pro- 
jection. The  relation  between  the  two  projections  is  shown  in  Fig.  59. 


GENERAL   MATHEMATICAL   RELATIONS   OF   CRYSTALS 


33 


oft 


111 


010 


Fig.  60  shows  the  same  stereographic  projection  without  the  foreshortening 
of  Fig.  59.  Commonly  only  the  poles  that  lie  in  the  northern  hemisphere, 
including  those  on  the  equator,  are  transferred  to  the  stereographic  projection. 

Certain  facts  concerning  the  stereographic  projection  need  to  be  noted. 
Its  most  important  charac-  -* 

ter  is  that  all  circles  or  cir- 
cular arcs  on  the  spherical 
projection  are  projected  as 
arcs  of  true  circles  on  the 
stereographic  projection.* 
The  poles  of  all  crystal 
faces  that  are  parallel  to 
the  vertical  crystallogra- 
phic  axis  fall  on  the  equa- 
tor of  the  spherical  pro- 
jection and  occupy  the 
same  positions  in  the  stere- 
ographic projection.  The 
pole  of  a  horizontal  face 
will  fall  on  the  center  of 
the  stereographic  projec- 
tion. All  north  and  south 
meridians  of  the  spherical 
projection  will  appear  as 
straight  radial  lines  in  the 
stereographic  projection 
(i.e.  as  arcs  of  circles  hav- 
ing infinite  radii).  Other  Relation  between  Spherical  and  Stereographic  Projections 
great  circles  on  the  spher- 
ical projection,  as  already  stated,  will  be  transferred  to  the  stereographic  as 
circular  arcs.  Examples  of  all  these  are  shown  in  Fig.  60. 

The  angular  relations  between  the  poles  of  the  various  faces  are  preserved 
in  the  stereographic  projection  but  the  linear  distance  corresponding  to  a 
degree  of  arc  naturally  increases  from  the  center  of  the  projection  toward  its 
circumference.  This  is  illustrated  in  Fig.  61  where  the  circle  represents  a 
vertical  section  through  the  spherical  projection  and  the  line  A-B  represents 
the  trace  of  the  horizontal  plane  of  the  stereographic  projection.  A  point 
20°  from  N  on  the  sphere  is  projected  to  the  point  a  on  the  stereographic 
projection,  a  point  45°  from  N  is  projected  to  b,  etc.  In  this  way  a  protractor 
can  be  made  by  means  of  which  angular  distances  from  the  center  of  the 
stereographic  projection  can  be  readily  determined.  Fig.  62  represents  such 
a  protractor  which  was  devised  by  Penfield.f  The  mathematical  relation 
between  the  linear  distance  from  the  center  of  the  projection  and  its  angular 
value  is  seen  by  study  of  Fig.  61.  If  the  radius  of  the  circle  of  the  projection 
is  taken  as  unity  the  distance  from  its  center  to  any  desired  point  is  equal  to 
the  tangent  of  one  half  of  the  angle  represented.  For  instance  the  distance 


*  For  proof  of  this  statement  see  Penfield,  Am.  Jour.  Sci.,  11,  10,  1901. 

f  This  protractor  and  the  other  protractors  and  scales  used  by  Penfield  ?pan  be  ob- 
tained from  the  Mineralogical  Laboratory  of  the  Sheffield  Scientific  School  of  Yale  Uni- 
versity, New  Haven,  Ct. 


34 


CR  YSTALLO  GR  APH  Y 


60 


duo 


dlio 


a  01 


a  010 


a  100 


Stereographic  Projection  of  the  Isometric  Forms,  Cube,  Octahedron,  and  Dodecahedron 

61 


from  the  center  to  the  point  a  is  equivalent  to  the  tangent  of  10°,  to  point  c 
the  tangent  of  35°,  etc. 

Fig.  63  represents  a  chart  used  by  Penfield  for  making  stereographic 
projections.  The  circle  has  a  diameter  of  14  cm.  and  is  graduated  to  de- 
grees. With  it  go  certain  scales  that  are  very  useful  in  locating  the  desired 
points  and  zonal  circles.  These  will  be  briefly  described  later. 


GENERAL   MATHEMATICAL   RELATIONS   OF   CRYSTALS 


35 


For  detailed  descriptions  of  the  principles  of  the  stereographic  projection 
and  the  methods  of  its  use  the  reader  is  referred  to  the  various  books  and 
articles,  the  titles  of  which  are  given  beyond.  It  is  possible  here  to  give  only 
a  brief  outline  of  the  more  important  methods  of  construction  used. 

62 


Stereographic  Protractor  for  plotting  Stereographic  Projections  (after  Penfield; 

reduced  one-half) 

(1) .  To  locate  the  pole  of  a  face  lying  on  a  known  north  and  south  great  circle, 
its  angular  distance  from  the  center  or  a  point  on  the  circumference  of  the  pro- 
jection being  given.  The  stereographic  protractor,  Fig.  62,  or  the  tangent  rela- 
tion as  stated  above,  gives  the  proper  distance.  The  poles  labeled  o  (iso- 
metric octahedron),  Fig.  60,  may  be  located  in  this  way. 

(2)  To  locate  the  projection  of  the  arc  of  a  great  circle  which  is  not  a  north 
and  south  meridian  or  the  equator.     The  projections  of  three  points  on  the 
arc  must  be  known.     Then,  since  the  projection  of  the  circle  will  be  still  a 
circular  arc,  its  position  can  be  determined  by  the  usual  geometric  construc- 
tion for  a  circle  with  three  points  on  its  arc  given.     If,  as  is  commonly  the 
case,  the  points  where  the  great  circle  crosses  the  equator  and  the  angle  it 
makes  with  the  equator  are  known  it  is  possible  to  get  the  radius  of  the  pro- 
jected arc  directly  from  Scale  No.  1,  Fig.  63.     The  location  of  such  a  desired 
arc  is  shown  in  Fig.  64.     The  arcs  shown  in  Fig.  60  were  also  located  in  this 
way. 

(3)  To  locate  the  position  of  the  pole  of  a  face  lying  on  a  known  great  circle, 
which  is  not  a  north  and  south  meridian,  its  angle  from  a  point  on  the  circum- 
ference of  the  projection  being  known.     The  projected  arc  of  a  small  vertical 
circle,  whose  radius  is  the  known  angle,  is  drawn  about  the  point  on  the  cir- 
cumference of  the  projection  and  since  all  points  on  this  arc  must  have  the 
required  angular  distance  from  the  given  point  the  intersection  of  this  circle 
with  the  known  great  circle  will  give  the  desired  point.     The  radius  of  the 
projected  arc  of  the  small  vertical  circle  can  be  determined  by  finding  the 
position  of  three  points  on  the  projection  which  have  the  required  angular 
distance  from  the  point  given  on  the  circumference  of  the  projection  and 
then  obtaining  the  center  of  the  required  circle  in  the  usual  way.     Or  by  the 
use  of  Scale  No.  2,  Fig.  63,  the  required  radius  is  obtained  directly.     It  is 
to  be  noted  that  the  known  point  on  the  circumference  of  the  projection, 
while  the  stereographic  center  of  the  small  circle,  is  not  the  actual  center  of 
the  projected  arc.     The  center  will  lie  outside  the  circumference  on  a  con- 
tinuation of  the  radial  line  that  joins  the  given  point  with  the  center  of  the 
projection.     Therefore,  even  if  the  radius  of  the  required  arc  is  taken  from 


36 


CRYSTALLOGRAPHY 


s  i 


II 


3— 


E 

E 


•a 


r- 

3- 


P 


GENERAL  MATHEMATICAL   RELATIONS   OF   CRYSTALS 


37 


Scale  No.  2,  it  will  be  necessary  to  establish  at  least  one  point  on  the  re- 

Zed  circle  in  order  to  find  its  center.     These  methods  of  construction  are 
trated  in  Fig.  65,  in  which  the  position  is  determined  of  the  pole  n  (iso- 


Location  of  the  arc  of  a  great  circle  in  the  Stereographic  Projection  at  a  given  angle 

above  the  equator 


a  Oil 


dllQ 


Location  of  pole  of  trapezohedron,  n(211),  in  Stereographic  Projection 


metric  trapezohedron)  which  lies  on  the  great  circle  passing  through  the 
poles  a  (isometric  cube)  and  o  (isometric  octahedron),  and  makes  a  known 
angle  (35J°)  with  a. 


38 


CRYSTALLOGRAPHY 


(4)  To  locate  the  position  of  the  pole  of  a  face  given  the  angles  between  it  and 
two  other  faces  whose  poles  lie  within  the  divided  circle.  Circumscribe  about 
the  poles  of  the  two  known  points  small  circles  with  the  proper  radii  and 
the  desired  point  will  be  located  at  their  intersection.  The  two  small  circles 
may  touch  at  only  a  single  point  or  they  may  intersect  in  two  points.  In 
the  latter  case  both  points  will  meet  the  required  conditions.  The  positions 
of  the  projected  small  circles  are  readily  found  by  drawing  radii  from  the 
center  of  the  projection  through  the  two  known  poles  and  then  laying  off  on 
these  radii  points  on  either  side  of  the  known  poles  with  the  required  angular 
distances.  The  center  is  then  found  between  these  two  points  in  each  case 
and  a  circle  drawn  through  them.  This  line  of  this  circle  will  then  be  every- 
where the  required  number  of  degrees  away  from  the  known  pole.  The  re- 
quired points  may  be  found  readily  by  means  of  the  Stereographic  Protrac- 
tor, Fig.  62,  remembering  that  the  zero  point  on  the  protractor  must  always 
lie  at  the  center  of  the  projection.  This  construction  is  illustrated  in  Fig.  66, 
in  which  the  points  s  (isometric  hexoctahedron),  are  22°  12'  and  19°  5'  from 
the  points  o  (isometric  octahedron),  and  d  (isometric  dodecahedron).  It  is 
to  be  noted  here,  also,  that  while  the  points  o  and  d  are  the  stereographic 
centers  of  the  circles  about  them,  the  actual  centers  are  points  which  are 
somewhat  farther  out  from  the  center  of  the  projection. 


a  010 


duo 


a  loo 


Location  of  two  poles  of  hexoctahedron,  s,  in  Stereographic  Projection 

(5)  To  measure  the  angle  between  two  given  points  on  the  stereographic 
projection.  If  the  two  points  lie  on  the  circumference  of  the  projection  the 
angle  between  them  is  read  directly  from  the  divisions  of  the  circle.  If  they 
lie  on  the  same  radial  line  in  the  projection,  the  angle  is  given  by  the  use  of 
the  Stereographic  Protractor,  Fig.  62.  In  other  cases  it  is  necessary  first  to 
find  the  arc  of  a  great  circle  upon  which  the  two  points  lie.  This  is  most 
easily  accomplished  by  the  use  of  a  transparent  celluloid  protractor  upon 
which  the  arcs  of  great  circles  are  given,  Fig.  67.  Place  this  protractor  over 
the  projection  with  its  center  coinciding  with  the  center  of  the  projection  and 
turn  it  about  until  the  required  great  circle  is  found.  Note  the  points  where 
this  circle  intersects  the  circumference  of  the  projection.  Then  place  a 
second  transparent  protractor  on  which  small  vertical  circles  are  given, 
Fig.  68,  over  the  projection  with  its  ends  on  the  points  of  the  circumference 


GENERAL   MATHEMATICAL   RELATIONS    OF   CRYSTALS 


39 


just  determined.  Now  note  the  angular  distance  between  the  two  given 
points.  The  whole  operation  may  also  be  done  by  use  of  a  third  trans- 
parent protractor,  on  which  the  arcs  of  both  great  and  small  circles  are 
given. 

67 


Stereograph! c  Protractor,  giving  the  great  circles  of  every  alternate  degree  (second,  fourth, 
etc.)     (After  Penfield,  reduced  one-half) 


Stereograph]  c  Protractor,  giving  small  circles  for  every  degree  measured  from  a  given  point 
on  the  circumference.     (After  Penfield,  reduced  one-half) 

(6)  To  measure  the  angle  between  the  arcs  of  two  great  circles  on  the  stereo- 
graphic  projection.  This  is  most  conveniently  accomplished  by  construct- 
ing the  arc  of  a  great  circle  which  shall  have  a  90°  radius  about  the  point  at 
which  the  two  arcs  in  question  cross  each  other  and  then  measuring  the 
angular  distance  between  the  two  points  at  which  they  intersect  this  great 
circle.  Fig.  69,  after  Penfield,  will  serve  to  illustrate  the  method.  First,  if 
it  is  wished  to  measure  the  angle  between  the  divided  circle  and  the  arc  of 
the  great  circle  that  crosses  it  at  C  it  is  only  necessary  to  draw  a  straight 
line  through  the  center  of  the  projection,  N,  which  shall  intersect  the  divided 
circle  at  points  90°  distant  from  C.  This  line  will  be  the  projection  of  the 
arc  of  a  great  circle  about  the  sphere  at  90°  distant  from  C.  The  angle  at  C 
is  then  determined  by  measuring  with  the  stereographic  protractor  the  angle 
between  u  and  v. 

In  the  case  of  the  angle  between  two  great  circles  that  meet  at  some 
point  within  the  divided  circle  as  at  A,  Fig.  69,  it  is  necessary  to  construct 
the  projected  arc  of  the  great  circle  90°  distant  from  this  point  This  is  done 


40 


CRYSTALLOGRAPHY 


69 


by  drawing  the  radial  line  through  N  and  A  and  measuring  with  the  stereo- 
graphic  protractor  an  angle  of  90°  from  A  to  the  point  B.  The  required  arc 
will  pass  through  this  point  and  the  points  p  and  pf  which  are  each  90°  away 
from  the  points  at  which  the  line  A-N-B  crosses  the  divided  circle.  The 
angle  between  x  and  y  measured  on  this  great  circle  gives  the  value  of  the 

required  angle  at  A.  This  is  most 
readily  measured  by  the  use  of  the 
transparent  protractor  showing  small 
circles,  Fig.  68.  This  is  placed  across 
the  projection  from  p  to  p'  and  the 
angle  between  x  and  y  read  directly 
from  it. 

Wiilfing  has  described  a  stereo- 
graphic  net,  which  gives  both  great 
and  small  circles  for  every  two  de- 
grees. Over  this  is  placed  a  sheet  of 
tracing  paper  upon  which  the  stereo- 
graphic  projection  is  made.  If  the 
paper  is  fastened  at  the  center  of  the 
drawing  so  that  it  can  be  turned  into 
various  positions  in  respect  to  the 
stereographic  net  below,  the  various 
great  and  small  circles  needed  can  be 
sketched  directly  upon  the  drawing. 
Or  the  required  points  can  be  trans- 
ferred from  the  net  to  a  separate  drawing  by  means  of  three  point  dividers. 
Examples  of  the  use  of  the  stereographic  projection  will  be  given  later 
under  each  crystal  system. 

70 


no 


^100 


Relation  between  Spherical  and  Gnomonic  Projections 

42.  The  Gnomonic  Projection.  —  The  characters  of  the  gnomonic  pro- 
jection can  best  be  understood  by  considering  it  to  be  derived  from  the 
spherical  projection  (see  Art.  40).  In  the  case  of  the  gnomonic  projection 
the  plane  of  the  projection  is  usually  taken  as  the  horizontal  plane  which 


, 


GENERAL   MATHEMATICAL   RELATIONS   OF   CRYSTALS 


41 


lies  tangent  to  the  north  pole  of  the  sphere  of  the  spherical  projection.  Im- 
aginary lines  are  then  taken  from  the  center  of  the  sphere  through  the  poles 
of  the  crystal  faces  that  lie  on  its  surface  and  extended  until  they  touch  the 
plane  of  the  projection.  The  points  in  which  these  lines  touch  that  plane 
constitute  the  gnomonic  projection  of  the  forms  represented.  Fig.  70  shows 
the  relations  between  the  spherical  and  gnomonic  projections,  using  the  same 
isometric  crystal  forms  (cube,  octahedron  and  dodecahedron)  as  were  em- 
ployed to  illustrate  the  principles  of  the  Stereographic  Projection  (Art.  41). 
Fig.  71  shows  the  gnomonic  projection  of  the  same  set  of  forms. 


100 


Gnomonic  Projection  of  Cube,  Octahedron  and  Dodecahedron 

The  following  features  of  the  gnomonic  projection  are  important.  All 
great  circles  on  the  spherical  projection  become  straight  lines  when  trans- 
ferred to  tho  gnomonic.  The  poles  of  a  series  of  crystal  faces  which  belong 
in  the  same  zone  will,  therefore,  on  the  gnomonic  projection,  lie  on  a  straight 
line.  This  primary  distinction  between  the  stereographic  and  gnomonic  pro- 
jections will  be  readily  seen  by  a  comparison  of  Figs.  60  and  71.  The  pole 
of  a  horizontal  crystal  face  (like  the  top  face  of  the  cube)  will  fall  at  the  center 
of  the  projection.  The  poles  of  vertical  crystal  faces  will  lie  on  the  plane 
of  projection  only  at  infinite  distances  from  the  center.  This  is  shown  by  a 
consideration  of  Fig.  70.  Such  faces  are  commonly  indicated  on  the  pro- 
jection by  the  use  of  radial  lines  or  arrows  which  indicate  the  directions  in 
which  their  poles  lie.  This  is  illustrated  in  the  case  of  the  vertical  cube  and 
dodecahedron  faces  in  Fig.  71.  Crystal  faces  having  a  steep  inclination  with 
the  horizontal  plane  must  frequently  be  indicated  in  the  same  way. 


42 


CRYSTALLOGRAPHY 


A  simple  relation  exists  between  the  linear  distance  from  the  center  of 
the  projection  to  a  given  point  and  the  angular  distance  represented.  This 
is  shown  in  Fig.  72  where  the  circle  is  assumed  to  be  a  vertical  cross-section 
of  the  sphere  of  the  spherical  projection  and  the  line  A-B  represents  the 
trace  of  the  plane  of  the  gnomonic  projection.  It  is  evident  from  this  figure 

that  if  the  radius  of  the 
circle  is  taken  as  unity 
d'  B  the  linear  distances 
N-a',  N-b',  etc.,  are  the 
tangents  of  the  angles 
20°,  35°,  etc.  Conse- 
quently in  the  gnomonic 
projection  the  distance 
of  a  given  pole  from  the 
center  of  the  projection, 
considering  the  funda- 
mental distance  0-Ar, 
Fig.  72,  to  be  unity,  is 
equal  to  the  tangent  of 
the  angle  represented. 
In  the  case  of  the  stereo- 
graphic  projection  this 
distance  is  equal  to  the 
tangent  of  one  half  the  angle,  see  Art.  41.  The  stereographic  scale,  used 
hi  trie  stereographic  protractor,  Fig.  62,  can  therefore  be  adapted  for  use 
in  the  gnomonic  projection  by  taking  the  point  on  it  reading  at  twice  the 
desired  angle.  The  simplest  method  of  plotting,  however,  is  to  make  a 
direct  use  of  the  tangent  relation.  The  distance  0-Nt  Fig.  72,  is  taken  at 
some  convenient  length  and  then 
by  multiplying  this  distance  by  the 
natural  tangent  of  the  angle  desired 
the  linear  distance  of  the  pole  in 
question  from  the  center  of  the 
projection  is  obtained.  Frequently 
the  distance  0-N  is  taken  as  5  cm. 
In  making  a  gnomonic  projection 
a  circle  is  commonly  drawn  about 
the  center  of  the  projection,  known 
as  the  fundamental  circle,  with  a 
radius  equal  to  this  chosen  dis- 
tance. Points  th  at  have  an  angular 
distance  of  45°  with  the  center 
point  of  the  projection  will  lie  on 
the  circumference  of  this  circle.  Measurement  of  angle  between  any  two  poles 
Commonly  also  the  gnomonic  pro-  (Ai,  A2)  on  the  Gnomonic  Projection 

jection  is  surrounded  by  a  square 

border  of  two  parallel  lines  on  which  is  indicated  the  directions  in  which  lie 
the  poles  that  cannot  appear  on  the  projection  because  of  the  vertical  or 
steeply  inclined  position  of  their  faces.  These  characters  are  shown  in 
Fig.  71. 

To  measure  the  angle  between  two  poles  on  the  gnomonic  projection.     In 


GENERAL   MATHEMATICAL   RELATIONS   OF   CRYSTALS  43 

Fig.  73  let  Ai  and  A2  be  any  two  points  the  angle  between  which  is  desired. 
First  draw  a  straight  line  through  them  or,  in  other  words,  find  the  direction 
of  the  zonal  line  upon  which  they  lie.  Next  erect  the  line  0-A  perpendicular 
to  this  zonal  line  and  passing  through  the  center  0  of  the  projection.  On 
this  line  establish  the  point  N,  the  distance  A-N  being  equal  to  the  hypo- 
thenuse  of  the  right  triangle  A  OP  or  the  distance  A-P.  The  point  TV  is 
known  as  the  angle-point  of  the  zone  Ai-Az.  The  angle  AiNAz  is  equal  to 
the  desired  angle  between  the  points  AI  and  A2.  In  the  case  of  zonal  lines 
that  pass  through  the  center  of  the  projection  this  angle-point  will  lie  on 
the  circumference  of  the  fundamental  circle  at  the  terminus  of  a  radius 
which  is  at  right  angles  to  the  zonal  line  in  question.  In  the  case  of  vertical 
crystal  faces  whose  poles  lie  at  an  infinite  distance  the  center  of  the  projec- 
tion is  itself  the  angle-point. 

The  explanation  of  the  above  method  may  be  given  as  follows.  In  Fig.  74  let  the  circle 
represent  a  vertical  section  through  the  sphere  of  the  spherical  projection  and  the  line 
N-A  the  trace  of  the  plane  of  the  gnomonic  projection.  Let  the  line  A-C  represent  the 
intersection  of  a  zonal  plane  lying  at  right  angles  to  the  plane  of  the  drawing.  The  zonal 
line  representing  the  intersection  of  this  zonal  plane  with  the  plane  of  the  gnomonic  pro- 
jection would  therefore  be  a  straight 

line  through  point  A  which  would  be                                            74 
perpendicular  to  the  plane  of  the  draw- 
ing.    The  angle  between  any  two  poles    N     O A 

lying  on  this  zonal  line  would  be  deter- 
mined by  the  angle  formed  by  the  lines 
drawn  from  these  poles  to  the  point  C. 
Ifj  we  consider  this  zonal  line  which 
passes  through  A  perpendicular  to  the 
drawmg  as  an  axis  around  which  we 
may  revolve  its  zonal  plane,  the  point 
C  may  be  moved  so  that  it  will  lie 'in 
the  plane  of  the  gnomonic  projection 
and  fall  at  N,  the  distance  A-N  being 
equal  to  A-C.  The  character  of  the 
point  C  has  not  been  changed  by  this 
transfer  and  the  point  N  becomes  the 
angle-point  of  the  zonal  line  running 

through  A  and  the  angle  between  any  two  poles  on  this  line  may  be  determined  by  running 
lines  from  them  to  this  point  and  measuring  the  included  angle.  The  point  N  lies  on  the 
line  running  through  O  (center  of  the  gnomonic  projection)  and  the  distance  A-N  is  equal 
to  the  hypothenuse,  A-C,  of  the  right  triangle  one  side  of  which  is  equal  to  A-O  and 
the  other  to  O-C  (the  raclius  of  the  fundamental  circle). 

To  measure  the  angle  between  parallel  zonal  lines  on  the  gnomonic  projection. 
In  Fig.  75  let  the  two  lines  Zone  1  and  Zone  2  represent  two  parallel  zonal 
lines  the  angle  between  which  is  desired.  Draw  the.  radial  line  trom  the 
center  of  the  projection,  0,  at  right  angles  to  these  zonal  lines  intersecting 
them  at  the  points  AI  and  A2.  Make  0-P  at  right  angles  to  0-AiA2.  The 
angle  AiPAz  will  give  the  angle  between  the  two  zones.  The  construction 
will  be  readily  understood  if  the  figure  is  supposed  to  be  turned  on  the  line 
0-AiAz  as  on  an  axis  until  the  point  P  becomes  the  center  of  the  spherical 
projection  The  broken  arc  now  represents  a  vertical  cross  section  of  the 
sphere  of  the  spherical  projection  and  the  points  «i  and  02  the  points  where 
the  two  zonal  lines  cross  it.  The  angle  at  P  is  obviously  the  angle  between 
the  two  zones. 

The  angle  between  Zone  2  and  the  prism  zone,  the  line  of  which  lies  at 
infinity  on  the  gnomonic  projection,  is  given  in  Fig.  75  by  the  angle  A%PN 
which  is  the  same  as 


44 


CRYSTALLOGRAPHY 


A  gnomonic  net,  similar  in  character  to  the  stereographic  net  described 
in  Art.  41,  is  useful  in  plotting  the  points  of  a  projection  or  in  making  meas- 
urements upon  it.  The  straight  lines  upon  it  represent  the  projection  of  the 

arcs  of  great  circles  of  the  spherical 
projection,  while  the  hyperbola  curves 
represent  those  of  the  small  vertical 
circles. 

The  gnomonic  projection  is  most 
commonly  used  in  connection  with 
the  measurement  of  crystal  angles  by 
means  of  the  two-circle  goniometer. 
This  use  will  be  explained  later,  see 
Art.  232.  For  more  detailed  descrip- 
tions of  the  principles  and  uses  of 
the  gnomonic  projection  the  reader  is 
referred  to  the  literature  listed  below. 


References  on  the  Stereographic  and 
Gnomonic  Projections. 

In  addition  to  the  descriptions  of  these 
Measurement  of  the  angle  between  parallel   projections  that  are  given  in  many  general 
zones  on  the  Gnomonic  Projection  crystallographic  texts  the  following  books 

and  papers  are  of  value. 

Boecke,  H.  E.  Die  Anwendung  der  stereographischen  Projektion  bei  kristallographi- 
schen  Untersuchungen,  1911.  Die  gnomonische  Projektion  in  ihrer  Anwendung  auf  kris- 
tallographische  Aufgaben,  1913. 

Evans,  J.  W.     Gnomonic  Projections  in  two  planes.     Min.  Mag.,  14,  149,  1905. 

Goldschmidt,  V.     Uber  Projektion  und  graphische  Kristallberechnung,  1887. 

Gossner,  B.     Kristallberechnung  und  Kristallzeichnung,  1914. 

Hilton,  H.  The  Gnomonic  Net,  Min.  Mag.,  14,  18-20,  1904.  The  Construction  of 
Crystallographic  Projections,  Min.  Mag.,  14,  99-103,  1905.  Some  Applications  of  the 
Gnomonic  Projection  to  Crystallography,  Min.  Mag.,  14,  104-108,  1905. 

Hutchinson,  A.  On  a  protractor  for  use  in  constructing  stereographic  and  gnomonic 
projections  of  the  sphere,  Min.  Mag.,  15,  94-112,  1908. 

Palache,  Charles.     The  Gnomonic  Projection.     Amer.  Min.,  6,  67,  1920. 

Penfield,  S.  L.  The  Stereographic  Projection  and  Its  Possibilities  from  a  Graphical 
Standpoint,  Am.  J.  Sci.,  9,  1-24,  115-144,  1901.  On  the  Solution  of  Problems  in  Crystal- 
lography by  Means  of  Graphical  Methods  based  upon  Spherical 
and  Plane  Trigonometry.  Am.  J.  Sci.,  14,  249-284,  1902.  On  the 
Drawing  of  Crystals  from  Stereographic  and  Gnomonic  Projections, 
Am.  J.  Sci.,  21,  206-215,  1906. 

Smith,  G.  H.  H.  On  the  Advantages  of  the  Gnomonic  Projec- 
tion and  its  use  in  the  Drawing  of  Crystals,  Min.  Mag.,  13,  309-321, 
1903. 


43.  Angles  between  Faces.  —  The  angles  most  con- 
veniently used  with  the  Miller  symbols,  and  those  given 
in  this  work,  are  the  normal  angles,  that  is,  the  angles  be- 
tween the  poles  or  normals  to  the  facts,  measured  on  arcs 
of  great  circles  joining  the  poles  as  shown  on  the  stereo  Chrysolite 

graphic  projection.     These  normal  angles  are  the  supple- 
ments of  the  actual  interfacial  angles,  as  has  been  explained. 

The  relations  between  these  normal  angles,  for  example  in  a  given  zone,  is  much  simpler 
than  those  existing  between  the  actual  interfacial  angles.  Thus  it  is  always  true  that,  for  a 
series  of  faces  in  the  same  zone,  the  normal  angle  between  two  end  faces  is  equal  to  the 
sum  of  the  angles  of  faces  falling  between.  Thus  (Figs.  76,  77)  the  normal  angle  of 


GENERAL   MATHEMATICAL   RELATIONS    OF   CRYSTALS 


45 


06(100  A  010)   is   the  sum  of  aw(100  A  110),  ms(110  A  120),  and  s6(120  A  010).     This 
relation  holds  true  in  all  the  systems. 

Furthermore,  it  will  be  seen  that,  supposing  oca!  (Fig.  77)  is  a  plane  of  symmetry  as  in 
the    orthorhombic    system,    the   angle 

100  A  110,    or   am    (Fig.    76),    is   half  77 

the  angle  110  A  110(rara'").  Similarly 
010  A  120(6s)  is  half  the  angle  120  A 
120(ss')j  again,  100  A  lll(ae)  is  the 
complement  of  half  the  angle  111  A 
111(66')  and  010  A  lll(6e)  the_comple- 
ment  of  half  the  angle  111  A  111(60. 

Here,  as  throughout  this  work,  the 
sign  A  is  used  to  represent  the  angle 
between  two  faces,  usually  designated 
by  letters. 

44.  Use  of  the  Stereographic 
Projection  to  Exhibit  the  Sym- 
metry. —  The  symmetry  of  any 
one  of  the  crystalline  classes  may 
be  readily  exhibited  by  the  help 
of  the  stereographic  projection. 

The  axes  of  binary,  trigonal, 
tetragonal  and  hexagonal  sym- 
metry are  represented  respec- 
tively by  the  following  signs: 


fcoio 


010  ft 


.    Further,  a  plane  of   stereographic  Projection  of  Faces  on  Chrysolite 

symmetry  is  represented  by  a  full  Crystal,  Fig.  76 

line  (zone-circle),  while  a  dotted 

line  indicates  that  the  plane  of  symmetry  is  wanting.     The  position  of  the 
crystallographic  axes  is  shown  by  arrows  at  the  extremities  of  the  lines.     The 

pole  of  a  face  in  the  upper  half  of 
the  crystal  (above  the  plane  of  pro- 
jection) is  represented  by  a  cross; 
one  below  by  a  circle.  If  two  like 
faces  fall  in  a  vertical  zone  a  double 
sign  is  used,  a  cross  within  the 
circle.  Figs.  91,  128,  140,  etc., 
give  illustrations. 

45.  General  Relations  be- 
tween Planes  in  the  Same  Zone. 
-  Certain  important  relations 
•Y  exist  between  the  indices  of  faces 
that  lie  in  the  same  zone.  All 
faces  to  belong  to  the  same  zone, 
tautozonal  faces  as  they  are  called, 
must  have  their  mutual  intersec- 
tions parallel  to  a  given  direction, 
see  Art.  38.  This  direction  is 
known  as  the  axis  of  the  zone. 
The  position  of  this  zonal  axis  can 
be  expressed  by  what  is  known  as 
the  zonal  symbol.  Consider  Fig.  78,  where  is  represented  two  crystal  faces, 
ABC,  and  CDE,  intersecting  the  crystallographic  axes  X,  Y  and  Z.  In  the 
illustration,  for  simplicity,  both  faces  have  been  assumed  to  pass  through 


46  CRYSTALLOGRAPHY 

the  point  C  on  the  axis  Z.  This,  of  course,  is  possible  since  any  crystal 
plane  may  be  moved  parallel  to  itself  without  altering  its  relative  intercepts 
on  the  crystal  axes.  These  two  planes  intersect  in  the  line  C-W,  which 
then  becomes  the  direction  of  the  zonal  axis  for  the  zone  in  which  they 
lie.  Let  the  line  0—P  which  has  been  drawn  parallel  to  this  direction 
represent  that  axis.  In  the  parallelogram  of  which  it  is  the  diagonal  the 
length  of  the  edge  0-S  and  its  parallel  edges  have  been  taken  as  equal  to  the 
distance  0-C.  The  point  P  on  the  zonal  axis  and  therefore  the  direction 
of  the  axis  itself  is  fixed  by  the  three  coordinates,  0-M,  0-R,  and  0-S.  By 
means  of  the  consideration  of  similar  triangles  it  is  possible  to  prove  that  the 
values  of  these  coordinates  may  be  expressed  by, 

0-M  =  (Ar  -  lq)a;  0-R  =  (Ip  -  hr)b;  0-S  =  (hq  -  kp)c, 

where  a,  6,  c  represent  the  unit  lengths  of  the  three  crystallographic  axes, 
X,  Y,  Z  and  (hkl)  and  (pqr)  represent  the  indices  of  the  two  faces  ABC  and 
CDE.  These  expressions  are  usually  simplified  by  substituting  u  =  kr  —  Iq, 
v  =  Ip  —  hr,  w  =  hq  —  kp,  giving  0-M  =  ua,  0-R  =  vb  and  0-S  =  we. 
The  three  figures  [uvw]  are  said  to  be  the  symbol  of  the  zone  in  question. 
They  represent  the  reciprocals  of  the  values  of  the  three  coordinates,  or  in 
other  words  are  the  indices  of  a  point,  P,  on  the  zonal  axis.  They  may 
most  readily  be  obtained  by  a  system  of  cross-multiplication  and  subtraction 
according  to  the  following  scheme.  Write  the  indices  of  one  face  twice  in 
their  proper  order  and  directly  under  them  the  corresponding  indices  of  the 
second  face.  Cross  off  the  first  and  last  number  of  each  series.  Then  mul- 
tiply the  figures  joined  by  the  cross  lines,  see  below,  and  substract  the  prod- 
uct of  the  two  joined  by  light  lines  from  that  of  those  joined  by  heavy  lines, 
working  from  left  to  right.  The  three  numbers  obtained  will  in  their  order 
correspond  to  u,.v  and  w. 


P 


k        I        h        k 

XXX 

q        r         p        q 


I 


u  =  kr  —  Iq,  v  =  Ip  —  hr,  w  =  hq  —  kp. 

Since  the  zonal  symbol  for  a  given  zone  may  be  obtained  from  the  indices 
of  any  two  faces  lying  in  that  zone  it  follows  that  the  indices  of  every  pos- 
sible face  in  that  zone  must  have  definite  relations  to  the  zonal  symbol.  For 
a  given  face  with  indices  (xyz),  in  a  zone  having  the  symbol  [uvw]  the  follow- 
ing equation,  known  as  the  zonal  equation,  must  hold  true. 

ux  -\-  vy  +  wz  =  0. 

In  this  way  it  can  be  readily  shown  whether  or  not  a  given  face  can  lie  in  a 
certain  zone. 

Further  if  [uvw]  be  the  symbol  of  one  zone  and  [efg]  that  of  another  inter- 
secting it,  then  the  point  of  intersection  will  always  be  the  pole  of  a  possible 
crystal  face.  Its  indices  (hkl)  must  satisfy  the  equations  of  both  zones  and 
may  be  obtained  by  combining  them  or  the  same  result  may  be  had  by  tak- 
ing the  symbols  of  the  two  zones  and  subjecting  them  to  the  same  sort  of  cross- 
multiplication  by  which  they  were  themselves  originally  derived. 


GENERAL   MATHEMATICAL   RELATIONS   OF   CRYSTALS 


47 


46.  —  Examples  of  Zones  and  Zonal  Relations.  —  The  following  are  cases  in  which  the 
zonal  equation  is  seen  at  once.  In  Figs.  76  and  77  the  faces  a(100),  ra(110),  s(120),  6(010) 
form  a  vertical  zone  with  mutually  parallel  intersections,  since  they  are  all  parallel  to  the 
vertical  axis;  that  is,  for  all  faces  in  this  zone  it  must  be  true  that  I  =  0. 

Again,  the  faces  a(100),  d(101),  c(001)  are  in  a  zone,  all  being  parallel  to  the  horizontal 
axis  6;  hence  for  them  and  all  others  in  this  zone  k  =  0.  Also  6(010),  fc(ti21),  /i(011),  c(001) 
are  in  a  zone,  all  being  parallel  to  the  axis  a,  so  that  h  =  0. 

Also  the  faces /(121),  e(lll),  d(101),  e' ''(111),  /"'(121)  are  in  a  zone,  since  they  have  a 
common  ratio  for  the  axes  arc.  With  them,  obviously,  h  =  I. 

The  faces  c(001),  e(lll),  m(110)  are  also  in  a  zone,  and  again  c(001),  /(121),  s(120), 
though  intersections  do  not  happen  to  be  made  between  c  and  e  in  the  one  case,  and  c  and 
/  in  the  other.  For  each  of  these  zones  it  is  true  that  there  is  a  common  ratio  of  the  hori- 
zontal axes,  that  is,  of  h  to  k  in  the  indices.  For  the  first  it  may  be  shown  that  h  =  k;  for 
the  second,  that  2h  =  k. 

All  the  relations  named  may  be  obtained  at  once  from  the  79 

above  scheme.     For  example,  for  the  faces  s(120)  and  /(121) 
the  scheme  gives 


0 


XXX 


0 


2. 


T, 


0; 


.'.  2h  -  k  =  0,  or  2h  =  k. 


The  symbol  of  a  face  lying  at  once  in  two  zones,  as  stated 
above,  must  satisfy  the  zonal  equation  of  each;  these  symbols 
are  hence  easily  obtained  either  by  combining  the  equations 
or  by  a  scheme  of  multiplication  like  that  given  above. 

For  example,  in  Fig.  79,  of  sulphur,  the  face  lettered  x  is  in 
the  zone  (l)_with  6(010)  andsdlS),  als9  in  zone  (2)  with  p(lll) 
and  n(01T).  These  zones  give,  respectively: 

01         0        0         1      0     (2)     1 


Sulphur 


(1) 


3 


0 


1 


0        1 

v  =  0, 


w  =  1. 


0 

6=0, 


9 


1. 


Hence  for  (1)  the  zonal  equation  is   3h  =  I:   for  (2)  k  =  I.     Combining  these,  we  obtain 
h  =  1,  k  =  3, -I  =  3. 

The  symbol  of  the  face  x  is,  therefore,  133. 

The  same  result  is  given  by  multiplying  the  zonal  symbols  Oil,  301,  together  after  the 
same  method,  thus; 

01         10         11 


133  Hence,  again,  x  =  133. 

This  method  of  calculation  belongs  to  all  the  different  systems.  In  the  hexagonal 
system,  in  which  there  are  four  indices,  one  of  the  three  referring  to  the  horizontal  axes 
(usually  the  third)  is  omitted  when  the  zonal  relations  are  applied.  See  Art.  166. 

47.  Methods  of  Calculation.  —  In  general  the  angles  between  the  poles 
can  be  calculated  by  the  methods  of  spherical  trigonometry  from  the  tri- 
angles shown  in  the  spherical  projection  —  which  for  the  most  part  are  right- 
angled.  Certain  fundamental  relations  connect  the  axes  with  the  elemental 
angles  of  the  projection;  the  most  important  of  these  are  given  under  the 
individual  systems.  Some  general  relations  only  are  explained  here. 


48 


CRYSTALLOGRAPHY 


80 


48.    Relations  between  the  Indices  of  a  Plane  and  the  Angle  made  by  it 
with  the  Axes.  —  In  Fig.  80  let  the  three  lines,  X,  Y,  and  Z  represent  three 

crystallographic  axes  making  any  angles  with  each 
other  and  let  a,  b  and  c  represent  their  unit  lengths. 
Assume  any  face  HKL  cutting  these  axes  with  the 
intercepts  0-H,  O-K  and  0-L.  Let  0-p-P  be  a 
normal  to  the  plane  HKL  intersecting  the  plane  at 
p  and  the  enveloping  surface  of  the  spherical  pro- 
jection at  P.  Let  hkl  represent  the  indices  of  the 
given  form.  Since  the  line  0-p  is  normal  to  the 
plane  HKL  the  triangles  HOp,  KOp  and  LOp  are 
right  angles  and  the  following  relations  hold  true. 

-  cos  HOp;   Qr  =  cos  KOp;          =  cos  LOp. 


The  angles  HOp,  KOp,  and  LOp  are  equal,  respectively,  to  the  angles  repre- 
sented on  the  spherical  projection  by  the  arcs  PX,  PY  and  PZ  and  OH  =  ^, 

=  7 ,  OL  =  •= .     By  substituting  we  have, 


OP  = 

h 


=     cos  PY  =  j  cos  PZ. 

n  I 


This  equation  is  fundamental,  and  several  of  the  relations  given  beyond  are 
deduced  from  it. 

81 


no 


The  most  useful  application  is  that  when  the  axial  angles  are  90°,  as  represented  in  Fig. 
81;  then  X,  Y,  Z  are  the  normals  to  100,  010,  001,  respectively.  Also  if  the  plane  HKL  is 
taken  as  a  face  of  the  unit  pyramid,  that  is,  if  its  intercepts  on  the  axes  are  taken  as  the 
unit  lengths 

OH  =  a,  OK  =  b,  OL  =  c. 

Then  the  lines  HK,  HL,  KL  give  also  the  intersections  of  the  planes  110,  101,  Oil  on 
the  three  axial  planes,  and  their  poles  are  hence  at  the  points  fixed  by  normals  to  these 


GENERAL  MATHEMATICAL   RELATIONS   OF   CRYSTALS  49 

lines  drawn  from  O.     It  will  be  obvious  from  this  figure,  then,  that  the  following  relations 
hold  true: 

tan  (100  A  110)  =  ^ ; 
tan  (001  A  101)  =  -  ; 
tan  (001  A  Oil)  =  ^- 
These  values  are  often  used  later. 

49.   Cotangent  and  Tangent  Relations.  —  In  the  case  of  four  faces  in  a 

zone  concerning  which  we  know,  either  the  angles  between  all  the  faces  and 

the  indices  of  three  of  them,  or  the  angles  between  three  faces  and  all  the 

indices,  it  is  possible  by  either  a  simple  graphical  method  of  plotting  or  by 

^calculation  to  determine  the  missing  angle  or  indices. 

To  illustrate  the  graphic  method  first  let  Fig.  82  represent  a  cross  section 
perpendicular  to  the  prism  zone  of  a  rhodonite  crystal.  The  traces  upon  the 
plane  of  the  drawing  of  the  faces  a(100)  and  6(010)  provide  the  direction 
of  the  lines  of  reference  X  and  Y.  It  is  assumed  that  the  position  of  the  third 
face  w(110)  is  known  and  a  line  drawn  parallel  to  its  trace  upon  the  plane  of 
the  drawing  from  the  point  X  will  give  its  relative  intercepts  upon  the  two 
lines  of  reference.  These  intercepts  do  not  correspond  to  the  unit  lengths 
of  the  axes  a  and  6  since,  rhodonite  being  triclinic,  these  axes  do  not  lie  in 
the  plane  of  the  drawing  but  they  represent  rather  the  unit  lengths  of  these 
axes  as  foreshortened  by  projection  upon  that  plane.  This  makes  no  dif- 
ference, however,  since  it  will  still  be  true  that  all  faces  lying  in  the  prism 
zone  of  rhodonite  must  intercept  these  two  lines  in  distances  which  will  have 
rational  relations  to  the  lengths  of  the  intercepts  of  w(110).  It  is  now  as- 
sumed that  a  fourth  face  /  has  the  indices  (130)  and  its  angular  position  in 
respect  to  the  other  faces  in  the  zone  is  required.  From  its  indices  it  must 
intercept  the  two  lines  of  reference  X-X'  and  Y-Y'  in  the  ratio  of  1  to  ^. 
Let  OX  equal  1  on  X-X'  and  OZ  equal  f  on  Y-Y'.  Then  a  line  joining 
these  two  points  will  give  the  direction  of  the  trace  of  /  upon  the  plane  of 
the  drawing  and  so  determine  the  angles  it  will  make  with  the  other  faces  in 
the  zone. 

If,  on  the  other  hand,  the  angles  between  /  and  the  other  faces  in  the 
zone  were  known,  the  position  of  the  trace  of  /  upon  the  plane  of  the  drawing 
could  be  found,  and  so  its  relative  intercepts  (and  indices)  upon 
the  two  lines  of  reference  be  determined. 

If  the  method  of  calculation  is  used  let  P,  Q,  S  and  R  be  the  poles  of 
four  faces  in  a  zone  (Fig.  83)  taken  in  such  an  order  *  that  PQ  <  PR  and 
let  the  indices  of  these  faces  be  respectively 

P  Q  R  S  fs 

hkl  pqr  uvw  xyz 

Then  it  may  be  proved  that 

cot  PS  -  cot  PR  =  (P.Q)       (S.R) 
cot  PQ  -  cot  PR      (Q.R)       (P.S) 


*  In  the  application  of  this  principle  it  is  essential  that  the  planes  should  be  taken  in 
the  proper  order,  as  shown  above ;  to  accomplish  this  it  is  often  ne_cessary  to  use  th&  in- 
dices and  corresponding  angles,  not  of  (hkl),  but  the  face  opposite  (h  k  F),  etc.  r 


50 


CRYSTALLOGRAPHY 


where 


(P.Q) 
(Q.R) 

(S.R) 
(P.S) 

123 
"P,  hkl~ 
Q,  pqr 

Q,  pqr 
_R,  uvw_ 

123 

R,  uvw 

P,  hkl 
_S,    xyz] 

1  X  2 


2X3 


3  X  1 


hq  —  kp  _  kr  —  Iq  _  Ip  —  hr 
pv  —  qu       qw  —  rv       ru  —  pw 


2X3 

yw  —  zv 
kz  -   ly 


3  X  1 


Ix    -  hz 


If  one  of  these  fractions  reduces  to  an  indeterminate  form,  -,  then  one  of  the  others 

must  be  taken  in  its  place. 

This  formula  is  chiefly  used  in  the  monoclinic  and  triclinic  systems;  and  some  special 
cases  are  referred  to  under  these  systems. 

The  cotangent  relation  becomes  much  simplified  for  a  rectangular  zone, 
that  is,  a  zone  between  a  pinacoid  and  a  face  lying  in  a  zone  at  right  angles 
to  it  so  that  the  angle  PR,  becomes  90°.  In  Fig.  83  let  P(hkl)  and  Q(pgr) 
be  two  faces  lying  in  the  zone  between  a(100)  and  d(011)  with  the  angle 
a  A  d  =  90°.  Let  Pa  and  Qa  represent  the  angles  between  the  two  faces 
and  the  pinacoid  a.  Then  the  following  holds  true. 

h      tan  Pa      k      I 

"*\s    :         ___.    _ 

p       tan  Qa      q      r 

or      the  faces  P  and  Q  lie  in  zones  with  the  other  pinacoids  6(010)  or  c(001) 
the  expression  becomes 

h      k  .  .  tan  P6      I 
P 


k      tan  Pb 
q      tan  Q6 


h  _  k  _  I     tan  PC 
pqr     tan  Qc 

If  the  zone  in  question  lies  between  two  pinacoids  which  are  at  right 
angles  to  each  other  so  that  the  indices  of  the  faces  P  and  Q  become  either 
hkQ  and  p#0,  hQl  and  pOr  or  OH  and  Qqr,  we  have 

tan  (100  A  hkQ)  =  k 
tan  (100  A  pqQ)       h 
tan  (001  A  MM)  =  h    r_  . 
tan  (001  A  pQr)  ~  I  '  p  ' 
tan  (001  A  Qkl)  =  k    r 
tan  (001  A  Qqr)  ~  I  '  q ' 

These  equations  are  the  ones  ordinarily  employed  to  determine  the  symbol  of  any  pris- 
matic plane  or  dome. 

The  most  common  and  important  application  of  this  tangent  principle  is  where  the 
positions  of  the  unit  faces  110,  101,  Oil  are  known,  then  the  relation  becomes 


p. 

q  ' 


Also, 


tan  (100  A  fe/cO)  =k 
tan  (100  A  110)      h' 

tan  (001  A  MM)  =  h 
tan  (001  A  101)  ~  I ' 


tan  (010  A  hkO)  =  h 
tan  (010  A  110)       k' 

tan  (001  A  0/cQ  =k 
tan  (001  A  Oil)  ~  I 


GENERAL   MATHEMATICAL   RELATIONS   OF   CRYSTALS 


51 


Thus  the  tangents  of  angles  between  the  base,  001,  and  102,  203,  302,  201,  etc.,  are 
respectively  |,  f,  |,  2  times  the  tangent  of  the  angle  between  001  and   101.     Again,  the 

tangent  of  the  angle  100  A  120  is  twice  the  tangent  of  100  A  110  (here  v  =  2  V  and  one- 
half  the  tangent  of  010  A  110. 

These  last  relations  are  shown  clearly  in  Fig. 
84  which  represents  a  cross-section  of  a  barite 
crystal  showing  the  macrodome  zone  between 
a(100)  and  c(001).  It  is  assumed  that  the  angles 
between  the  faces  a,  u,  d,  I  and  c  have  been 
measured  and  the  positions  of  their  poles  deter- 
mined as  indicated  in  the  figure.  The  broken 
lines  drawn  from  a  point  x  on  the  line  represent- 
ing the  a  crystallographic  axis  show  the  direction 
of  the  traces  of  these  faces  upon  the  plane  of  the 
a  and  c  axes.  If  the  face  u  is  assumed  to  be  the 
unit  dome  (101)  it  will  intersect  the  two  axes  at 
distances  proportional  to  their  unit  lengths, 
namely  O-X  and  O-Y.  The  other  faces  d  and  I 
are  seen  to  intersect  the  c  axis  at  |  and  i  the 
distance  O-Y,  giving  them  the  indices  (102)  and 
(104).  But  the  intercepts  on  O-Y  for  the  three 
faces  u,  d  and  I  are  proportional  to  the  tangents 
of  the  angles  between  their  poles  and  that  of 
c(001)  as  shown  below. 

tan  58°  10%'  =  1.6112  =  1 

tan  38°  5H'  =    .8056  =  % 

tan  21°  56|'  =    .4028  =  i 


52  CRYSTALLOGRAPHY 

I.  ISOMETRIC   SYSTEM 

(Regular  or  Cubic  System) 

50.  THE  ISOMETRIC  SYSTEM  embraces  all  the  forms  which  are  referred  to 
three  axes  of  equal  lengths  and  at  right  angles  to  each  other.     Since  these 
axes  are  mutually  interchangeable  it  is  customary  to  designate  them  all  by 

85  the  letter  a.     When  properly  orientated  (i.e.  placed  in 

the  commonly  accepted  position  for  study)  one  of 
a3  these  axes  has  a  vertical   position  and  of  the  two 

which  lie  in  the  horizontal  plane,  one  is  perpendicular 
and  the  other  parallel  to  the  observer.     The  order  in 
—  which  the  axes  are  referred  to  in  giving  the  relations 

^^      -i     of  any  face  to  them  is  indicated  in  Fig.  85  by  lettering 

ox  a*     them  ai,  0%  and  as.     The  positive  and  negative  ends 

of  each  axis  are  also  shown. 

There  are  five  classes  here  included;  of  these  the 
normal  class,*  which  possesses  the  highest  degree  of 
Isometric  Axes  symmetry  for  the  system  and,  indeed,  for  all  crystals, 

is  by  far  the  most  important.     Two   of  the  other 

classes,  the  pyritohearal  and  tetrahedral,  also  have  numerous  representatives 
among  minerals. 

1.   NORMAL  CLASS   (1).     GALENA  TYPE 
(Hexoctahedral  or  Holohedral  Class) 

51.  Symmetry.  —  The  symmetry  of  each  of  the  types  of  solids  enumer- 
ated in  the  following  table,  as  belonging  to  this  class,  and  of  all  their  com- 
binations, is  as  follows. 

Axes  of  Symmetry.  There  are  three  principal  axes  of  tetragonal  sym- 
metry which  are  coincident  with  the  crystallographic  axes  and  are  some- 
times known  as  the  cubic  axes  since  they  are  perpendicular  to  the  faces  of 
the  cube.  There  are  three  diagonal  axes  of  trigonal  symmetry  which  emerge 
in  the  middle  of  the  octants  formed  by  the  cubic  axes.  These  are  known  as 
the  octahedral  axes  since  they  are  perpendic  ular  to  the  faces  of  the  octahedron. 
Lastly  there  are  six  diagonal  axes  of  binary  symmetry  which  bisect  the  plane 
angles  made  by  the  cubic  axes.  These  are  perpendicular  to  the  faces  of  the 
dodecahedron  and  are  known  as  the  dodecahedral  axes.  These  symmetry 
axes  are  shown  in  the  Figs.  86-88. 

Planes  of  Symmetry.  There  are  three  principal  planes  of  symmetry 
which  are  at  right  angles  to  each  other  and  whose  intersections  fix  the  posi- 

*  It  is  called  normal,  as  before  stated,  since  it  is  the  most  common  and  hence  by  far  the 
most  important  class  under  the  system ;  also,  more  fundamentally,  because  the  forms  here 
included  possess  the  highest  grade  of  symmetry  possible  in  the  system.  The  cube  is  a  pos- 
sible form  in  each  of  the  five  classes  of  this  system,  but  although  these  forms  are  alike  geo- 
metrically, it  is  only  the  cube  of  the  normal  class  that  has  the  full  symmetry  as  regards 
molecular  structure  which  its  geometrical  shape  suggests.  If  a  crystal  is  said  to  belong  to 
the  isometric  system,  without  further  qualification-,  it  is  to  be  understood  that  it  is  included 
here.  Similar  remarks  apply  to  the  normal  classes  of  the  other  systems. 


ISOMETRIC    SYSTEM 


53 


tion  of 
planes 
Fig.  90 


the  crystallographic  axes,  Fig.  89.     In  addition  there  are  six  diagonal 
of  symmetry  which  bisect  the  angles  between  the  principal  planes, 


87 


Axes  of  Tetragonal  Symmetry        Axes  of  Trigonal  Symmetry          Axes  of  Binary  Symmetry 

(Dodecahedral  Axes) 


(Cubic  Axes) 


(Octahedral  Axes) 


90 


Principal  Symmetry  Planes 

The  accompanying  stereographic  projection 
(Fig.  91),  constructed  in  accordance  with  the 
principles  explained  in  Art.  44,  shows  the  dis- 
tribution of  the  faces  of  the  general  form,  hkl 
(hexoctahedron)  and  hence  represents  clearly 
the  symmetry  of  the  class.  Compare  also  the 
projections  given  later. 

52.  Forms.  —  The  various  possible  forms 
belonging  to  this  class,  and  possessing  the 
symmetry  denned,  may  be  grouped  under  seven 
types  of  solids.  These  are  enumerated  in  the 
following  table,  comiQencing  with  the  sim- 
plest. 


Diagonal  Symmetry  Planes 


Symmetry  of  Normal  Class, 
Isometric  System 


54 


CRYSTALLOGRAPHY 


1.  Cube (100) 

2.  Octahedron (Ill) 

3.  Dodecahedron .' (110) 

4.  Tetrahexahedron (AfcQ)  as,  (310) 

5.  Trisoctahedron (hhl)  as,  (331) 

6.  Trapezohedron (hll)  as,  (311) 


Indices 


(210);  (320),  etc. 
(221);  (332),  etc. 
(211);  (322),  etc. 


7.   Hexoctahedron (hkl)  as,  (421);   (321),   etc. 

Attention  is  called  to  the  letters  uniformly  used  in  this  work  and  in  Dana's  System  of 
Mineralogy  (1892)  to  designate  certain  of  the  isometric  forms.*     They  are: 

Cube:  a. 

Octahedron:  o. 

Dodecahedron:  d. 

Tetrahexahedrons:  e  =  210;  /  =  310;  g  =  320;  h  =  410. 

Trisoctahedrons:  p  =  221;  q  =  331;  r  =  332;  p  =  441. 

Trapezohedrons:  m  =  311;  n  =  211;  /3  =  322. 

Hexoctahedrons:  s  =  321;  t  =  421. 

53.  Cube.  —  The  cube,  whose  general  symbol  is  (100),  is  shown  in 
Fig.  92.  It  is  bounded  by  six  similar  faces,  each  parallel  to  two  of  the  axes. 
Each  face  is  a  square,  and  the  interfacial  angles  are  all  90°.  The  faces  of 
the  cube  are  parallel  to  the  principal  or  axial  planes  of  symmetry. 

92 


^^\ 

,001 

010 

— 

100 

._._„, 

,^.. 

. 

,--'' 

...._. 

^ 

Cube 


Octahedron 


Dodecahedron 


54.  Octahedron.  —  The  octahedron,  shown  in' Fig.  93,  has  the  general 
symbol  (111).     It  is  bounded  by  eight  similar  faces,  each  meeting  the  three 
axes  at  equal  distances.     Each  face  is  an  equilateral_  triangle  with  plane 
angles  of  60°.     The  normal  interfacial  angle,  (111  A  111),  is  70°  31'  44". 

55.  Dodecahedron.  —  The  rhombic  dodecahedron,  f  shown  in  Fig.  94, 
has  the  general  symbol  (110).     It  is  bounded .  by  twelve  faces,  each  of  which 
meets  two  of  the  axes  at  equal  distances  and  is  parallel  to  the  third  axis. 
Each  face  is  a  rhomb  with  plane  angles  of  7Q§°  and  109  J°.     The  normal  in- 
terfacial angle  is  60°.     The  faces  of  the  dodecahedron  are  parallel  to  the  six 
auxiliary,  or  diagonal,  planes  of  symmetry. 


*  The  usage  followed  here  (as  also  in  the  other  systems)  is  in  most  cases  that  of  Miller 
(1852). 

t  The  dodecahedron  of  the  crystallographcr  is  this  fc 
commonly  found  on  crystals  of  garnet.     Geometricians  reco 
by  twelve  similar  faces;   of  these  the  regular  (pentagonal) 
portant.     In  crystallography  this  solid  is  impossible  th< 
mates  to  it.     (See  Art.  68.) 


rhombic  shaped  faces 
various  solids  bounded 
ledron  is  the  most  im- 

pyritohedron  approxi- 


ISOMETRIC    SYSTE!^ 


55 


It  will  be  remembered  that,  while  the  forms  described  are  designated  respectively  by 
the  symbols  (100),  (111),  and  (110),  each  face  of  any  one  of  the  forms  has  its  own  indices. 
Thus  for  the  cube  the  six  faces  have  the  indices 

100,     010,     001,     TOO,     OTO,     001. 


For  the  octahedron  the  indices  of  the  eight  faces  are: 

Above     111,       111,      TTl, 
Below     111,       111, 


111; 
ITT. 


For  the  dodecahedron  the  indices  of  the  twelve  faces  are: 


110,       110, 
101,     Toi, 

Oil,       Oil, 


no, 
Toi, 
on; 


110, 
101, 

on. 


These  should  be  carefully  studied  with  reference  to  the  figures  (and  to  models),  and  also 
to  the  projections  (Figs.  125,  126).  The  student  should  become  thoroughly  familiar  with 
these  individual  indices  and  the  relations  to  the  axes  which  they  express,  so  that  he  can 
give  at  once  the  indices  of  any  face  required. 


95 


96 


Cube  and  Octahedron 


Cube  and  Octahedron 


Octahedron  and  Cube 
100 


Dodecahedron  and  Cube 


Octahedron  and 
Dodecahedron 


Dodecahedron  and 
Octahedron 


56.   Combinations  of  the  Cube,   Octahedron,  and  Dodecahedron.  — 

Figs.  95,  96,  97  represent  combinations  of  the  cube  and  octahedron;  Figs. 
98,  101  of  the  cube  and  dodecahedron;  Figs.  99,  100  of  the  octahedron  and 
dodecahedron;  finally,  Figs.  102,  103  show  combinations  of  the  three  forms. 
The  predominating  form,  as  the  cube  in  Fig.  95,  the  octahedron  in  Fig.  97, 
etc.,  is  usually  said  to  be  modified  by  the  faces  of  the  other  forms.  In  Fig. 
96  the  cube  and  octahedron  are  sometimes  said  to  be  "in  equilibrium," 
since  the  faces  of  the  octahedron  meet  at  the  middle  points  of*  the  edges  of 
the  cube. 


56 


CRYSTALLOGRAPHY 


It  should  be  carefully  noticed,  further,  that  the  octahedral  faces  replace 
the  solid  angles  of  the  cube,  as  regular  triangles  equally  inclined  to  the  adja- 
cent cubic  faces,  as  shown  in  Fig.  95.  Again,  the  square  cubic  faces  replace 
the  six  solid  angles  of  the  octahedron,  being  equally  inclined  to  the  adjacent 
octahedral  faces  (Fig.  97) .  The  faces  of  the  dodecahedron  truncate  *  the 
twelve  similar  edges  of  the  cube,  as  shown  in  Fig.  101.  They  also  truncate 
the  twelve  edges  of  the  octahedron  (Fig.  99).  Further,  in  Fig.  98  the  cubic 
faces  replace  the  six  tetrahedral  solid  angles  of  the  dodecahedron,  while  the 
octahedral  faces  replace  its  eight  trihedral  solid  angles  (Fig.  100). 


101 


102 


103 


^--^ 

/if    ^ 

a      i 

i 

] 

L 

\ 

a 
\ 

d 

c 

^'J 

\ 

I             , 

_ 

W 

Cube  and  Dodeca- 
hedron 


Cube,  Octahedron  and 
Dodecahedron 


Octahedron,  Cube  and 
Dodecahedron 


The  normal  interfacial  angles  for  adjacent  faces  are  as  follows: 

Cube  on  octahedron,  ao.  100  A  111  =  54°  44'    8". 

Cube  on  dodecahedron,  ad,  100  A  110  =  45°    0'    0". 

Octahedron  on  dodecahedron,  od,  111  A  110  =  35°  15'  52". 

67.  As  explained  in  Art.  18  actual  crystals  always  deviate  more  or  less  widely  from  the 
ideal  solids  figured,  in  consequence  of  the  unequal  development  of  like  faces.  Such  crystals, 
therefore,  do  not  satisfy  the  geometrical  definition  of  right  symmetry  relatively  to  the  three 
principal  and  the  six  auxiliary  planes  mentioned  on  p.  53  but  they  do  conform  to  the  con- 
ditions of  crystallographic  symmetry,  requiring  like  angular  position  for  similar  faces. 
Again,  it  will  be  noted  that  in  a  combination  form  many  of  the  faces  do  not  actually  meet 
the  axes  within  the  crystal,  as,  for  example,  the  octahedral  face  o  in  Fig.  95.  It  is  still  true, 
however,  that  this  face  would  meet  the  axes  at  equal  distances  if  produced;  and  since  the 
axial  ratio  is  the  essential  point  in  the  case  of  each  form,  and  the  actual  lengths  of  the  axes 
are  of  no  importance,  it  is  not  necessary  that  the  faces  of  the  different  forms  in  a  crystal 
should  be  referred  to  the  same  actual  axial  lengths.  The  above  remarks  will  be  seen  to 
apply  also  to  all  the  other  forms  and  combinations  of  forms  described  in  the  pages  following. 

58.  Tetrahexahedron.  —  The  tetrahexahedron  (Figs.  104,  105,  106)  is 
bounded  by  twenty-four  faces,  each  of  which  is  an  isosceles  triangle.  Four 
of  these  faces  together  occupy  the  position  of  one  face  of  the  cube  (hexahe- 
dron) whence  the  name  commonly  applied  to  this  form.  The  general  symbol 
is  (hkQ),  hence  each  face  is  parallel  to  one  of  the  axes  while  it  meets  the  other 
two  axes  at  unequal  distances  which  are  definite  multiples  of  each  other. 
There  are  two  kinds  of  edges,  lettered  A  and  C  in  Fig.  104;  the  interfacial 
angle  of  either  edge  is  sufficient  to  determine  the  symbol  of  a  given  form 
(see  below).  The  angles  of  some  of  the  common  forms  are  given  on  a  later 
page  (p.  63). 


*  The  words  truncate,  truncation,  are  used  only  when  the  modifying  face  makes  equal 
with  the  adjacent  similar  faces. 


ISOMETRIC   SYSTEM 


57 


There  may  be  a  large  number  of  tetrahexahedrons,  as  the  ratio  of  the 
intercepts  of  the  two  axes,  and  hence  of  h  to  k  varies;  for  example  (410) 
(310),  (210),  (320),  etc.  The  form  (210)  is  shown  in  Fig.  104;  (410)  in 
Fig.  105,  and  (530)  in  Fig.  106.  All  the  tetrahexahedrons  fall  in  a  zone 
with  a  cubic  face  and  a  dodecahedral  face.  As  h  increases  relatively  to  k  the 
form  approaches  the  cube  (in  which  h  :  k  =  <x>  :  1  or  1  :  0),  while  as  it  dimin- 
ishes and  becomes  more  and  more  nearly  equal  to  k  in  value  it  approaches 
the  dodecahedron;  for  which  h  =  k.  Compare  Fig.  105  and  Fig.  106;  also 
Figs.  125,  126.  The  special  symbols  belonging  to  each  face  of  the  tetra- 
hexahedron  should  be  carefully  noted. 

106 


107 


Tetrahexahedrons 
108 


109 


Cube  and  Tetrahexa- 
hedron 


Octahedron  and 
Tetrahexahedron 


Dodecahedron  and 
Tetrahexahedron 


The  faces  of  the  tetrahexahedron  bevel  *  the  twelve  similar  edges  of  the 
cube,  as  in  Fig.  107;  they  replace  the  solid  angles  of  the  octahedron  by  four 
faces  inclined  on  the  edges  (Fig.  108;/  =  310),  and  also  the  tetrahedral 
solid  angles  of  the  dodecahedron  by  four  faces  inclined  on  the  faces  (Fig. 
109;  h  =  410). 

59.  Trisoctahedron.  —  The  trisoctahedron  (Fig.  110)  is  bounded  by 
twenty-four  similar  faces;  each  of  these  is  an  isosceles  triangle,  and  three 
together  occupy  the  position  of  an  octahedral  face,  whence  the  common 
name.  Further,  to  distinguish  it-  from  the  trapezohedron  (or  tetragonal 
trisoctahedron),  it  is  sometimes  called  the  trigonal  trisoctahedron.  There  are 
two  kinds  of  edges,  lettered  A  and  B  in  Fig.  110,  and  the  interfacial  angle 
corresponding  to  either  is  sufficient  for  the  determination  of  the  special 
symbol. 


*  The  word  bevel  is  used  when  two  like  faces  replace  the  edge  of  .a  form  and  hence  are 
inclined  at  equal  angles  to  its  adjacent  similar  faces. 


58 


CRYSTALLOGRAPHY 


The  general  symbol  is  (hhl)',  common  forms  are  (221),  (331),  etc.  Eacn 
face  of  the  trisoctahedron  meets  two  of  the  axes  at  a  distance  less  than  unity 
and  the  third  at  the  unit  length,  or  (which  is  an  identical  expression*)  it 
meets  two  of  the  axes  at  the  unit  length  and  the  third  at  a  distance  greater 
than  unity.  The  indices  belonging  to  each  face  should  be  carefully  noted. 
The  normal  interfacial  angles  for  some  of  the  more  common  forms  are  given 
on  a  later  page. 


Ill 


112 


Trisoctahedron 


Cube  and  Trisoctahedron 


Octahedron  and 
Trisoctahedron 


60.  Trapezohedron.  —  The  trapezohedron  f  (Figs.  113,  114)  is  bounded 
by  twenty-four  similar  faces,  each  of  them  a  quadrilateral  or  trapezium.     It 
also  bears  in  appearance  a  certain  relation  to  the  octahedron,  whence  the 
name,   sometimes  employed,    of   tetragonal   trisoctahedron.     There   are  two 
kinds  of  edges,  lettered  B  and  C,  in  Fig.  113.     The  general  symbol  is  hll\ 
common  forms  are  (311),  (211),  (322),  etc.     Of  the  faces,  each  cuts  an  axis 
at  a  distance  less  than  unity,  and  the  other  two  at  the  unit  length,  or  (again, 
an  identical  expression)  one  of  them  intersects  an  axis  at  the  unit  length  and 
the  other  two  at  equal  distances  greater  than  unity.     The  indices  belonging 
to  each  face  should  be  carefully  noted.     The  normal  interfacial  angles  for 
some  of  the  common  forms  are  given  on  a  later  page.     Another  name  for  this 
form  is  icositetrahedron. 

61.  The  combinations  of  these  forms  with  the  cube,  octahedron,  etc., 
should  be  carefully  studied.     It  will  be  seen  (Fig.  Ill)  that  the  faces  of  the 
trisoctahedron  replace  the  solid  angles  of  the  cube  as  three  faces  equally 
inclined  on  the  edges;  this  is  a  combination  which  has  not  been  observed  on 
crystals.     The  faces  of  the  trapezohedron  appear  as  three  equal  triangles 
equally  inclined  to  the  cubic  faces  (Fig.  115). 

Again,  the  faces  of  the  trisoctahedron  bevel  the  edges  of  the  octahedron, 
Fig.  112,  while  those  of  the  trapezohedron  are  triangles  inclined  to  the  faces 
at  the  extremities  of  the  cubic  axes,  Fig.  119;  m(311).  Still  again,  the  faces 
of  the  trapezohedron  n(211)  truncate  the  edges  of  the  dodecahedron  (110), 
as  shown  in  Fig.  118;  this  can  be  proved  to  follow  at  once  from  the  zonal 


*  Since  \a  :  %b  :  {c  =  la  :  16  :  2c.  The  student  should  read  again  carefully  the  ex- 
planations in  Art.  35. 

t  It  will  be  seen  later  that  the  name  trapezohedron  is  also  given  to  other  solids  whose 
faces  are  trapeziums  conspicuously  to  the  tetragonal  trapezohedron  and  the  trigonal 
trapezohedron. 


ISOMETRIC    SYSTEM 


59 


relations  (Arts.  45,  46),  cf.  also  Figs.  125,  126.  The  position  of  the  faces  of 
the  form  m(311),  in  combination  with  o,  is  shown  in  Fig.  119;  with  d  in 
Fig.  120. 

113  114 


Trapezohedrons 

It  should  be  added  that  the  trapezohedron  n(211)  is  a  common  form  both 
alone  and  in  combination;  m(311)  is  common  in  combination.  The  trisoc- 
tahedron  alone  is  rarely  met  with,  though  in  combination  (Fig.  112)  it  is  not 
uncommon. 

115 


Analcite.    Cube  and 
Trapezohedron 

118 


Analcite.    Trapezohedron    Garnet.     Trapezohedron  and 
and  Octahedron  Dodecahedron 


119 


Garnet.     Dodecahedron 
and  Trapezohedron 


Spinel.     Octahedron 
and  Trapezohedron 


Magnetite.     Dodecahedron 
and  Trapezohedron 


62.  Hexoctahedron,  —  The  hexoctahedron.  Figs.  121,  122,  is  the  gen- 
eral form  in  this  system;  it  is  bounded  by  forty-eight  similar  faces,  each  of 
which  is  a  scalene  triangle,  and  each  intersects  the  three  axes  at  unequal 


60 


CRYSTALLOGRAPHY 


distances.  The  general  symbol  is  (hki)\  common  forms  are  s(321),  shown  in 
Fig.  121,  and  £(421),  in  Fig.  122  The  indices  of  the  individual  faces,  as 
shown  in  Fig.  121  and  more  fully  in  the  projections  (Figs.  125,  126),  should 
be  carefully  studied 


The  hexoctahedron  has  three  kinds  of  edges  lettered  A,  B,  C  (longer, 
middle,  shorter)  in  Fig.  122;  the  angles  of  two  of  these  edges  are  needed  to 
fix  the  symbol  unless  the  zonal  relation  can  be  made  use  of  In  Fig.  124  the 
faces  of  the  hexoctahedron  bevel  the  dodecahedral  edges,  and  hence  for  this 
form  h  =  k  +  1;  the  form  s  has  the  special  symbol  (321).  The  hexocta- 
hedron alone  is  a  very  rare  form,  but  it  is  seen  in  combination  with  the  cube 
(Fig  123,  fluorite)  as  six  small  faces  replacing  each  solid  angle.  Fig.  124  is 
common  with  garnet. 

123 


Fluorite     Cube  and 
Hexoctahedron 


Garnet     Dodecahedron 
and  Hexoctahedron 


64.  Pseudo-symmetry  in  the  Isometric  System.  —  Isometric  forms,  by 
development  in  the  direction  of  one  of  the  cubic  axes,  simulate  tetragonal 
forms.     More  common,  and  of  greater  interest,  are  forms  simulating  those  of 
rhombohedral  symmetry  by  extension,  or  by  flattening;  in  the  direction  of  an 
octahedral  axis.     Both  these  cases  are  illustrated  later.     Conversely,  certain 
rhombohedral  forms  resemble  an  isometric  octahedron  in  angle. 

65.  Stereographic   and    Gnomonic    Projections.  —  The    stereographic 
projection,    Fig  125,  and  gnomonic  projection,  Fig.  126,  show  the  positions 
of  the  poles  of  the  faces  of  the  cube  (100),  octahedron  (111),  and  dodecahe- 
dron  (110);  also  the  tetrahexahedron  (210),  the  trisoctahedron  (221),  the 
trapezohedron  (211),  and  the  hexoctahedron  (321). 


ISOMETRIC    SYSTEM 


61 


126 


110 


010  H 


Stereographic  Projection  of  Isometric  Forms  (Cube  (100),  Octahedron  (111),  Dodecanedron 
(110),  Tetrahexahedron  (210),  Trisoctahedron  (221),  Trapezohedron  (211),  Hexocta- 
hedron  (321)) 

Finally,  note  the  prominent  zones  of  planes;  for  example,  the  zone  between  two  cubic 
faces  including  a  dodecahedral  face  and  the  faces  of  all  possible  tetrahexahedrons.  Again, 
the  zones  from  a  cubic  face  (as  001)  through  an  octahedral  face  (as  111)  passing  through 
the  trisoctahedrons,  as  113,  112,  223,  and  the  trapezohedrons  332,  221,  331,  etc.  Also  the 
zone  from  one  dodecahedral  face,  as  110,  to  another,  as  101,  passing  through  321,  211,  312, 
etc.  At  the  same  time  compare  these  zones  with  the  same  zones  shown  on  the  figures 
already  described.  A  study  of  the  relations  illustrated  in  Fig.  127  will-^e  found  useful. 
From  it  is  seen  that  any  crystal  face  falling  in  the  zone  between  the  cube  and  dodecahedron 
must  belong  to  a  tetrahexahedron;  any  face  falling  in  the  zone  between  the  cube  and  octa- 
hedron must  belong  to  a  trapezohedron;  and  any  face  falling  in  the  zone  between  the 
octahedron  and  dodecahedron  must  belong  to  a  trisoctahedron,  further  any  face  falling 
outside  these  three  zones  must  belong  to  a  hexoctahedron. 


62 


CRYSTALLOGRAPHY 
126 


821 


•321 


120 


321 


Gnomonic  Projection  of  Isometric  Forms  (Cube  (100),  Octahedron  (111),  Dodecahedron 
(110),  Tetrahexahedron  (210),  Trisoctahedron  (221),  Trapezohedron  (211),  Hexocta- 
hedron  (321)) 


128 


UOO) 


Symmetry  of  Pyritohedral  class 


ISOMETRIC   SYSTEM 

66.   Angles  of  Common  Isometric  Forms.* 

TETRAHEXAHEDRONS. 


63 


Cf.  Fig.  104. 
410 
310 
520 
210 
530 
320 
430 
540 

Edge  A 
210  A  201, 
19°  45' 
25  50* 
30  27 
36  52} 
42  40 
46  11} 
50  12* 
52  251 

EdgeC 
etc.  210  A  120 
61°  55-4 
53  17^ 
46  23; 
36  52; 
28  4; 
22  37; 
16  15i 
12  40^ 

Angle  on 
etc.    a(100) 
14°  2}' 
18  26 
21  48 
26  34 
30  571 
33  41* 
36  52} 
38  39* 

Angle  on 

0(111) 

45°  33f 
43  5} 
41  22 
39  14 
37  37 
36  48* 
36  4} 
35  45* 

TRISOCTAHEDBONS. 

/-^   •         Edge  4\.       Edge  B      Angle  on 

Angle  on 

221 
552 
331 

772 
441 

27  16 
33  33* 
37  511 
40  59 
43  20* 

etc.  221  A  221, 
50°  28| 
38  56* 
31  35} 
26  31* 
22  50f 
20  21 

etc.    a(100) 
50°  14}' 
48  11 
47  7* 
46  30* 
46  7* 
45  52 

0(111) 

10°  1*' 
15  47* 
19  28i 
22  0 
23  50* 
25  14* 

TRAPEZOHEDRONS. 

Cf.  Fig.  113. 
411 
722 

EdgeB 
211  A  2ll, 

27°  16' 
30  43} 

EdgeC 
etc  211  A  121, 
60°  0' 
55  501 

Angle  on 
etc.    a(100) 
19°  28} 
22  0 

Angle  on 

0(111) 

35°  15f 
32  44 

311 

35  51 

50  281 

25  14} 

29  291 

522 

40  45 

43  20* 

29  291 

25  14} 

211 

48  11* 

33  33* 

35  151 

19  28} 

322 

58  2 

19  45 

43  181 

11  25} 

HEXOCTAHEDRONS. 

«,  „.         Edge  A       EdgeB       Edge  C     Angle  on   Angle  on 
Ct.  Fig.  121.  321  A  312,  etc.  321  A  321,  etc.  321  A  231,  etc.    o(100)    o(lll) 
17°  45}'       25°  12*'       35°  57'       29°  12*'   28°  f4' 

531       27 

39* 

19  271 

27  39* 

32  18|   28  331 

321       21 

47} 

31  0^ 

21  47} 

36  42    22  12* 

432       15 

5* 

43  36f 

15  5* 

42  11    15  13* 

431       32 

.12} 

22  37f 

15  56* 

38  191   25  4 

2.   PYRITOHEDRAL  CLASS   (2).     PYRITE  TYPE 
(Dyakisdodecahedral  or  Pentagonal  Hemihedral  Class) 

67.  Typical  Forms  and  Symmetry.  —  The  typical  forms  of  the  pyrito- 
hedral  class  are  the  pyritohedron,  or  pentagonal  dodecahedron,  Figs.  129,  130, 
and  the  d^plo^d,  or  dyakisdodecahedron,  Fig.  135.  The  symmetry  of  these 
forms;  as  of  the  class  as  a  whole,  is  as  follows:  The  three  crystallographic 
axes  are  axes  of  binary  symmetry  only;  there  are  also  four  diagonal  axes  of 
trigonal  symmetry  coinciding  with  the  octahedral  axes.  There  are  but  three 
planes  of  symmetry;  these  coincide  with  the  planes  of  the  crystallographic 
axes  and  are  parallel  to  the  faces  of  the  cube. 

The  stereographic  projection  in  Fig.  128  shows  the  distribution  of  the 
faces  of  the  general  form  (hkl),  diploid,  and  thus  exhibits  the  symmetry  of 
the  class.  This  should  be  carefully  compared  with  the  corresponding  pro- 

*  A  fuller  list  is  given  in  the  Introduction  to  Dana's  System  of  Mineralogy,  1892, 
pp.  xx-xxiii. 


64 


CRYSTALLOGRAPHY 


jection  (Fig.  91)  for  the  normal  class,  so  that  the  lower  grade  of  symmetry 
here  present  be  thoroughly  understood.  In  studying  the  forms  described 
and  illustrated  in  the  following  pages,  this  matter  of  symmetry,  especially  in 
relation  to  that  of  the  normal  class,  should  be  continually  before  the  mind. 

It  will  be  observed  that  the  faces  of  both  the  pyritohedron  (Fig.  129)  and 
the  diploid  (Fig.  135)  are  arranged  in  parallel  pairs,  and  on  this  account 
these  forms  have  been  sometimes  called  parallel  hemihedrons.  Further,  those 
authors  who  prefer  to  describe  these  forms  as  cases  of  hemihedrism  call  this 
type  parallel-faced  hemihedrism  or  pentagonal  hemihedrism. 

68.  Pyritohedron.  —  The  pyritohedron  (Fig.  129)  is  so  named  because 
it  is  a  typical  form  with  the  common  species,  pyrite.  It  is  a  solid  bounded 
by  twelve  faces,  each  of  which  is  a  pentagon,  but  with  one  edge  (A,  Fig.  129) 
longer  than  the  other  four  similar  edges  (C).  It  4s  often  called  a  pentagonal 
dodecahedron,  and  indeed  it  resembles  closely  the  regular  dodecahedron  of 
geometry,  in  which  the  faces  are  regular  pentagons.  This  latter  form  is, 
however,  an  impossible  form  in  crystallography. 


129 


130 


Pyritohedrons 


Showing  Relation  between 
Pyritohedron  and  Tetra- 
hexahedron 


The  general  symbol  is  (MO)  or  like  that  of  the  tetrahexahedron  of  the 
normal  class.  Hence  each  face  is  parallel  to  one  of  the  axes  and  meets  the 
other  two  axes  at  unequal  distances.  Common  forms  are  (410),  (310),  (210), 
(320),  etc.  Besides  the  positive  pyritohedron,  as  (210),  there  is  also  the  com- 
plementary negative  form  *  shown  in  Fig.  130;  the  symbol  is  here  (120). 
Other  common  forms  are  (250),  (230),  (130),  etc. 

The  positive  and  negative  pyritohedrons  together  embrace  twenty-four 
faces,  having  the  same  position  as  the  twenty-four  like  faces  of  the  tetra- 
hexahedron of  the  normal  class.  The  relation  between  the  tetrahexahedron 
and  the  pyritohedron  is  shown  in  Fig.  131,  where  the  alternate  faces  of  the 
tetrahexahedron  (indicated  by  shading)  are  extended  to  form  the  faces  of 
the  pyritohedron. 

69.  Combinations.  —  The  faces  of  the  pyritohedron  replace  the  edges 
of  the  cube  as  shown  in  Fig.  132;  this  resembles  Fig.  101  but  here  the  faces 
make  unequal  angles  with  the  two  adjacent  cubic  faces.  On  the  other 
hand,  when  the  pyritohedron  is  modified  by  the  cube,  the  faces  of  the  latter 
truncate  the  longer  edges  of  the  pentagons. 

*  The  negative  forms  in  this  and  similar  cases  have  sometimes  distinct  letters,  some- 
times the  same  as  the  positive  form,  but  are  then  distinguished  by  a  subscript  accent,  as 
e(210)  and  e4  (120). 


ISOMETRIC   SYSTEM 


65 


Fig.  133  shows  the  combination  of  the  pyritohedron  and  octahedron,  and 
m  Fig.  134  these  two  forms  are  equally  developed.  The  resulting  combina- 
tion bears  a  close  similarity  to  the  icosahedron,  or  regular  twenty-faced  solid 
of  geometry  Here,  however  of  the  twenty  faces,  the  eight  octahedral  are 
equilateral  triangles,  the  twelve  others  belonging  to  the  pyritohedron  are 
isosceles  triangles. 


132 


Cube  and  Pyritohedron 


134 


Octahedron  and 
Pyritohedron 


Octahedron  and 
Pyritohedron 


Diploid 


70.  Diploid.  —  The  diploid  is  bounded  by  twenty-four  similar  faces, 
each  meeting  the  axes  at -unequal  distances;  its  general  symbol  is  hence 
(hkl),  and  common  forms  are  s(321),  2(421),  etc.  The  form  (321)  is  shown 
in  Fig.  135;  the  symbols  of  its  faces,  as  giveii,  should 
be  carefully  studied.  As  seen  in  the  figure,  the  faces 
are  quadrilaterals  or  trapeziums;  moreover,  they  are 
grouped  in  pairs,  hence  the  common  name  diploid.  It 
is  also  sometimes  called  a  dyakisdodecahedron. 

The  complementary  negative  form  bears  to  the 
positive  form  of  Fig.  135  the  same  relation  as  the 
negative  to  the  positive  pyritohedron.  Its  faces  have 
the  symbols  312,  231,  123,  in  the  front  octant,  and 
similarly  with  the  proper  negative  signs  in  the  others. 
The  positive  and  negative  forms  together  obviously 
embrace  all  the  faces  of  the  hexoctahedron  of  the 
normal  class.  The  diploid  can  be  considered  to  be 
derived  from  the  hexoctahedron  by  the  extension  of  the  alternate  faces  of 
the  latter  and  the  omission  of  the  remaining  faces,  exactly  as  in  the  case 
of  the  pyritohedron  and  tetrahexahedron  (Art.  68). 

In  Fig.  136  the  positive  diploid  is  shown  in  combination  with  the  cube. 
Here  the  three  faces  replace  each  of  its  solid  angles.  This  combination  form 
resembles  that  of  Fig.  Ill,  but  the  three  faces  are  here  unequally  inclined 
upon  two  adjacent  cubic  faces.  Other  combinations  of  the  diploid  with  the 
cube,  octahedron,  and  pyritohedron  are  given  in  Figs.  137  and  138. 

71.  Other  Forms.  —  If  the  pyritohedral  type  of  symmetry  be  applied  to 
planes  each  parallel  to  two  of  the  axes,  it  is  seen  that  this  symmetry  calls  for 
six  of  these,  and  the  resulting  form  is  obviously  a  cube.  This  cube  cannot  be 
distinguished  geometrically  from  the  cube  of  the  normal  class,  but  it  has  its 
own  characteristic  molecular  symmetry.  Corresponding  to  this  ijb  is  com- 
mon to  find  cubes  of  pyrite  with  fine  lines  (striations)  parallel  to  the  alter- 
nate edges,  as  indicated  in  Fig.  139.  These  are  due  to  the  partial  develop- 


66 


CRYSTALLOGRAPHY 


ment  of  pyritohedral  faces  (210).     On  a  normal  cube  similar  striations,  if 
present,  must  be  parallel  to  both  sets  of  edges  on  each  cubic  face. 

136 


Cube  and  Diploid 


Cube,  Octahedron  and 
Diploid 


Cube,  Diploid  and 
Pyritohedron 


Similarly  to  the  cube,  the  remaining  forms  of  this 
pyritohedral  class,  namely,  (111),  (110),  (hhl),  (Ml),  have 
the  same  geometrical  form,  respectively,  as  the  octahedron, 
dodecahedron,  the  trisoctahedrons  and  trapezohedrons  of 
the  normal  class.  In  molecular  structure,  however,  these 
forms  are  distinct,  each  having  the  symmetry  described 
in  Art.  67. 

Pyrite.  Striated  Cube       ^2>   A^g*68-  —  The  following  tables  contain  the  angles 
of  some  common  forms. 

PYBITOHEDRONS. 


Cf.  Fig.  129. 

Edge  A 
210  A  210,  etc. 

Edge  C 
210  A  102,  etc. 

410 

28°  4J' 

76°  23|' 

310 

36  52| 

72  32^ 

520 

43  36£ 

69  49| 

210 

53  7f 

66  25i 

530 

61  55f 

63  49i 

320 

67  22| 

62  30| 

430 

73  44£ 

61  19 

540 
650 

77  19i 
79  36| 

60  48i 
60  32^ 

Angle  on 
a(100) 
14°    2J' 
18   26 
21    48 
26    34 
30   57| 
33   41 
36   52 

38  3 

39  48 


Angle  on 
o(lll) 
456  33f 
43  5| 
41  22 
39  14 
37  37 
36  48£ 
36  4i 
35  45£ 
35  35f 


DlPLOIDS. 

Edge  A  Edge  B  Edge  C 

Cf.  Fig.  135.  321  A  321,  etc.     321  A  321,  etc.   321  A  213,  etc. 

421  51°  45|'  25°  12£'  48°  114' 

532  58    14|  37   51f  35   20 

531  60   56|  19   27f  19   27f 

851  63    36f  12     6  53    55i 

321  64   37£  31      0|  38    12i 

432  67   42^  43    36^  26    m 

431  72     4|  22    37 J  43      3 

3.   TETRAHEDRAL  CLASS   (3).     TETRAHEDRITE  TYPE 

(Hextetrahedral,  Tetrahedral  Hemihedral  Class) 

73.   Typical  Forms  and  Symmetry.  —  The  typical  form  of  this  class, 
and  that  from  which  it  derives  its  name,  is  the  tetrahedron,  shown  in  Figs. 


bigle  on 

Angle  on 

a(100) 
29°  12*' 

0(111) 

28°  6*' 

35  47f 

20  30f 

32  18| 
32  30| 

28  33| 
31  34 

36  42 

22  12| 

42   If 

15  13* 

38  19f 

25  4 

ISOMETRIC   SYSTEM 


67 


141,  142.     There  are  also  three  other  distinct  forms,  shown  in  Figs.  149, 
150,  151. 

The  symmetry  of  this  class  is  as  follows.  There  are  three  axes  of  binary 
symmetry  which  coincide  with  the  crystallographic  axes.  There  are  also 
four  diagonal  axes  of  trigonal  symmetry  which  coincide  with  the  octahedral 
axes.  There  are  six  diagonal  planes  of  sym- 
metry. There  is  no  center  of  symmetry. 

The  stereographic  projection  (Fig.  140) 
shows  the  distribution  of  the  faces  of  the 
general  form  (hkl),  hextetrahedron,  and  thus 
exhibits  the  symmetry  of  the  class.  It  will  be 
seen  at  once  that  the  like  faces  are  all  grouped 
in  the  alternate  octants,  and  this  will  be  seen 
to  be  characteristic  of  all  the  forms  peculiar 
to  this  class.  The  relation  between  the  sym- 
metry here  described  and  that  of  the  normal 
class  must  be  carefully  studied. 

In  distinction  from  the  pyritohedral  forms 
whose  faces  were  in  parallel  pairs,  the  faces  of 
the  tetrahedron  and  the  analogous  solids  are 
inclined  to  each  other,  and  hence  they  are 


Symmetry  of  Tetrahedral  Class 


sometimes  spoken  of  as  inclined  hemihedrons,  and  the  type  of  so-called  hemi- 
hedrism  here  illustrated  is  then  called  inclined  or  tetrahedral  hemihedrism. 

74.  Tetrahedron.  —  The  tetrahedron,*  as  its  name  indicates,  is  a  four- 
faced  solid,  bounded  by  planes  meeting  the  axes  at  equal  distances.  Its 
general  symbol  is  (lll)_,_and_the_four  faces  of  the  positive  form  (Fig.  141) 
have  the  symbols  111,  111,  111,  111.  These  correspond  to  four  of  the  faces 
of  the  octahedron  of  the  normal  class  (Fig.  93).  The  relation  between  the 
two  forms  is  shown  in  Fig.  143. 


Positive  Tetrahedron 


Negative  Tetrahedron 


Showing  Relation  between 
Octahedron  and  Tetrahedron 


Each  of  the  four  faces  of  the  tetrahedron  is  an  equilateral  triangle;  the 
(normal)  interfacial  angle  is  109°  29'  16".  The  tetrahedron  is  the  regular 
triangular  pyramid  of  geometry,  but  crystallographically  it  must  be  so  placed 
that  the  axes  join  the  middle  points  of  opposite  edges,  and  one  axis  is  vertical. 

*  This  is  one  of  the  five  regular  solids  of  geometry,  which  include  also  the  cube,  octa- 
hedron, the  regular  pentagonal  dodecahedron,  and  the  icosahedron;  the  last  two,  as  already 
noted,  are  impossible  forms  among  crystals. 


68 


CRYSTALLOGRAPHY 


There  are  two  possible  tetrahedrons:  the  positive  tetrahedron  (111), 
designated  by  the  letter  o,  which  has  already  been  described,  and  the  nega- 
tive tetrahedron,  having  the_same_geometrica_l  form  and  symmetry,  but  the 
indices  of  its  four  faces  are  111,  111,  111,  111.  This  second  form  is  shown 
in  Fig.  142;  it  is  usually  designated  by  the  letter  o,.  These  two  forms  are, 
as  stated  above,  identical  in  geometrical  shape,  but  they  may  be  distinguished 
in  many  cases  by  the  tests  which  serve  to  reveal  the  molecular  structure, 
particularly  the  etching-figures;  also  in  many  cases  by  pyro-electricity  (see 
under  boracite,  p.  306),  Art.  438.  It  is  probable  that  the  positive  and 
negative  tetrahedrons  of  sphalerite  (see  that  species)  have  a  constant  differ- 
ence in  this  particular,  which  makes  it  possible  to  distinguish  them  on  crystals 
from  different  localities  and  of  different  habit. 


144 


145 


146 


\/ 


Positive  and  Negative 
Tetrahedrons 


Cube  and  Tetrahedron 


Tetrahedron  and  Cube 


If  both  tetrahedrons  are  present  together,  the  form  in  Fig.  144  results. 
This  is  geometrically  an  octahedron  when  the  two  forms  are  equally  de- 
veloped, but  crystallographically  it  is  always  only  a  combination  of  two 
unlike  forms,  the  positive  and  negative  tetrahedrons,  which  can  be  distin- 
guished as  already  noted. 


147 


Tetrahedron  and 
Dodecahedron 


Boracite.   Cube,  Dodecahedron  with 
Positive  and  Negative  Tetrahedrons 


The  tetrahedron  in  combination  with  the  cube  replaces  the  alternate  solid 
angles  as  in  Fig.  145.  The  cube  modifying  the  tetrahedron  truncates  its 
edges  as  shown  in  Fig  146.  The  normal  angle  between  adjacent  cubic  and 
tetrahedral  faces  is  54°  44'.  In  Fig.  147  the  dodecahedron  is  shown  modify- 

fnL     -tPl?S^1Ve  tet™hedr°n'  whlle  m  FlS-  148  the  cube  is  the  predominating 
form  with  the  positive  and  negative  tetrahedrons  and  dodecahedron. 


ISOMETRIC   SYSTEM  gg 

75.  Other  Typical  Forms.  -  There  are  three  other  distinct  types  of 
solids  in  this  class,  having  the  general  symbols  (hhl),  (hll),  and  (hkl)  The 
first  of  these  is  shown  in  Fig  149;  here  the  symbol  is  221).  There  are  twelve 
faces  each  a  quadrilateral  belonging  to  this  form,  distributed  as  determined 
by  the  tetrahedral  type  of  symmetry.  They  correspond  to  twelve  of  the 
faces  of  the  trisoctahedron,  namely,  all  those  falling  in  alternate  octants 
I  his  type  of  solid  is  sometimes  called  a  tetragonal  tristetrahedron,  or  a  deltoid 
dodecahedron  It  does  not  occur  alone  among  crystals,  but  its  faces  are 
observed  modifying  other  forms 


Tetragonal  Tristetrahedron         Trigonal  Tristetrahedron 


Hextetrahedron 


There  is  also  a  complementary  negative  form,  corresponding  to  the  posi- 
tive form,  related  to  it  in  precisely  the  same  way  as  the  negative  to  the  posi- 
tive tetrahedron.  Its  twelve  faces  are  those  of  the  trisoctahedron  which 
belong  to  the  other  set  of  alternate  octants. 

152 


Tetrahedrite 


Sphalerite 


Boracite 


Another  form,  shown  in  Fig.  150,  has  the  general  symbol  (hll),  here  (211); 
it  is  bounded  by  twelve  like  triangular  faces,  distributed  after  the  type  de- 
manded by  tetrahedral  symmetry,  and  corresponding  consequently  to  the 
faces  of  the  alternate  octants  of  the  form  (hU)  —  the  trapezohedron  —  of  the 
normal  class.  This  type  of  solid  is  sometimes  called  a  trigonal  tristetrahedron 
or  trigondodecahedron.*  It  is  observed  both  alone  and  in  combination, 


*  It  is  to  be  noted  that  the  tetragonal  tristetrahedron  has  faces  which  resemble  those  of 
the  trapezohedron  (tetragonal  trisoctahedron),  although  it  is  related  not  to  this  but  to  the 
trisoctahedron  (trigonal  trisoctahedron).  On  the  other  hand,  the  faces  of  the  trigonal  tris- 
tetrahedron resemble  those  of  the  trisoctahedron,  though  in  fact  related  to  the  trapezo- 
hedron. 


70 


CR  YST  ALLO  GR  APH  Y 


especially  with  the  species  tetrahedrite;  it  is  much  more  common  than  the 
form  (hhl).  There  is  here  again  a  complementary  negative  form.  Fig.  152 
shows  the  positive  form  n(211)  with  the  positive  tetrahedron,  and  Fig.  153 
the  form  m(311)  with  a(100),  o(lll),  and  d(110).  In  Fig.  154,  the  negative 
form  71X211)  is  present. 

The  fourth  independent  type  of  solids  in  this  class  is  shown  in  Fig.  151. 
It  has  the  general  symbol  (hkl),  here  (321),  and  is  bounded  by  twenty-four 
faces  distributed  according  to  tetrahedral  symmetry,  that  is,  embracing  all 
the  faces  of  the  alternate  octants  of  the  forty-eight-faced  hexoctahedron. 
This  form  is  sometimes  called  a  hextetrahedron  or  hexakistetrahedron.  The 
complementary  negative  form  (hkl)  embraces  the  remaining  faces  of  the 
hexoctahedron.  The  positive  hextetrahedron,  0(531),  is  shown  in  Fig.  154 
with  the  cube,  octahedron,  and  dodecahedron,  also  the  negative  trigonal 
tristetrahedron  nt  (2 1 1 ) . 

76.  If  the  tetrahedral  symmetry  be  applied  in  the  case  of  planes  each 
parallel  to  the  two  axes,  it  will  be  seen  that  there  must  be  six  such  faces. 
They  form  a  cube  similar  geometrically  to  the  cube  both  of  the  normal  and 
pyritohedral  class  but  differing  in  its  molecular  structure,  as  can  be  readily 
proved,  for  example,  by  pyro-electricity  (Art.  438).     Similarly  in  the  case 
of  the  planes  having  the  symbol  (110),  there  must  be  twelve  faces  forming  a 
rhombic  dodecahedron  bearing  the  same  relation  to  the  like  geometrical 
form  of  the  normal  class.     The  same  is  true  again  of  the  planes  having  the 
position  expressed  by  the  general  symbol  (hkQ);   there  must  be  twenty-four 
of  them  and  they  together  form  a  tetrahexahedron. 

In  this  class,  therefore,  there  are  also  seven  types  of  forms,  but  only  four 
of  them  are  geometrically  distinct  from  the  corresponding  forms  of  the 
normal  class. 

77.  Angles.  —  The  following  tables  contain  the  angles  of  some  com- 
mon forms : 


TETRAGONAL  TRISTETRAHEDRONS. 


Cf.  Fig.  149. 

Edge  A 
221  A  212,  etc. 

Edge  B 
221  A  212,  etc. 

332 

17°  20£' 

97°  50i' 

221 

27  16 

90  0 

552 

33  33£ 

84  41 

331 

37  51f 

80  55 

TRIGONAL  TRISTETRAHEDRONS. 


Cf.  Fig.  150 
411 

Edge  B        Edge  C 
211  A  211,  etc.   211  A  121,  etc. 
38°56f        60°  0' 

722 

44  0; 

55  50| 

311 

50  28i 

50  28! 

522 

58  59^ 

43  20£ 

211 

70  31i 

33  33^ 

322 

86  37i 

19  45 

HEXTETRAHEDRONS. 


Angle  on 

o(100) 

50°  14J' 

48    111 

47      1\ 
46 


Angle  on 
o(100) 
19°  28i' 
22     0 
25    14i 
29   29| 
35    15f 
43    18f 


Angle  on 
o(lll) 
10°  If 
15  47| 
19  28| 
22  0 


Angle  on 
o(lll) 
35°  15f ' 
32   44 
29   29f 
25    14£ 
19   28£ 
11    25| 


Cf.  Fig.  151. 
531 
321 
432 
431 


Edge  A 

321  A  312,  etc. 
27°  39|' 
21  47i 
15  5i 
32  12J 


EdgeB       EdgeC  Angle  on  Angle  on 

321  A  312  etc.  321  A  231,  etc.  o(100)    o(lll) 

57°  7i'       27°  39f  32°  18f  28°  33fr 

69  4i       21  47i  36  42  22  124 

82  4f       15  5£  42   If  15  13* 

67  22f       15  56|  38  19|  25   4 


ISOMETRIC   SYSTEM 


71 


4.   PLAGIOHEDRAL  CLASS   (4).     CUPRITE  TYPE. 

(Pentagonal  Icositetrahedral,  Plagiohedral  Hemihedral  Class) 

78.  Typical  Forms  and  Symmetry.  -  The  fourth  class  under  the  iso- 
metric system  is  called  the  plagiohedral  or  gyroidal  class  because  the  faces 
of  the  general  form  (hkl)  are  arranged  in  spiral  order.  This  is  shown  on  the 
stereographic  projection,  Fig.  155,  and  also  in 
Figs.  156,  157,  which  represent  the  single  typ- 
ical form  of  the  class.  These  two  complemen- 
tary solids  together  embrace  all  the  faces  of  the 
hexoctahedron.  They  are  distinguished  from 
one  another  by  being  called  respectively  right- 
handed  and  left-handed  pentagonal  icositetra- 
hedrons.  The  other  forms  of  the  class  are 
geometrically  like  those  of  the  normal  class. 

The  symmetry  characteristic  of  the  class  in 
general  is  as  follows: 

There  are  no  planes  of  symmetry  and  no 
center  of  symmetry.  There  are,  however,  three 
axes  of  tetragonal  symmetry  normal  to  the 
cubic  faces,  four  axes  of  trigonal  symmetry 
normal  to  the  octahedral  faces,  and  six  axes  of 
binary  symmetry  normal  to  the  faces  of  the  dodecahedron.  In  other  words, 
it  has  all  the  axes  of  symmetry  of  the  normal  class  while  without  planes  or 
center  of  symmetry. 


Symmetry  of  Plagiohedral  Class 


156 


168 


Right  and  Left-handed  Pentagonal  Icositetrahedrons 


Cuprite 


79.  It  is  to  be  noted  that  the  two  forms  shown  in  Figs.  156,  157  are  alike 
geometrically,  but  are  not  superposable;  in  other  words,  they  are  related 
to  one  another  as  is  a  right-  to  a  left-hand  glove.  They  are  hence  said  to  be 
enantiomorphous,  and,  as  explained  elsewhere,  the  crystals  belonging  here 
may  be  expected  to  show  circular  light  polarization.  It  will  be  seen  that 
the  complementary  positive  and  negative  forms  of  the  preceding  classes, 
unlike  those  here,  may  be  superposed  by  being  rotated  90°  about  one  of  the 
crystallographic  axes.  This  distinction  between  positive  and  negative 
forms,  and  between  right-  and  left-handed  enantiomorphous  forms,  exists 
also  in  the  case  of  the  classes  of  several  of  the  other  systems. 

This  class  is  rare  among  minerals;  it  is  represented  by  cuprite,  sal  am- 


72 


CR  YSTALLO  GR  APH  Y 


moniac,  sylvite,  and  halite.  It  is  usually  shown  by  the  distribution  of  the 
small  modifying  faces,  or  by  the  form  of  the  etching  figures.  Fig.  158  shows 
a  crystal  of  cuprite  from  Cornwall  (Pratt)  with  the  form  2(13' 10' 12). 

5.   TETARTOHEDRAL  CLASS    (5).     ULLMANNITE  TYPE. 
(Tetrahedral  Pentagonal  Dodecahedral  Class) 

80.  Symmetry  and  Typical  Forms.  —  The  fifth  remaining  possible  class 
under  the  isometric  system  is  illustrated  by  Fig.  160,  which  represents  the 
twelve-faced  solid  corresponding  to  the  general  symbol  (hkl).  The  distri- 

bution of  its  faces  is  shown  in  the  projection, 
Fig.  159.  This  form  is  sometimes  called  a 
tetrahedral-pentagonal  dodecahedron.  It  is 
seen  to  have  one-fourth  as  many  faces  as  the 
form  (hkl)  in  the  normal  class,  hence  there  are 
four  similar  solids  which  together  embrace  all 
the  faces  of  the  hexoctahedron.  These  four 
solids,  which  are  distinguished  as  right-handed 
(positive  and  negative)  and  left-handed  (posi- 


circular  polarization.     The  remaining  forms  of 
the  class  are  (besides  the  cube  and  rhombic 
Symmetry  of  Tetartohedral  Class  dodecahedron)  the  tetrahedrons,  the  pyritohe- 

drons,  the  tetragonal  and  trigonal  tnstetrahe- 

drons;  geometrically  they  are  like  the  solids  of  the  same  names  already 
described.  This  class  has  no  plane  of  symmetry  and  no  center  of  symmetry. 
There  are  three  axes  of  binary  symmetry  normal  to  the  cubic  faces,  and  four 
axes  of  trigonal  symmetry  normal  to  the  faces  of  the  tetrahedron. 

160 


This  group  is  illustrated  by  artificial  crystals  of  barium  nitrate,  stron- 
tium nitrate,  sodium  chlorate,  etc.  Further,  the  species  ullmannite,  which 
shows  sometimes  pyritohedral  and  again  tetrahedral  forms,  both  having 
the  same  composition,  must  be  regarded  as  belonging  here. 

MATHEMATICAL  RELATIONS  OF  THE  ISOMETRIC  SYSTEM 

81.  Most  of  the  problems  arising  in  the  isometric  system  can  be  solved  at  once  by  the 
right-angled  triangles  in  the  sphere  of  projection  (Fig.  125)  without  the  use  of  any  special 
formulas. 


ISOMETRIC   SYSTEM 


73 


It  will  be  remembered  that  the  angles  between  a  cubic  face,  as  100,  and  the  adjacent 
face  of  a  tetrahexahedron,  310,  210,  320,  etc    can  be  obtained  at  once,  since  the >  tangent '  of 

this  angle  is  equal  to  ->->->  or  in  general  r 
o    £    6  h 

tan  (hkO  A  100)  =  ~ 


162 


ac 

6c 

Z 


k  =  1 

ft  =  2 
c  =  90 


Z  a&c 
(100)  A  (210) 


=  26°  34' 


This  relation  is  illustrated  in  Fig.  162,  which  also  shows  the  method  of  graphically 
determining  the  indices  of  a  tetrahexahedron,  the  angle  between  one  of  its  faces  and  an 
adjacent  cube  face  being  given. 

Since  all  the  forms  of  a  given  symbol  under  different  species  have  the  same  angles,  the 
tables  of  angles  already  given  are  very  useful. 

These  and  similar  angles  may  be  calculated  immediately  from  the  sphere,  or  often  more 
simply  by  the  formulas  given  in  the  following  article. 

82.  Formulas.  —  (1)  The  distance  of  the  pole  of  any  face  P(hkl)  from  the  cubic  faces  is 
given  by  the  following  equations.  Here  Pa  is  the  distance  between  (hkl)  and  (100);  Pb  is 
the  distance  between  (hkl)  and  (010);  and  PC  that  between  (hkl)  and  (001). 

These  equations  admit  of  much  simplification  in  the  various  special  cases,  for  (hkQ), 
(hfd),  etc.: 


(2)  The  distance  between  the  poles  of  any  two  faces  P(hkl)  and  Q(pqr)  is  given  by  the 
following  equation,  which  in  special  cases  may  also  be  more  or  less  simplified: 

hp  +  kq+  Ir 


cosPQ 


(p* 


(3)  The  calculation  of  the  supplement  interfacial  or  normal  angles  for  the  several  forms 
may  be  accomplished  as  follows: 

Trisoctahedron.  —  The  angles  A  and  B  are,  as  before,  the  supplements  of  the  interfacial 
angles  of  the  edges  lettered  as  in  Fig.  110. 

V  +  2hl.  9/,2_/2 

cos  A  =     ,  2       ,2 ,  cos  B  = 

For  the  tetragonal-tristetrahedron  (Fig.  149),     cos  B  = 

Trapezohedron  (Fig.  113).  B  and  C  are  the  supplement  angles  of  the  edges  as  lettered  in 
the  figure. 

cos  B  =  T0   ,   ^70  J  cos  C 


For  the  trigonal-tristetrahedron  (Fig.  150),        cos  B  = 
Tetrahexahedron  (Fig.  104). 

cos  A  =  ,  2   .   ^2  >*  cos  C  = 


74 


CR YST ALLO  GR  APH  Y 


h2  —  k2  hk 

Forthepyritohedron(Fig.  129),  cos  A  =  ^2  _^_  fc2  >'  cos  C  =  ^rqrp* 

Hexoctahedron  (Fig.  122). 


-  I2 


cos  A  =  /+y;v    ^  B  =  ;2;^  +  ;8;  cOS  c  =  /;y;p- 

For  the  diploid  (Fig.  135),        cos  A  -  M   ,   M   ,   n;    cos  C  =  „,«,„• 


For  the  hextetrahedron  (Fig.  151), 


cos  B  = 


h2  -  2kl 
h2  +  k2  +  I2 


83.  To  determine  the  indices  of  any  face  (fcfel)  of  an  isometric  form,  given  the  posi- 
tion of  its  pole  on  the  stereographic  projection.  As  an  illustrative  example  of  this  problem 
the  hexoctahedron  (321)  has  been  taken,  It  is  assumed  that  the  angles  100  A  321  =  36°  42' 


ISOMETRIC    SYSTEM 


75 


and  111  A  321  =  22°  12'  are  given.  The  methods  by  which  the  desired  pole  is  located 
from  these  measurements  have  been  described  on  page  38  and  are  illustrated  in  Fig.  163. 
Having  located  the  pole  (hkl)  a  line  is  drawn  through  it  from  the  center  O  of  the  projec- 
tion. This  line  O-P  represents  the  intersection  with'  the  horizontal  plane  (which  is  the 
plane  of  the  horizontal  crystal  axes,  a  and  6)  of  a  plane  which  is  normal  to  the  crystal  face 
(hkl) .  Since  two  planes  which  are  at  right  angles  to  each  other  will  intersect  a  third  plane 
in  lines  that  are  at  right  angles  to  each  other,  it  follows  that  the  plane  of  the  hexoctahedral 
face  will  intersect  the  plane  of  the  horizontal  axes  in  a  line  at  right  angles  to  O-P.  If, 
therefore,  the  distance  0-M  be  taken  as  representing  unity  on  the  a  axis  and  the  line 
M-P-N  be  drawn  at  right  angles  to  O-P  the  distance  0-N  will  represent  the  intercept  of 
the  face  in  question  upon  the  6  axis.  0-N  is  found  in  this  case  to  be  f  0-M  in  value. 
The  intercepts  upon  the  two  horizontal  axes  are,  therefore  la,  |6.  The  plotting  of  the 
intercept  upon  the  c  axis  is  shown  in  the  upper  left  hand  quadrant  of  the  figure.  The 
angular  distance  from  0  to  the  pole  (hkl)  is  measured  by  the  stereographic  protractor  as 
74°  30'.  This  angle  is  then  laid  off  from  the  line  representing  the  c  axis  and  the  line  repre- 
senting the  pole  (hkl)  is  drawn.  The  distance  O-P.  is  transferred  from  the  lower  part  of 
the  figure.  Then  we  can  construct  the  right  triangle,  the  vertical  side  of  which  is  the 
c  axis,  the  horizontal  side  is  this  line  O-P  (the  intersection  of  the  plane  which  is  normal  to 
the  crystal  face  with  the  horizontal  plane)  and  the  hypothenuse  is  a  line  lying  in  the  face 
and  therefore  at  right  angles  to  the  pole  of  the  face.  This  line  would  intersect  the  c  axis 
at  a  distance  equal  to  30-M.  The  same  relation  may  be  shown  by  starting  this  last  line 
from  a  point  on  the  c  axis  which  is  at  a  distance  from  the  center  of  the  figure  equal  to  0-M. 
In  this  case  the  intercept  on  the  horizontal  line  O-P  would  be  at  one  third  its  total  length. 
By  these  constructions  the  parameters  of  the  face  in  question  are  shown  to  be  la,  |6,  3c, 
giving  (321)  as  its  indices. 


84.   To  determine  the  indices  of  the  faces  of  teometac 

their  poles  on  the  gnomonic  projection.  -  As  an  illustrative  m  2 

lower  right  hand  quadrant  of  the  gnomonic  projection  of  ^ometric  forn^    Fig    126 
been  taken  and  reproduced  in  Fig.  164.     The  lines  O-M  and  (  re  at  ""* 

each  other  and  may  represent  the  horizontal  ?3^^^^^¥ 
pole  of  the  projection  lines  are  drawn  perpendicular  to ^ these  two  axial 
seen  that  the  intercepts  made  upon  these  lines  have  rational  relations  to 


76 


CRYSTALLOGRAPHY 


since  we  are  dealing  with  the  isometric  system  in  which  the  crystallographic  axes  are  all 
alike  and  interchangeable  with  each  other,  it  follows  that  the  different  intercepts  upon 
O-M  and  O-N  are  identical.  The  distance  O-R  (i.e.  the  distance  from  the  center  to  the 
45°  point  of  the  projection)  must  equal  the  unit  length  of  the  axes.  That  this  is  true  is 
readily  seen  by  the  consideration  of  Fig.  165.  The  intercepts  of  the  lines  drawn  from  the 
different  poles  to  the  lines  O-M  and  O-N  are  found  to  be  |,  5,  f,  1,  |,  2  and  3  times  this 
unit  distance.  To  find  the  Miller  indices  of  any  face  represented,  it  is  only  necessary  to 

165 

Plane  of  Gnomonic  Projection 


take  the  intercepts  of  the  two  lines  drawn  from  its  pole  upon  the  two  axes  a\  and  ct2,  place 
these  numbers  in  their  proper  order  and  add  a  1  as  a  third  figure  and  then  if  necessary 
clear  of  fractions.  Take  for  exa'mple  the  hexoctahedrqn  face  with  indices  312.  The  lines 
drawn  from  its  pole  intercept  the  axes  at  lai  and  £a2,  which  gives  the  expression  |  \ 1,  which, 
again,  on  clearing  of  fractions,  yields  312,  the  indices  of  the  face  in  question.  In  the  case 
of  a  face  parallel  to  the  vertical  axis,  the  pole  of  which  lies  at  infinity  on  the  gnomonic 
projection,  the  indices  may  be  obtained  by  taking  any  point  on  the  radial  line  that  points 
to  the  position  of  the  pole  and  dropping  perpendiculars  to  the  lines  representing  the  two 
horizontal  axes.  The  relative  intercepts  formed  upon  these  axes  will  give  the  first  two 
numbers  of  the  required  indices  while  the  third  number  will  necessarily  be  0. 


TETRAGONAL   SYSTEM 


77 


II.   TETRAGONAL   SYSTEM 

85.  THE  TETRAGONAL  SYSTEM  includes  all  the  forms  which  are  referred 
to  three  axes  at  right  angles  to  each  other  of  which  the  two  horizontal  axes 
are  equal  to  each  other  in  length  and  interchangeable  and  the  third,  the 
vertical  axis,  is  either  shorter  or  longer.     The  horizontal  axes  are  desig- 
nated by  the  letter  a;   the  vertical  axis  by  c  (see  Fig.  166).     The  length  of 
the  vertical  axis  expresses  properly  the  axial  ratio  of  a  :  c,  a  being  uniformly 
taken  as  equal  to  unity.     The  axes  are  orientated  and  their  opposite  ends 
designated  by  plus  and  minus  signs  exactly  as  in  the  case  of  the  Isometric 
System. 

Seven  classes  are  embraced  in  this  system.  Of  these  the  normal  class  is 
common  and  important  among  minerals;  two  others  have  several  represen- 
tatives, and  another  a  single  one  only.  It  may  be  noted  that  in  four  of  the 
classes  the  vertical  axis  is  an  axis  of  tetragonal  symmetry;  in  the  remaining 
three  it  is  an  axis  of  binary  symmetry  only. 

1.  NORMAL  CLASS   (6).    ZIRCON  TYPE 
(Ditetragonal  Bipyramidal  or  Holohedral  Class) 

86.  Symmetry.  —  The  forms  belonging  to  the  normal   class  of  the 
tetragonal  system  (cf .  Figs.  170  to  192)  have  one  principal  axis  of  tetragonal 
symmetry  (whence  name  of  the  system)  which  coincides  with  the  vertical 
crystallographic  axis,  c.     There  are  also  four  horizontal  axes  of  binary  sym- 
metry,  two  of  which   coincide  with  the  horizontal   crystallographic   axes 
while  the  other  two  are  diagonal  axes  bisecting  the  angles  between  the  first 
two. 

166  167 


eta 


Axes  of  Tetragonal  Mineral, 
Octahedrite  a  :  c  =  1  : 178 


Symmetry  of  Normal  Class 
Tetragonal  System 


Further  they  have  one  principal  plane  of  symmetry,  the  plane  of  the 
horizontal  crystallographic  axes.  There  are  also  four  vertical  planes  of 
symmetry  which  pass  through  the  vertical  crystallographic  axis  c  and  make 
angles  of  45°  with  each  other.  Two  of  these  latter  planes  include  the  hori- 
zontal crystallographic  axes  and  are  known  as  axial  planes  of  symmetry. 
The  other  two  are  known  as  diagonal  planes  of  symmetry. 


78 


CRYSTALLOGRAPHY 


The  axes  and  planes  of  symmetry  are  shown  in  Figs.  168  and  169. 

The  symmetry  and  the  distribution  of  the  faces  of  the  general  form,  hkl, 
is  shown  in  the  stereographic  projection,  Fig.  167. 

87.   Forms.  —  The  various  possible  forms  under  the  normal  class  of 
this  system  are  as  follows: 

Symbols 

1.  Base  or  basal  pinacoid (001) 

2.  Prism  of  the  first  order (110) 

3.  Prism  of  the  second  order (100) 

4.  Ditetragonal  prism (hkO)  as,  (310) ;   (210)  f  (320),  etc. 

5.  Pyramid  of  the  first  order (hhl)  as,  (223);    (111);  (221),  etc. 

6.  Pyramid  of  the  second  order (hQl)  as,  (203) ;    (101) ;  (201),  etc. 

7.  Ditetragonal  pyramid (hkl)  as,  (421);    (321);   (122),  etc. 


168 


169 


Symmetry  of  Normal  Class,  Tetragonal  System 

88.  Base  or  Basal  Pinacoid.  —  The  6ase  is  that  form  which  includes 
the  two  similar  faces  which  are  parallel_to  the  plane  of  the  horizontal  axes. 
These  faces  have  the  indices  001  and  001  respectively;  it  is  an  "open  form," 
as  they  do  not  inclose  a  space,  consequently  this  form  can  occur  only  in  com- 
bination with  other  forms.  Cf.  Figs.  170-173,  etc.  This  form  is  always 
lettered  c  in  this  work. 


170 

OQL 

4- 

i 


171 


172 


no 


First  Order  Prism 


001 


100 


010 


Second  Order  Prism 


First  and  Second 
Order  Prisms 


89.  Prisms.  —  Prisms,  in  systems  other  than  the  isometric,  have  been 
defined  to  be  forms  whose  faces  are  parallel  to  the  vertical  axis  (c)  of  the 
crystal,  while  they  meet  the  two  horizontal  axes;  in  this  system  the  four- 
faced  form  whose  planes  are  parallel  both  to  the  vertical  and  one  horizontal 


TETRAGONAL   SYSTEM 


79 


axis  is  also  called  a  prism.     There  are  hence  three  types  of  prisms  here 
included. 

90.  Prism  of  First  Order.  —  The  prism  of  the  first  order  includes  the 
four  faces  which,  while  parallel  to  the  vertical  axis,  meet  the  horizontal 
axes  at  equal  distances;   its  general  symbol  is  consequently  (110).     It  is  a 
square  prism,  with  interfacial  angles  of  90°.     It  is  shown  in  combination  with 
the  base  in  Fig.  170.     It  is  uniformly  designated  by_the  letter  m.     The  in- 
dices of  its  faces,  taken  in  order,  are  110,  110,  110,  110. 

91.  Prism  of  Second  Order.  —  The  prism  of  the  second  order  shown* 
in  combination  with  the  base  in  Fig.  171  includes  the  four  faces  which  are 
parallel  at  once  to  the  vertical  and  to  a  horizontal  axis;  it  has,  therefore,  the 
general  symbol  (100).     It  is  a  square  prism  with  an  angle  between  any  two 
adjacent  faces  of  90°.     It  is  uniformly  designated  by  _the  letter  a,  and  its 
faces,  taken  in  order,  have  the  indices  100,  010,  100,  010. 

It  will  be  seen  that  the  combination  of  this  form  with  the  base  is  the 
analogue  of  the  cube  of  the  isometric  system. 

The  faces  of  the  prism  of  the  first  order  truncate  the  edges  of  the  prism 
of  the  second  order  and  vice  versa.  When  both  are  equally  developed,  as  in 
Fig.  172,  the  result  is  a  regular  eight-sided  prism,  which,  however,  it  must 
be  remembered,  is  a  combination  of  two  distinct  forms. 

It  is  evident  that  the  two  prisms  described  do  not  differ  geometrically 
from  one  another,  and  furthermore,  in  a  given  case,  the  symmetry  of  this 
class  allows  either  to  be  made  the  first  order,  and  the  other  the  second  order, 
prism  according  to  the  position  assumed  for  the  horizontal  axes.  If  on  crys- 
tals of  a  given  species  both  forms  occur  together  equally  developed  (or,  on 
the  other  hand,  separately  on  different  crystals)  and  without  other  faces 
than  the  base,  there  is  no  means  of  telling  them  apart  unless  by  minor  char- 
acteristics, such  as  striations  or  other  markings  on  the 
surface,  etchings,  etc. 

92.  Ditetragonal  Prism.  —  The  ditetragonal  prism  is 
the  form  which  is  bounded  by  eight  similar  faces,  each  one 
of  which  is  parallel  to  the  vertical  axis  while  meeting  the 
two  horizontal  axes  at  unequal  distances.     It  has  the  general 
symbol  (hkQ).     It  is  shown  in  Fig.  173,  where  (hkO)  =  (210). 
The  successive  faces_  have  here  the  indices  210,  120,  120, 
210,  210,  120,  120,  210. 

In  Fig.  185  a  combination  is  shown  of  this  form  (y  =  310) 
with  the  second  order  prism,  the  edges  of  which  it  bevels. 
In  Fig.  189  (h  =  210)  it  bevels  the  edges  of  the  first  order 
prism  m.     In  Fig.  190  (I  =  310)  it  is  combined  with  both  Ditetragonal  Prism 
orders  of  prisms. 

93.  Pyramids.  —  There  are  three  types  of  pyramids  in  this  class,  cor- 
responding, respectively,  to  the  three  prisms  which  have  just  been  described. 

*  In  Figs.  170-173  the  dimensions  of  the  form  are  made  to  correspond  to  the  assumed 
length  of  the  vertical  axis  (here  c  =  178  as  in  octahedrite)  used  in  Fig.  177.  It  must  be 
noted,  however,  that  in  the  case  of  actual  crystals  of  these  forms,  while  the  tetragonal 
symmetry  is  usually  indicated  by  the  unlike  physical  character  of  the  face  c  as  compared 
with  the  faces  a,  m,  etc.,  in  the  vertical  prismatic  zone,  no  inference  can  be  drawn  as  to  the 
relative  length  of  the  vertical  axis.  This  last  can  be  determined  only  when  a  pyramid  is 
present;  it  is  fixed  for  the  species  when  a  particular  pyramid  is  chosen  as  fundamental  or 
unit  form,  as  explained  later. 


173 

001 

|  i_ 

~z* 

4 

210 

fl 

120 

-210 

•^^—^ 

\ 

-U 

*•••' 

80 


CRYSTALLOGRAPHY 


As  already  stated,  the  name  pyramid  is  given  (in  systems  other  than  the  iso- 
metric) to  a  form  whose  planes  meet  all  three  of  the  axes;  in  this  system 
the  form  whose  planes  meet  the  axis  c  and  one  horizontal  axis  while  parallel 
to  the  other  is  also  called  a  pyramid.  The  pyramids  of  this  class  are  strictly 
double  pyramids  (bipyramids  of  some  authors). 

94.  Pyramid  of  First  Order.  —  A  pyramid  of  the  first  order,  is  a  form 
whose  eight  similar  faces  intersect  the  two  horizontal  axes  at  equal  distances 
and  also  intersect  the  vertical  axis.  It  has  the  general  symbol  (hhl).  It  is 
a  square  pyramid  with  equal  interfacial  angles  over  the  terminal  edges,  and 
the  faces  replace  the  horizontal,  or  basal,  edges  of  the  first  order  prism  and 
the  solid  angles  of  the  second  order  prism.  If  the  ratio  of  the  vertical  to  the 
horizontal  axis  for  a  given  first  order  pyramid  is  the  assumed  axial  ratio  for 
the  species,  the  form  is  called  the  fundamental  form,  and  it  has  the  symbol 
(lll)_as  in_Fig.  174.  The  indices  of  its_faces_ me  oned  in  order  are:  Above 
111,  111,  111,  111;  below  111,  111,  111,  111. 


175 


176 


177 


in 


in 


First  Order 
Pyramid 


Zircon,  First  Order 
Prism  and  Pryamid 


Zircon,  First  Order 
Prism  and  Pyramids 


Apophyllite,  Second 
Order  Prism  and 
First  Order  Pyramid 

Obviously  the  angles  of  the  first  order  pyramid,  and  hence  its  geometrical 
aspect,  vary  widely  with  the  length  of  the  vertical  axis.  In  Figs.  174  and 
182  the  pyramids  shown  have  in  both  cases  the  symbol  (111)  but  in  the  first 
case  (octahedrite)  c  =  1.78,  while  in  the  second  (vesuvianite),  c  =  0.64. 

For  a  given  species  there  may  be  a  number  of  second  order  pyramids, 
varying  in  position  according  to  the  ratio  of  the  intercepts  upon  the  vertical 
and  horizontal  axes.  Their  symbols,  passing  from  the  base  (001)  to  the  unit 
prism  (110),  may  thus  be  (115),  (113),  (223),  (111),  (332),  (221),  (441),  etc. 
In  the  general  symbol  of  these  forms  (hhl),  as  h  diminishes,  the  form  approx- 
imates more  and  more  nearly  to  the  base  (001),  for  which  h  =  0-  as  h  in- 
creases, the  form  passes  toward  the  first  order  prism.  In  Fig.  176  two  pvra- 
mids  of  this  order  are  shown,  p(lll)  and  w(331). 

95.  Pyramid  of  Second  Order.  —  The  pyramid  of  the  second  order  is 
the  iorm,  .big.  178,  whose  faces  are  parallel  to  one  of  the  horizontal  axes 
while  meeting  the  other  two  axes.  The  general  symbol  is  (hOl) .  These  faces 
replace  the  basal  edges  of  the  second  order  prism  (Fig.  179),  and  the  solid 
angles  of  the  first  order  prism  (cf.  Fig.  180).  It  is  a  square  pyramid  since  its' 
basal  section  is  a  square,  and  the  interfacial  angles  over  the  four  terminal 


TETRAGONAL   SYSTEM 


81 


edges,  above  and  below,  are  equal.     The  successivejaces  of  the  form  (101) 
are  as  follows:   Above  101,  Oil,  101,  Oil;  below  101,  Oil,  101,  Oil. 

If  the  ratio  of  the  intercepts  on  the  horizontal  and  vertical  axes  is  the 
assumed  axial  ratio  of  the  species,  the  symbol  is  (101),  and  the  form  is  desig- 
nated by  the  letter  e.  This  ratio  can  be  deduced  from  the  measurement  of 
either  one  of  the  interfacial  angles  (y  or  z,  Fig.  178)  over  the  terminal  or  basal 
edges,  as  explained  later.  In  the  case  of  a  given  species,  a  number  of  second 

180 


Second  Order 
Pyramid 


Second  Order  Prism 
and  Pyramid 


Rutile,  First  and  Second 
Order  Prisms  and  Pyra- 
mids 


order  pyramids  may  occur,  varying  in  the  ratio  of  the  axes  a  and  c.  Hence 
there  is  possible  a  large  number  of  such  forms  whose  symbols  may  be,  for 
example,  (104),  (103),  (102),  (101),  (302),  (201),  (301),  etc.  Those  men- 
tioned first  come  nearest  to  the  base  (001),  those  last  to  the  second  order 
prism  (100);  the  base  is  therefore  the  limit  of  these  pyramids  (hQl)  when 
h  =  0,  and  the  second  order  prism  (100)  when  h  =  1  and  I  =  0.  Fig.  186 
shows  the  three  second  order  pyramids  w(105),  6(101),  g(201). 


182 


183 


Vesuvianite 
First  Order  Prism, 
Pyramid  and  Base 


Vesuvianite 

First  Order  Pyramid  and 

First  and  Scond  Order 

Prisms 


Cassiterite 

First  and  Second  Order 
Pyramids 


A  second  order  pyramid  truncating  the  pyramidal  edges  of  a  given  first 
order  pyramid  as  in  Fig.  183  has  the  same  ratio  as ,  it Jor >h  to  I  Thus  ( 
truncates  the  terminal  edge  of  (111);  (201)  of  (221),  etc.  This  is  obvious 
because  each  face  has  the  same  position  as  the  corresponding  edge  of  the 
other  form  (see  Fig.  183,  when  «  -  111  and  e  =  101;  also  Figs.  186,  191, 
where  r  =  115,  u  =  105).  Again,  if  a  first  order  pyramid  truncates  the 
pyramidal  edges  of  a  given  second  order  pyramid,  its  ratio  for  h  to  I  is  half 


82 


CRYSTALLOGRAPHY 


that  of  the  other  form;  that  is,  (112)  truncates  the  pyramidal  edges  of  (101); 
(111)  of  (201),  etc.  This  relation  is  exhibited  by  Fig.  186,  where  p(lll) 
truncates  the  edges  of  0(201).  In  both  cases  the  zonal  equations  prove  the 
relations  stated. 

186 


184 


185 


m 


Vesuvianite 

First  and  Second  Order 
Prisms,  First  Order  Pyr- 
amid and  Base 


Apophyllite 

Second  Order  Prism,  Dite- 
tragonal  Prism,  First 
Order  Pyramid  and  Base 


Octahedrite 

Two  First  Order  Pyra- 
mids, First  Order  Prism, 
Three  Second  Order 
Pyramids  and  Base 


96.  Ditetragonal  Pyramid.  —  The  ditetragonal  pyramid,  or  double  eight- 
sided  pyramid,  is  the  form  each  of  whose  sixteen  similar  faces  meets  the 
three  axes  at  unequal  distances.  This  is  the  most  general  case  of  the  symbol 
(hkl),  where  h,  k,  I  are  all  unequal  and  no  one  is  equal  to  0.  That  there  are 
sixteen  faces  in  a  single  form  is  evident.  Thus,  for  example,  for  the  form 
(212)  the  face  212  is  similar  to  122,  the  two  lateral  axes  being  equal  (not, 
however,  to  221).  Hence  there  are  two  like  faces  in  each  octant.  Similarly 
the  indices  of  all  the  faces  in  the  successive  octants  are,  therefore,  as  follows: 


Above    212     122     122     212     212     122     122     212 
Below    212     122     122     212     212     122     122     212 
187  188  189 


190 


Ditetragonal  Pyramid  Zircon  Cassiterite  Rutile 

First  and  Second  Order 
Prisms,  First  Order 
Pyramid,  Ditetrag- 
onal Pyramid 

This  form  is  common  with  the  species  zircon,  and  is  hence  often  called  a 
zirconoid.    It  is  shown  in  Fig.  187-    It  is  not  observed  alone,  though  some- 


TETRAGONAL   SYSTEM 


83 


times,  as  in  Figs.  188  (x  =  311)  and  189  (z  =  321),  it  is  the  predominating 
form.     In  Fig.   190  two  ditetragonal  pyramids  occur,  namely,  /(313)  and 

Z\OZ\.),  -g- 

97.  In  addition  to  the  perspective  figures  already 
given,  a  basal  projection  (Fig.  191)  is  added  of 
the  crystal  of  octahedrite  already  referred  to  (Fig. 
186) ;  also  a  stereographic  (Fig.  192)  and  gnomonic 
(Fig.  193)  projections  of  the  same  with  the  faces  of 
the  forms  w(22l)  and  $(313)  added.  These  exhibit 
well  the  general  relations  of  this  normal  class  of  the 
tetragonal  system.  The  symmetry  here  is  to  be 
note<l  first,  with  respect  to  the  similar  zones  100, 
001,  100  and  010,  001,  OH);  also,  to  the  other  pair  of 
similar  zones,  110,  001,  110,  and  110,  001,  110.  Octahedrite 


192 


no 


010* 


:010 


11 


Stereographic  Projection  of  Octahedrite 


84 


CRYSTALLOGRAPHY 
193 


110\_ 221 


110 


4* 

Gnomonic  Projection  of  Octahedrite 


\UO 


2.   HEMIMORPHIC   CLASS   (7). 
IODOSUCCINIMIDE  TYPE 

(Ditetragonal  Pyramidal  or  Holohedral 
Hemimorphic  Class) 

98.  Symmetry.  —  This  class  differs  from 
the  normal  class  only  in  having  no  horizontal 
plane  of  symmetry;  hence  the  forms  are  hemi- 
morphic  as  defined  in  Art.  29.  It  is  not  known 
to  be  represented  among  minerals,  but  is  shown 
on  the  crystals  of  iodosuccinimide.  Its  sym- 

Symmetry  of  Hemimorphic  Class      P6^  Sf  "lufor^ed  &  *»  stereographic  pro- 

jection  (Fig.  194).     Here  the  two  basal  planes 
are  distinct  forms,  001  and  001;  the  prisms  do  not  differ  geometrically  from 


TETRAGONAL   SYSTEM 


85 


those  of  the  normal  class,  though  distinguished  by  their  molecular  structure; 
further,  the  pyramids  are  no  longer  double  pyramids,  but  each  form  is  rep- 
resented by  one  half  of  Figs.  174,  178,  187  (cf.  Fig.  44,  p.  22).  There  are 
hence  six  distinct  pyramidal  forms,  corresponding  to  the  upper  and  lower 
halves  of  the  first  and  second  order  pyramids  and  the  ditetragonal  pyramid. 

3.   TRIPYRAMIDAL  CLASS   (8).    SCHEELITE  TYPE. 

( Tetragonal  Bipyramidal  or  Pyramidal  Hemihedral  Class) 

99.  Typical  Forms  and  Symmetry.  —  The   forms   here  included   have 
one  plane  of  symmetry  only,  that  of  the  horizontal  crystallographic  axes, 
and  one  axis  of  tetragonal  symmetry  (the  vertical  crystallographic   axis) 
normal  to  it.     The  distinctive  forms  are  the  tetragonal  prism  (hkO)  and 
pyramid  (hkl)  of  the  third  order,  shown  in  Figs.  196,  197. 

The   stereographic   projection,   Fig.    195,  195 

exhibits  the  symmetry  of  the  class  and  the 
distribution  of  the  faces  of  the  general  form 
(hkl).  Comparing  this,  as  well  as  the  figures 
immediately  following,  with  those  of  the  nor- 
mal class,  it  is  seen  that  this  class  differs  from 
it  in  the  absence  of  the  vertical  planes  of  sym- 
metry and  the  horizontal  axes  of  symmetry. 

100,  Prism  and  Pyramid  of  the  Third 
Order.  —  The    typical   forms    of   the    class, 
as  above  stated,  are  a  square  prism  and  a 
square    pyramid,    which    are    distinguished 
respectively  from  the  square  prisms  a  (100) 

and  m(110),  shown  in  Figs.  170  and  171   and  Tri-Pyramidal  Class 

from   the  square   pyramids   (hOl)   and   (hhl)       y 
of  Figs.  174  and  178  by  the  name  "  third  order." 


196 


197 


198 


120 


Third  Order  Prism 


100 


Third  Order  Pyramid 


The  third  order  prism  and  pyramid  may  be  considered  as  derived  from 
the  ditetragonal  forms  of  the  normal  class  by  taking  only  one  half  the  faces 
of  the  latter  and  the  omission  of  the  remaining  faces.  There  are  therefore 
two  complementary  forms  in  each  case,  designated  left  and  right,  which 
together  include  all  the  faces  of  the  ditetragonal  prism  (Fig.  173)  and  dite- 
tragonal pyramid  (Fig.  187)  of  the  normal  class. 


CRYSTALLOGRAPHY 


.  The  indices  of  the  faces  of  the  two  complementary  prisms,  as  (210),  are: 

Left:       210,     120,     210,     120. 
Right:     120,     210,     120,     210. 

The  indices  of  the  faces  of  the  corresponding  pyramids,  as  (212),  are: 

Left:     above  212,    122,   212,    122;    below  212,    122,   212,    122. 
Right:  above  122,   212,    122,   212;     below  122,   212,    122,   212. 

Fig.  198  gives  a  transverse  section  of  the  prisms  a(100)  and  m(110),  also 
the  prism  of  the  third  order  (120).  Figs.  196,  197  show  the  right  prism  (120) 
and  pyramid  (122)  of  the  third  order. 

101.  Other  Forms.  —  The  other  forms  of  this  class,  that  is,  the  base 
c(001);   the  other  square  prisms,  a(100)  and  ra(110);   also  the  square  pyra- 
mids (hQl)  and  (hhl)  are  geometrically  like  the  corresponding  forms  of  the 
normal  class  already  described.     The  class  shows  therefore  three  types  of 
square  pyramids  and  hence  is  called  the  tripyramidal  .class. 

102.  To  this  class  belongs  the  important  species  scheelite;    also  the 
isomorphous  species  stolzite  and  powellite,  unless  it  be  that  they  are  rather 
to  be  classed  with  wulfenite  (p.  87).     Fig.  199  shows  a  typical  crystal  of 


199 


201 


Scheelite 


Scheelite 


Meionite 


scheelite,  and  Fig.  200  a  basal  section  of  one  similar;  these  illustrate  well  the 
characteristics  of  the  class.  Here  the  forms  are  e(101),  p(lll),  and  the 
third-order  pyramids  0(212),  s/131).  Fig.  201  represents  a  meionite  crystal 
withr(lll),  and  the  third-order  pyramid  2(311).  See  also  Figs.  203,  204,  in 
which  the  third-order  prism  is  shown. 

The  forms  of  this  class  are  sometimes  described  (see  Art.  28)  as  showing 
pyramidal  hemihedrism. 

4.  PYRAMID AL-HEMIMORPHIC   CLASS  (9).     WULFENITE   TYPE 
(Tetragonal  Pyramidal  or  Hemihedral  Hemimorphic  Class) 

103.  Symmetry.  —  The  fourth  class  of  the  tetragonal  system  is  closely 
related  to  the  class  just  described.  It  has  the  same  vertical  axis  of  tetrag- 
onal symmetry,  but  there  is  no  horizontal  plane  of  symmetry.  The  forms 
are,  therefore,  hemimorphic  in  the  distribution  of  the  faces  (cf.  Fig.  202). 
The  species  wulfenite  of  the  Scheelite  Group  among  mineral  species  prob- 
ably belongs  here,  although  the  crystals  do  not  always  show  the  difference 


TETRAGONAL   SYSTEM 


87 


between  the  pyramidal  faces,  above  and  below,  which  would  characterize 
distinct  complementary  forms.  Figs.  203,  204  could,  therefore,  serve  as 
illustrations  of  the  preceding  class,  but  in  203 

Fig.  205  a  characteristic  distinction  is  exhib-  M 

ited.     In  these  figures  the  forms  are  u(W2),  *». 

e(101),    n(lll);    also  /(230),   fc(210).  z(432),  S* 


5.   SPHENOIDAL  CLASS  (10). 
CHALCOPYRITE  TYPE 

(Tetragonal    Sphenoidal,  Sphenoidal 
Hemihedral   or   Scalenohedral  Class) 

104.    Typical  Forms   and   Symmetry.  - 

The  typical  forms  of  this  class  are  the 
sphenoid  (Fig.  207)  and  the  tetragonal  sca- 
lenohedron  (Fig.  208).  They  and  all  the 
combinations  of  this  class  show  the  following  symmetry. 

203 


Symmetry  of  Pyramidal-Hemi- 
morphic  Class 


The    three 


206 


Wulfenite 

crystallographic   axes    are   axes   of  binary  symmetry   and   there   are    two 

vertical  diagonal  planes  of  symmetry. 

This  symmetry  is  exhibited  in  the  stereo- 
graphic  projection  (Fig.  206),  which  shows 
also  the  distribution  of  the  faces  of  the  gen- 
eral form  (hkl).  It  is  seen  here  that  the  faces 
are  present  in  the  alternate  octants  only,  and 
it  will  be  remembered  that  this  same  state- 
ment was  made  of  the  tetrahedral  class  under 
the  isometric  system.  There  is  hence  a  close 
analogy  between  these  two  classes.  The  sym- 
metry of  this  class  should  be  carefully  compared 
with  that  of  the  first  and  third  classes  of  this 
system  already  described. 

105.  Sphenoid.  —  The  sphenoid,  shown  in 
Fig.  207,  is  a  four-faced  solid,  resembling 
a  tetrahedron,  but  each  face  is  an  isosceles 
(not  an  equilateral)  triangle.  It  may  be1  consid- 


-t" 

Symmetry  of  Sphenoidal  Class 


88 


CRYSTALLOGRAPHY 


ered  as  derived  from  the  first  order  pyramid  of  the  normal  class  by  the 
development  of  only  the  alternate  faces  of  the  latter.  There  are  therefore 
possible  two  complementary  forms  known  as  the  positive  and  negative 
sphenoids.  The  general  symbol  qf_the_  positive  unit  sphenoid  is  (111),  and 
its  faces  have  the  jndices:  111,  111,  111,  111,  while  the  negative  sphenoid 
has  the  symbol  (111).  When  the  complementary  forms  occur  together,  if 
equally  developed,  the  resulting  solid,  though  having  two  unlike  sets  of  faces, 
cannot  be  distinguished  geometrically  from  the  first  order  pyramid  (111). 

208 


Sphenoid 


Tetragonal  Scalenohedron 


In  the  species  chalcopyrite,  which  belongs  to  this  class,  the  deviation  in 
angle  and  in  axial  ratio  from  the  isometric  system  is  very  small,  and  hence 
the  unit  sphenoid  cannot  by  the  eye  be  distinguished  from  a  tetrahedron 
(compare  Fig.  209  with  Fig.  144,  p.  68).  For  this  species  c  =  0'985  (instead 
of  1,  as  in  the  isometric  system),  and  the  normal  sphenoidal  angle  is  108°  40', 
instead  of  109°  28',  the  angle  of  the  tetrahedron.  Hence  a  crystal  of  chal- 
copyrite with  both  the  positive  and  negative  sphenoids  equally  developed 
closely  resembles  a  regular  octahedron. 

In  Fig.  210  the  second  order  pyramids  e(101)  and  z(201)  and  base  c(001) 
are  also  present. 

209 


Chalcopyrite 

106.  Tetragonal  Scalenohedron.  —  The  sphenoidal  symmetry  yields 
another  distinct  type  of  form,  that  shown  in  Fig.  208.  It  is  bounded  by 
eight  similar  scalene  triangles,  and  hence  is  called  a  tetragonal  Scalenohedron; 
the  general  symbol  is  (hkl).  It  may  be  considered  as  derived  from  the 
ditetragenal  pyramid  of  the  normal  class  by  taking  the  alternate  pairs  of 


TETRAGONAL   SYSTEM  89 

faces  of  the  latter  form.  The  faces  of  the  complementary  positive  and  nega- 
tive forms  therefore  embrace  all  the  faces  of  the  ditetragonal  pyramid.  This 
form  appears  in  combination  in  chalcopyrite,  but  is  not  observed  inde- 
pendently. In  Fig.  211  the  form  s(531)  is  the  positive  tetragonal  scaleno- 
hedron. 

107.  Other  Forms.  —  The  other  forms  of  the  class,  namely,  the  first  and 
second  order  prisms,,  the  ditetragonal  prism,  and  the  first  and  second  order 
pyramids  (hhl)  and  (MM),  are  geometrically  like  those  of  the  normal  class. 
The  lower  symmetry  in  the  molecular  structure  is  onlv  revealed  by  special 
investigation,  as  by  etching. 

6.  TRAPEZOHEDRAL  CLASS   (11).     NICKEL  SULPHATE  TYPE 

(Tetragonal  Trapezohedral  or  Trapezohedral  Hemihedral  Class) 

108.  The  trapezohedral  class  is  analogous  to  the  plagiohedral  class  under 
the  isometric  system;    it  is  characterized  by  the  absence  of  any  plane  or 
center  of  symmetry;  the  vertical  axis,  however,  is  an  axis  of  tetragonal  syi:  - 
metry,  and  perpendicular  to  this  there  are  four  axes  of  binary  symmetry. 
This  symmetry  and  the  distribution  of  the  faces  of  the  general  form  (hkl) 

212  213 


Symmetry  of  Trapezohedral  Class  Tetragonal  Trapezohedron 

are  shown  in  the  stereographic  projection,  Fig.  212,  and  Fig.  213  gives  the 
resulting  solid,  a  tetragonal  trapezohedron.  It  may  be  derived  from  the  dite- 
tragonal pyramid  of  the  normal  class  by  the  extension  of  the  alternate  faces 
of  that  form.  There  are  two  complementary  forms  called  right-  and  left- 
handed  which  embrace  all  the  faces  of  the  ditetragonal  pyramid  of  the  normal 
class.  These  two  forms  are  enantiomorphous,  and  the  salts  belonging  to 
this  class  show  circular  polarization. 

Nickel  sulphate  and  a  few  other  artificial  salts  belong  in  this  class. 

7.   TETARTOHEDRAL  CLASS   (12) 
(Tetragonal  Bisphenoidal  or  Sphenoidal  Tetartohedral  Class) 

109  Symmetry.  —  The  seventh  and  last  possible  class  under  this 
system  has  no  plane  nor  center  of  symmetry,  but  the  vertical  axis  is  an  axis 
of  binary  symmetry.  The  symmetry  and  the  distribution  of  the  faces  of  the 


90 


CRYSTALLOGRAPHY 


general  form  (hkl)  are  shown  in  the  stereograph] c  projection  (Fig.  214),  and 
the  solid  resulting  is  known  as  a  sphenoid  of  the  third  order.     It  can  be  derived 

from  the  ditetragonal  pyramid  of  the  normal 
class  by  taking  only  one  quarter  of  the  faces 
of  that  form.  There  are  therefore  four  com- 
plementary forms  which  are  respectively 
distinguished  as  right  (  +  and  —  )  and  left 
(+  and  — ). .  These  four  together  embrace  all 
the  sixteen  faces  of  the  ditetragonal  pyramid. 
The  other  characteristic  forms  of  this  class 
are  the  prism  of  the  third  order  ](hkty,  the 
positive  and  negative  sphenoids  of  the  first 
order  (111),  and  also  those  of  the  second 
order  (101).  It  is  said  that  an  artificial 
compound,  2CaO.Al203.SiO2,  crystallizes  in 
Symmetry  of  Tetartohedral  Class  this  class. 

MATHEMATICAL  RELATIONS  OF  THE  TETRAGONAL  SYSTEM 

llOo  Choice  of  Axes.  —  It  appears  from  the  discussion  of  the  symmetry  of  the  seven 
classes  of  this  system  that  with  all  of  them  the  position  of  the  vertical  axis  is  fixed.  In 
classes  1,  2,  however,  where  there  are  two  sets  of  vertical  planes  of  symmetry,  either  set 
may  be  made  the  axial  planes  and  the  other  the  diagonal  planes.  The  choice  between  these 
two  possible  positions  of  the  horizontal  axes  is  guided  particularly  by  the  habit  of  the 
occurring  crystals  and  the  relations  of  the  given  species  to  others  of  similar  form.  With 
a  species  whose  crystal  characters  have  been  described  it  is  customary  to  follow  the  orien- 
tation given  in  the  original  description. 

111.  Determination  of  the  Axial  Ratio,  etc.  —  The  following  relations  serve  to  connect 
the  axial  ratio,  that  is,  the  length  of  the  vertical  axis  c,  when  a  =  1,  with  the  fundamental 
angles  (001  A  101)  and  (001  A  111): 


tan  (001  A  101)  -  c;  tan  (001  A  111)  X 

For  faces  in  the  same  rectangular  zone  the  tangent  principle  applies.     The  most  im- 
portant cases  (cf.  Fig.  214)  are: 

tan  (001  A  hOl)  =  h 

tan  (001  A  101)  ~  I  ' 

tan  (001  A  OfcQ  =  k 

tan  (001  A  Oil)  "  I  ' 

tan  (001  A  hhl)  =  h 

tan  (001  A  111)  ~  l' 
For  the  prisms 


tan  (010  A  fcfcO)  =     » 


tan  (100  A  hkQ]  =     • 


112.  Other  Calculations.  —  It  will  be  noted  that  in  the  stereographic  projection  (Fig. 
214)  all  those  spherical  triangles  are  right-angled  which  are_  formed  by  great  circles  (diam- 
eters) which  meet  the  prismatic  zone-circle  100,  010,  100,_010.  Again,  all  those  formed  by 
great  circles  drawn  between  100  and  100,  or  010  and  010,  and  crossing  respectively  the 
zone-circles  100,  001,  100,  or  010,  001,  010.  Also,  all  those  formed  by  great  circles  drawn 
between  110  and  110  and  crossing  the_zone-circle  110,  001,  110,  or  between  110  and  110 
and  crossing  the  zone-circle  110,  001,  110. 

These  spherical  triangles  may  hence  be  readily  used  to  calculate  any  angles  desired;  for 
example,  the  angles  between  the  pole  of  any  face,  as  hkl  (say  321),  and  the  pinacoids  10_0, 
010,  001.  The  terminal  angles  (x  and  z,  Fig.  187)  of  the  ditetragonal  pyramid,  212  A  212 
(or  313  A  313,  etc.),  and  212  A  122  (or  313  A  133,  etc.),  can  also  be  obtained  in  the  same 
way.  The  zonal  relations  give  the  symbols  of  the  poles  on  the  zones  001,  100  and  001,  110 
for  the  given  case.  For  example,  the  zone-circle  110,  313,  133,  110  fneets  110,  001,  110  at 


TETRAGONAL   SYSTEM  91 

angle  313  A  223  is  half  the  angle  313  A  133      If  a  laree 
**  Calculated>  tt  is  more  Convenient  to  use  a  formula  £ 

113.   Formulas.  —  It  is  sometimes  convenient  to  have  the  normal  interfacial  angles 
expressed  directly  in  terms  of  the  axis  c  and  the  indices  h,  k,  and  I     Thus 

' 


the  pole  223,  and  the  calculated  angle  313  A  223  is  half  the  angle  313  A  133      If  a  laree 
™  given  bek>wr  ^      "*  tO  **  Calculated>  tt  is  more  Convenient  to  use  a  formula  £ 


These  may  also  be  expressed  in  the  form 


P&  =  — |Ti —  ',      tan2  PC  —  — 

'«-  <-  /C2C2  £2 

(2)  For  the  distance  between  the  poles  of  any  two  faces  (hkl),  (pqr),  we  have  in  general 

cos  PQ  =  — : — -^ 

v  [(#  +  k2)c2  +  I2]  [(p2  -f  o2)c2  +  rz] 

The  above  equations  take  a  simpler  form  for  special  cases  often  occurring;  for  example, 
for  hkl  and  the  angle  of  the  edge  y  of  Fig.  187. 

114.  Prismatic  Angles.  —  The  angles  for  the  commonly  occurring  ditetragonal  prisms 
are  as  follows* 

Angle  on  Angle  on                                                     Angle  on  Angle  on 

0(100)  w(110)                                                      o(100)  w(llO) 

410         14°    21'  30°57f  530        30°  57*'  14°    21' 

310         18   26  26    34  320        33   41J  11    18| 

210        26    34  18   26  430        36   521  8     7| 

115.  To  determine,  by  plotting,  the  axial  ratio,  a  :  c,  of  a  tetragonal  mineral  from  the 
stereographic  projection  of  its  crystal  forms.     As  an  illustrative  example  it  has  been 
assumed  that  the  angles  between  the  faces  on  the  crystal  of  rutile,  represented  in  Fig  180, 
have  been  measured  and  from  these  measurements  the  poles  of  the  faces  in  one  octant 
located  on  the  stereographic  projection,  see  Fig.  215.     In  determining  the  axial  ratio  of  a 
tetragonal  crystal  (or  what  is  the  same  thing,  the  length  of  the  c  axis,  since  the  length  of 
the  a  axes  are  always  taken  as  equal  to  1)  it  is  necessary  to  assume  the  indices  of  some 
pyramidal  form.     It  is  customary  to  take  a  pyramid  which  is  prominent  upon  the  crystals 
of  the  mineral  and  assume  that  it  is  the  fundamental  or  unit  pyramid  of  either  the  first  or 
second  order  and  has  as  its  symbol  either  (111)  or  (101).     In  the  example  chosen  both  a 
first  order  and  a  second  order  pyramid  are  present  and  from  their  zonal  relations  it  is  evi- 
dent that  if  the  symbol  assigned  to  the  first  order  form  be  (111)  that  of  the  second  order 
form  must  be  (101),     In  order  to  determine  the  relative  length  of  the  c  axis  in  respect  to 
the  length  of  the  a  axis  for  rutile  therefore,  it  is  only  necessary  to  plot  the  intercept  of 
either  of  these  forms  upon  the  axes.     In  the  case  of  the  second  order  pyramid  it  is  only 
necessary  to  construct  a  right  angle  triangle  (see  upper  left  hand  quadrant  of  Fig.  215)  in 
which  the  horizontal  side  shall  equal  the  length  of  the  a  axis,  (1),  the  vertical  side  shall 
represent  the  c  axis  and  the  hypothenuse  shall  show  the  proper  angle  of  slope  of  the  face. 
The  angle  between  the  center  of  the  projection  and  the  pole  e(101)  is  measured  by  the 
stereographic  protractor  and  a  line  drawn  making  that  angle  with  the  line  representing  the 
c  axis.     The  hypothenuse  of  the  triangle  must  then  be  at  right  angles  to  this  pole.     Its 
intercept  upon  the  vertical  side  of  the  triangle,  when  expressed  in  relation  to  the  distance 
(0-M)  which  was  chosen  as  representing  unity  on  the  a  axis,  will  therefore  give  the  length 
of  the  c  axis.     In  rutile  this  is  found  to  be  0.644. 

The  same  value  is  obtained  when  the  position  of  the  pyramid  of  the  first  order  s(lll) 
is  used.  In  this  case  the  line  M-P-N  is  first  drawn  at  right  angles  to  the  radial  line  0-P 
drawn  through  the  pole  s(lll).  The  triangle  to  be  plotted  in  this  case  has  the  distance 
O-P  as  the  length  of  its  horizontal  side.  Its  hypothenuse  must  be  at  right  angles  to  the 
line  representing  the  pole  to  (111).  The  intercept  on  the  c  axis  is  the  same  as  in  the  first 
case. 


CRYSTALLOGRAPHY 
216 


H010 


TETRAGONAL   SYSTEM 


93 


116.  To  determine,  by  plotting,  the  indices  of  any  face  (hkl)  of  a  tetragonal  form  from 
the  position  of  its  pole  on  the  stereographic  projection.     The  solution  of  this  problem  is 
like  that  given  in  a  similar  case  under  the -Isometric  System,  see  p.  74,   except  that  the 
intercept  of  the  face  on  the  vertical  axis  must  be  referred  to  the  established  unit  length  of 
that  axis  and  not  to  the  length  of  the  a  axis.     The  method  is  exactly  the  reverse  of  the 
one  used  in  the  problem  discussed  directly  above. 

117.  To  determine,  by  plotting,  the  axial  ratio,  a  :  c,  of  a  tetragonal  mineral  from  the 
gnomonic  projection  of  its  crystal  forms.     As  an  illustrative  example  consider  the  crystal 
of  rutile,  Fig.  180,  the  poles  to  the  faces  of  which,  are  shown  plotted  in  gnomonic  projec- 
tion in  Fig.  216.     The  pyramids  of  the  first  and  second  order  present  are  taken  as  the 
unit  forms  with  the  symbols,  s(lll)  and  e(101).     The  lines  O-M  and  O-N  represent  the 
two  horizontal  axes  a\  and  az  and  the  distance  from  the  center  O  to  the  circumference  of 
the  fundamental  circle  is  equal  to  unity  on  these  axes.     The  intercepts  on  O-M  and  O-N 
made  by  the  poles  of  e (101)  or  the  perpendiculars  drawn  from  the  poles  of  s(lll)  give  the 
unit  length  of  the  vertical  axis,  c.     In  this  case  this  distance,  when  expressed  in  terms  of 
the  assumed  length  of  the  horizontal  axes  (which  in  the  tetragonal  system  always  equals 
1)  is  equal  to  0.64. 

That  the  above  relation  is  true  is  -obvious  from  a  consideration  of  Fig.  216.  This  rep- 
resents a  vertical  section  through  the  spherical  and  gnomonic  projection  including  the 
horizontal  axis,  02.  The  slope  of  the  face  e(011)  is  plotted  with  its  intercepts  on  the  a2 
and  c  axes  and  the  position  of  its  pole  in  both  the  spherical  and  gnomonic  projections  is 
shown.  It  is  seen  through  the  two  similar  triangles  in  the  figure  that  the  distance  from 
the  center  to  the  pole  e(011)  in  the  gnomonic  projection  must  be  the  same  as  the  intercept 
of  the  face  e  upon  the  vertical  axis  c.  And  as  e  is  a  unit  form  this  must  represent  unity  on  c. 

118.  To  determine,  by  plotting,  the  indices  of  any  face  of  a  tetragonal  form  from  the 
position  of  its  pole  on  the  gnomonic  projection.     It  is  assumed  that  in  this  case  a  mineral 
is  being  considered  whose 

axial  ratio  is  known.    Un-  217 

der  these  conditions  draw 
perpendiculars  from  the 
pole  in  question  to  the 
lines  representing  the  two 
horizontal  axes.  Then 
space  off  on  these  lines 
distances  equivalent  to  the 
length  of  the  c  axis,  remem- 
bering that  it  must  be 
expressed  in  terms  of  the 
length  of  the  horizontal 
axes  which  in  turn  is  equal 
to  the  distance  from  the 
center  of  the  projection 
to  the  circumference  of  the 
fundamental  circle.  Give 
the  intercepts  of  the  lines 
drawn  from  the  pole  of 
the  face  to  the  axes  a\ 
and  a2  in  terms  of  the 
length  of  the  vertical  axis, 
add  a  1  as  the  third  figure 
and  if  necessary  clear  of 
fractions  and  the  required 
indices  are  the  result.  This 
is  illustrated  in  Fig.  217, 
which  is  the  lower  right 
hand  quadrant  of  the  gno- 
monic projection  of  the 
forms  shown  on  the  rutile 

e  dttetragonal  pyramid  ,(321),  Perpendiculars  drawn  from  its  pole  .interact 

as  •-   h     sr 


94  CRYSTALLOGRAPHY 

the  indices  of  the  face  in  question.  The  indices  of  a  prism  face  like  £(310)  can  be  readily 
obtained  in  exactly  the  same  manner  as  described  under  the  Isometric  System,  Art.  84. 
p.  75. 

III.   HEXAGONAL  SYSTEM 

119.  The  HEXAGONAL  SYSTEM  includes  all  the  forms  which  are  referred 
to  four  axes,  three  equal  horizontal  axes  in  a  common  plane  intersecting  at 
angles  of  60°,  and  a  fourth,  vertical  axis,  at  right  angles  to  them. 

Two  sections  are  here  included,  each  embracing  a  number  of  distinct 
classes  related  among  themselves.  They  are  called  the  Hexagonal  Division 
and  the  Trigonal  (or  Rhombohedral)  Division.  The  symmetry  of  the  former, 
about  the  vertical  axis,  belongs  to  the  hexagonal  type,  that  of  the  latter  to 
the  trigonal  type. 

Miller  (1852)  referred  all  the  forms  of  the  hexagonal  system  to  three  equal  axes  parallel 
to  the  faces  of  the  fundamental  rhombohedron,  and  hence  intersecting  at  equal  angles,  not 
90°.  This  method  (further  explained  in  Art.  169)  had  the  disadvantage  of  failing  to  bring 
out  the  relationship  between  the  normal  hexagonal  and  tetragonal  types,  both  characterized 
by  a  principal  axis  of  symmetry,  which  (on  the  system  adopted  in  this  book)  is  the  vertical 
crystallographic  axis.  It  further  gave  different  symbols  to  faces  which  are  crystallq- 
graphically  identical.  It  is  more  natural  to  employ  the  three  rhombohedral  axes  for  tri- 
gonal forms  only,  as  done  by  Groth  (1905),  who  includes  these  groups  in  a  Trigonal  System; 
but  this  also  has  some  disadvantages.  The  indices  commonly  used  in  describing  hexagonal 
forms  are  known  as  the  Miller-Bravais  indices,  since  they  were  adopted  by  Bravais  for  use 
with  the  four  axes  from  the  scheme  used  by  Miller  in  the  other  crystal  systems. 

120.  Symmetry  Classes.  —  There  are  five  possible  classes  in  the  Hex- 
agonal Division.     Of  these  the  normal  class  is  much  the  most  important,  and 
two  others  are  also  of  importance  among  crystallized  minerals. 

In  the  Trigonal  Division  there  are  seven  classes;  of  these  the  rhombo- 
hedral class  or  that  of  the  Calcite  Type,  is  by  far  the  most  common,  and 
three  others  are  also  of  importance. 

121.  Axes  and  Symbols.  —  The  position  of  the  four  axes  taken    is 
shown  in  Fig.  218;  the  three  horizontal  axes  are  called  a,  since  they  are  equal 
and  Interchangeable,  and  the  vertical  axis  is  c,  since  it  has  a  different  length, 

218  being  either  longer  or  shorter  than  the  horizontal 

axes.  The  length  of  the  vertical  axis  is  expressed 
in  terms  of  that  of  the  horizontal  axes  which  in  turn 
is  always  taken  as  unity.  Further,  when  it  is  de- 
sirable to  distinguish  between  the  horizontal  axes 
they  may  be  designated  «i,  a2,  a3.  When  properly 
orientated  one  of  the  horizontal  axes  (a2)  is  par- 
allel to  the  observer  and  the  other  two  make  angles 
of  30°  either  side  of  the  line  perpendicular  to  him. 
The  axis  to  the  left  is  taken  as  ai,  the  one  to  the 
right  as  a3.  The  positive  and  negative  ends 
Hexagonal  Axes  of  ^e  axes  are  shown  in  Fig.  218.  The  general 

position  of  any  plane  may  be  expressed  in  a 
manner  analogous  to  that  applicable  in  the  other  systems,  viz.- 

1111 

h^'-k^'-i"*''!*'       .   ; 

The  corresponding  indices  for  a  given  plane  are  then  h,  k,  i,  I;  these  always 
refer  to  the  axes  named  in  the  above  scheme.  Since  it  is  found  convenient 


HEXAGONAL   SYSTEM  95 

to  consider  the  axis  a3  as  negative  in  front  and  positive  behind,  the  general 
symbol  becomes  hkll.  Further,  as  following  from  the  angular  relation  of 
the  three  horizontal  axes,  it  can  be  readily  shown  to  be  always  true  that  the 
algebraic  sum  of  the  indices  h,  kf  i.  is  equal  to  zero: 

h  +  k  +  i  =  0. 
A.   Hexagonal  Division 

1.   NORMAL  CLASS   (13).     BERYL  TYPE 
(Dihexagonal  Bipyramidal  or  Holohedral  Class)         • 

122.  Symmetry.  —  Crystals  belonging  to  the  normal  class  of  the  Hex- 
agonal Division  have  one  principal  axis  of  hexagonal,  or  sixfold,  symmetry, 
which  coincides  with  the  vertical  crystallographic  axis;  also  six  horizontal 
axes  of  binary  symmetry;  three  of  these  coincide  with  the  horizontal  crystal- 
lographic axes,  the  others  bisect  the  angles  between  them.  There  is  one 
principal  plane  of  symmetry  which  is  the  plane  of  the  horizontal  crystallo- 
graphic axes  and  six  vertical  planes  of  symmetry  219 
which  meet  in  the  vertical  crystallographic  axis. 
Three  of  these  vertical  planes  include  the  hori- 
zontal crystallographic  axes  and  the  other  three 
bisect  the  angles  between  the  first  set. 

The  symmetry  of  this  class  is  exhibited  in  the 
accompanying  stereographic  projection,  Fig. 
219,  and  by  the  following  crystal  figures. 

The  analogy  between  this  class  and  the 
normal  class  of  the  tetragonal  system  is 
obvious  at  once  and  will  be  better  appreciated 
as  greater  familiarity  is  gained  with  the  indi- 
vidual forms  and  their  combinations. 

123.    Forms.  -  The  possible  forms  in  this  of  Normal  claas 

class  are  as  follows: 

MUler-Bravaia. 

1.  Base (0001) 

2.  Prism  of  the  first  order (1010) 

3.  Prism  of  the  second  order (1120) 

4.  Dihexagonal  prism (hkiG)  as,  (2130) 

5.  Pyramid  of  the  first  order (M)W)_as,  (1011);  (2021)  etc. 

6.  Pyramid  of  the  second  order (h-h-Zh-l)  as,  (1122) 

7.  Dihexagonal  pyramid (ftM)  as,  (2131) 

In  the  above  h  >  k,  and  h  +  k  =  —  i. 

124.  Base.  —  The  base,  or  basal  pinacoid,  includes  the  two  faces,  0001 
and  OOOT,  parallel  to  the  plane  of  the  horizontal  axes.     It  is  uniformly  d 
nated  by  the  letter  c;  see  Fig.  220  et  seq.  . 

125,  Prism  of  the  First  Order.  —  There  are  three  types  of  prisms,  or 
forms  in  which  the  faces  are  parallel  to  the  vertical  axis. 


96 


CRYSTALLOGRAPHY 


The  prism  of  the  first  order.  Fig.  220,  includes  six  faces,  each  one  of  which 
is  parallel  to  the  vertical  axis  and  meets  two  adjacent  horizontal  axes  at 
equal  distances,  while  i^is  parallel  to  the  third  horizontal  axis.  It  has  hence 
the  general  symbol  (1010)  and  is  uniformly  designated  by  the  letter  m;  the 
indices  of  its  six  faces  taken  in  order  (see  Figs.  220  and  229,  230)  are: 

10TO,     OlTO,     TlOO,     1010,     0110,     lIOO. 
221 


220 

a. 

J^—- 

0001 

V, 
r— 

i 

i 

;    i 

iiu 

If 

-n<: 
10 

0, 

r,, 

^ 

r 

_.  —  • 

2110 


T<~~ 

i  1120 


--1210 


•First  Order  Prism 


Second  Order  Prism 


Dihexagonal  Prism 


126.  Prism  of  the  Second  Order.  —  The  prism  of  the  second  order, 
Fig.  221,  has  six  faces,  each  one  of  which  is  parallel  to  the  vertical  axis,  and 
meets  the  three  horizontal  axes,  two  alternate  axes  at  the  unit  distance,  the 
intermediate  axis  at  one-half  this  distance;  or,  which  is  the  same  thing,  it 
meets  the  last-named  axis  at  the  unit  distance,  the  others  at  double  this 
distance.*  The  general  symbol  is  (1120)  and  it  is  uniformly  designated  by 
the  letter  a;  the  indices  of  the  six  faces  (see  Figs.  221  and  229,  230)  in  order 
are: 

1120,     1210,     2110,     1120,     1210,     2110. 

The  first  and  second  order  prisms  are  not  to  be  distinguished  geometric- 
ally from  each  other  since  each  is  a  regular  hexagonal  prism  with  normal 
interfacial  angles  of  60°.  They  are  related  to  each  other  in  the  same  way  as 
the  two  prisms  ra(110)  and  a(100)  of  the  tetragonal  system. 

The  relation  in  position  between  the  first  order 
prism  (and  pyramids)  on  the  one  hand  and  the 
second  order  prism  (and  pyramids)  on  the  other 
will  be  understood  better  from  Fig.  223,  repre- 
senting a  cross  section  of  the  two  prisms  parallel 
to  the  base  c. 

127.  Dihexagonal  Prism.  —  The  dihexagonal 
prism,  Fig.  222,  is  a  twelve-sided  prism  bounded 
by  twelve  faces,  each  one  of  which  is  parallel 
to  the  vertical  axis,  and  also  meets  two  adjacent 
horizontal  axes  at  unequal  distances,  the  ratio  of 
which  always  lies  between  1  :  1  and  1:2.  This 
prism  has  two  unlike_  edges,  lettered  x  and  y,  as 
shown  in  Fig.  222.  The  general  symbol  is  (hkzO)  and  the  indices  of  the 
faces  of  a  given  form,  as  (2130),  are: 


*  Since  lai  :  la-j  :  —  |a3  :  a>c  is  equivalent  to  2ai  :  2a2  :  —  Ia3  : 


HEXAGONAL   SYSTEM 


97 


2130,      1230,      1320,     2310,     3210,     3120, 
2130,      1230,      1320,      2310,     32lO,     3l20. 


128.  Pyramids  of  the  First  Order.  —  Corresponding  to  the  three  types 
of  prisms  just  mentioned,  there  are  three  types  of  pyramids 

A  pyramid  of  the  first  order,  Fig.  224,  is  a  double  six-sided  pyramid  (or 
bipyramid)  bounded  by  twelve  similar  triangular  faces  —  six  above  and  six 
below  —  which  have  the  same  position  relative  to  the  horizontal  axes  as  the 
faces  of  the  first  order  prism,  while  they  also  intersect  the  vertical  axis  above 
and  below.  The  general  symbol  is  hence  (hOhl).  The  faces  of  a  given  form, 
as  1011),  are: 

Above    1011,     0111,     1101,     1011,     0111,     1101. 
Below    1011,     0111,     1101,,     1011,     0111,      lIOl. 

On  a  given  species  there  may  be  a  number  of  pyramids  of  the  first  order, 
differing  in  the  ratio  of  the  intercepts  on  the  horizontal  to  the  vertical  axis, 
and  thus  forming  a  zone  between  the  base  (0001)  and  the  faces  of  the  unit 
prism  (1010).  Their  symbols,  passing  from  the  base  (0001)  tojthe  unit 
prism  (1010),  would  be,  for  example,  1014,  1012,  2023,  1011,  3032,  2021, 
etc.  In  Fig.  228  the  faces  p_and  u  are  first  order  pyramids  and  they  have 
the  symbols  respectively  (1011)  and  (2021),  here  c  =  0.4989.  As  shown  in 
these  cases  the  faces  of  the  first  order  pyramids  replace  the  edges  of  the  first 
order  prism.  On  the  other  hand,  they  replace  the  solid  angles  of  the  second 
order  prism  a(112Q). 

224  226 


First  Order  Pyramid          Second  Order  Pyramid  Dihexagonal  Pyramid 

129.  Pyramids  of  the  Second  Order.  —  The  pyramid  of  the  second  order 
(Fig.  225),  is  a  double  six-sided  pyramid  including  the  twelve  similar  faces 
which  have  the  same  position  relative  to  the  horizontal  axes  as  the  faces 
of  the  second  order  prism,  and  which  also  intersect  the  vertical  axis.  They 
have  the  general  symbol  (h'h-2h-l).  The  indices  of  the  faces  of  the  form 
(1122)  are: 

Above    1122,      1212,     2112,      1122,      1212,     2112. 
Below    1122,     1212,     2112,      1122,      1212,     2112. 

The  faces  of  the  second  order  pyramid  replace  the  edges  between  the  faces 
of  the  second  order  prism  and_the  base.  Further,  they  replace  the  solid  angles 
of  the  first  order  prism  m(1010).  There  may  be  on  a  single  crystal: a .num- 
ber of  second  order  pyramids  forming  a  zone  between  the  base  c(0( 


98 


CRYSTALLOGRAPHY 


the  faces_of  the  second  order  prism  a(1120),  as,  naming  them  in  order:  JL 124, 
1122,  2243,  1121,  etc.  In  Fig.  227,  s  is  the  second  order  pyramid  (1121). 

130.  Dihexagonal  Pyramid.  —  The  dihexagonal  pyramid,  Fig.  226,  is  a 
double  twelve-sided  pyramid,  having  the  twenty-four  similar  faces  embraced 
under  the  general  symbol   (hk'd).     It  is  bounded  by  twenty-four  similar 
faces,  each  meeting  the  vertical  axis,  and  also  meeting  two  adjacent  hori- 
zontal axes  at  unequal  distances,  the  ratio   of  which   always   lies  between 
1  :  1  and  1:2.     Thus  the  form  (2131)  includes  the  following  twelve  faces  in 
the  upper  half  of  the  crystal: 

2131,     1231,     1321,     2311,     3211,     3121, 
2131,     1231,     1321,     2311,     3211,     3121. 

And  similarly  below  with  I  (here  1)  negative,  2131,  etc.  The  dihexagonal 
pyramid  is  often  called  a  berylloid  because  a  common  form  with  the  species 
beryl.  The  dihexagonal  pyramid  v(2131)  is  shown  on  Figs.  224,  225. 

131.  Combinations.  —  Fig.  227  of  beryl  shows  a  combination  of  the 


227 


Beryl 

base_c(0001)  and  prism  m(1010)  with  the_first  order  pyramids  p(10ll)  and 
tt(2Q21);  the  second  order  pyramid  s(1121)  and  the  dihexagonal  pyramid 
p(2131).  Both  the  last  forms  lie  in  a  zone  between  m  and  s,  for  which  it  is 
true  that  k  =  I.  The  basal  projection  of  a  similar  crystal  shown  in  Fig.  228 
is  very  instructive  as  exhibiting  the  symmetry  of  the  normal  hexagonal 
class.  This  is  also  true  of  the  stereographic  and  gnomonic  projections  in 
Figs.  229  and  230  of  a  like  crystal  with  the  added  form  0(1122). 

2.   HEMIMORPHIC   CLASS   (14).     ZINCITE  TYPE 

(Dihexagonal  Pyramidal  or  Holohedral  Hemimorphic  Class) 

132.  Symmetry.  —  This  class  differs  from  the  normal  class  only  in 
having  no  horizontal  plane  of  principal  symmetry  and  no  horizontal  axes 
of  binary  symmetry.  It  has,  however,  the  same  six  vertical  planes  of  sym- 
metry meeting  at  angles  of  30°  in  the  vertical  crystallographic  axis  which  is 


0110 


2110 


1100 


1010 


100 


CRYSTALLOGRAPHY 


an  axis  of  hexagonal  symmetry.     There  is  no  center  of  symmetry.     The 


symmetry   is   exhibited   in   the  stereographic 
projection,  Fig.  231. 

133.  Forms.  -  -  The  forms  belonging  to 
this  class  are  the  two  basal  planes,  0001 
and  0001,  here  distinct  forms,  the  positive 
(upper)  and  negative  (lower)  pyramids  of 
each  of  the  three  types;  also  the  three  prisms, 
which  last  do  not  differ  geometrically  from 
the  prisms  of  the  normal  class.  An  example 
of  this  class  is  found  in  zincite,  Fig.  44, 
p.  22.  lodyrite,  greenockite  and  wurtzite  are 
also  classed  here. 


Symmetry  of  Hemimorphic  Class 


3.   TRIPYRAMIDAL   CLASS   (15).     APATITE   TYPE 
(Hexagonal  Bipyramidal  or  Pyramidal  Hemihedral  Class) 

134.  Typical  Forms  and  Symmetry.  —  This  class  is  important  because 
it  includes  the  common  species  of  the  Apatite  Group,  apatite,  pyromorphite, 
mimetite,  vanadinite.  The  typical  form  is  the  hexagonal  prism  (hklO)  and 
the  hexagonal  pyramid  (hktl),  each  designated  as  of  the  third  order.  These 
forms  which  are  shown  in  Figs.  233  and  234  may  be  considered  as  derived 
from  the  corresponding  dihexagonal  forms  of  the  normal  class  by  the  omis- 
sion of  one  half  of  the  faces  of  the  latter.  They  and  the  other  forms  of  the 
class  have  only  one  plane  of  symmetry,  the  plane  of  the  horizontal  axes,  and 
also  one  axis  of  hexagonal  symmetry  (the  vertical  axis). 

The  symmetry  is  exhibited  in  the  stereo- 
graphic  projection  (Fig.  232).  It  is  seen  here, 
as  in  the  figures  of  crystals  given,  that,  like 
the  tripyramidal  class  under  the  tetragonal 
system,  the  faces  of  the  general  form  (hk~l) 
present  are  half  of  the  possible  planes  belong- 
ing to  each  sectant,  and  further  that  those 
above  and  below  fall  in  the  same  vertical 


zone. 

135.  Prism  and  Pyramid  of  the  Third 
Order.  —  The  prism  of  the  third  order  (Fig. 
233)  has  six  like  faces  embraced  under  the 
general  symbol  (hkiQ) ,  and  the  form  is  a  regular 
hexagonal  prism  with  angles  of  60°,  not  to  be 
distinguished  geometrically,  if  alone,  from  the  Symmetry  of  Tripyramidal  Class 
other  hexagonal  prisms;  cf.  Figs.  220,  221, 

p.  96.     The  six  faces  of  the  right-handed  form  (2130)  have  the  indices 
2130,     1320,     3210,     2l30,     1320,     32lO. 

The  faces  of  the  complementary  left-handed  form  have  the  indices: 
1230,     23lO,     3120,     1230,     2310,     3l20 

As  already  stated  these  two  forms  together  embrace  all  the  faces  of  the 
dihexagonal  prism  (Fig.  222). 


233 


HEXAGONAL  SYSTEM 
234 


101 


236 


Third  Order  Prism 


Third  Order  Pyramid 


The  pyramid  is  also  a  regular  double  hexagonal  pyramid  of  the  third 
order,  and  in  its  relations  to  the  other  hexagonal  pyramids  of  the  class  (Figs. 
224,  225)  it  is  analogous  to  the  square  pyramid  of  the  third  order  met  with 
in  the  corresponding  class  of  the_  tetragonal  system  (see  Art.  100).  The 
faces  of  the  right-handed  form  (2131)  are: 

Above    2131,     1321,     3211,     2131,     1321,     3211. 
Below     2131,     1321,     3211,     2131,     1321,     3211. 

There  is  also  a  complementary  left-handed  form,  which  with  this  embraces 
all  the  faces  of  the  dihexagonal  pyramid.  The  cross  section  of  Fig.  235  shows 
in  outline  the  position  of  the  first  order  prism,  and  also  that  of  the  right- 
handed  prism  of  the  third  order. 

The  prism  and  pyramid  just  described  do  not  often  appear  on  crystals  as 
predominating  forms,  though  this  is  sometimes  the  case,  but  commonly  these 
faces  are  present  modifying  other  fundamental  forms. 

136.  Other  Forms.  —  The  remaining  forms  of  the  class  are  geometri- 
cally like  those  of  the  normal  class,  viz.,  the  base  (0001) ;  the  first  order  prism 
(1010);  the  second  order  prism  (1120);_  the  first  order  pyramids  (hQhl); 
and  the  second  order  pyramids  (h'h'2h'l).  That  their  molecular  struc- 
ture, however,  corresponds  to  the  symmetry  of  this  class  is  readily  proved,  for 
example,  by  etching.  In  this  way  it  was  shown  that 
pyromorphite  and  mimetite  belonged  in  the  same 
group  with  apatite  (Baumhauer),  though  crystals  with 
the  typical  forms  had  not  been  observed.  This  class 
is  given  its  name  of  Tripyramidal  because  its  forms 
include  three  distinct  types  of  pyramids. 

137.  A  typical  crystal  of  apatite  is  given_  in  Fig. 
236.  It  shows  the  third  order  pjism  ft(2130),  and 
the  third  order  pyramids,  M_(2131),  n_(3141);  also 
the  first  order  pyramids  r(1012),  z(1011),  </(2021), 
the  second  order  pyramids  K1122),  s(1121); 
finally,  the  prism  w(1010),  and  the  base  c(0001).  Apatite 

4    PYRAMIDAL-HEMIMORPHIC  CLASS  (16).     NEPHELITE  TYPE 
(Hexagonal  Pyramidal  or  Pyramidal  Hemihedral  Hemimorphic  Class) 
138.   Symmetry.  —  A  fourth  class  under  the  hexagonal  division,  the 

pyramidal-hemimorphic  class,  is  like  that  just  described,  except  that  the 


102 


CRYSTALLOGRAPHY 


forms  are  hemimorphic.  The  single  horizontal  plane  of  symmetry  is  absent, 
but  the  vertical  axis  is  still  an  axis  of  hexagonal  symmetry.  This  symmetry 
is  shown  in  the  stenographic  projection  of  Fig.  237.  The  typical  form  would 
be  like  the  upper  half  of  Fig.  234  of  the  pyramid  of  the  third  order.  The 
species  nephelite  is  shown  by  the  character  of  the  etching-figures  (Kg. 
Groth  after  Baumhauer)  to  belong  here. 

237 


Symmetry  of  Pyramidal-Hemimorphic  Class 


Nephelite 


5.  TRAPEZOHEDRAL  CLASS   (17) 
(Hexagonal  Trapezohedral  or  Trapezohedral  Hemihedral  Class) 

139.  Symmetry.  —  The  last  class  of  this  division  is  the  trapezohedral 
class.  It  has  no  plane  of  symmetry,  but  the  vertical  axis  is  an  axis  of  hex- 
agonal symmetry,  and  there  are,  further,  six  horizontal  axes  of  binary  sym- 
metry. There  is  no  center  of  symmetry.  The  symmetry  and  the  distribu- 
tion of  the  faces  of  the  typical  form  (hkll)  is  shown  in  the  stereographic  pro- 
jection (Fig.  239).  The  typical  forms  may  be  derived  from  the  dihexagonal 
pyramid  by  the  omission  of  the  alternate  faces  of  the  latter.  There  are  two 
possible  types  known  as  the  right  and  left  hexagonal  trapezohedroris  (see 


239 


240 


/     V   o,{     > 

(--AA-H 

V  ?  %  / 


Symmetry  of  Trapezohedral  Class 


Hexagonal  Trapezohedron 


Fig.  240),  which  are  enantiomorphous,  and  the  few  crystallized  salts  falling 
in  this  class  show  circular  polarization.     A  modification  of  quartz  known  as 


HEXAGONAL   SYSTEM  103 

/3-quartz  is  also  described  as  belonging  here.     The  indices  of  the  right  form 
(2131)  are  as  follows: 

Above    2131,     1321,     3211,     2131,     1321,     32ll. 
Below     1231,     2311,     3121,     1231,     23ll,     3l2l. 

B.   Trigonal  or  Rhombohedral  Division 

(Trigonal  System) 

140.  General  Character.  —  As  stated  on  p.  19,  the  classes  of  this  division 
are  characterized  by  a  vertical  axis  of  trigonal,  or  threefold,  symmetry. 
There  are  seven  classes  here  included  of  which  the  rhombohedral  class  of  the 
Calcite  Type  is  by  far  the  most  important. 

1.   TRIGONAL  CLASS   (18).     BENITOITE  TYPE 
(Ditrigonal  Bipyramidal,  Trigonal  Hemihedral  or  Trigonotype  Class) 

141.  Typical  Forms  and  Symmetry.  —  This  class  has,  besides  the  ver- 
tical axis  of  trigonal  symmetry,  three  horizontal  axes  of  binary  symmetry 
which  are  diagonal  to  the  crystallographic  axes.     There  are  four  planes  of 
symmetry,  one  horizontal,  and  three  vertical  diagonal  planes  intersecting  at 
angles  of  60°  in  the  vertical  axis.     The  symmetry  and  the  distribution  of  the 
faces  of  the  positive  ditrigonal  pyramid  is  shown  in  Fig.  241.     The  char- 
acteristic forms  are  as  follows.     Trigonal  prism  consisting  of  three  faces 
comprising  one  half  the  faces  of  the  hexagonal  prism  of  the  first_order.     They 
are  of  two  types,   called  positive   (1010)   and  negative  (0110).     Trigonal 

241  242 


Symmetry  of  Trigonal  Class  Benitoite  (Palache) 

pyramid,  a  double  three-faced  pyramid,  consisting  of  six  faces  corresponding 
to  one  half  the  faces  of  the  hexagonal  pyramid  of  the  first  order.  The  faces 
of  the  upper  and  lower  halves  f alj_  in  vertical  zones  with  each  other.  There 
are  two  types,  called  positive  (1011)  and  negative  (0111).  Ditrigonal  prism 
consists  of  six  vertical  faces  arranged  in  three  similar  sets  of  two  faces  and 
having  therefore  the  alternate  edges  of  differing  character.  It  may  be  de- 
rived from  the  dihexagonal  prism  by  taking  alternating  pairs  of  faces.  Ditri- 
gonal pyramid  consists  of  twelve  faces,  six  above  and  six  below.  It,  like  the 
prism,  may  be  derived  from  the  dihexagonal  form  by  taking  alternate  pairs 
of  faces  of  the  latter.  The  faces  of  the  upper  and  lower  halves  fall  in  vertical 


104 


CRYSTALLOGRAPHY 


zones.  The  only  representative  of  this  class  known  is  the  rare  mineral 
benitoite,  a  crystal  of  which  is  represented  in  Fig.  242.  This  crystal  shows 
the  trigonal  prisms  m(1010)  and  ^(01 10),  the  hexagonal_ prism  of_the  second 
order,  a(1120),  the  trigonal  pyramids,  p(1011]  and  Tr(Olll);  6(0112)  and  the 
hexagonal  pyramid  of  the  second  order,  x(2241) 

2.   RHOMBOHEDRAL  CLASS   (19).     CALCITE  TYPE     . 

(Ditrigonal  Scalenohedral  or  Rhombohedral  Hemihedral  Class) 

142.  Typical  Forms  and  Symmetry.  —  The  typical  forms  of  the  rhom- 
bohedral  class  are  the  rhombohedron  (Fig.  244)  and  the  scalenohedron  (Fig. 

259).     These    forms,    with    the    projections, 

243  Figs.  243    and    269,  illustrate  the  symmetry 

>.--— I -^  !    characteristic  of  the  class.     There  are  three 

planes  of  symmetry  only;  these  are  diangoal 
to  the  horizontal  crystallographic  axes  and 
intersect  at  angles  of  60°  in  the  vertical  crystal- 
lographic axis.  This  axis  is  with  these  forms 
an  axis  of  trigonal  symmetry;  there  are, 
further,  three  horizontal  axes  diagonal  to  the 
crystallographic  axes  of  binary  symmetry. 
Compare  Fig.  244,  also  Fig.  245  et  seq. 

By   comparing  Fig.   269    with  Fig.  229,  p. 
99,  it  will  be  seen  that  all  the  faces  in  half 
the  sectants  are  present.     This  group  is  hence 
analogous  to  the  tetrahedral  class  of  the  iso- 
metric system,  and  the  sphenoidal  class  of  the  tetragonal  system. 

143.  Rhombohedron.  —  Geometrically  described,  the  rhombohedron  is 
a  solid  bounded  by  six  like  faces,  each  a  rhomb.     It  has  six  like  lateral  edges 
forming  a  zigzag  line  about  the  crystal,  and  six  like  terminal  edges,  three 
above  and  three  in  alternate  position  below.     The  vertical  axis  joins  the  two 
trihedral  solid  angles,  and  the  horizontal  axes  join  the  middle  points  of  the 
opposite  sides,  as  shown  in  Fig.  244. 

244  245  246 


Symmetry  of  Rhombohedral 
Class 


Positive  Rhombohedron  Calcite     Negative  Rhombohedron 


Positive  Rhombohedron 
Hematite 


The  general  symbol  of  the  rhombohedron  is  (hQhl),  and  the  successive 
faces  of  the  unit  form  (1011)  have  the  indices: 

Above,  lOll,    IlOl,    Olll;        below,    OlIT,    Toil,     llol. 


HEXAGONAL   SYSTEM 


105 


The  geometrical  shape  of  the  rhombohedron  varies  widely  as  the  angles 
change,  and  consequently  the  relative  length  of  the  vertical  axis  c  (expressed 
in  terms  of  the  horizontal  axes,  a  =  1).  As  the  vertical  axis  diminishes,  the 
rhombohedrons  become  more  and  more  obtuse  or  flattened;  and  as  it  increases 
they  become  more  and  more  acute.  A  cube  placed  with  an  octahedral  axis 
vertical  is  obviously  the  limiting  case  between  the  obtuse  and  acute  forms 
where  the  interfacial  angle  is  90°.  In  Fig.  244  of  calcite  the  normal  rhom- 
bohedral  angle  is  74°  55'  and  c  =  0-854,  while  for  Fig.  246  of  hematite  this 
angle  is  94°  and  c  =  1-366.  Further,  Figs.  246-251  show  other  rhombohe- 
drons of  calcite,  namely,  I  (0112),  </>  (0554),  /(0221),  M(4041),  and  p(16-0-16-l) ; 
here  the  vertical  axes  are  in  the  ratio  of  J,  f ,  2,  4,  16,  to  that  of  the  funda- 
mental (cleavage)  rhombohedron  of  Fig.  244,  whose  angle  determines  the 
value  of  c. 


247 


249 


250 


261 


253 


254 


Figs.  247-252,  Calcite     Figs.  253-254,  Gmelinite 

144.  Positive  and  Negative  Rhombohedrons.  —  To  every  positive 
rhombohedron  there  may  be  an  inverse  and  complementary  form,  identical 
geometrically,  but  bounded  by  faces  falling  in  the_  alternate  sectants.  Thus 
the  negative  form  of  the  unit  rhombohedron  (0111)  shown  in  Fig.  245  has 
the  faces: 

Above,  Olll,     1011,     1101;        below,  1101,    0111,     1011. 

The  position  of  these  in  the  projections  (Figs.  269,  270)  should  be  care- 
fully studied.  Of  the  figures  already  referred  to  Figs .244,  246,  250  are 
positive,  and  Figs.  245,  247,  248,  249  negative,  rhombohedrons;  Fig.  251 
shows  both  forms.  .  , 

It  will  be  seen  that  the  two  complementary  positive  and  negative  rhom- 
bohedrons of  given  axial  length  together  embrace  all  the  like  faces  of  the 
double  six-sided  hexagonal  pyramid  of  the  first  order.  When  these  two 
rhombohedrons  are  equally  developed  the  form  is  geometrically  .identical 
with  this  pyramid.  This  is  illustrated  by  Fig.  254  of  gmelimte  r(1011), 


106 


CRYSTALLOGRAPHY 


p(0111)  and  by  Figs.  284,  285,  p.  113,  of  quartz,  r(1011),  3(0111).*  In  each 
case  the  form,  which  is  geometrically  a  double  hexagonal  pyramid  (in  Fig. 
254  with  c  and  m),  is  in  fact  a  combination  of  the  two  unit  rhombohedrons, 
positive  and  negative.  Commonly  a  difference  in  size  between  the  two  forms 
may  be  observed,  as  in  Figs.  253  and  286,  where  the  form  taken  as  the  posi- 
tive rhombohedron  predominates.  But  even  if  this  distinction  cannot  be 
established,  the  two  rhombohedrons  can  always  be  distinguished  by  etching, 
or,  as  in  the  case  of  quartz,  by  pyro-electrical  phenomena. 

145.  Of  the  two  series,  or  zones,  of  rhombohedrons  the  faces  of  the  posi- 
tive rhombohedrons  replace  the  edges  between  the  base  (0001)  and  the  first 
order  prism  (1010).  Also  the  faces  of  the  negative  rhombohedrons  replace  the 
alternate  edges  of  the  same  forms,  that  is,  the  edges  between  (0001)  and 
(0110)  (compare  Figs.  253,  254,  etc.).  Fig.  255  shows  the  rhombohed_ron 
in  combination  with  the  base.  Fig.  256  the  same  with  the  prism  a(1120). 
When  the  angle  between  the  two  forms  happens  to  approximate  to  70°  32' 
the  crystal  simulates  the  aspect  of  a  regular  octahedron.  This  is  illustrated 
by  Fig.  257;  here  co  =  69°  42',  also  oo  =  71°  22',  and  the  crystal  resembles 
closely  an  octahedron  with  truncated  edges  (cf.  Fig.  99,  p.  55). 
255  257  258 


Figs.  255,  256,  Hematite  Coquimbite  Eudialyte 

146.  There  is  a  very  simple  relation  between  the  positive  and  negative 
rhombohedrons  which  it  is  important  to  remember.     The  form  of  one  series 
which  truncates  the  terminal  edges  of  a  given  form  of  the  other  will  have  one 
half  the  intercept  on  the  vertical  crystallographic  axis  of  the  latter.     This 
ratio  is  expressed  in  the  values  of  the  indices  of  the  two  forms.     Thus  (0112), 
truncates  the  terminal  edges  of  the  positive  unit  rhombohedron   (1011); 
(1014)  truncates  the  terminal  edges_of  (0112),_(1015)  of  (2025).     Again  (1011) 
truncates  the  edges  of  (0221),  (4041)  of  _(0221),  etc.     This  is  illustrated  by 
Fig.  252  with  the  forms  r(1011)  and  /(0221).     Also  in  Fig.  258,_a  basal  pro- 
jection^ 2(1014)  truncates  the  edges  of  e(0112);  c(0112)  of  r(1011);   r(1011) 
of  s(0221). 

147.  Scalenohedron.  —  The  scalenohedron,  shown   in  Fig.  259,  is   the 
general  form  for  this  class  corresponding  to  the  symbol  hkll.     It  is  a  solid, 
bounded  by  twelve  faces,  each  a  scalene  triangle.     It  has  roughly  the  shape 
of  a  double  six-sided  pyramid,  but  there  are  two  sets  of  terminal  edges,  one 
more  obtuse  than  the  other,  and  the  lateral  edges  form  a  zigzag  edge  around 
the  form  like  that  of  the  rhombohedron.     It  may  be  considered  as  derived 
from  the  dihexagonal  pyramid  by  taking  the  alternating  pairs  of  faces  of 

*  Quartz  serves  as  a  convenient  illustration  in  this  case,  none  the  less  so  notwithstand- 
ing the  fact  that  it  belongs  to  the  trapezohedral  class  of  this  division. 


HEXAGONAL   SYSTEM 


107 


•an 


that  form.  It  is  to  be  noted  that  the  faces  in  the  lower  half  of  the  form  do 
not  fall  in  vertical  zones  with  those  of  the  upper  half.  Like  the  rhombohe- 
drons, the  scalenohedrons  may  be  either  positive  or  negative. 
The  positive  forms  correspond  in  position  to  the  positive 
rhombohedrons  and  conversely. 

The  positive  scalenohedron  (2131),  Fig.  259,  has  the  fol- 
lowing indices  for  the  several  faces: 

Above     2131,     2311,     3211,     1231,     1321,     3l21 
Below     1231,     1321,     3121,     2131,     2311,     3211. 
For  the  complementary  negative  scalenohedron  (1231)  the 
indices  of  the  faces  are: 

Above     1231,     1321,     3121,     2131,     2311,     32ll. 
Below     2311,     3211,     1231,     1321,     3l2l,     2131. 

148.     Relation    of    Scalenohedrons    to    Rhombohedrons.  —  It    was 
noted    above    that    the    scalenohedron    in     general    has    a    series    of    Q    ,     X     , 
zigzag   lateral  edges   like  the  rhombohedron.     It    is   obvious,  further,     bcaler 
that    for    every    rhombohedron    there    will    be    a    series   or   zone   of    scalenohedrons 
having  the  same  lateral  edges.     This  is  shown   in   Fig.  262,  where   the   scalenohedron 

260  261  262  263 


264 


Figs.  260-263,  Calcite 
265  266 


267 


Figs.  264,  265,  Corundum  Figs.  266,  267,  Spangolite* 

w(2l3l)  bevels  the  lateral  edges  of  the  fundamental  rhombohedron  r(10Tl);  the  same 
would  be  true  of  the  scalenohedron  (3251),  etc.  Further,  in  Fig.  263,  the  negative  scaleno- 
hedron 3(1341)  bevels  the  lateral  edges  of  the  negative  rhombohedron  /(0221).  The  rela- 
tion of  the  indices  which  must  exist  in  these  cases  may  be  shown  to  be,  for  example,  for  the 
rhombohedron  r(lOTl),  h  -  k  +  l\  again  for  /(0221),  h  +  21  =  k,  etc.  See  also  the  pro- 
jections, Figs.  269,  270.  Further,  the  position  of  the  scalenohedron  may  be  defined  with 
reference  to  its  parent  rhombohedron.  For  example  in  Fig.  262  the  scalenohedron  y  (2 131) 
has  three  times  the  vertical  axis  of  the  unit  rhombohedron  r(1011).  Again  in  Fig.  263 

re  (1341)  has  twice  the  vertical  axis  of /(0221). 

*  Spangolite  belongs  properly  to  the  next  (hemimorphic)  group,  but  this  fact  does  not 
destroy  the  value  of  the  illustration. 


108 


CR  YSTALLO  GR  APH  Y 


149.    Other  Forms.  —  The  remaining  forms  of  the  normal  class  of  the 

rhombohedral  division  are  geometrically  like 
those  of  the  corresponding  class  of  the  hexa- 
gonal division  —  viz._,  the  base  c(0001);  the 
prisms  ra(lOlO),  a(1120),  (teO);  also  the  second 
order  pyramids,  as  (1121).  Some  of  these 
forms  are  shown  in  the  accompanying  figures. 
For  further  illustrations  reference  may  be  made 
to  typical  rhombohedral  species,  as  calcite,  hema- 
tite, etc. 

With  respect  to  the  second  order  pyramid,  it 
is  interesting  to  note  that  if  it  occurs  alone 
(as  in  Fig.  264,  n  =  2243)  it  is  impossible  to 
say,  on  geometrical  grounds,  whether  it  has  the 
trigonal  symmetry  of  the  rhombohedral  type 
or  the  hexagonal  symmetry  of  the  hexagonal  type.  In  the  latter  case, 


2110 


Calcite 


ml 


1120 


1010 
m 

Calcite 


the  form  might  be  made  a  first  order  pyramid  by  exchanging  the  axial  and 
diagonal  planes  of  symmetry.     The  true  symmetry,  however,  is  often  indi- 


HEXAGONAL   SYSTEM 


109 


cated,  as  with  corundum,  by  the  occurrence  on_  other  crystals_^)f  rhombo- 
hedral faces,  as  r(1011)  in  Fig.  265  (here  z  =  2241,  co  =  14-14-28-3).  Even 
if  rhombohedral  faces  are  absent  (Fig.  266),  the  etching-figures  (Fig.  267) 
will  often  serve  to_  reveal  the  true  trigonal  molecular  symmetry;  here 
o  =  (1124),  p  =  (1122). 

150.  A  basal  projection  of  a  somewhat  complex  crystal  of  calcite  is  given 
in  Fig.  268,  and  stereographic  and  gnomonic  projections  of  the  same  forms 
in  Figs.  269  and  270;  both  show  well  the  symmetry  in  the  distribution 

270 


of  the  faces.  Here  the  forms  are:  prisms,  a(l_120),  ra(10lO);  rhombohedrons, 
positive,    r(lOll),   negative,     e(0112),   /(0221);     scalenohedrons.    positive, 


3.   RHOMBOHEDRAL-HEMIMORPHIC 
CLASS  (20).    TOURMALINE  TYPE 

(Ditrigonal   Pyramidal  or  Trigonal 

Hemihedral  Hemimorphic  Class) 
151.  Symmetry.  —  A  number  of  prominent 
rhombohedral  species,  as  tourmaline,  pyrar- 
gyrite,  proustite,  belong  to  a  hemimorphic  class 
under  this  division.  For  them  the  symmetry 
in  the  grouping  of  the  faces  differs  at  the  two 
extremities  of  the  vertical  axis.  The  forms  have 
the  same  three  diagonal  planes  of  symmetry 
meeting  at  angles  of  60°  in  the  vertical  axis, 


Symmetry  of 

Rhombohedral-Hemimorphic 
Class 


110 


CRYSTALLOGRAP 


which  is  an  axis  of  trigonal  symmetry.  There  are,  however,  no  hori- 
zontal axes  of  symmetry,  as  in  the  rhombohedral  class,  and  there  is  no 
center  of  symmetry.  Cf.  Fig.  271. 

152.  Typical  Forms.  —  In  this  class  the  basal  planes  (0001)  and  (0001) 
are  distinct  Jorms.  The  other  characteristic  forms  are  the  two  trigonal 
prisms  ra(1010)  and  ra/0110)  of  the  first  order  series;  also  the  four  trigonal 
first  order  pyramids,  corresponding  respectively  to  the  three  upper  and 
three  lower  faces  of  a  positive  rhombohedron,  and  the  three  upper  and 
three  lower  faces  of  the  negative  rhombohedron;  also  the  hemimorphic 
second  order  hexagonal  pyramid;  finally,  the  four  ditrigonal  pyramids, 
corresponding  to  the  .  upper  and  lower  faces  respectively  of  the  positive 

and    negative   scalenohedrons. Figs.  272-275  illustrate  these  forms.     Fig. 

274  is  a  basal  section  with  r/0111^  and  e/1012)  below. 


272 


274 


275 


276 


Figs.  272-275,  Tourmaline 

4.   TRI-RHOMBOHEDRAL  CLASS  (21).     PHENACITE  TYPE 
(Rhombohedral  or  Rhombohedral  Tetartohedral  Class) 

153.    Symmetry.  —  This    class,   illustrated   by    the    species    dioptase, 
phenacite,   willemite,  dolomite,  ilmenite,  etc.,   is  an  important  one.     It  is 

characterized  by  the  absence  of  all  planes  of 
symmetry,  but  the  vertical  axis  is  still  an  axis 
of  trigonal  symmetry,  and  there  is  a  center  of 
symmetry.  Cf.  Fig.  276. 

154.  Typical  Forms.  —  The  distinctive  forms 
of  the  class  are  the  rhombohedron  of  the  second 
order  and  the  hexagonal  prism  and  rhombo- 
hedron, each  of  the  third  order.  The  class  is 
thus  characterized  by  three  rhombohedrons  of 
distinct  types  (each  +  and  -  ),  and  hence  the 
name  given  to  it. 

^  The  second  order  rhombohedron  may  be  de- 
rived by  taking  one  half  the  faces  of  the  nor- 
mal hexagonal  pyramid  of  the  second  order. 
There  will  be  two  complementary  forms  known 
as  positive  and  negative.  For  example,  in  a  given  case  the  indices  of  the 
faces  for  the  positive  and  negative  forms  are: 

Positive      (above)     1122,     2112,     1212;     (below)     12l2,     Il22,     2ll2 
Negative     (above)     1212,     1122,     2112;     (below)     2112,     1212,     1122! 


;.._..,.   v_... 


Symmetry  of 
Tri-Rhombohedral  Class 


HEXAGONAL   SYSTEM 


111 


The  rhombohedron  of  the  third  order  has  the  general  symbol  (hkll),  and 
may  be  derived  from  the  normal  dihexagonal  pyramid,  Fig.  226,  by  taking 
one  quarter  of  the  faces  of  the  latter. 

There  are  therefore  four  complementary  third  order  rhombohedrons,  dis- 
tinguished respectively  as  positive  right-handed  (2131),  positive  left-handed 
(3121),  negative  right-handed  (1321),  and  negative  left-handed  (1231).  The 
indices  of  the  six  like  faces  of  the  positive  right-handed  form  (2131)  are: 

Above    2131,     3211,     1321;     below    1321,     2l3l,     3211. 

The  hexagonal  prism  of  the  third  order  may  be  derived  from  the  normal 
dihexagonal  prism,  Fig.  219,  by  taking  one  half  the  faces  of  the  latter.  There 
are  two  complementary  forms  known  as  right-  and  left-handed.  The  faces 
of  these  forms  in  a  given  case  (2130)  have  the  indices: 

Right        2130,         1320,        3210,        2130,         1320,        32lO 
Left  1230         2310         3120          1230         2310,        3l20. 

155.  The  remaining  forms  are  geometrically  like  those  of  the  rhombo- 
hedral  class,  viz. :    Base  c(0001) ;  first  order  prism  m(1010) ;_  second    order 
prism  a(1120);     rhombohedrons    of    the  first  order,   as   (1011)  and  (0111), 
etc. 

156.  The  forms  of  this  group  are  illustrated  by  Figs.  277-279.     Fig.  277 
is  of  dioptase  and  shows  the  hexagonal  prism_of  the  second  order  a(1120) 
with  a  negative  first  order  rhombohedron,  s(0221)  and  the  third  order  rhom- 
bohedron #(1341).     Figs.  278  and  279  show  the  horizontal  and  clinographic 

279 


Dioptase 


Phernacite 


projections  of  a  crystal  of  phenacite  with_the  following  forms:  first  order 
prism,  ra(1010);  _second  order  prism,  a(1120);  third  _order  rhombohedrons, 
x(1232)  and  s(2131);  first  order  rhombohedrons,  r(1011)  and  d(0112). 

In  order  to  make  clearer  the  relation  of  the  faces  of  the  different  types  of 
forms  under  this  class,  Fig.  280  is  added.  Here  the  zones  of  the  positive  and 
negative  rhombohedrons  of  the  first  order  are  indicated  (+R  and  —  R) 
also  the  general  positions  of  the  four  types  of  the  third  order  rhombohedrons 

(_l_p     f      I   I     l\ 

The  following  scheme  may  also  be  helpful  in  connection  with  Fig.  280.     It 


112 


CRYSTALLOGRAPHY 

loio 


280 


1100 


10J50 


shows  the  distribution  of  the  faces  of  the  four  rhombohedrons  of  the  third  ojder 
(+r,  +/,  — r,  —I)  relatively  to  the  faces  of  the  unit  hexagonal  prism  (1010). 

PHENACITE  TYPE 


+1   +r 
3121  2131 

-I   -r 
1231  1321 

+1    +T 

2311  3211 

-I   -r 
3121  2131 

+1   +r 
1231  1321 

-/   -r 
2311  3211 

1010 

OlTO 

IlOO 

1010 

olio 

1TOO 

-I   -r 
3121  2131 

+Z   +r 
1231  1321 

-I   -r 
2311  3211 

+1   +r 
3121  2131 

-I   -r 
1231  1321 

+Z   +r 
2311  3211 

5.   TRAPEZOHEDRAL   CLASS    (22).     QUARTZ   TYPE 
(Trigonal  Trapezohedral  or  Trapezohedral  Tetartohedral  Class) 
157.    Symmetry.  —  This  class  includes,   among  minerals,   the  species 
quartz  and  cinnabar.     The  forms  have  no  plane  of  symmetry  and  no  center 
of  symmetry;    the  vertical  axis  is,  however,  an  axis  of  trigonal  symmetry, 
and  there  are  also  three  horizontal  axes  of  binary  symmetry,  coinciding  in 
direction  with  the  crystallographic  axes;   cf.  Fig.  281 

281  282  283 


o 

\  r 

* 


Symmetry  of  Trapezohedral  Class 


Trigonal  Trapezohedrons 


HEXAGONAL   SYSTEM 


113 


158.  Typical   Forms.  —  The   characteristic   form  of  the   cJass  is  the 
trigonal  trapezohedron  shown  in  Fig.  282.     This  is  the  general  form  corre- 
sponding to  the  symbol  (hkil),  the  faces  being  distributed  as  indicated  in  the 
accompanying  stereographic  projection  (Fig.  281).     The  faces  of  this  form 
correspond  to  one  quarter  of  the  faces  of  the  normal  dihexagonal  pyramid, 
Fig.  226.     There  are  therefore  four  such  trapezohedrons,  two  positive,  called 
respectively  right-handed  (Fig.  282)  and  left-handed  (Fig.  283),  and  two  simi- 
lar negative  forms,  also  right-  and  left-handed  (see  the  scheme  given  in 
Art.  160).     It  is  obvious  that  the  two  forms  of  Figs.  282,  283  are  enantio- 
morphous,  and  circular  polarization  is  a  striking  character  of  the  species 
belonging  to  the  class  as  elsewhere  discussed. 

The  indices  of  the  six  faces  belonging  to  each  of  these  will  be  evident  on 
consulting  Figs.  281  and  229  and  230.  The  complementary  positive  form 
(r  and  I)  of  a  given  symbol  include  the  twelve  faces  of  a  positive  scalenohe- 
dron,  while  the  faces  of  all  four  as  already  stated  include  the  twenty-four 
faces  of  the  dihexagonal  pyramid. 

Corresponding  to  these  trapezohedrons  there  are_two  ditrigonal  prisms, 
respectively  right-  and  left-handed,  as  (2130)  and  (3120). 

The  remaining  characteristic  forms  are  the  right-  and  left-handed  trigonal 
prism  a(H20)  and_a(2110);  also  the  right-  and  left-handed  trigonal  pyramid, 
as  (1122)  and  (2112).  They  may  be  derived  by  taking  respectively  one  half 
the  faces  of  the  hexagonal  prism  of  the  second  order  (1120)  or  of  the  corre- 
sponding pyramid  (1122);  these  are  shown  in  Figs.  221  and  225. 

159.  Other  Forms.  —  The  other  forms  of  the  class  are  geometrically 
like  those  of  the  normal  class.     They  are  the  base  c(0001),  the  hexagonal 
first  order  prism  ra(1010),  and  the  positive  and  negative  rhombohedrons  as 
(1011)  and  (0111).     These  cannot  be  distinguished  geometrically  from  the 
normal  forms. 

160.  Illustrations.  —  The  forms  of  this  class  are  best  shown  in  the 
species  quartz.     As  already  remarked  (p.  106),  simple  crystals  often  appear 
to  be  of  normal  hexagonal  symmetry,  the  rhombohedrons  r(1011)  and  2(0111) 
being  equally  developed  (Figs.  284,  285).     In  many  cases,  however,  a  differ- 
ence in  molecular  character  between  them  can  be  observed,  and  more  com- 


284 


285 


288 


Figs.  284-288,  Quartz 


monly  one  rhombohedron,  r(1011),  predominates  in  size;  the  distinction  can 
always  be  made  out  by  etching.  Some  crystals,  like  Fig.  286,  show  as 
modifying  faces  the  right  trigonal  pyramid  *(ll2l),  with  a  right  positive 
trapezohedron,  as  z(5161).  Such  crystals  are  called  right-handed  and  rotate 


114 


CRYSTALLOGRAPHY 


the  plane  of  polarization  of  light  transmitted  in  the  direction  of  the  vertical 
axis  to  the  right.  A  crystal,  like  Fig.  287,  with  _the  left  trigonal  pyramid 
s(2111)  and  one  or  more  left  trapezohedrons,  as  x(6151),  is  called  left-handed, 
and  as  regards  light  has  the  opposite  character  to  the  crystal  of  Fig.  286. 
Fig.  288  shows  a  more  complex  right-handed  crystal  with  several  positive 
and  negative  rhombohedrons,  several  positive  right  trapezohedrons  and  the 
negative  left  trapezohedron,  N. 

The  following  scheme  shows  the  distribution  of  the  faces  of  the  four 
trapezohedrons  (+r,  -\-l,  —r,  —I)  relatively  to  the  faces  of  the  unit  hex- 
agonal prism  (lOlO);  it  is  to  be  compared  with  the  corresponding  scheme, 
given  in  Art.  156,  of  crystals  of  the  phenacite  type.  _In  the  case  of  the  nega- 
tive forms  some  authors  prefer  to  make  the  faces  2131,  1231,  etc.,  right,  and 
3121,  1321,  etc.,  left. 

QUARTZ  TYPE 


+1   +r 
3121  2131 

-I   -r 
1231  1321 

+1  •  +r 
2311  3211 

-I   -r 
3121  2131 

+1   +r 
1231  1321 

-I   -r 
2311  3211 

1010 

0110 

TlOO 

1010 

olio 

1100 

-r   -I 
3121  2131 

+r   +1 
1231  1321 

-r   -I 
2311  3211 

+r   +1 
3121  2131 

-r   -I 
1231  1321 

-fr   +1 
2311  32TT 

161.  Other  Classes.  —  The  next  class  (23)  is  known  as  the  Trigonal 
Bipyramidal  or  Trigonal  Tetartohedral  class.  It  has  one  plane  of  sym- 
metry—  that  of  the  horizontal  axes,  and  one  axis  of  trigonal  symmetry  — 
the  vertical  axis.  There  is  no  center  of  symmetry.  Its  characteristic  forms 
are  the  three  types  of  trigonal  prisms  and  the  three  corresponding  types  of 
trigonal  pyramids.  Cf.  Fig.  289.  This  class  has  no  known  representation 
among  crystals. 

The  last  class  (24)  of  this  division  is  known  as  the  Trigonal  Pyramidal 
or  Trigonal  Tetartohedral  Hemimorphic  class.     It  has  no  plane  of  symmetry 


289 


290 


Symmetry  of  Trigonal  Bipyramidal  Class       Symmetry  of  the  Trigonal  Pyramidal  Class 

and  no  center  of  symmetry,  but  the  vertical  axis  is  an  axis  of  trigonal  sym- 
metry. The  forms  are  all  hemimorphic,  the  prisms  trigonal  prisms,  and  the 
pyramids  hemimorphic  trigonal  pyramids.  Cf.  Fig.  290.  The  crystals  of 
sodium  periodate  belong  to  this  class. 


HEXAGONAL   SYSTEM  115 

MATHEMATICAL  RELATIONS  OF  THE  HEXAGONAL  SYSTEM. 

162.  Choice  of  Axis.  —  The  position  of  the  vertical  crystallographic  axis  is  fixed  in  all 
the  classes  of  this  system  since  it  coincides  with  the  axis  of  hexagonal  symmetry  in  the 
hexagonal  division  and  that  of  trigonal  symmetry  in  the  rhombohedral  division.     The  three 
horizontal  axes  are  also  fixed  in  direction  except  in  the  normal  class  and  the  subordinate 
hemimorphic  class  of  the  hexagonal  division;    in  these  there  is  a  choice  of  two  positions 
according  to  which  of  the  two  sets  of  vertical  planes  of  symmetry  is  taken  as  the  axial  set. 

163.  Axial  and  Angular  Elements.  —  The  axial  element  is  the  length  of  the  vertical 
axis,  c,  in  terms  of  a  horizontal  axis,  a;   in  other  words,  the  axial  ratio  of  a  :  c.     A  single 
measured  angle  (in  any  zone  but  the  prismatic)  may  be  taken  as  the  fundamental  angle 
from  which  the  axial  ratio  can  be  obtained. 

The  angular  element  is  usually  taken  as  the  angle  between  tfhe  base  c(0001)  and  the 
unit  first  order  pyramid  (1011),  that  is,  0001  A  1011. 

The  relation  between  this  angle  and  the  axis  c  is  given  by  the  formula 

tan  (0001  A  lOll)  X  -  Vs  =  c. 

The  vertical  axis  is  also  easily  obtained  from  the  unit  second  order  pyramid,  since 

tan  (0001  A  1122)  =  c. 
These  relations  become  general  by  writing  them  as  follows: 

tan  (0001  A  hOhl)  X-^3  =  -Xc; 
2i  I 

tan  (0001  A  h'h'2h'l)  =  —  X  c. 

In  general  it  is  easy  to  obtain  any  required  angle  between  the  poles  of  two  faces  on  the 
spherical  projection  either  by  the  use  of  the  tangent  (or  cotangent)  relation,  or  by  the 
solution  of  spherical  triangles,  or  by  the  application  of  both  methods.  In  practice  most  of 
the  triangles  used  in  calculation  are  right-angled. 

164.  Tangent  and  Cotangent  Relations.  —  The  tangent  relation  holds  good  in  any  zone 
from  c(0001)  to  a  face  in  the  prismatic  zone.     For  example: 

tan  (0001  A  hOhl)  =h.     tan  (0001  A  h'h'2Ji'l)  _  2h 
tan  (0001  A  lOll)      I  '       tan  (0001  A  1122)    "     l" 

In  the  prismatic  zone,  the  cotangent  formula  takes  a  simplified  form;  for  example,  lor  a 
dihexagonal  prism,  hklQ,  as  (2130)  : 

cot  (1010  A  M*0)  =  ^ 
cot  (1120  A  feHO)  =  ML 

— 


The  sum  of  the  angles  (lOlO  A  hkiO)  and  (1120  A  MnO)  is  equal  to  30°. 
Further,  the  last  equations  can  be  written  in  a  more  general  form,  applying  to  any 
pyramid  (hkil)  in  a  zone,  first  between  1010  and  a  face  in  the  zone  0001  to  0110,  where  the 
angle  between  1010  and  this  face  is  known;  or_again,  for  the  same  pyramid,  in  a  zone 
between  1120  and  a  face  in  the  zone  0001  to  1010,  the  angle  between  1120  and  this  face 
being  given.  For  example  (cf.  _Fig.  229,  p.  99),  if  the  first-mentioned  zone  is 
lOlO'/iEZ-OlIl  and  the  second  is  llSfrAHMOll,  then 

cot  (10TO  A  hM)  =  cot  (lOlO  A  Olll)  .  —  ^  —  » 
and  • 

cot  (1120  A  Mil)  =  cot  (1120  A  lOll)  .  j-£p 
Also  similarly  for  other  zones, 

cot  (1010  A  MB)  =  cot  (1010  A  0221)  .  —  f->  etc. 


116 


CRYSTALLOGRAPHY 
cot  (1120  A  hkil)  =  cot  (1120  A  2021)  .  £~7£»  etc. 


165.    Other  Angular  Relations.  —  The  following  simple  relations  are  of  frequent  use: 

(1)  For  a  hexagonal  pyramid  of  the  first  order, 

tan  \  (lOTl  A  OlTl)  =  sin  £  Vj,    where  tan  £  =  c, 
and  in  general 

tan  \  (hOhl  A  Qhhl)  =  sin  £,V|,    where  tan  £,=  ^-c. 

(2)  For  a  hexagonal  pyramid  of  the  second  order,  as  (1122), 

2  sin  \  (1122  A  I2l2)  =  sin  £,        and        tan  £  =  c. 

(3)  For  a  rhombohedron 

sin  £  (lOTl  A  TlOl)  =  sin  a  Vf,    where  a  =  (0001  A  lOTl); 
in  general 

sin  \  (hOhl  A   hhOl)  =  sin  a,  Vf ,  where  a,  =  (0001  A 


166.  Zonal  Relations.  —  The  zonal  equations,  described  in  Arts  45,  46,  apply  here  as 
in  other  systems,  only  that  it  is  to  be  noted  that  one  of  the  indices  referring  to  the  horizontal 
axes,  preferably  the  third,  i,  is  to  be  dropped  in  the  calculations  and  only  the  other  three 
employed.  Thus  the  indices  (u,  v,  w)  of  the  zone  in  which  the  faces  (hkil),  (pqft)  lie  are 
given  by  the  scheme 


I 


XXX 


where  u  =  kt  —  Iq,         v  =  lp  —  ht,         w  =  hq  —  kp. 

For  example  (Fig.  226)  the  face  n  lies  in  the  zone  mv,  IOTO'2131  and^  also  in  the  zone 
au,  1120  '  2021.  For  the_first  zone  the  values  obtained  are:  u  =  0,  v  =  I,  w  =  1;  for  the 
second  zone,  e  =  !,/=!,  0  =  2.  Combining  these  zone  symbols  according  to  the  usual 
scheme 


1 


0 


\ 


The  face  n  has,  therefore,  the  indices  314i,  since  further  i  =  —  (h  +  k). 

167.  Formulas.  —  The  following  formulas  in  which  c  equals  the  unit  length  of  the 
vertical  axis  are  sometimes  useful: 

(1)  The_distances  (see  Fig.  229)  of  the  pole  of  any  face  (hkil)  from  the  poles  of  the  faces 
(10TO),  (0110),  (1100),  and  (0001)  are  given  by  the  following  equations, 


cos  (hkil)  (1010)  = 
cos  (M#)  (OlTO)  = 
cos  (hkil)  (TlOO)  = 
cos  (hkil)  (0001) 


c  (k  +  2h) 


+  4c2  (h2  +  k2  +  hk) 
c  (2k  +  h)  _ 

+  4c2  (/i9-  +  k2  +  hk) 
c  (h  -  k) 


4c2  (As 


hk) 


v  3?2  +  4c2  (A2  +  fc2  4-  A/c) 

(2)  The  distance  (PQ)  between  the  poles  of  anv  two  faces  P(hkil)  and  Q(pqrt)  is  given 
by  the  equation 


HEXAGONAL   SYSTEM 


117 


W,  +  2c2  (hq  +  pk  +  2hp  +  2kq) 


cos  PQ  =  -7= 

v  [3J2  +  4c2  (h2  +  k2 

(3)  For  special  cases  the  above  formula  becomes  simplified;  it  serves  to  give  the  value 
of  the  normal  angles  for  the  several  forms  in  the  system.     They  are  as  follows: 
(a)  Pyramid  of  First  Order  (hQhl),  Fig.  224: 


cos  X  (terminal) 


cos  Z  (basal)  = 


3/2 


(6)  Pyramid  of  Second  Order  (h'h'2fcl),  Fig.  225: 

cos  Y  (terminal)  = 
(c)   Dihexagonal  Pyramid  (hkil) : 


P  +  4W'    cosZ(basal)-P  +  4^ 


Q/2     I     O~2  /J,2  _|_  ]fZ  . 

cos  X  (see  Fig.  226)  -  ^2+  J(^  fc2  ;  —  - 

„,       3l2  +  2c2  (2h2  +  2hk  -  k2) 
cos  Y  (see  Fig.  226)  = .    3.  +  4^  fr,  +  &.  +  M.) 

=  3/2  +  4c2  (h2  +  k2  +  hk) ' 


cos  Z  (basal) 

(d)  Dihexagonal  Prism  (hkiQ),  Fig.  222: 

cos  X  (axial)  =  ^^^  . 

(e)  Rhombohedron  (1011): 

cos  X  (terminal)         = 

(f)  Scalenohedron  (hkil): 

cos  X  (see  Fig.  259)  = 


cos  Y  (diagonal) 


2ft2  +  2hk  - 
2  (h*  +  A;2  + 


2c  (2A:2  +  2hk  - 


Cft. 
cos  Y  (see  Fig.  259) 


3/2 
3Z2  +  2c2  (2h* 


==    &  +  4**  (h*  +  k*  +  hk) 
2c2  (W  + 


168.   Angles.  —  The  angles  for  some  commonly  occurring  dihexagonal  prisms  with  the 
n    second  order    risms  are    iven  in  the  following  table: 


first  and  second  order  prisms  are  given 


169. 


5160 
4150 
3140 
5270 
2130 
3250 
5490 

The  Miller  Axes  and  Indices. 
291 


w(1010) 
8°  57' 
10   53^ 
54 
6 


owng 

a(1120) 


21° 
19  61 
16  6 
13  54 
10  53^ 


13 

16 

19 

23   24i 

26    19{ 

The  forms  of  the  hexagonal  system  were  referred 
by  Miller  to  a  set  of  three  equal 
oblique  axes  which  were  taken 
parallel  to  the  edges  of  the  unit 
positive  rhombohedron  of  the 
species.  Fig.  291  represents 
such  a  rhombohedron  with  the 
position  of  the  Miller  axes  shown. 
This  choice  of  axes  for  hexa- 
gonal forms  has  the  grave  objec- 
tion that  in  several  cases  the 
faces  of  the  same  form  are  rep- 
resented by  two  sets  of  different 
indices;  for  example  the  faces  of 
.the  pyramid  of  the  first  order 
would  have  the  indices,  100, 221,010, 122,  001, 2l2.  This  objection,  however,  disappears  if  the 


118 


CRYSTALLOGRAPHY 


Miller  axes  and  indices  are  used  only  for  forms  in  the  Rhombohedral  Division,  that  is  for  forms 
belonging  to  classes  which  are  characterized  by  a  vertical  axis  of  trigonal  symmetry.  It  is 
believed,  however,  that  the  mutual  relations  of  all  the  classes  of  both  divisions  of  the  hex- 
agonal system  among  themselves  (as  also  to  the  classes  of  the  tetragonal  system),  both 
morphological  and  physical  are  best  brought  out  by  keeping  throughout  the  same  axes, 
namely  those  of  Fig.  218,  Art.  121.  The  Miller  method  has,  however,  been  adopted  by  a 
number  of  authors  and  consequently  it  is  necessary  to  give  the  following  brief  description. 


(1120) 


110 


0210) 
Oil 


(1010) 
Miller  and  Miller-Bravais  Indices  Compared 

Fig.  292  shows  in  stereographic  projection  the  common  hexagonal-rhombohedral  forms 
.vith  their  Miller  indices  and  in  parentheses  the  corresponding  indices  when  the  faces  are 
referred  to  the  four  axial  system.  It  will  be  noted  that  the  faces  of  the  unit  positive  rhom- 
bohedron  have  the  indices  100,  010,  and  001  and  those  of  the  negative  unit  rhombohedron 
have  221,  122,  212.  These  two  forms  together  give  the  faces  of  the  hexagonal  pyramid_of 
the  first  order  (see  above).  The  hexagonal  prism  of  the  first  order  is  represented  by  211, 
etc.,  while  the  second  order  prism  has  101,  etc.  The  dihexagonal  pyramid  has  also  two 
sets  of  indices  (hid)  and  (efg) ;  of  these  the  symbol  (hkl)  belongs  to  the  positive  scaleno- 
hedron  and  (efg)  to  the  negative  form.  In  this  as  in  other  cases  it  is  true  that 
e  =  2h  +  2k  -  I,  f  =  2h  -  k  +  21,  g  =  -  h  +  2k  +  21.  For  example,  the  faces  of  the 
form  201,  etc.,  belong  in  the  Rhombohedral  Division  of  this  system  to  the_scalenohedron 
(2131)  while  the  complementary  negative  form  would  have  the  indices  524,  etc. 

The  relation  between  the  Miller-Bravais  and  the  Miller  indices  for  any  form  can  be 


HEXAGONAL   SYSTEM 


119 


obtained  from  the  following  expression,  where  (hktt)  represents  the  first  and  (pqr)  the 
second. 

h              k  i             _ 

p  -  q      p  -r  r-p~p 


The  relation  between  the  Miller  indices  for  hexagonal  forms  and  those  of  isometric 
forms  should  be  noted.  If  we  conceive  of  the  isometric  cube  as  a  rhombohedron  with 
interfacial  angles  of  90°  and  change  the  orientation  so  that  the  normal  to  the  octahedral 
face  (111)  becomes  vertical  we  get  a  close  correspondence  between  the  two.  This  will  be 
seen  by  a  comparison  of  the  two  stereographic  projections,  Figs.  292  and  125. 

170.  To  determine,  by  plotting,  the  length  of  the  vertical  axis  of  a  hexagonal  mineral, 
given  the  position  on  the  stereographic  projection  of  the  pole  of  a  face  with  known  indices. 
To  illustrate  this  problem  it  is  assumed  that  the  mineral  in  question  is  beryl  and  that  the 
position  of  the  pole  p(10ll)  is  known,  Fig.  293.     Let  the  three  lines  ai,  a2,  a3  represent  the 
horizontal  axes  with  their  unit  lengths  equalling  the  radius  of  the  circle.     Draw  a  line 
from  the  center  of  the  projec- 
tion through  the  pole  p.     Draw 

another  line  (which  will  be  at 
right  angles  to  the  first)  joining 
the  ends  of  ai  and  —  «3.  This 
will  be  parallel  to  a2  and  will 
represent  the  intercept  of 
p(1011)  upon  the  plane  of  the 
horizontal  axes.  In  order  to 
plot  the  intercept  of  p  upon  the 
vertical  axis  construct  in  the 
upper  left-hand  quadrant  of 
the  figure  a  right-angle  triangle 
the  base  of  which  shall  be  equal 
to  O-P,  the  vertical  side  of 
which  shall  represent  the  c  axis 
and  the  hypothenuse  shall  show 
the  slope^  of  the  face  and  give 
its  intercept  upon  the  c  axis. 
The  direction  of  the  hypothe- 
nuse is  determined  by  locating 
the  normal  to  p  from  the  angle 
measured  from  the  center  of 
the  projection  to  its  pole. 
Since  the  face  has  been  as- 
sumed to  have  an  unit  intercept 
on  the  vertical  axis  the  dis- 
tance O-M.  which  equals  0-49  Determination  of  unit  length  of  c  axis,  having  given  the 
(in  terms  of  the  length  of  the  position  of  p(10Tl) 

horizontal  axes,  which  equals 
1*00),  gives  the  unit  length  of  the  c  axis  for  beryl. 

171.  To  determine  the  indices  of  a  face  of  a  hexagonal  form  of  a  known  mineral,  given 
the  position  of  its  pole  on  the  stereographic  projection.     In  Fig.  294  it  is  assumed  that  the 
position  of  the  pole  v  of  a  crystal  face  on  calcite  is  known.   To  determine  its  indices,  first  draw 
a  radial  line  through  the  pole  and  then  erect  a  perpendicular  to  it,  starting  the  line  from  the 
end  of  one  of  the  horizontal  axes.     This  line  will  represent  the  direction  of  the  intersection  of 
the  crystal  face  with  the  horizontal  plane  and  its  relative  intercepts  on  the  horizontal  axes 
will  give  the  first  three  numbers  of  the  parameters  of  the  face,  namely  lai,  2a2,  3-«3-     To 
determine  the  relative  intercept  on  the  c  axis  transfer  the  distance  O-P  to  the  upper  left- 
hand  quadrant  of  the  figure,  then  having  measured  the  angular  distance  between  the  center 
of  the  projection  and  v  by  means  of  the  stereographic  protractor  draw  the  pole  to^tne  face 
in  the  proper  position.     Draw  then  a  line  at  right  angles  to  this  pole  starting  from  the 
point  P'.     This  line  gives  the  intercept  of  the  face  upon  the  line  representing  the  vertical 
axis.     In  this  case  the  intercept  has  a  value  of  17  when  the  length  of  the  horizontal  axes 
is  taken  as  equal  to  I'O.     This  distance  17  is  seen  to  be  twice  the  unit  length  of  the 
c  axis  for  calcite,  0'85.     Therefore  the  parameters  of  the  face  in  question  upon  the  four 
axes  are  lai,  2a2,  |— a3,  2c,  which  give  2131  for  the  indices  of  the  face  v. 


120 


CRYSTALLOGRAPHY 
2  e  =1,70  294 


Determination  of  the  indices  for  v  on  calcite 

172.  To  determine,  by  plotting,  the  indices  of  hexagonal  forms,  given  the  position  of 
295  then:  poles   on  the  gno- 

monic  projection.  To 
illustrate  this  problem 
one  sectant  of  the  gno- 
monic  projection  of  the 
important  forms  of  beryl, 
Fig.  228,  is  reproduced  in 
Fig.  295.  The  directions 
of  the  three  horizontal 
axes,  ai,  02  and  «3  are  in- 
dicated by  the  heavy  lines. 
From  the  poles  of  the  faces 
perpendiculars  are  drawn 
to  these  three  axes.  It 
will  be  noted  that  the  va- 
rious intercepts  made 
upon  the  axes  by  these 
lines  have  simple  rational 
relations  to  each  other. 
One  of  these  intercepts  is 
chosen  as  having  the 
length  of  1  (this  length 
will  be  equivalent  to  the 
unit  length  of  the  c  crys- 
tallographic  axis,  see 
below)  and  the  others  are 
then  given  in  terms  of  it. 


ORTHORHOMBIC    SYSTEM 


121 


The  indices  of  each  face  are  obtained  directly  by  taking  these  intercepts  upon  the  three 
horizontal  axes  in  their  proper  order  and  by  adding  a  1  as  the  fourth  figure  If  necessarv 
clear  of  fractions,  as  in  the  case  of  the  second  order  pyramid,  1122. 

173.  To  determine  the  axial  ratio  of  a  hexagonal  mineral  from  the  gnomonic  projection 
of  its  forms.  The  gnomonic  projection  of  the  beryl  forms,  Fig.  295,  may  be  used  as  an 
illustrative  example.  The  radius  of  the  fundamental  circle,  a,  is  taken  as  equal  to  the 
length  of  the  horizontal  axes  and  is  given  a  value  of  1.  Then  the  length  of  the  funda- 


296 


in  the  same  manner  as  in  the  case  of  the  tetragonal  system,  see  Art.  117,  p. 

IV.   ORTHORHOMBIC   SYSTEM 

(Rhombic  or  Prismatic  System) 

174.    Crystallographic  Axes.  —  The  orthorhombic  system  includes  all  the 
forms   which    are   referred   to   three    axes    at    right 
angles  to  each  other,  all  of  different  lengths. 

Any  one  of  the  three  axes  may  be  taken  as  the 
vertical  axis,  c.  Of  the  two  horizontal  axes  the 
longer  is  always  taken  as  the  b  or  macro-axis  *  and 
when  orientated  is  parallel  to  the  observer.  The 
a  or  brachy-axis  is  the  shorter  of  the  two  horizontal 
axes  and  is  perpendicular  to  the  observer.  The  length 
of  the  b  axis  is  taken  as  unity  and  the  lengths  of 
the  other  axes  are  expressed  in  terms  of  it.  The 
axial  ratio  for  barite,  for  instance,  is  a  :  b  :  c  =  0*815 
:  TOO  :  1*31.  Fig.  296  shows  the  crystallographic 
axes  for  barite. 


1.  NORMAL  CLASS  (25).  BARITE  TYPE 


Orthorhombic  Axes 
(Barite) 


297 


(Orthorhombic  Bipyramidal  or  Holohedral   Class) 

175.  Symmetry.  —  The  forms  of  the  normal  class 
of  the  orthorhombic  system  are  characterized  by  three  axes  of  binary  sym- 
metry, which  directions  are  coincident  with 
the  crystallographic  axes.  There  are  also 
three  unlike  planes  of  symmetry  at  right 
angles  to  each  other  in  which  lie  the  crystal- 
lographic axes. 

The  symmetry  of  the  class  is  exhibited  in 
the  accompanying  stereographic  projection, 
Fig.  297.  This  should  be  compared  with  Fig. 
91  (p.  53)  and  Fig.  167  (p.  77),  representing 
the  symmetry  of  the  normal  classes  of  the 
isometric  and  tetragonal  systems  respec- 
tively. It  will  be  seen  that  while  normal  iso- 
metric crystals  are  developed  alike  in  the 
three  axial  directions,  those  of  the  tetragonal 
type  have  a  like  development  only  in  the 
direction  of  the  two  horizontal  axes,  and 


Symmetry  of  Normal  Class 
Orthorhombic  System 


this  system  (and  also  in  the  triclinic  system) 


are 


*  The  prefixes  brachy-  and  macro-  used  in  this  system  ( 
from  the  Greek  words,  ppaxvs,  short,  and  M«KPOS,  long. 


122 


CRYSTALLOGRAPHY 


those  of  the  orthorhombic  type  are  unlike  in  the  three  even  axial  directions. 
Compare  also  Figs.  92  (p.  54),  171  (p.  78)  and  298  (p.  122). 

176.   Forms.  —  The  various  forms  possible  in  this  class  are  as  follows : 

jr>^  Indices 

1.  Macropinacoid  or  a-pinacoid (100) 

2.  Brachypinacoid  or  6-pinacoid (010) 

3.  Base  or  c-pinacoid (001) 

4.  Prisms (hkO) 

5.  Macrodomes .  (hQl) 


6.   Brachydomes 


(OfcZ) 


7.   Pyramids (hkl) 

In  general,  as  defined  on  p.  31,  a  pinacoid  is  a  form  whose  faces  are  parallel  to  two  of 
the  axes,  that  is,  to  an  axial  plane;  a  prism  is  one  whose  faces  are  parallel  to  the  vertical 
axis,  but  intersect  the  two  horizontal  axes;  a  dome  *  (or  horizontal  prism)  is  one  whose 
faces  are  parallel  to  one  of  the  horizontal  axes,  but  intersect  the  vertical  axis.  A  pyramid 
is  a  form  whose  faces  meet  all  the  three  axes. 

These  terms  are  used  in  the  above  sense  not  only  in  the  orthorhombic  system,  but  also 
in  the  monoclinic  and  triclinic  systems;  in  the  last  each  form  consists  of  two  planes  only. 

177.  Pinacoids.  —  The  macropinacoid  includes  two  faces,  each  of  which 
is  parallel  both  to  the  macro-axis  b  and  to  the  vertical  axis  c;  their  indices 
are  respectively  100  and  100.  This  form  is  uniformly  designated  by  the 
letter  a,  and  is  conveniently  and  briefly  called  the  a-face  or  the  a-pinacoid. 

The  brachypinacoid  includes  two  faces,  each  of  which  is  parallel  both  to 
the  brachy-axis  a  and  to  the  vertical  axis  c;  they  have  the  indices  010  and 
010.  This  form  is  designated  by  the  letter  6;  it  is  called  the  b-face  or  the 
b-pinacoid. 

The  base  or  basal  pinacoid  includes  the  two  faces  parallel  to  the  plane  of 
the  horizontal  axes,  and  having  the  indices  001  and  001.  This  form  is  desig- 
nated by  the  letter  c;  it  is  called  the  c-face  or  the  c-pinacoid. 

Each  one  of  these  three  pinacoids  is  an  open-form,!  but  together  they 
make  the  so-called  diametral  prism,  shown  in  Fig.  298,  a  solid  which  is  the 
analogue  of  the  cube  of  the  isometric  system.  Geometrically  it  cannot  be 
distinguished  from  the  cube,  but  it  differs  in  having  the  symmetry  unlike  in 


299 


300 


! 

no" 

,  \      iib~~ 

I 

j 
H—  *— 

Prism  and  Basal 
Pinacoid 

120-  - 


110 


120 

n  \ 


Macro-,  Brachy-  and 
Basal  Pinacoids 

the  three  axial  directions;  this  may  be  shown  by  the  unlike  physical  char- 
acter of  the  faces,  a,  6,  c,  for  example  as  to  luster,  striations,  etc.;  or,  again, 
by  the  cleavage.  Further,  it  is  proved  at  once  by  optical  properties.  This 

*  From  the  Latin  domus,  because  resembling  the  roof  of  a  house;   cf.  Figs.  301,  302. 
J  feee  p.  30. 


ORTHORHOMBIC   SYSTEM 


123 


diametral  prism,  as  just  stated,  has  three  pairs  of  unlike  faces.  It  has  three 
kinds  of  edges,  four  in  each  set,  parallel  respectively  to  the  axes  a,  6,  and  c; 
it  has,  further,  eight  similar  solid  angles.  In  Fig.  298  the  dimensions  are 
arbitrarily  made  to  correspond  to  the  relative  lengths  ojkthe  chosen  axes, 
but  the  student  will  understand  that  a  crystal  of  this  shape  gives  no  informa- 
tion as  to  these  values. 

178.  Prisms.  —  The  prisms  proper  include  those  forms  whose  faces  are 
parallel  to  the  vertical  axis,  while  they  intersect  both  the  horizontal  axes; 
their  general  symbol  is,  therefore,  (hkQ).  These  all  belong  to  one  type  of 
rhombic  prism,  in  which  the  interfacial  angles  corresponding  to  the  two  un- 
like vertical  edges  have  different  values. 

The  unit  prism,  (110),  is  that  form  whose  faces  intersect  the  horizontal 
axes  in  lengths  having  a  ratio  corresponding  to  the  accepted  axial  ratio  of 
a  :  b  for  the  given  species;  in  other  words,  the  angle  of  this  unit  prism  fixes 
the  unit  lengths  of  the  horizontal  axes .  This  form  is  shown  in  combination 
with  the  basal  pinacoid  in  Fig.  299;  it  is  uniformly  designated  by  the  letter 
m.  The  four  faces  of  the  unit  prism  have  the  indices  110,  IlO,  TlO,  iTO. 

There  is,  of  course,  a  large  number  of  other  possible  prisms  whose  inter- 
cepts upon  the  horizontal  axes  are  not  proportionate  to  their  unit  lengths. 
These  may  be  divided  into  two  classes  as  follows:  macroprisms,  whose  faces 
lie  between  those  of  the  macropinacoid  and  the  unit  prism,  brachyprisms 
with  faces  between  those  of  the  brachypinacoid  and  the  unit  prism.  A 
macroprism  has  the  general  symbol  (hkQ)  in  which  h  >  k  and  is  represented 
by  the  form  Z(210),  Fig.  300.  A  brachyprism  has  the  general  symbol  (hkQ) 
with  h  <  k  and  is  represented  by  n(120),  Fig.  300. 

301  302  303 


101 


Brachydqme 
and  Macropinacoid 


Pyramid 


Macrodome  and 
Brachypinacoid 

179.  Macrodomes,  Brachydomes.  —  The  macrodomes  are  forms  whose 
faces  are  parallel  to  the  macro-axis  b,  while  they  intersect  the  vertical  axis 
c  and  the  horizontal  axis  a;  hence  the  general  symbol  is  (hOl).  The  angle 
of  the  unit  macrodome,  (101),  fixes  the  ratio  of  the  axes  a  :  c.  This  form  is 
shown  in  Fig.  301  combined  (since  it  is  an  open  form)  with  the  brachypinacoid. 

In  the  macrodome  zone  between  the  base  c(001)  and  the  macropinacoid 
a  (100)  there  may  be  a  large  number  of  macrodomes  having  the  symbols, 
taken  in  the  order  named,  (103),  (102),  (203),  (101),  (302),  (201),  (301);  etc. 
Cf.  Figs.  318  and  319  described  later. 

The  brachydomes  are  forms  whose  faces  are  parallel  to  the  brachy-axis,  a, 
while  they  intersect  the  other  axes  c  and  6;  their  general  symbol  is  (0/cZ). 
The  angle  of  the  unit  brachydome,  (Oil),  which  is  shown  with  a(100)  in 
Fig.  302,  determines  the  ratio  of  the  axes  b  :  c. 

The  brachydome  zone  between  c(001)  and  6(010)  includes  the  forms 
(013),  (012),  (023),  (Oil),  (032),  (021),  (031),  etc.  Cf.  Figs.  318  and  319. 


124 


CRYSTALLOGEAPHY 


Both  sets  of  domes  are  often  spoken  of  as  horizontal  prisms.  The  pro- 
priety of  this  expression  is  obvious,  since  they  are  in  fact  prisms  in  geo- 
metrical form;  further,  the  choice  of  position  for  the  axes  which  makes 
them  domes,  instead  of  prisms  in  the  narrower  sense,  is  more  or  less  arbitrary, 
as  already  explained  elsewhere. 

180.  Pyramids.  —  The  pyramids  in  this  system  all  belong  to  one  type, 
the  double  rhombic  pyramid,  bounded  by  eight  faces,  each  a  scalene  triangle. 
This  form  has  three  kinds  of  edges,  x,  y,  z  (Fig.  303),  each  set  with  a  different 
interfacial  angle;  two  of  these  angles  suffice  to  determine  the  axial  ratio. 
The  symbol  for  this,  the  general  form  for  the  system,  is  (hkl). 

The  pyramids  may  be  divided  into  three  groups  corresponding  respec- 
tively to  the  three  prisms  just  described,  namely,  unit  pyramids,  macro- 
pyramids,  and  br  achy  pyramids. 

The  unit  pyramids  are  characterized  by  the  fact  that  their  intercepts  on 
the  horizontal  axes  have  the  same  ratio  as  those  of  the  unit  prism;  that  is, 
the  assumed  axial  ratio  (a  :  b)  for  the  given  species.  For  them,  therefore, 
the  general  symbol  becomes  (hhl). 

There  may  be  different  unit  pyramids  on  crystals  of  the  same  species 
with  different  intercepts  upon  the  vertical  axis,  and  these  form  a  zone  of  faces 
lying  between  the  base  c(001)  and  the  unit  prism  m(110).  This  zone  would 
include  the  forms,  (119),  (117),  (115),  (114),  (113),  (112),  (111).  In  the 
symbol  of  all  of  the  forms  of  this  zone  h  =  k,  and  the  lengths  of  the  vertical 
axes  are  hence,  in  the  example  given,  ^,  \,  £,  J,  f ,  J  of  the  vertical  axis  c  of 
the  unit  pyramid. 

The  macropyramids  and  brachypyramids  are  related  to  each  other  and  to 
the  unit  pyramids,  as  were  the  macroprisms  and  brachyprisms  to  themselves 
and  to  the  unit  prism.  Further,  each  vertical  zone  of  macropyramids  (or 
brachypyramids),  having  a  common  ratio  for  the  horizontal  axes  (or  of  h  :  k 
in  the  symbol),  belongs  to  a  particular  macroprism  (or  brachy prism)  char- 
acterized by  the  same  ratio.  Thus  the  macropyramids  (214),  (213),  (212), 
(421),  etc.,  all  belong  in  a  common  vertical  zone  between  the  base  (001)  and 
the  prism  (210).  Similarly  the  brachypyramids  (123),  (122),  (121),  (241), 
etc.,  fall  in  a  common  vertical  zone  between  (001)  and  (120). 

181.   Illustrations.  —  The   following   figures   of   barite    (304-311)    give 


305 


306 


307 


Barite  Crystals 

excellent  illustrations  of  crystals  of  a  typical  orthorhombic  species,  and  show 
also  how  the  habit  of  one  and  the  same  species  may  vary.  The  axial  ratio 
for  this  species  is  a  :  b  :  c  =  0'815  :  1  : 1'314.  Here  d  is  the  macrodome 


ORTHORHOMBIC   SYSTEM 


125 


(102)  and  o  the  brachydome  (Oil);  m  is,  as  always,  the  prism  (110).  Figs. 
304-307  and  309  are  described  as  tabular  j|  c;  Fig.  308  is  prismatic  in  habit 
in  the  direction  of  the  macro-axis  (6),  and  310,  311  prismatic  in  that  of  the 
brachy-axis  (a). 

Figs.  312-314  of  native  sulphur  show  a  series  of  crystals  of  pyramidal 
habit  with  the  dome  n(011),  and  the  pyramids  p(lll),  s(113).  Note  n  trun- 
cates the  terminal  edges  of  the  fundamental  pyramid  p.  In  general  it  should 

314 


315 


Sulphur  Crystals 
316  317 


Staurolite 


Figs.  316-318,  Topaz 


be  remembered  that  a  macrodome  truncating  the  edge  of  a  pyramid  must 
have  the  same  ratio  oth:l',  thus,  (201)  truncates  the  edge  of  (221),  etc. 
Similarly  of  .the  brachydomes:  (021)  truncates  the  edge  of  (221),  etc.  Ji. 
Figs.  319-321. 

Again,  Fig.  315,  of  staurolite,  shows  the 
pinacoids  6(010),  c(001),  the  prism  m(110), 
and  the  macrodome  r(101). 

Figs.  316-318  are  prismatic  crystals  of 
topaz.  Here  m  is  the  prism  (110);  I  and  n 
are  the  prisms  (120),  (140);  d  and  p  are  the 
macrodomes  (201)  and  (401);  /and  y  are  the 
brachydomes  (021)  and  (041);  i,  u,  and  o  are 
the  pyramids  (223),  (111),  (221). 

182.  Projections.  -  -  Basal,  stereographic, 
and  gnomonic  projections  are  given  in  Figs. 
319-320a,  on  pp.  125, 126, 127  for  a  crystal  of  the 
species  topaz.  Fig.  319  is  the  basal  projection  Topaz 


126 


CR  YST  ALLO  GR  APH  Y 


of  the  crystal  shown  in  *ig.  318.     Figs.  320  and  320a  give  the  stereographic 
and  gnomonic  projections  of  these  forms  present  upon  it. 


110 


Stereographic  Projection  Topaz  Crystal 

2.  HEMIMORPHIC  CLASS   (26).     CALAMINE  TYPE 

(Orthorhombic  Pyramidal  Class) 

183.  Class  Symmetry  and  Typical  Forms.  —  The  forms  of  the  ortho- 
rhombic-hemimorphic  class  are  characterized  by  two  unlike  planes  of  sym- 
metry and  one  axis  of  binary  symmetry,  the  line  in  which  they  intersect; 
there  is  no  center  of  symmetry.  The  forms  are  therefore  .hemimorphic,  as 
defined  in  Art.  29.  For  example,  if,  as  is  usually  the  case,  the  vertical  axis 
is  made  the  axis  of  symmetry,  the  two  planes  of  symmetry  are  parallel  to  the 
pinacoids  a(100)  and  6(010).  The  prisms  are  then  geometrically  like  those 
of  the  normal  class,  as  are  also  the  macropinacoid  and  brachypinacoid; 
but  the  two  basal  planes  become  independent  forms,  (001)  and  (001).  .  There 
are  also  two  macrodomes,  (101)  and  (101),  or  in  general  (hQl)  and  (MM);  and 
similarly  two  sets,  for  a  given  symbol,  of  brachydomes  and  pyramids. 

The  general  symmetry  of  the  class  is  shown  in  the  stereographic  projec- 


120 


120 


041     r010 


Gnomonic  Projection  Topaz  Crystal 
321  322 


-*^ 


Symmetry  of  Hernimorphic  Class  Calamine 


Struvite        (127) 


128 


CR  YSTALLO  GR  APH  Y 


324 


325 


tion  Fig  321.  Further,  Figs.  322,  of  calamine,  and  323,  of  struvite,  represent 
typical  crystals  of  this  class.  In  Fig.  322_the  forms  present  are  £(301),  i(031), 
t>(12l);  in  Fig.  323  they  are  8(101),  «i(101),  0(011). 

3.  SPHENOIDAL  CLASS   (27).     EPSOMITE  TYPE. 
(Orthorhombic  Bisphenoidal  Class) 

184.   Symmetry  and  Typical  Forms.  —  The  forms  of  the  remaining 

class  of  the  system,  the  ortho- 
rhombic-sphenoidal  class,  are  char- 
acterized by  three  unlike  rec- 
tangular axes  of  binary  symme- 
try which  coincide  with  the  crys- 
tallographic  axes,  but  they  have 
no  plane  and  no  center  of  sym- 
metry (Fig.  324).  The  general 
form  hkl  here  has  four  faces  only, 
and  the  corresponding  solid  is  a 
rhombic  sphenoid,  analogous  to 
the  sphenoid  of  the  tetragonal 
system.  The  complementary  pos- 
itive and  negative  sphenoids  are 


Symmetry  of  Sphenoidal  Class 


Epsomite 

enantiomorphous.  Fig.  325  represents  a  typical  crystal,  of  epsomite,  with 
the  positive  sphenoid,  z(lll).  Other  crystals  of  this  species  often  show 
both  positive  and  negative  complementary  forms ,  but  usually  unequally 
developed.  • 

MATHEMATICAL  RELATIONS  OF  THE  ORTHORHOMBIC  SYSTEM 

186.  Choice  of  Axes.  —  As  explained  in  Art.  175,  the  three  crystallographic  axes  are 
fixed  as  regards  direction  in  all  orthorhombic  crystals,  but  any  one  of  them  may  be  made 
the  vertical  axis,  c;  and  of  the  two  horizontal  axes,  which  is  the  longer  (6)  and  which  the 
snorter  (a)  cannot  be  determined  until  it  is  decided  which  faces  to  assume  as  the  funda- 
mental, or  unit,  pyramid,  prism,  or  domes. 

The  choice  is  generally  so  made,  in  a  given  case,  as  to  best  bring  out  the  relation  of  the 
crystals  of  the  species  in  hand  to  others  allied  to  them  in  form  or  in  chemical  composition, 
or  in  both  respects;  or,  so  as  to  make  the  cleavage  parallel  to  the  fundamental  form;  or,  as 
suggested  by  the  common  habit  of  the  crystals,  or  other  considerations. 

186.  Axial  and  Angular  Elements.  —  The  axial  elements  are  given  by  the  ratio  of  the 
lengths  of  the  three  axes  in  terms  of  the  macro-axis,  b,  as  unity.  For  example,  with  barite 
the  axial  ratio  is 

a  :  6  :  c  =  0'81520  :  1  :  1'31359. 

The  angular  elements  are  usually  taken  as  the  angles  between  the  three  pinacoids  and 
the  unit  faces  in  the  three  zones  between  them.  Thus,  again  for  barite,  these  elements  are 

100  A  110  =  39°  11'  13",     001  A  101  =  58°  10'  36",     001  A  Oil  =  52°  43'  8".  ' 

Two  of  these  angles  obviously  determine  the  third  angle  as  well  as  the  axial  ratio.  The 
degree  of  accuracy  to  be  attempted  in  the  statement  of  the  axial  ratio  depends  upon  the 
character  of  the  fundamental  measurements  from  which  this  ratio  has  been  deduced.  There 
is  no  good  reason  for  giving  the  values  of  a  and  c  to  many  decimal  places  if  the  probable 
error  of  the  measurements  amounts  to  many  minutes.  In  the  above  case  the  measurements 
(by  Helmhacker)  are  supposed  to  be  accurate  within  a  few  seconds.  It  is  convenient,  how- 
ever, to  have  the  angular  elements  correct,  say,  within  10",  so  that  the  calculated  angles 
obtained  from  them  will  not  vary  from  those  derived  direct  from  the  measured  angles  by 
more  than  30"  to  1'. 


ORTHORHOMBIC    SYSTEM 


129 


187.   Calculation  of  the  Axes.  —  The  following  simple  relations  (cf .  Art.  48)  connect  the 
axes  with  the  angular  elements : 

tan  (100  A  110)   =  a,     tan  (001  A  Oil)  =  c,     tan  (001  A  101)   =  - 

These  equations  serve  to  give  either  the  axes  from  the 'angular  elements, 
or  the  angular  elements  from  the  axes.  It  will  be  noted  that  the  axes  are  not 
needed  for  simple  purposes  of  calculation,  but  it  is  still  important  to  have 
them,  for  example  to  use  in  comparing  the  morphological  relations  of  allied 
species. 

In  practice  it  is  easy  to  pass  from  the  measured  angles,  assumed  as  the 
basis  of  calculation  (or  deduced  from  the  observations  by  the  method  of 
least  squares),  to  the  angular  elements,  or  from  either  to  any  other  angles 
by  the  application  of  the  tangent  principle  (Art.  49)  to  the  pinacoidal  zones, 
and  by  the  solution  of  the  right-angled  spherical  triangles  given  on  the  sphere 
of  projection. 

Thus  any  face  hkl  lies  in  the  three  zones,  100  and  Qkl,  010  and  hOl,  001 
and  hkO.  For  example,  the  position  of  the  face  312  is  fixed  if  the  positions 
of  two  of  the  poles,  302,  012,  310,  are  known.  These  last  are  given,  respec- 
tively, by  the  equations 

Stibnite  tan  (001  A  302)   =  f  x  tan  (001  A  101), 

tan  (001  A  012)  =  \  x  tan  (001  A  Oil)     tan  (100  A  310)    =  \    X  tan  (100  A  110). 


m' 


:010 


Stereographic  Projection  Stibnite  Crystal 


130  CRYSTALLOGRAPHY 

188  Example.  —  Fig.  326  represents  a  crystal  of  stibnite  from  Japan  and  Fig.  327 
the  stereographic  projection  of  its  forms,  p(lll),  r(343),  77(353),  co3(5-10'3),  ra(110)  and 
6(010).  On  this  the  following  measured  angles  were  taken  as  fundamental: 

7777'    (353  A  353)  =55°    1'  0", 

7777'"  (353  A  353)  =  99°  39'  0". 

Hence,  the  angles  353  A  010  =  40°  10*'  and  353  A  053  =  27°  30|'  are  known  with- 
out calculation.  The  right-angled  spherical  triangle  *  010'053'353  yields  the  angle 
(010  A  053)  and  hence  (001  A  053);  also  the  angle  at  010,  which  is  equal  to  (001  A  101). 
But  tan  (001  A  Oil)  =  f  X  tan  (001  A  053),  and  tan  (001  A  Oil)  =  c.  Also,  since  tan 

(001  A  101)  =  --,  the  axial  ratio  is  thus  known,  and  two  of  the  angular  elements. 

The  third  angular  element  (001  A  110)  can  be  calculated  independently,  for  the  angle 
at  001  in  the  triangle  001'053'353  is  equal  to  (010  A  350)  and  tan  (010  A  350)  x  f  = 
(010  A  110),  the  complement  of  (100  A  110). 

Then  since  tan  (100  A  110)  =  a,  this  can  be  used  to  check  the  value  of  a  already 
obtained.  The  further  use  of  the  tangent  principle  with  the  occasional  solution  of  a  right- 
angled  triangle  will  serve  to  give  any  desired  angle  from  either  the  fundamental  angles 
direct,  or  from  the  angular  elements. 

Again,  the  symbol  of  any  unknown  face  can  be  readily  calculated  if  two  measured 
angles  of  tolerable  accuracy  are  at  hand.  For  example,  for  the  face  co,  suppose  the  meas- 
ured angles  to  be 

6co  (010  A  hkl)  =  30°  15',     coco'  (hkl  A  hkl)  =  51°  32'. 

The  solution  of  the  triangle  b'u'Okl  gives  the  angle  (010  A  Okl)  =  16°  25'  20",  and 

tan  (001  A  Okl)   _  tan  73°  34|'  =  k 

tan  (001  A  Oil)  ~  tan  45°  30^'  I  ' 

But  the  ratio  of  k  :  I  must  be  rational  and  the  number  derived  agrees  most  closely  with 
10  :  3. 

Again,  the  angle  (001  A  hOl)  may  now  be  calculated  from  the  same  triangle  and  the 
value  59°  38 f  obtained.  From  this  the  ratio  of  h  to  I  is  derived  since 


tan  (001  A  hOl )  =  tan  59°  38f '  =         _  =  h 
tan  (001  A  101)      tan  45°  43J'  I  ' 

This  ratio  is  nearly  equal  to  5  :  3,  and  the  two  values  thus  obtained  give  the  symbol  5'10'3. 
If,  however,  from  the  triangle  001'  Okl'u,  the  angle  at  001  is  calculated,  the  value  26°  42f 
is  obtained,  which  is  also  the  angle  (010  A  MO).  From  this  the  ratio  h  :  k  is  deduced,  since 

tan  (010  A  110)      tan  45°  12f  =  k 

tan  (010  A  hkO)  ~  tan  26°  42f  "  ~  h  ' 

The  value  of  -r  is  hence  closely  equal  to  2;  this  combined  with  that  first  obtained  f =-  =  -5-  J 

gives  the  same  symbol  5"  10*3. 

This  symbol  being  more  than  usually  complex  calls  for  fairly  accurate  measurements. 
How  accurate  the  symbol  obtained  is  can  best  be  judged  by  comparing  the  measured  angles 
with  those  calculated  from  the  symbol.  For  example,  in  the  given  case  the  calculated 
angles  for  u(5'10'3)  are  6«(010  A  5'10'3)  =  30°  16',  coco'(5'10-3)  =  51°  35'.  The  correctness 
of  the  value  deduced  is  further  established  if  it  is  found  that  the  given  face  falls  into 
prominent  zones. 

It  will  be  understood  further  that  the  zonal  relations,  explained  on  pp.  45-47,  play  an 
important  part  in  all  calculations.  For  example,  in  Fig.  326,  if  the  symbol  of  r  were  un- 
known, it  could  be  obtained  from  a  single  angle  (as  br),  since  for  this  zone  h  =  I. 

189.  Formulas.  —  Although  it  is  not  often  necessary  to  employ  formulas  in  calculations, 
a  few  are  added  here  for  sake  of  completeness.  Here  a  and  c  in  the  formulas  are  the  lengths 
of  the  two  axes  a  and  c. 

*  The  student  in  this  as  in  every  similar  case  should  draw  a  projection,  cf.  Fig.  327 
(not  necessarily  accurately  constructed),  to  show,  if  only  approximately,  the  relative  posi- 
tion of  the  faces  present. 


ORTHORHOMBIC    SYSTEM 


131 


(1)  For  the  distance  between  the  pole  of  any  face  P(hkl)  and  the  pinacoids  a,  6,  c,  we 
have  in  general: 


cos2  Pa  =  cos2  (Md  A  100)  = 
cos2  P6  =  cos2  (Md  A  010)  = 
cos2  PC  =  cos2  (Md  A  001)  = 


he2  +  k2a?c2  +  I2a? 


Me*  +  A;2a2c2  +  Pa?  ' 

_  Pa? 

We2  +  /c2a2c2  +  I2a?  ' 


102 


Oil 


111 


(2)  For  the  distance  (PQ)  between  the  poles  of  any  two  faces  (Md)  and  (par) 

hpc2  +  kqa?c2  +  Ira2 

cos  PQ  =     ,  ' 

V(h2c2  +  &2a2c2  +  Z2a2]  [p2c2  +  ?2a2c2  +  r2a2] 

190.  To  determine,  by  plotting,  the  axial  ratio  of  an  orthorhombic  crystal,  having  given 
the  stereographic  projection  of  its  forms.  In  order  to  solve  this  problem  it  is  necessary 
that  the  position  of  the  pole  of  a  pyramid  face  of  known  indices  be  given  or  the  position 
of  the  faces  of  a  prism  and  one  dome  or  of  both  a  macro-  and  a  brachydome.  For  illus- 
tration it  is  assumed  that  a  crystal  of  barite,  such  as  represented  in  Fig.  305,  has  been 
measured  on  the  goniometer  and  the  poles  of  its  faces  plotted  in  the  stereographic  projec- 
tion. The  lower  right- 
hand  quadrant  of  this 
projection  is  shown  in  Fig. 
328.  The  forms  present 
are  common  ones  on  bar- 
ite crystals  and  have 
been  given  the  symbols, 
ro(110),  d(102),  o(011), 
c(001).  The  ratio  of  a  :  6 
can  be  determined  readily 
from  the  position  of  the 
pole  m(110).  A  radial 
line  is  drawn  to  the  pole 
of  the  face  and  then  a 
perpendicular  erected  to 
it  from  the  end  of  the  line 
representing  the  b  crys- 
tallographic  axis.  The 
intercept  of  this  perpen- 
dicular on  the  line  repre- 
senting the  a  axis,  when 
expressed  in  terms  of  the 
assumed  unit  length  of 
the  b  axis,  gives  the  length 
of  a.  It  is  to  be  noted 
that  the  fact  that  this 
line  in  the  present  case 
passes  very  nearly  through 
the  pole  111  is  wholly 
accidental.  The  length 
of  the  vertical  axis  can 
be  determined  from  the 
position  of  the  pole  of 
either  d(102)  or  o(011). 

given^n8  the  upper  left- 

hand    quadrant     of     the  .  ,       .     ,. 

figure.  If  the  brachydome,  o(011),  is  used  the  sloping  line  that  gives  the  inchnA- 
tion  of  the  face  is  started  from  a  distance  on  the  horizontal  line  equivalent  to  the  length 
of  the  6  axis,  or  1,  and  its  intercept  .on  the  c  axis  will  equal  the  unit  length  of  that  axis. 
If  however,  the  position  of  d(102)  is  used  the  base  line  of  the  triangle  must  be  made  equal 
to  the  unit  length  of  the  a  axis  as  already  established  and  the  intercept  on  the  c  axis  will 
equal  ?  of  the  Tatter's  unit  length. 


Determination  of  the  Axial  Ratio  for  Barite 


132 


CRYSTALLOGRAPHY 


The  problem  could  have  been  wholly  solved  from  the  position  of  the  pyramid  face,  111, 

if  that  form  had  been  present  on  the  crystal.     The  construction  in  this  case  is  also 

illustrated. 

191.   To  determine,  by  plotting,  the  indices  of  a  face  upon  an  orthorhombic  crystal, 

given     the    position    of    iis 

329  pole  upon  the  stereographic 

projection  and  the  axial  ratio 
of  the  mineral.  To  illustrate 
this  problem  it  is  assumed 
that  the  position  of  the 
pole  in  the  stereographic 
projection  of  the  face  o,  Fig. 
329,  upon  a  topaz  crystal  is 
known.  First  draw  a  radial 
line  through  the  pol  e  o .  Next 
erect  a  perpendicular  to  this 
line,  starting  it  from  the 
distance  selected  as  repre- 
senting 1  on  the  b  crystallo- 
graphic  axis.  The  intercept 
of  this  line  upon  the  line 
representing  the  a  axis  when 
expressed  in  terms  of  the 
unit  length  of  the  b  axis  is 
0'53.  This  is  equivalent  to 
the  established  unit  length 
of  the  a  axis  and  therefore 
the  parameters  of  the  face  o 
on  the  horizontal  crystallo- 
graphic  axes  are  la,  16.  Next 
the  distance  O-P  is  transfer- 
red into  the  upper  left-hand 
quadrant  of  the  figure.  The 

position  of  the  normal  to  the  face  is  determined  by  measuring  with  a  protractor  the  angular 

distance  between  O  and  o.     The  line  giving  the  slope  of  the  face  is  next  drawn  perpendicu- 
lar to  this  normal  and  its  intercept  upon  the  line  representing  the  vertical  axis  determined. 

This  distance  when  expressed  in 

terms  of  the  length  of  the  6  axis  is 

0'95.    This  is  twice  the  established 

length  of  the  c  axis  (0'476)  and 

consequently  the  third  parameter 

of  the  face  o  is  2c.     This  gives  the 

indices  221  for  the  face. 

192.  To  deter  mine,  by  plotting, 

the  axial  ratio  of  an  orthorhombic 

crystal  having  given  the  gnomonic 

projection  of  its  forms.     To  illus- 
trate this  problem  the  gnomonic 

projection  of  the  crystal  of  topaz 

already  given  in  Fig.  320a  will  be 

used.      In  Fig.  330  one  quadrant 

of  this  projection  is  reproduced. 

From  each  pole  lines  are  drawn 

perpendicular    to    the    two    lines 

representing  the  a  and  b  crystal- 

lographic  axes.     It  will  be  found 

that  the  intercepts  made  in  this 

way  upon  the  a  axis  have  rational 

relations  to  each  other.     The  same 

is    true    of    the   intercepts  upon 

the  6  axis.      The  intercepts  upon 

the     two      axes,      however,     are 

irrational  in  respect  to  each  other.     A  convenient  intercept  upon  each  axis  is  chosen  as  1 

and  the  other  intercepts  upon  that  axis  are  then  expressed  in  terms  of  this  length.     Of 


2< 


MONOCLINIC   SYSTEM 


133 


course  with  a  known  mineral,  whose  forms  have  already  had  indices  assigned  to  them, 
the  intercept  that  shall  be  considered  as  1  is  fixed. 

If  we  take  r  as  equivalent  to  the  radius  of  the  fundamental  circle  of  the  projection, 
q  as  equal  to  the  chosen  intercept  upon  the  6  crystallographic  axis  and  p  that  upon  the 
a  axis,  then  the  axial  ratio  can  be  derived  from  the  following  expressions: 

b      r  .     a      r 


c      q       c       p 

The  proof  of  these  relationships  is  similar  to  that  already  given  under  the  Tetragonal 
System,  Art.  117,  p.  93. 

193.  To  determine,  by  plotting,  the  indices  of  a  face  upon  an  orthorhombic  crystal, 
given  the  position  of  its  pole  upon  the  gnomonic  projection  and  the  axial  ratio  of  the  min- 
eral. The  method  of  construction  in  this  case  is  the  reverse  of  that  given  in  the  problem 
above  and  is  essentially  the  same  as  given  under  the  Isometric  and  Tetragonal  Systems, 
Arts.  84  and  118.  In  the  case  of  an  orthorhombic  mineral  the  intercepts  of  the  perpendicu- 
lars drawn  from  the  pole  of  the  face  to  the  a  and  b  axes  must  be  expressed  in  each  case  in 
terms  of  the  unit  intercept  on  that  axis.  These  values,  p  and  q,  can  be  determined  from  the 
equations  given  in  the  preceding  problem. 


V.   MONOCLINIC  SYSTEM 

(Obliqw  System) 


331 

i 


194.   Crystallographic  Axes.  —  The  monoclinic  system  includes  all  the 
forms  which  are  referred  to  three 
unequal  axes,  having  one  of  their 
axial  inclinations  oblique. 

The  axes  are  designated  as 
follows:  the  inclined  or  clino-axis 
is  a;  the  ortho-axis  is  b,  the  ver- 
tical axis  is  c.  The  acute  angle 
between  the  axes  a  and  c  is  rep- 
resented by  the  letter  (3;  the 
angles  between  a  and  b  and  b  and  c 
are  right  angles.  See  Fig.  331. 
When  properly  orientated  the 
inclined  axis,  a,  dopes  dawn .toward  S^Omi^^W1 


the  observer,  the  b  axis  is  hori- 
zontal and  parallel  to  the  observer  and  the  c  axis  vertical. 

1.  NORMAL  CLASS  (28).     GYPSUM  TYPE 
(Prismatic  or  Holohedral  Class) 

195.  Symmetry.  —  In  the  normal  class  of  the 
monoclinic  system  there  is  one  plane  of  sym- 
metry and  one  axis  of  binary  symmetry  normal 
to  it.  The  plane  of  symmetry  is  always  the 
plane  of  the  axes  a  and  c,  and  the  axis  of  sym- 
metry coincides  with  the  axis  b,  normal  to  this 
plane.  The  position  of  one  axis  (6)  and  that  of 
the  plane  of  the  other  two  axes  (a  and  c)  is  thus 
fixed  by  the  symmetry;  but  the  latter  axes  may 
occupy  different  positions  in  this  plane.  Fig.  332 
Symmetry  of  Normal  Class  snows  the  typical  stereographic  projection,  pro- 
jected on  the  plane  of  symmetry.  Figs.  347, 348  are  the  projections  of  an  actual 


134 


CR  YST  ALLO  GR  APH  Y 


crystal  of  epidote;  here,  as  is  usual,  the  plane  of  projection  is  normal  to  the 
prismatic  zone. 

196.  Forms.  —  The  various  forms  *  belonging  to  this  class,  with  their 
symbols,  are  given  in  the  following  table.  As  more  particularly  explained 
later,  an  orthodome  includes  two  faces  only,  and  a  pyramid  four  only. 


Symbols 

Orthopinacoid  or  a-pinacoid (100) 

Clinopinacoid  or  6-pinacoid (010) 

Base  or  c-pinacoid (001) 

Prisms (hkO) 

Orthodomes..  '  (/^ 


1. 
2. 
3. 
4. 

5. 

6.   Clinodomes. . 


7. 


197.  Pinacoids.  —  The  pinacoids  are  the  orthopinacoid,  clinopinacoid, 
and  the  basal  plane. 

The  orthopinacoid,  (100),  includes  the  two  faces  parallel  to  the  plane  of 
the  ortho-axis  b  and  the  vertical  axis  c.  They  have  the  indices  100  and  100. 
This  form  is  designated  by  the  letter  a,  since  it  is  situated  at  the  extremity  of 
the  a  axis;  it  is  hence  conveniently  called  the  a-face  or  a-pinacoid. 

The  clinopinacoid,  (010),  includes  the  two  faces  parallel  to  the  plane  of 
symmetry,  that  is,  the  plane  of  the  clino-axis  a  and  the  axis  c.  They 
have  the  indices  010  and  010.  The  clinopinacoid  is  designated  by  the  letter 
6,  and  is  called  the  b-face  or  b-pinacoid. 

The  base  or  basal  pinacoid,  (001),  includes  the  two  terminal  faces,  above 
and  below,  parallel  to  the  plane  of  the  axes  a,  6;  they  have  the  indices  001 
and  001.  The  base  is  designated  by  the  letter  c,  and  is  often  called  the 
c-face  or  c-pinacoid.  It  is  obviously  inclined  to  the  orthopinacoid,  and  the 
normal  angle  between  the  two  faces  (100  A  001)  is  the  acute  axial  angle  0. 


333 


335 


101  I 


Ortho-,  Clmo  - 
and  Basal  Pinacoids 


Prism  and 
Basal  Pinacoid 


Orthodomes 
and  Clinopinacoid 


The  diametral  prism,  formed  by  these  three  pinacoids,  taken  together, 
Fig.  333,  is  the  analogue  of  the  cube  in  the  isometric  system.  It  is  bounded 
by  three  sets  of  unlike  faces;  it  has  four  similar  vertical  edges;  also 
four  similar  edges  parallel  to  the  axis  a,  but  the  remaining  edges,  parallel 
to  the  axis  b,  are  of  two  sets.  Of  its  eight  solid  angles  there  are  two  sets  of 


On  the  general  use  of  the  terms  pinacoid,  prisms,  domes,  pyramids,  see  pp.  31,  122. 


MONOCLINIC    SYSTEM 


135 


four  each;    the  two  above  in  front  are  similar  to  those  below  behind,  and 
the  two  below  in  front  to  those  above  in  behind. 

198.  Prisms.  --  The  prisms  are  all  of  one  type,  the  oblique  rhombic 
prism.     They  may  be  divided  into  three  classes  as  follows:   the  unit  prism, 
(110),  designated  by  the  letter  m,  shown  in  Fig.  334;  the  orthoprisms,  (hkQ), 
where  h  >  k,  lying  between  a(100)  and  m(110),  and  the  clinoprisms,  (MO) 
where  h  <  k,  lying  between  m(110)  and  6(010).     The  orthoprisms  and  clino- 
prisms correspond  respectively  to  the  macroprisms  and  brachyprisms  of  the 
orthorhombic  system,  and  the  explanation  on  p.  123  will  hence  make  their  rela- 
tion clear.     Common  cases  of  these  prisms  are  shown  in  the  figures  given  later, 

199.  Orthodomes.  —  The  four  faces  parallel  to  the  ortho-axis  6,  and 
meeting  the  other  two  axes,  fall  into  two  sets  of  two  each,  having  the  general 
symbols  (hOl)  and  (hOl).     These  forms  are  called  orthodomes;  they  are  strictly 
hemiprthodomes.     For  example,  the  unit  orthodome  (101)  has  the  faces  101 
and  101;  they  would  replace  the  two  obtuse  edges  between  a(100)  and  c(001) 
in  Fig.  333.     The  other  unit  orthodome  (101)  has  the  faces  101  and  101,  and 
they  would  replace  the  acute  edges  between  a(100)  and  c(001).     These  two 
independent  forms  are  shown  _together,  with  6(010),  in  Fig.  33_5. 

Similarly  the  faces  201,  201  belong  tq_the  form  (201),  and  201,  201  to  the 
independent  but  complementary  form  (201). 

200.  Clinodomes.  —  The   clinodomes  are   the   forms   whose   faces  are 
parallel  to  the  inclined  axis,  a,  while  intersecting  the  other  two  axes.     Their 
general  symbol  is  hence  (Qkl)  and  they  lie  between  the  base  (001)  and  the 
clinopinacoid  (010).     Each  form  has  Jour  Jaces ;   thus  for  the  unit  clinodome 
these  have  the  symbols,  Oil,  Oil,  Oil,  Oil.     The  form  n(021)  in  Fig.  342  is 
a  clinodome. 

201.  Pyramids.  —  The  pyramids  in  the  monoclinic  system  are  all  hemi- 
pyramids,  embracing  four  faces  only  in  each  form,  corresponding  to  the 
general  symbol   (hkl) .     This  obviously  follows  from  the  symmetry;    it  is 
shown,  for  example,  in  the  fact  already  stated  that  the  solid  angles  of  the 
diametral  prism  (Fig.  333,  see  above),  which  are  replaced  by  these  pyramids, 
fall  into  two  sets  of  four  each.     Thus  any  general  symbol,  as  (321),  includes 
the  two  independent  forms  (321)  and  (321)  with  the  faces 


321,         321,         321,         321, 


and 


321,        321,        321,        321 


336 


337 


339 


The  pyramids  may  also  be  divided  into  three  classes  as  unit  pyramids, 
(hhl)'  orthopyramids,  (hkl),  when  h  >  fc;  or  clinopyramids,  (hkl),  when  h  <  k. 
These  correspond  respec- 
tively to  the  three  prisms 
•already  named.  They  are 
analogous  also  to  the  unit 
pryamids,  rnacropyramids, 
anTf  brachypyramids  of  the 
orthorhombic  system,  and 
the  explanation  given  on 
p.  124,  should  serve  to 
make  their  relations  clear. 
But  it  must  be  remembered 
that  each  general  symbol 


7 


embraces  two  forms,  (hhl) 

and  (hkl)  with  four  faces  each,  as  above  explained. 


Pyroxene 


136 


CRYSTALLOGRAPHY 


202.  Illustrations.  —  Figs.  336-339  of  pyroxene  (a  :  b  :  c  =  1'092  :  1  : 
0-589,  ft  =  74°  =  o(100)  A  c(001))  show  typical  monoclinic  forms.  Fig.  336 
shows  the  diametral  prism.  Of  the  other  forms,  m  is  the  unit  prism  (110); 
p(101)  is  an  orthodome;  w(lll),  0(221),  s(lll)  are  pyramids;  for  other 
figures  see  p.  475.  Again,  Figs.  340-342  represent  common  crystals  of 
orthoclase  (aj  b  :  c  =  0'659  :  1  :  0'555,  ft  =  64°).  Here  z  (130)  is  a  prism; 
#(101)  and  2/(201)  are orthodomes ;  n(021)  is  a  clinodome;  0(111)  a  pyramid. 
Since  (Fig.  340)  c  and  x  happen  to  make  nearly  equal  angles  with  the  vertical 
edge  of  the  prism  m,  the  combination  often  simulates  an  orthorhombic 
crystal. 

340  341  342 


Orthoclase 


Fig.  343  shows  a  monoclinic  crystal,  epidote,  prismatic  in  the  direction  of 
the  ortho-axis;  the  forms  are  a(100),  c(001),  r(101)  and  w(Ill).  Fig.  344 
of  gypsum  is  flattened  ||  6(010);  it  shows  the  unit  pyramid  /(111)  with  the 
unit  prism  w(110). 


Epidote 


Epidote 


203.  Projections.  —  Fig.  345  shows  a  projection  of  a  crystal  of  epidote 
(cf.  Fig.  897,  p.  531)  on  a  plane  normal  to  the  prismatic  zone,  and  Fig.  346 
one  of  a  similar  crystal  on  a  plane  parallel  to  6(010) ;  both  should  be  care- 
fully studied,  as  also  the  stereographic  and  gnomonic  projections  of  the  same 
species,  Figs.  347,  348.  The  symbols  of  the  prominent  faces  are  given  in 
the  latter  figures. 


Stereographic  Projection  of  Epidote  Crystal 


210 


IV  211 


10211 


a  100 


Gnomonic  Projection  of  Epidote  Crystal 


(137) 


138 


CRYSTALLOGRAPHY 


2.   HEMIMORPHIC  CLASS   (29).     TARTARIC  ACID   TYPE 

(Sphenoidal  Class) 

204.   The  monoclinic-hemimorphic  class  is  characterized  by  a  single  axis 

of  binary  symmetry,  the 

349  350  crystallographic  axis  6,  but 

^  it  has  no  plane   of  sym- 

metry.     It    is   illustrated 

X.  ^^— 7^        by  the  stereographic  pro- 

jection (Fig.  349)  made 
upon  a  plane  parallel  to 
6(010).  Fig.  350  shows  a 
common  form  of  tartaric 
acid;  sugar  crystals  also 
belong  here.  The  hemi- 
morphic  character  is  dis- 
tinctly shown  in  the 
distribution  of  the  clino- 
domes  and  pyramids;  cor- 
responding to  this  the 


Tartaric  Acid 


Symmetry  of  Hemimorphic  Class 

artificial  salts  belonging  here  often  exhibit   marked  pyroelectrical  pheno- 


mena. 

3.   CLINOHEDRAL  CLASS   (30).     CLINOHEDRITE  TYPE 
(Domatic  or  Hemihedral  Class) 

205.  The  monoclinic-clinohedral  class  is  characterized  by  a  single  plane 
of  symmetry,  parallel  to  the  clinopinacoid,  6(010),  but  it  has  no  axis  of  sym- 
metry. This  symmetry  is  shown  in  the  stereographic  projection  made  upon 
a  plane  parallel  to  6(010),  Fig.  351.  In  this  class,  therefore,  the  forms  parallel 
to  the  6  axis,  viz.,  c(001),  a(100),  and  the  orthodomes,  are  represented  by  a 

353 


Symmetry  of  Clinohedral  Class 


Clinohedrite 


single  face  only.  The  other  forms  have  each  two  faces,  but  it  is  to  be  noted 
that,  with  the  single  exception  of  the  clinopinacoid  6(010),  the  faces  of  a 
given  form  are  never  parallel  to  each  other.  The  name  given  to  the  class  is 
based  on  this  fact. 

Several  artificial  salts  belong  here  in  their  crystallization,  but  the  only 


MONOCLINIC   SYSTEM  139 

known  representative  among  minerals  is  the  rare  silicate,  clinohedrite 
(H2CaZnSiO5),*  a  complex  crystal  of  which  is  shown  in  two  positions  in  Figs. 
352,  353.  As  seen  in  these  figures,  the  crystals  of  the  group  have  a  hemi- 
morphic  aspect  with  respect  to  their  development  in  the  direction  of  the 
vertical  axis,  although  they  cannot  properly  be  called  hemimorphic  since  this 
is  not  an  axis  of  symmetry.  The  forms  shown  in  Figs.  352  353  are  as 
follows:  pinacoid,  b (010) ;_ prisms,  w(110),  Wi(IlO),  fc(3_20),  n_(120),  Z(130); 
orthodomes,  e(10_l),  ei(l_01);  pyramids,  p(lll),  Pi(lll),  tf(lll),  r(331), 
s(551),  *(771),  w(531),  o(131),  z(131),  y(121). 

It  is  to  be  noted  that  crystals  of  the  common  species  pyroxene  (also  of 
segirite  and  titanite)  occasionally  show  this  habit  in  the  distribution  of  their 
faces,  but  it  is  not  certain  that  this  may  not  be  accidental^ 

MATHEMATICAL  RELATIONS  OF  THE  MONOCLINIC  SYSTEM 

206.  Choice  of  Axes.  —  It  is  repeated  here  (Art.  196)  that  the  fixed  position  of  the 
plane  of  symmetry  establishes  the  direction  of  the  plane  of  the  a  and  c  crystallographic 
axes  and  also  of  the  axis  b  which  is  the  symmetry  axis  and  lies  at  right  angles  to  this  plane. 
The  a  and  c  axes,  however,  may  have  varying  positions  in  the  symmetry  plane  according 
to  which  faces  are  taken  as  the  pinacoids  a(100)  and  c(001),  and  which  the  unit  pyramid, 
prism,  or  domes. 

207.  Axial  and  Angular  Elements.  —  The  axial  elements  are  the  lengths  of  the  axes 
a  and  c  in  terms  of  the  unit  axis  b,  that  is.  the  axial  ratio,  with  also  the  acute  angle  of 
inclination  of  the  axes  a  and  c,  called  /3.     Thus  for  orthoclase  the  axial  elements  are: 

a  :  b  :  c  =  0'6585  :  1  :  0'5554    0  =  63°  56f. 

The  angular  elements  are  usually  taken  as  the  angle  (100  A  001)  which  is  equal  to  the  angle 
/3;  also  the  angles  between  the  three  pinacoids  100,  010,  001,  respectively,  and  the  unit 
prism  110,  the  unit  orthodome  (101  or  101)  and  the  unit  clinodomeOll.  Thus,  again,  for 
orthoclase,  the  angular  elements  are: 

001  A  100  =  63°  56f ,     100  A  110  =  30°  36£'. 
001  A  101  =  50°  16£',     001  A  Oil  =  26°  31'. 

208.  The  mathematical  relations  connecting  axial  and  angular  elements  are  given  in 
the  following  equations  in  which  a,  b,  and  c  represent  the  unit  lengths  of  the  respective 
crystallographic  axes. 

a  =  tan  (10°  A  110)         or        tan  (100  A  110)=  a.  sin  0;  (1) 

sin  /3 

=  tan  (001  A  Oil)         Qr        tan  (001  A  Oil)  =  c  .  sin /3;  (2) 

sin.tf 


a  .  tan  (001  A  101)  .       (m  A  101) 


sin  ?  -  cos  0  .  tan  (001  A  101)  a  +  c  .  cos 

a.  tan  (001  A  101)  .    or    tan  (001  A  101)  = 


(3) 


(•    =    — : — Ul          UCkU    ^vyv/i     /\    J.WA/     — 

sin  0  +  cos  0  .  tan  (001  A  101)  a  -  c  .  cos  0 

These  relations  may  be  made  more  general  by  writing  in  the  several  cases  — 

i 

in  (1)     MO  for  110    and    ^  a  for  a;  in  (2)     OW  for  Oil    and    Before; 

in  (3)     hOl  for  101     and    j-  c  for  c.. 


,  38,  115,  ,889. 


140  CRYSTALLOGRAPHY 

Also 

c  =  sin  (001  A  101)  =  sin  (001  A  101); 

a      sin  (100  A  101)       sin  (TOO  A  TOl)' 

and  more  generally 

h    c      sin  (001  A  hOl)  =  sin  (001  A  hQl) 

a  '  I  ~  sin  (100  A  hOl)  ~  sin  (TOO  A  hQl) 

Note  also  that 

tan  0  =  a        and         tan  f  =  c, 

where  <f>  is  the  angle  (Fig.  347)  between  the  zone-circles  (001,  100)  and  (001,  110);  also  f  is 
the  angle  between  (100,  001)  and  (100,  Oil). 

All  the  above  relations  are  important  and  should  be  thoroughly  understood. 

209.  The  problems  which  usually  arise  have  as  their  object  either  the  deducing  of  the 
axial  elements,  i.e.,  the  angle  /3  and  the  values  of  a  and  c  in  terms  of  6(=  1),  from  three 
measured  angles,  or  the  finding  of  any  required  interfacial  angles  from  these  elements  or 
from  the  fundamental  angles. 

The  simple  relations  of  the  preceding  article  connect  the  angular  and  axial  elements, 
and  beyond  this  all  ordinary  problems  can  be  solved  *  either  by  the  solution  of  spherical 
triangles  on  the  sphere  of  projection,  or  by  the  aid  of  the  cotangent  (and  tangent)  relation. 

It  is  to  be  noted,  in  the  first  place,  that  all  great  circles  on  the  sphere  of  projection  (see 
the  stereographic  projection,  Fig.  347)  from  010  cut  the  zone  circle  100,  001,  100  at  right 
angles,  but  those  from  100  cut  the  zone  circles  010,  001,  010  obliquely,  as  also  those  from 
001  cutting  the  zone  circle  100,  010,  100. 

210.  Tangent  and  Cotangent  Relations.  —  The  simpje  tangent  relation  holds  good  for  all 
zones  from  010  to  any  pole  on  the  zone  circle  100,  001.  100;  in  other  words,  for  the  prisms, 
clinodomes,  and  also  zones  of  pyramids  in  which  the  ratio  of  h  :  I  is  constant  (from  001  to 
hOl  or  to  £(M).     Thus  it  is  still  true,  as  in  the  orthorhombic  system,  that  the  tangents  of  the 
angles  of  the  prisms  210,  110,  120,  130  from  100  are  in  the  ratio  of  *  :  1  :  2  :  3,  or,  more 
generally,  that 

tan  (100  A  MO)  =  k  tan  (010  A  hkO)  _  h 

tan  (100  A  110)  ~~  h  tan  (010  A  110)  ~  k' 

Also  for  the  clinodomes  the  tangents  of  the  angles  of  012,  Oil,  021  from  001  are  in  the 
ratio  of  \ i  :  1  :  2,  etc.  A^similar  relation  holds  for  the  tangents  of  the  angles  of  pyramids  in 
the  zones  mentioned,  as  121,  111,  212,  etc. 

For  zones  other  than  those  mentioned  as  from  100  to  a  clinodome,  or  from  001  to  a 
prism,  the  more  general  cotangent  formula  given  in  Art.  49  must  be  employed.  This  rela- 
tion is  simplified  for  certain  common  cases. 

For  any  zone  starting  from  001,  as  the  zone  001,  100,  or  001,  110,  or  001,  210,  etc.;  if 
two  angles  are  known,  viz.,  the  angles  between  001  and  those  two  faces  in  the  given  zone 
which  fall  (1)  in  the  zone  010,  101,  and  (2)  in  the  prismatic  zone  010,  100;  then  the  angle 
between  001  and  any  other  face  in  the  given  zone  can  be  calculated. 
Thus, 

Let  001  A  101  =  PQ        and        001  A  100  =  PR, 
or    "    001  A  111  =  PQ  "          001  A  110  =  PR, 

or    "    001  A  212  =  PQ  001  A  210  =  PR,  etc. 

Then  for  these,  or  any  similar  cases,  the  angle  (PS)  between  001  and  any  face  in  the  given 
zone  (as  201,  or  221,  or  421,  etc.,  or  in  general  hQl,  hhl,  etc.)  is  given  by  the  equation 

cot  PS  -  cot  PR  =  l_ 
cotPQ  -  cot  PR  ~  h 

For  the  corresponding  zones  from  001  to  100,  to  110,  to  210,  etc.,  the  expression  has  the 
same  value;  but  here 

PQ  =  001  A  TOl,      PR  =  001  A  TOO,     PS  =  001  A  hOl, 
or  001  A  Til,  etc.,         001  A  TlO,  etc.,       001  A  hhl,  etc. 

*  The  general  formulas,  from  which  it  is  possible  to  calculate  directly  the  angles  between 
any  face  and  the  pinacoids,  or  the  angle  between  any  two  faces  whatever,  are  so  complex 
as  to  be  of  little  value. 


MONOCLINIC   SYSTEM 


141 


If,  however,  100  is  the  starting-point,  and 

100  A  101 
or  100  A  111 

then  the  relation  becomes 


100  A  001 
100  A  Oil 


PR, 
PR,  etc., 


cot  PS  -  cot  PR 
cot  PQ  -  cot  PR 


211  To  determine,  by  plotting,  the  axial  elements  of  a  monoclinic  crystal  eiven  the 
stereographjc  projection  of  its  forms.  As  an  example  of  this  problem  °t  [fassumld  that 
an  orthoclase  crystal  similar  to  the  one  shown  in  Fig  341  has  been  measured  andThe  pol?s 
of  its  faces  located  on  the  stenographic  projection,  Fig.  354.  The  inclination  of  the a axis 
or  the  angle  0  is  given  directly  by  measuring,  by  means  of  the  stenographic  protractor  the 
angular  distance  between  the  poles  of  a(100)  and  c(001).  In  the  present  case  the  a(100) 
form  does  not  actually  occur  on  the  crystal,  p  is  measured  as  64°  If  thp  basp  ii  rmt 
present  upon  the  crystal  it  will  be  usualfy  possible  to  locate  its  position  by  mean^ of  some 
zone  circle  on  which  it  must  he  In  the  present  case  the  great  circle  of  the  zone  of  m'(TlO), 
the  oiemto  the  base  "^  t0  ba°k  llne  (Z°ne  °f  the  orthodomes)  at  ^  point  of 


mllO 


fc'oio* 


6010 


a  100 


Determination  of  Axial  Elements  of  Orthoclase  from  Stereographic  Projection 

The  ratio  between  the  lengths  of  the  a  and  b  axes  can  be  readily  determined  from  the 
position  of  the  pole,  m(110).  Draw  the  radial  line  O-P  from  the  center  of  the  projection 
to  m(110).  From  the  end  of  the  b  axis  draw  a  line  at  right  angles  to  O-P.  This  repre- 
sents the  intersection  of  the  prism  face  with  the  horizontal  plane  and  the  distance  O-R 
gives  the  intercept  of  the  prism  upon  the  horizontal  projection  of  the  a  axis.  The  distance 
O-R  therefore  is  not  the  unit  length  of  the  a  axis  but  is  that  distance  foreshortened  some- 
what because  of  the  inclination  of  that  axis.  The  construction  by  which  the  true  length 
of  the  a  axis  is  obtained  is  shown  in  Fig.  355.  The  line  R-O-S-T  represents  the  horizontal 
projection  of  the  a  axis  upon  which  the  distance  O-R  is  transferred  from  Fig.  354.  As  the 
prism  face  is  vertical  its  intercept  upon  the 'a  axis  can  be  found  by  dropping  a  perpendicu- 
lar from  R  to  intersect  the  line  which  represents  the  a  axis.  The  inclination  of  this  last 


142 


CRYSTALLOGRAPHY 


line  is  found  by  use  of  the  angle  ft,  which  has  been  already  determined.  The  length  of  the 
a  axis  when  expressed  in  terms  of  the  b  axis  (TOO)  was  found  to  be  0' 66. 

The  length  of  the  c  axis  can  be  found  best  from  the  inclination  of  the  ?/(201)  face.  This 
face  will  intersect  the  negative  end  of  the  a  axis  and  the  upper  end  of  the  c  axis  at  either 
\a,  Ic  or  la,  2c.  The  angle  between  the  center  of  the  projection,  O,  Fig.  354,  and  the 
pole  y  is  measured  by  means  of  the  stereographic  protractor.  From  this  angle  the  position 
of  the  normal  to  y,  as  shown  in  Fig.  355,  is  determined.  The  line  representing  the  slope  of 
the  face  is  drawn  at  right  angles  to  this  normal,  starting  from  the  negative  unit  length  of 
the  inclined  a  axis.  The  intercept  on  the  c  axis  was  found  to  be  equal  to  I'll,  which,  as 
it  is  equal  to  2c,  would  give  the  unit  length  of  the  c  axis  as,  0'55. 

The  length  of  the  c  axis  could  also  be  determined  from  the  inclination  of  the  pyramid 
face,  o(Tll).  The  method  of  construction  would  be  similar  to  that  described  in  the  prob- 
lem below. 

212.  To  determine  the  indices  of  a  face  upon  a  monoclinic  crystal,  having  given  the 
position  of  its  pole  upon  the  stereographic  projection  and  the  axial  elements  of  the  min- 
eral. The  pyramid  face  o  on  orthoclase  will  be  used  to  illustrate  the  problem.  First,  see 
Fig.  354,  a  radial  line  is  drawn  through  the  pole  o  and  a  perpendicular  S-T  erected  to  it, 
starting  from  the  unit  length  of  the  b  axis.  It  is  to  be  noted  that  the  point  T  is  the  inter- 
section of  the  face  o  with  the  horizontal  projection  of  the  a  axis  Transfer  the  distance 


Determination  of  Axial  Elements,  etc.  of  Orthoclase 

O-S  to  the  horizontal  line  in  Fig.  355  and  locate  the  position  of  the  normal  to  o  by  the 
angle,  Fig.  354,  between  O  and  o.  The  line  giving  the  slope  of  the  face  can  then  be  drawn 
from  the  point  S  (Fig.  355)  perpendicular  'to  the  normal.  This  line  intersects  the  line 
representing  the  vertical  axis  at  a  distance  equal  to  its  unit  length.  Two  points  of  inter- 
section of  the  pyramid  face  with  the  plane  of  the  a  and  c  axes  have  now  been  determined, 
namely  Ic  and  T.  A  line  joining  these  two  points  will  give  the  intersection  of  the  two 
planes  and  the  point  where  it  crosses  the  line  representing  the  a  axis  will  therefore  give 
the  intercept  of  the  pyramid  upon  that  axis.  This  is  also  found  to  be  at  the  unit  length 
and  therefore  the  indices  of  o  must  be  111. 

213.  To  determine,  by  plotting,  the  axial  elements  of  a  monoclinic  crystal,  having  given 
the  gnomonic  projection  of  its  forms.  The  construction  by  which  this  problem  is  solved 
is  shown  in  Fig.  356.  The  poles  of  the  unit  forms  (101),  (Oil),  (001)  and  (111)  are  located 
(in  this  case  tor  pyroxene)  and  the  zonal  lines  drawn.  The  angle  /S  is  complementary  to 


TRICLINIC   SYSTEM 


143 


the  angle  from  the  center  of  the  projection  to  001.  This  can  be  measured  directly  bv 
means  of  the  gnomonic  tangent  scale.  Then  construct  the  triangles  CST  and  XYZ  The 
angles  p  and  *,  and [v  and  .are  measured.  This  can  most  easily  be  done  by  means  of  the 
divided  circle  and  the  fact  that  an  angle  at  the  circumference  of  Lircle  ?s  mL?ureTby  one 
half  its  subtended  arc.  The  following  relations  will  then  yield  the  axial  ratio 


sin  p. 
sin  TT' 


sin  v 
sin  v 


the  explanation  °f  the 


366 


Determination  of  Axial  Elements  of  Pyroxene  from  Gnomonic  Projection 

214.  To  determine,  by  plotting,  the  indices  of  a  face  on  a  monoclinic  crystal,  having 
given  the  position  of  its  pole  upon  the  gnomonic  projection.  There  is  no  essential  differ- 
ence between  the  orthorhombic  and  monoclinic  systems  in  the  determination  of  indices 
from  the  gnomonic  projection.  The  intercepts  of  perpendiculars  from  the  poles  of  the 
faces  upon  th<  front  to  back  and  left  to  right  zonal  lines  running  through  the  pole  of  c(001) 
give  directly  the  first  two  numbers  of  the  indices.  The  gnomonic  projection  of  the  epi- 
dote  crystal  already  given  (Fig.  348)  will  serve  to  illustrate  this  problem. 


VI.   TRICLINIC   SYSTEM 

(Anorthic  System) 

215.   Crystallographic  Axes.  —  The  tridinic  system  includes  all  the  forms 

which  are  referred  to  three  unequal  axes  with  all  their  intersections  oblique. 

When  orientated  in  the  customary  manner  one  axis  has  a  vertical  posi- 


144 


CRYSTALLOGRAPHY 


357 


Triclinic  Axes 


tion  and  is  called  the  c  axis  (cf.  Fig.  357),  a  second  axis  lies  in  the  front-to- 
back  plane,  sloping  down  toward  the  observer,  and  is 
called  the  a  axis.  The  remaining  axis  is  designated  as 
the  b  axis.  Usually  the  a  and  b  axes  are  so  chosen  that 
the  a  axis  is  the  shorter  and,  like  in  the  orthorhombic 
system,  is  sometimes  called  the  brachy-axis.  In  that 
case  the  6  axis  is  longer  and  is  known  as  the  macro- 
axis.  But  this  is  not  invariably  true;  thus  with  rho- 
donite the  ratio  of  a  :b  =  1*073  :  1.  The  angle 
between  the  axes  b  and  c  is  called  a,  that  between  a 
and  c  is  0,  and  that  between  a  and  b  is  7  (Fig.  357). 
It  is  to  be  noted  that  there  is  no  necessary  relation  between  the  values  of 

a,  p,  and  7,  any  one  may  be  greater  or  less  than  90°;  this  is  determined  by 

the  choice  of  the  fundamental  forms. 

1.   NORMAL   CLASS   (31).     AXINITE   TYPE 

(Holohedral  or  Pinacoidal  Class) 

216.  Symmetry.  —  The  normal  class  of  the  triclinic  system  is  character- 
ized by  a  center  of  symmetry,  the  point  of  intersection  of  the  three  axes, 
but  there  is  no  plane  and  no  axis  of  symmetry.  This  symmetry  is  shown  in 
the  accompanying  stereographic  projection  (Fig.  358). 


358 


Symmetry  of  Normal  Class 


Triclim'c  Pinacoids 


217.  Forms.  —  Each  form  of  the  class  includes  two  faces,  parallel  to 
one  another  and  symmetrical  with  reference  to  the  center  of  symmetry. 
This  is  true  as  well  of  the  form  with  the  general  symbol  (hkl)  as  of  one  o£  the 
special  forms,  as,  for  example,  the  a-pinacoid  (100). 

__  Hence,  as  shown  in  the  following  table,  the  four  pjismatic  faces  110,  TlO, 
10,  110  include  two  forms,  namely,  110,  110,  and  110,  110.  The  same  is 
true  of  the  domes._  Further,  _any  eight  corresponding  pyramidal  faces,  as, 
for  example,  111,  111_,_111,_111,  111,  _1_11,  111,  111  belong  to  four  distinct 
forms,  namely,  111,  111;  111,  111;  Hi,  lll;-in,  111,  and  similarly  in 
general. 


TRICLINIC   SYSTEM 

The  various  types  of  forms  are  given  in  the  following  table: 

Indices 

Macropinacoid  or  a-pinacoid (100) 

Brachypinacoid  or  6-pinacoid '  "       (010) 

Base  or  c-pinacoid (001) 

Prisms { >,  W 

I  (MO) 

MacrodomeS (P) 

BrahydomeB (g 


145 


Pyramids 


I  (hkl) 
\(hkl) 

In  the  above  table  it  is  assumed  that  the  axial  ratio  is  such  that  a  <  b.  If  the  oppo- 
site were  true  the  names  brachy-  and  macro-  would  be  interchanged. 

218.  The  explanations  given  under  the  two  preceding  systems  make  it 
unnecessary  to  discuss  in  detail  the  various  forms  individually,  except  as 
illustrated  in  the  case  of  crystals  belonging  to  certain  typical  triclinic  species. 

It  may  be  mentioned,  however,  that  Fig.  359  shows  the  diametral  prism, 
which  is  bounded  by  three  sets  of  unlike  faces,  the  pinacoids  a,  6,  and  c. 
This  is  the  analogue  of  the  cube  of  the  isometric  system,  but  here  the  like 
faces,  edges,  and  solid  angles  include  only  a  given  face,  edge,  and  angle,  and 
that  opposite  to  it. 

219.  Illustrations.  —  A  typical  triclinic  crystal  is  shown  in_Fig.  360  of 
axinite.     Here  a  (100)  is  the  macropinacoid;    m(110)_and  M(110)  the  two 
unit  prisms;  s(201)  a  macrodome,  and  z(lll)  and  r(lll)  two  unit  pyramids. 
The  axial  ratio  is  as  follows: 

a  :  b  :  c  =  0'49  :  1  :  0'48,  a  =  82°  54',  ft  =  91°  52',  7  =  131°  32'. 

Figs.  361,  362  show  two  crystals  of  rhodonite,  a  species  which  is  allied  to 
pyroxene,  and  which  approximates  to  it  in  angle  and  habit.  Here  the  faces 


361 


362 


Rhodonite 

are:    Pina_coids  a(l_00),  6(010),  c(001);    prisms  m(110),  M(lTO);    pyramids 

Further  illustrations  are  given  by  Fig.  363  of  albite  and  Fig.  364  of  anor- 
thite.     The  symbols  of  the  faces,  besides  the  pinacoids  and  the  unit  prisms, 


146 


CRYSTALLOGRAPHY 


are  as  follows:    Fig.  363,  z(101);  _Fig.  364,  prisms /(1 30),  z(130);    domes 

*(207),  t/(201),  e(021),  r(061),   n(021);    pyramids   m(lll),    a(lll),   o(lll), 

363  365 


&0104 


&010 


mllO 


a  100 


MllQ 
Stereographic  Projection  of  an  Axinite  Crystal 

.     In  Fig.  364  of  anorthite  the  similarity  of  the  crystal  to  one  of  ortho- 
clase  is  evident  on  slight  examination  (cf.  Figs.  340,  341),  and  careful  study 


TRICLINIC   SYSTEM 


147 


with  the  measurement  of  angles  shows  that  the  correspondence  is  very  close 
Hence  in  this  case  the  choice  of  the  fundamental  planes  is  readily  made. 

Fig.  365  represents  a  crystal  of   axinite;    Figs.  366  and  367  its  stereo- 
graphic  and  gnomonic  projections. 


367 


M110 


6010-4 


K110 


Gnomonic  Projection  of  an  Axinite  Crystal 


a  100 


368 


2.   ASYMMETRIC  CLASS  (32).    CALCIUM  THIOSULPHATE  TYPE 

(Hemihedral  Class) 

220.   Besides  the  normal  class  of  the  triclinic  system  there  is  another 
possible   class,    possessing    symmetry    neither 
with  respect  to  a  plane,  axis  nor  center;  in  it 
a  given  form  has  one  face  only.     This  class  finds  ^- — *• — .. 

examples  among  a  number  of  artificial  salts. 
One  of  these  is  calcium  thiosulphate 
(CaS2O3.6H2O) ;  as  yet  no  mineral  species  is 
known  to  be  included  here.  This  is  the  most 
general  of  all  the  thirty-two  types  of  forms 
classified  according  to  their  symmetry  and 
comes  first,  therefore,  if  the  classes  are  arranged 
in  order  according  to  the  degree  of  symmetry 
characterizing  them.  This  class  is  one  of  those 
whose  crystals  may  show  circular  polarization. 
This  is  true  of  eleven  of  the  classes  which  have  Symmetry  of  Asymmetric  Class 
been  described  in  the  preceding  pages. 


\ 


148 


CRYSTALLOGRAPHY 


MATHEMATICAL  RELATIONS  OF  THE  TRICLINIC  SYSTEM 

221.  Choice  of  Axes.  —  It  is  obvious,  from  what  has  been  said  as  to  the  symmetry  of 
this  system,  that  any  three  faces  of  a  triclinic  crystal  may  be  chosen  as  the  pinacoids,  or 
the  faces  which  fix  the  position  of  the  axial  planes  and  the  directions  of  the  axes;  moreover, 
there  is  a  like  liberty  in  the  choice  of  the  unit  prisms,  domes  or  pyramids  which  further  fix 
the  lengths  of  the  axes. 

When  the  crystal  in  hand  is  allied  in  form  or  composition  to  other  species,  whether  of 
the  same  or  different  systems,  this  fact  simplifies  the  problem  and  makes  the  choice  of  the 
fundamental  forms  easy.  This  is  well  illustrated,  as  already  noted,  by  the  triclinic  feldspars 
(e.g.,  albite  and  anorthite,  Figs.  363,  364)  which  are  near  in  angle  to  the  allied  monoclinic 
species  orthoclase.  Rhodonite  (Figs.  361,  362),  the  triclinic  member  of  the  pyroxene 
group,  is  another  good  example. 

In  other  cases,  where  no  such  relationship  exists,  and  where  varied  habit  makes  different 
orientations  plausible,  there  is  but  little  to  guide  the  choice.  This  is  illustrated  in  the  case 
of  axinite  (Fig.  360),  where  at  least  ten  distinct  positions  have  been  assumed  by  different 
authors. 

222.  Axial  and  Angular  Elements.  —  The  axial  elements  of  a  triclinic  crystal  are : 
(1)  the  axial  ratio,  which  expresses  the  lengths  of  the  axes  a  and  c  in  terms  of  the  third 
axis,  6;  and  (2)  the  angles  between  the  axes  a,  3,  7  (Fig.  357).     There  are  here  five  quanti- 
ties to  be  determined  which  obviously  require  the  measurement  of  five  independent  angles 
between  the  faces. 

The  angular  elements  are  usually  taken  as  the  angles  between  the  pinacoids  and,  in 
addition,  those  between  each  pinacoid  and  the  unit  face  lying  in  the  zone  of  the  other  pina- 
coids; that  is, 

ac,     100  A  001,     be,    010  A  001; 
001  A  101,  001  A  Oil; 


100  A  010, 

also  am     100  A  110, 

or,  instead,  any  one  or  all  of  these, 
aM,     100  A  110, 


001  A  101, 


001  A  Oil. 


Of  these  six  angles  taken,  one  is  determined  when  the  others  are  known. 

223.  The  mathematical  relations  existing  between  the  axial  angles  and  axial  ratio,  on  the 
one  hand,  and  the  angles  between  the  faces  on  the  other,  admit  of  being  drawn  out  with 
great  completeness,  but  they  are  necessarily  complex  and  in  general  have  little  practical 
value.     In  fact,  most  of  the  problems  likely  to  arise  can  be  solved  by  means  of  the  triangles 
of  the  spherical  projection,  together  with  the  cotangent  formula  connecting  four  planes  in 
the  same  zone  (Art.  49,  p.  49);  this  will  often  be  laborious  and  may  require  some  ingenuity 
but  in  general  involves  no  serious  difficulty.     In  connection  with  the  use  of  the  cotangent 
formula,  it  is  to  be  noted  that  in  certain  commonly  occurring  cases  its  form  is  much  simpli- 
fied; some  of  these  have  already  been  explained  under  the  monoclinic  system  (Art.  210). 
The  formulas  given  there  are  of  course  equally  applicable  here. 

224.  The  first  problem  may  be  to  find  the  axial  elements  from  measured  angles.     Since 
these  elements  include  five  unknown  quantities,  viz.,  the  three  axial  angles  a   /3    7  and 
the  lengths  of  the  axes  a  and  c  in  terms  of  b,  five  measured  angles  are  required,  as  already 
stated. 

Fig.  369  represents  the  crystallographic  axes  of  the  triclinic  mineral  rhodonite  The 
positive  ends  of  the  three  axes  are  joined  by  lines  forming  three  triangles  the  angles  of 
which  are  very  important.  In  the  triangle,  for  instance,  which  has  the  b  and  c  axes  for 

two  of  its  sides  since  the  length 
of  the  b  axis  is  taken  as  I'O,  it 
is  only  necessary  to  know 
the  angle  a  and  either  p  or  ?r 
in  order  to  determine  the  length 
of  the  c  axis.  In  the  triangle 
that  has  the  a  and  b  axes  for 
two  of  its  sides  it  is  necessary 
to  know  the  value  of  7  and 
either  a  or  T  in  order  to  deter- 
mine the  length  of  the  a  axis. 
And  lastly  in  the  triangle 
formed  between  the  a  and  c 
axes,  if  the  length  of  either  of 

of  the  other  can  be  determined  from  the  angle  „  and  either'f orT  £  &S*?  ^af  a 


TRICLINIC   SYSTEM 


149 


aioo 


^*k    °i{   rhodonite   ?ho*jD£  the,  forms  o(100),  6(010),  c(001)    and    p(lll),   see   Fie 
370,  has  bee^me^ural  and^e  poles  of  the  faces  plotted  in  the  stereogr^hic'projectio^ 

great    circles    which   connect     these  371 

poles  are  the  same  as  those  shown  100 

in    the    triangles    built     upon    the 

crystallographic  axes,  Fig.  369.    With 

the  angles  between  the  different  crys- 
tal faces  known  by  measurement,  it 

is  easy,  by  the  formulas  of  spherical 

trigonometry,  to  calculate  the  value 

of  these  other  angles  and  from  them 

obtain  the  axial  ratio. 

That  the  angles  shown  on  the  stere- 
ographic   projection,   Fig.    371,    are 

identical  with  those  in  Fig.  369  may 

be  proved  as  follows.     Let  Fig.  372 

represent    a     vertical     section     cut 

through  the   spherical  projection  of 

rhodonite    in    such    a    way    as    to 

include  the  6  and  c  crystallographic 

axes.     The  triangle,  which  has  these 

axes   as    two    sides    and   the   three 

angles  a,  -K  and  p,  lies  therefore  in 

the  plane  of  the  figure.     The  nor- 
mals   to    all    faces    parallel    to    the 

c  axis,  i.e.  the  prism  zone,  would  lie  in  a  plane  at  right  angles  to  that  axis.     This  plane 

would  intersect  the  sphere  of  the  spher- 
ical projection  in  a  great  circle  which  is 
represented  on  the  stereographic  pro- 
jection, Fig.  371,  by  the  divided  circle. 
On  Fig.  372  this  great  circle  would 
appear  in  orthographic  projection  as  the 
line  C-C'  lying  at  right  angles  to  the  c 
axis.  In  the  same  way  all  faces  lying 
parallel  to  the  b  axis,  i.e.  the  zone  (100)- 
(101)- (001),  would  have  their  normals 
in  a  plane  which  would  be  foreshortened 
to  the  line  B-B'  in  Fig.  372.  Since 
the  lines  C-C'  and  B-B'  are  at  right 
angles  respectively  to  the  c  and  b  axes 
the  angle  between  them  must  equal  the 
axial  angle,  a.  This  same  angle  will 
appear  therefore  on  the  stereographic 
projection,  Fig.  371,  between  the  great 
circles  of  the  two  zones,  the  faces  of 
which  are  parallel  respectively  to  the  c 
and  b  axes.  Further  the  normals  to  all 
faces  which  intersect  the  b  and  c  axes  at 
their  unit  lengths  would  lie  in  a  plane  at 
right  angles  to  the  line  b-c,  Fig.  372. 

This  plane  would  appear  in  orthographic  projection  as  the  line  P-P'.     On  the  stereographic 


372 


projection,  Fig.  371,  this  would  be  represented 
as  the  zonal  circle  passing  through  (100),  (111), 
(Oil),  (100).  The  angle  between  B-B'  and  P-P' 
will  by  construction  equalV  and  that  between  C-C' 
and  P-P'  will  equal  p.  These  same  angles  will  appear 
therefore  in  the  stereographic  projection  between  the 
corresponding  zone  circles.  In  the  same  way  the 
identity  of  the  angles  j,  a,  T,  0,  n  and  v  in  Figs.  369 
and  371  can  be  proved. 

With  the  necessary  number  of  these  angles  given 
the  formulas  required  for  the  calculation  of  the 
axial  lengths  are  given  below.  The  angles  T',  a',  t>', 
//,  if'  and  p'  are  the  corresponding  angles  to  T,  o-,  etc.. 
in  the  adjacent  quadrants,  see  Fig.  373. 


373 


150  CRYSTALLOGRAPHY 

sin  T  _  sin  T'  _  a    sin  v  _  sin  v'  _  c    sin  -w  _  sin  TT'  _  c 
sin  <r  ~~  sin  a'  ~  b  '  sin  M  ~  sin  M'      « '  sin  p      sin  p'      b  ' 

If  the  angles  given  are  between  the  three  pinacoids  and  the  pyramid  hkl  (not  the  unit  form) 
the  relations  are  similar.  That  is,  if  for  the  face  hkl  the  corresponding  angles  be  represented 
by  TO,  ffo,  etc.,  where  TO,  <TO  are  the  angles  between  the  zone  circles  100,  001  and  100,  010 
respectively  and  the  zone  circle  001,  hkO,  these  relations  may  be  expressed  in  the  general 
form 

sin  TO  _  sin  TO' a_  _  k    a 

sin  o-o  ~  sin  o-0 '      h,        h    b' 

sin  vn      sin  VQ         c        he 

—  <> 


sin  MO      sin  MO'       I  la 

htt 

sin  TTO  _  sin  TH/  _     c  _  k    c 

sin  PO      sin  p0'       I,  I     b 


Thus  for  the  face  321  the  formulas  become 

sin  TO  _  a^  _  2_a    sin  v0  _  3c    sin  XQ  _  2c  ^ 
sin  (TO      |6      36    sin  MO       a     sin  po       b 
It  is  also  to  be  noted  that 

a  =  180°  -  A,        ft  =  180°  -  B,        7  =  180°  -  C, 

where  A,  B,  C  are  the  angles  in  the  pinacoidal  spherical  triangle  IOO'010'OOI  at  these 
poles  respectively.    That   is, 

A  =  *•  +  P  =  TO  +  PO  =  (180°  -  a); 
B  =  ^+M  =  ^  +  /io=  (180° -0); 

C  =  T-f-<r  =  T0  +  <r0=  (180°  -  7). 

Also 

180°  -  A  =  TT'  +  P'  =  TTO'  4-  PO'  =  «. 

Hence,  having  given,  by  measurement  or  calculation,  the  angles  between  the  faces 
ab(100  A  010),  ac(100  A  001)  and  6c(010  A  001),  which  are  the  sides  of  this  triangle,  the 
angles  A,  B,  C  are  calculated  and  their  supplements  are  the  axial  angles  a,  /3,  7  respectively. 
Still  another  series  of  equations  are  those  below,  which  give  the  relations  of  the  angles 
/*,  v,  p,  etc.,  to  the  axes  and  axial  angles.  By  means  of  them,  with  the  sine  formulas  given 
above,  the  angular  elements  (and  other  angles)  can  be  calculated  from  the  axial  elements. 

a  sin  )8  c  sin  8 

tan  fj.  —  — ; • ;    tan  v  =  —  —  . 

c  +  a  cos  /3  a  +  c  cos  8 

b  sin  a  c  sin  a 

tan  p  =  ,    ,    ,        -  ;    tan 


6  cos  a  '  b  +  c  cos  a  ' 

a  sin  7  6  sin  7 

tan  T  =  r—      — '—  ;    tan  a  = 


b  +  a  cos  7  '  a  +  b  cos  7  ' 

These  equations  apply  when  M  +  v,  etc.,  is  less  than  90°;   if  their  sum  is  greater  than 
90°  the  sign  in  the  denominator  is  negative. 

207.   The  following  equations  are  also  often  useful. 

tan  a  =  2  sin  P  sm  P'  =  2  sin  ?r  sin  w' 

sin  (p  -  p')   **  sin  (TT  -  TT')  ' 
,       ,,  _  2  sin  fj.  sin  //  _  2  sin  v  sin  v' 

sin  (n  —  n'}        sin  (v  —  v') 

2  sin  T  sin  T'      2  sin  a  sin  <r' 


tan 


sin  (T  -  T')        sin  (<r  -  a')  ' 
Also, 

a  +  7r+p=/3+M  +  y  =  7+r  +  (r  =  180°. 

The  calculation,  from  the  angular  elements  or  from  the  assumed  fundamental  measured 
angles,  either  (1)  of  the  angular  position  of  any  face  whose  symbol  is  given,  or  (2)  of  the 


TRICLINIC   SYSTEM 


151 


a(100) 


symbol  of  an  unknown  face  for  which  measured  angles  are  at  hand,  requires  no  further 

explanation.     The  cotangent  formula  is  all  that  is  needed  in  a  single  zone,  and  the  solution 

of  spherical  triangles  on  the  projection  (with  the  use  of  the  sine  formulas)  will  suffice  in 

addition  in  all  ordinary  cases. 

225.   To  determine,  by  plotting,  the  axial  elements  of  a  triclinic  crystal,  having  given 

the  stereographic  projection  of  its  forms.     In  order  to  solve  this  problem  it  is  necessary 

to  have  given  the  position   of  the  poles  of 

the  unit  forms  (100),  (010),  (001),  (111)  or 

to  be  able   to   locate    them    by  means   of 

their  zonal  relations.      Through  these  poles 

the    various    zonal    circles    are    drawn   as 

shown  in  the  case  of  rhodonite,  Fig.  371. 

The  angles  a,  /3,  7,  TT,  p,  etc.,  are  then  given 

upon  the  projection.      These  angles  can  be 

measured  as  described    in  Art.  41,  p.  39. 

Taking  next  a  certain  line  as  representing 

the  unit  length  of  the  b  axis  and  knowing 

the  angles  a,  TT   and   p  the    triangle  that 

includes  the  b  and  c  axes,  see  Fig.  369,  can 

be  drawn  to  scale   and  the  unit  length  of 

the  c  axis  determined.     In  a  similar  way 

the  length  of  the  a  axis  can  be  found. 
226.  To  determine,  by  plotting,  the  indices 

of  a  face  upon  a  triclinic   crystal,  having 

given  the  position  of  its  pole  in  the  stereo- 
graphic  projection  and  the  axial  elements 

of  the  mineral.     To  illustrate  this  problem 

a  possible  pyramid  face  on  rhodonite  will  be  used.     Its  pole  is  located  in  the  stereograp- 
hic projection  at  x,  Fig.  374.     The  position  of  the  poles  of  the  faces  a(100)  and  6(010) 

must  also  be  known.     The  directions  of  the  intersections  of  the  planes  of  the  a-c  and 

b-c  axes  with  the  plane  of  the 
projection  can  then  be  drawn. 
These  lines  will  represent  the 
horizontal  projections  of  the  a 
and  b  crystallographic  axes. 
A  radial  line  is  then  drawn  from 
the  center  of  the  projection,  O, 
through  x.  Another  line, 
A-P-B,  is  drawn  perpendicular 
to  this  line  at  any  convenient 
distance  from  the  center,  O. 
The  line  A-P-B  will  represent 
the  direction  of  intersection  of 
the  face  x  with  the  horizontal 
plane  of  the  projection.  The 
intercept  that  the  face  will 
make  upon  the  vertical  axis  can 
be  found  by  the  construction  of 
a  right  triangle  with  O-P  as  its 
base,  a  line  representing  the  c 
axis  as  its  vertical  side  and  the 
angle  between  O-x  as  the  angle 
between  the  base  and  the  hy- 
pothenuse,  see  Fig.  375.  Under 
the  assumed  conditions  the  face 
will  intersect  the  c  axis  at  a  dis- 
tance of  T93,  the  radius  of  the 
circle  in  the  figure  being 
TO.  The  face  will  also  pass 

through    the  points  A   and    B    on  the    horizontal    projections   of   the  a  and  6  axes. 

With  the  known  angles  0  and  a  it  is  possible  to  construct  the  a  and  b  axes  with  their  proper 

angular  relations  to  the  c  axis.     The  intercepts  of  the  face  upon  these  two  axes  will  be 

given  by  the  extension  of  the  lines  from  the  point  T93  on  the  c  axis  to  the  points  A  and  B. 

In  this  way  the  intercepts  of  the  face  upon  the  three  axes  were  obtained  as  1'lla,  1'556, 


375 

1-93 /C  Intercept  upon  O 


152 


CRYSTALLOGRAPHY 


;.     By  dividing  these  numbers  by  1'55  we  get  the  intercepts  expressed  in  terms  of  the 
h  of  the  6  axis,  considering  that  as  1*0.     The  intercepts  then  become  0'71a,  16,  l'24c. 


l'93c. 
length 

When  these  are  compared  with  the  axial  ratio  of  rhodonite,  a  :  b  :  c  =  T114  :  1  :  0'986, 
the  parameters  of  the  face  are  found  to  be  fa,  16,  2c.  The  indices  of  x  are  therefore  321. 
227.  To  determine,  by  plotting,  the  axial  elements  of  a  triclinic  crystal  having  given  the 
gnomonic  projection  of  its  forms.  To  illustrate  this  problem  it  is  assumed  that  the  posi- 
tions of  the  poles  of  the  faces,  (100),  (010),  (001),  (101),  (Oil)  and  (111)  On  rhodonite  are 
known,  see  Fig.  376.  If  this  figure  is  compared  with  the  stereographic  projection  of  the 
same  forms  given  in  Fig.  371,  it  will  be  seen  that  the  angle  between  the  zones  (100)-(101)- 
(001)  and  (100)-(111)-(011)  is  equal  to  TT,  that  between  the  zones  (100)-(111)-(011)  and 
(100)-(110)-(010)  is  equal  to  p,  between  (010)-(011)-(001)  and  (010)-(111)-(101)  is  equal 
to  v  and  between  (010)-(111)-(101)  and  (010)-(110)-(100)  is  equal  to  M-  The  method 
-by  which  the  angles  between  these  various  zones  may  be  measured  was  explained  in  Art. 
^2,  p.  43,  and  is  illustrated  by  the  construction  of  Fig.  376.  From  these  angles  triangles 
can  be  readily  constructed  to  give  the  lengths  of  the  a  and  c  axes  in  terms  of  the  6  axis, 
with  its  length  taken  as  equal  to  1  '0. 


228.  To  determine,  by  plotting,  the  indices  of  the  forms  of  a  triclinic  crystal,  having 
given  the  position  of  other  poles  upon  the  gnomonic  projection.     The  method  for  the  solu- 
tion of  this  problem  is  similar  to  that  already  described  under  the  previous  systems.     The 
difference  lies  in  the  fact  that  the  lines  of  reference  upon  which  are  plotted  the  intercepts 
of  the  lines  drawn  to  them  from  the  poles  of  the  faces  make  oblique  angles  with  each  other 
These  reference  lines  are  taken  as  the  zonal  lines  (OOl)-(lOl)  and  (OOl)-(Oll)  and  the 
intercepts  from  which  the  indices  are  determined  are  measured  from  the  pole  of  (001)      A 
study  of  the  gnomonic  projection  of  axinite,  Fig.  367,  will  illustrate  this  problem. 

MEASUREMENT  OF  THE  ANGLES  OF  CRYSTALS 

229.  Contact-Goniometers.  —  The   interfacial   angles   of   crystals   are 
measured  by  means  of  instruments  which  are  called  goniometers. 


MEASUREMENT  OF  THE   ANGLES   OF   CRYSTALS 


153 


COntact"  or  hand-goniometer  one  form  of  which  is 

This  contact-goniometer  consists  of  a  card  on  which  is  printed  a  semi- 
circular arc  graduated  to  half  degrees  at  the  center  of  which  is  fastened  a 
celluloid  arm  which  may  be  turned  to  any  desired  position.  The  method  of 
use  of  the  goniometer  is  illustrated  in  Fig.  377.  The  bottom  of  the  card  and 


•77 


Penfield  Contact  Goniometer,  Model  B 

the  blackened  end  of  the  celluloid  arm  are  brought  in  as  accurate  contact  as 
possible  with  the  two  crystal  faces,  the  angle  between  which  is  desired.  Care 
must  be  taken  to  see  that  the  plane  of  the  goniometer  is  at  right  angles  to  the 
edge  of  intersection  between  the  two  faces.  Another  model  of  the  contact- 
goniometer,  Fig.  378,  has  two  arms  swiveled  together  and  separate  from  the 
graduated  arc.  The  crystal  angle  is  obtained  by  means  of  the  arms  and  then 
the  angle  between  them  measured  by  placing  them  upon  the  graduated  arc. 
This  latter  type  is  employed  in  cases  where  the  crystal  lies  in  such  a  position 
as  to  prevent  the  use  of  the  former.* 


*  These  simple  types  of  contact-goniometers  were  devised  by  S  L.  Penfield  and  can  be 
obtained  by  addressing  the  Mineralogical  Laboratory  of  the  Sheffield  Scientific  School  of 
Yale  University,  New  Haven,  Ct. 


154 


CRYSTALLOGRAPHY 


The  contact-goniometer  is  useful  in  the  case  of  large  crystals  and  those 
whose  faces  are  not  well  polished;   the  measurements  with  it,  however,  are 


378 


379 


Penfield  Contact  Goniometer,  Model  A 

seldom  accurate  within  a  quarter  of  a  degree.  In  the  finest  specimens  of 
crystals,  where  the  faces  are  smooth  and  lustrous,  results  far  more  accurate 

may  be  obtained  by  means  of  a  different 
instrument,  called  the  reflecting  goni- 
ometer. 

230.  Reflecting  Goniometer.  -  This 
type  of  instrument  was  devised  by 
Wollaston  in  1809.  It  has  undergone  exten- 
sive modifications  and  improvements  since 
that  time.  Only  the  perfected  forms  that 
are  in  common  use  to-day  will  be 
described. 

The  principle  underlying  the  construction 
of  the  reflecting  goniometer  will  be 
understood  by  reference  to  the  figure  (Fig. 
379),  which  represents  a  section  of  a 

crystal,  whose  angle,  abc,  between  the  faces  ab,  be,  is  required.  Let  the 
eye  be  placed  at  P  and  the  point  M  be  a  source  of  light.  The  eye  at  P, 
looking  at  the  face  of  the  crystal,  be,  will  observe  a  reflected  image  of  m, 
in  the  direction  of  Pn.  The  crystal  may  now  be  so  changed  in  its  position 
that  the  same  image  is  seen  reflected  by  the  next  face  and  in  the  same  direction, 
fn.  lo  effect  this,  the  crystal  must  be  turned  around,  until  abd  has  the 


MEASUREMENT   OF   THE   ANGLES   OF   CRYSTALS 


155 


present  direction  of  be.  The  angle  dbc  measures,  therefore,  the  number  of 
degrees  through  which  the  crystal  must  be  turned;  it  may  be  measured  by 
attaching  the  crystal  to  a  graduated  circle,  which  turns  with  the  crystal. 
This  angle  is  the  supplement  of  the  interior  angle  between  the  two  faces,  or 
in  other  words  is  the  normal  angle,  or  angle  between  the  two  poles  (see  Art. 
43,  p.  44).  The  reflecting  goniometer  hence  gives  directly  the  angle  needed 
on  the  system  of  Miller  here  followed. 

231.  Horizontal  Goniometer.  —  A  form  of  reflecting  goniometer  well 
adapted  for  accurate  measurements  is  shown  in  Fig.  380.  The  particular 
form  of  instrument  here  figured  *  is  made  by  Fuess. 


One-circle  Reflection  Goniometer 

The  instrument  stands  on  a  tripod  with  leveling  screws.  The  central 
axis,  o,  has  within  it  a  hollow  axis,  6,  with  which  the  plate,  d,  turns,  carrying 
the  verniers  and  also  the  observing  telescope,  the  upright  support  of  which  is 
shown  at  B.  Within  b  is  a  second  hollow  axis,  e,  which  carries  the  graduated 
circle,  /,  above,  and  which  is  turned  by  the  screw-head,  0;  the  tangent  screw, 
a,  serves  as  a  fine  adjustment  for  the  observing  telescope,  B,  the  screw,  c,  being 
for  this  purpose  raised  so  as  to  bind  b  and  e  together.  The  tangent  screw,  0, 
is  a  fine  adjustment  for  the  graduated  circle.  Again,  within  e  is  the  third 
axis,  h,  turned  by  the  screw-head,  i,  and  within  h  is  the  central  rod,  which 
carries  the  support  for  the  crystal,  with  the  adjusting  and  centering  con- 
trivances mentioned  below.  This  rod  can  be  raised  or  lowered  by  the  screw,  fc, 


The  figure  here  used  is  from  the  catalogue  of  Fuess. 


156  CRYSTALLOGRAPHY 

so  as  to  bring  the  crystal  to  the  proper  height  —  that  is,  up  to  the  axis  of  the 
telescope;  when  this  has  been  accomplished,  the  clamp  at  p,  turned  by  a 
set-key,  binds  s  to  the  axis,  h.  The  movement  of  h  can  take  place  independ- 
ently of  g,  but  after  the  crystal  is  ready  for  measurement  these  two  axes  are 
bound  together  by  the  set-screw,  /.  The  signal  telescope  is  supported  at  C, 
firmly  attached  to  one  of  the  legs  of  the  tripod.  The  crystal  is  mounted  on 
the  plate,  u,  with  wax,  the  plate  is  clamped  by  the  screw,  v.  The  centering 
apparatus  consists  of  two  slides  at  right  angles  to  each  other  (one  of  these  is 
shown  in  the  figure)  and  the  screw,  a,  which  works  it;  the  end  of  the  other 
corresponding  screw  is  seen  at  a'.  The  adjusting  arrangement  consists  of 
two  cylindrical  sections,  one  of  them,  r,  shown  in  the  figure,  the  other  at  rf; 
the  cylinders  have  a  common  center.  The  circle  on  /  is  graduated  to  degrees 
and  quarter  degrees,  and  the  vernier  gives  the  readings  to  30". 

A  brilliant  source  of  light  is  placed  behind  the  collimator  tube  which  is 
at  the  top  of  the  support  C.  Openings  of  various  size  and  character  are  pro- 
vided at  the  rear  end  of  this  tube  in  order  to  modify  the  size  and  shape  of  the 
beam  of  light  that  is  to  be  reflected  from  the  crystal  faces.  The  most  com- 
monly used  opening  is  one  made  by  placing  two  circular  disks  nearly  in  con- 
tact with  each  other  leaving  between  them  an  hour-glass  shaped  figure.  The 
telescope  tube  L  is  provided  with  several  removable  telescopes  with  lenses 
which  have  different  angular  breadths  and  magnifying  powers  and  hence  are 
suitable  for  observing  faces  varying  in  size  and  degree  of  polish.  At  the  front 
of  the  tube  L  there  is  a  lens  which  is  so  pivoted  that  it  may  be  thrown  into  or 
out  of  the  axis  of  the  telescope.  When  this  lens  lies  in  the  axis  of  the  tube  it 
converts  the  telescope  into  a  low-power  microscope  with  which  the  crystal 
may  be  observed.  Without  this  lens  the  telescope  has  a  long-distance  focus 
and  only  the  beam  of  light  reflected  from  the  crystal  face  can  be  seen. 

The  method  of  use  of  the  instrument  is  briefly  as  follows.  The  little  plate  u  is  removed 
and  upon  it  is  fastened  by  means  of  some  wax  the  crystal  to  be  measured.  The  faces  of 
the  zone  that  is  to  be  measured  should  be  placed  as  nearly  as  possible  vertical  to  the  sur- 
face of  this  plate.  It  will  usually  facilitate  the  subsequent  adjustment  if  a  prominent  face 
in  this  zone  be  placed  so  that  it  is  parallel  to  one  of  the  edges  of  the  plate  u.  This  plate 
with  the  attached  crystal  is  then  fastened  in  place  by  the  screw  v.  During  the  preliminary 
adjustments  of  the  crystal  the  small  lens  in  front  of  the  tube  L  is  placed  in  its  axis  and  the 
crystal  observed  through  the  microscope  thus  formed.  It  is  usually  better  also  to  make 
these  first  adjustments  outside  the  dark  room  in  daylight.  By  means  of  the  screw-head  k 
the  central  post  is  raised  or  lowered  until  the  center  of  the  crystal  lies  in  the  plane  of  the 
telescope.  Next  by  means  of  the  two  sliding  tables  controlled  by  the  screw-heads  a  and  a' 
the  crystal  is  adjusted  so  that  the  edge  over  which  the  angle  is  to  be  measured  coincides 
with  the  axis  of  the  instrument.  This  adjustment  is  most  easily  accomplished  by  turning 
the  central  post  of  the  instrument  until  one  of  these  sliding  plates  lies  at  right  angles  to 
the  telescope  and  then  by  turning  its  screw-head  bring  the  intersection  in  question  to  coin- 
cide with  the  vertical  cross-hair  of  the  telescope  tube.  Then  turn  the  post  until  the  other 
plate  lies  at  right  angles  to  the  telescope  and  make  a  similar  adjustment.  Then  in  a  similar 
manner  by  means  of  the  tipping  screws  x  and  y  bring  the  intersection  between  the  faces 
to  a  position  parallel  with  the  vertical  cross-hair  of  the  telescope.  By  a  combination  of 
these  adjustments  this  edge  should  be  made  to  coincide  with  the  vertical  cross-hair  and  to 
remain  stationary  while  the  crystal  is  revolved  upon  the  central  post  of  the  instrument. 
Next  the  instrument  is  taken  into  the  dark  room  and  a  light  placed  behind  the  collimator 
tube,  and  the  crystal  turned  until  one  of  the  faces  is  seen  through  the  tube  L  to  be  brightly 
illuminated.  Then  the  little  lens  in  the  front  of  this  tube  is  raised  and  the  reflection  of  the 
beam  of  light,  or  signal  as  it  is  called,  should  lie  in  the  field.  If  the  preliminary  adjust- 
ments were  accurate  the  horizontal  cross-hair  will  bisect  this  signal.  In  the  majority  of 
cases,  however,  further  slight  adjustments  will  be  necessary.  Before  the  angles  between 
the  faces  can  be  measured  their  various  signals  must  all  be  bisected  by  the  horizontal  cross- 
hair. When  these  conditions  are  fulfilled  each  signal  in  turn  is  brought  into  place  so  that 


MEASUREMENT  OF   THE   ANGLES   OF   CRYSTALS 


157 


it  is  bisected  also  by  the  vertical  cross-hair  and  its  angular  position  read  by  means  of  the 
graduated  scale  and  vernier.  The  difference  between  the  angles  for  two  LeTgfves  the 
normal  angle  between  them.  In  making  these  readings  care  must  be  taken  that  the  plate 
on  which  the  graduated  circle  is  engraved  is  turned  with  the  central  post.  In  order  to 
do  this  only  the  screw-head  g  must  be  used  unless,  as  is  wise,  the  two  screw-heads  i  and  a 
have  been  previously  clamped  together  by  means  of  I.  For  the  accurate  adjustment  of  the 
signals  on  the  vertical  cross-hair  the  tangent  screw  /3  is  used.  In  making  a  record  of  the 
angles  measured  it  is  important  to  note  accurately  the  face  from  which  each  signal  is  derived 
a?i th®  character  of  the  signal.  It  is  frequently  helpful  to  make  a  sketch  of  the  outlines 
of  the  different  faces  and  number  or  letter  them. 

232.   Theodolite-Goniometer.  —  A  form  of  goniometer  *  having  many 
practical  advantages  and  at  present  in  wide  use  has  two  independent  circles 

381 


Two-circle  Reflection  Goniometer 

and  is  commonly  known  as  the  two-circle  goniometer.  It  is  used  in  a  manner 
analagous  to  that  of  the  ordinary  theodolite.  Instruments  of  this  type  were 
devised  independently  by  Fedorow,  Czapski  and  Goldschmidt.  Other 
models  have  been  described  since.  In  addition  to  the  usual  graduated  hori- 
zontal circle  of  Fig.  380,  and  the  accompanying  telescope  and  collimator,  a 
second  graduated  circle  is  added  which  revolves  in  a  plane  at  right  angles  to 
the  first.  Fig.  381,  after  Goldschmidt,  gives  a  cross-sectional  view  of  one  of 

*  Fedorow,  Universal  or  Theodolit-Goniometer,  Zs.  Kryst.,  21.  574,  1893;  22,  229, 
1893;  Czapski,  Zeitschr.  f.  Instrumentenkunde,  1,  1893;  Goldschmidt.  Zs.  Kryst.,  21,  210, 
1892;  24,  610,  1895;  25,  321,  538,  1896;  29,  333,  589,  1898.  On  the  method  of  Gold- 
schmidt, see  Palache,  Am.  J.  Sc.,  2,  279,  1896;  Amer.  Mineral,  6,  No.  2,  et  seq.,  1920.  A 
simplified  form  of  the  theodolite-goniometer  is  described  by  Stober,  Zs.  Kryst.,  29,  25, 
1897;  64,442. 


158 


CRYSTALLOGRAPHY 


the  earlier  machines  devised  by  him.     It  will  serve  to  illustrate  the  essential 
features  of  the  instrument. 

The  crystal  to  be  measured  is  attached  at  the  end  of  the  axis  (h)  of  the 
vertical  circle  and  so  adjusted  by  means  of  suitable  centering  and  tipping 
devices  that  a  given  plane,  called  the  polar  plane,  is  normal  to  this  axis  and 
lies  directly  over  the  axis  of  the  horizontal  circle.  In  using  the  instrument, 
instead  of  directly  measuring  the  interfacial  angles  of  the  crystal,  the  position 
of  each  face  is  determined  independently  of  the  others  by  the  measurement  of 
its  angular  co-ordinates,  or  what  might  be  called  its  latitude  and  longitude. 
These  co-ordinates  are  the  angles  (<f>  and  p  of  Goldschmidt)  measured,  respec- 
tively, in  the  vertical  and  horizontal  circles  from  an  assumed  pole  and  merid- 
ian, which  are  fixed,  in  most  cases,  by  the  symmetry  of  the  crystal.  In  prac- 
tice the  crystal  is  usually  so  mounted  that  its  prismatic  zone  is  perpendicular 
to  the  vertical  circle.  A  plane  at  right  angles  to  this  zone,  i.e.,  the  basal  plane 
in  the  first  four  systems,  is  known  as  the  polar  plane  and  its  position  when 
reflecting  the  signal  into  the  telescope  establishes  the  zero  position  for  the 
horizontal  circle.  The  position  of  a  pinacoid,  usually  the  010  plane,  in  the 
prism  zone  establishes  the  zero  position  for  the  vertical  circle.  For  example, 
with  an  orthorhombic  crystal,  for  the  pyramid  111,  the  angle  <f>  (measured  on 
the  vertical  circle)  is  equal  to  010  A  110  and  p  (measured  on  the  horizontal 
circle)  is  equal  to  001  A  111. 

Goldschmidt  has  shown  that  this  instrument  is  directly  applicable  to  the 

system  of  indices  and  methods  of 
calculation  and  projection  adopted 
by  him,  which  admit  of  the  deducing 
of  the  elements  and  symbols  of  a 
given  crystal  with  a  minimum  of 
labor  and  calculation.*  Fedorow 
has  also  shown  that  this  in- 
strument, with  the  addition  of  the 
appliances  devised  by  him,  can  be 
most  conveniently  used  in  the  crys- 
tallographic  and  optical  study  of 
crystals. 

The  following  hints  as  to  the  methods  of 
using  this  instrument  may  prove  helpful. 
The  telescope  and  colhmator  tube 
are  placed  at  some  convenient  angle 
to  each  other  (usually  about  70°) 
and  then  clamped  in  position.  The 
next  step  is  to  find  the  polar  posi- 
tion of  the  horizontal  circle,  i.e.,  the  position  at  which  a  crystal  plane  lying  at  right  angles 
to  the  axis  of  the  vertical  circle  will  throw  the  reflected  beam  of  light  on  to  the  cross-hairs 
of  the  telescope.  Obviously  the  plane  under  these  conditions  must  be  normal  to  the 
bisector  of  the  angle  between  the  axes  of  the  collimator  and  telescope,  the  line  B-P  Fig 
382.  The  method  by  which  this  polar  position  is  found  is  as  follows:  Some  reflecting  sur- 
face is  mounted  upon  the  end  of  the  post  h,  Figs.  381,  382,  making  some  small  inclined 
angle  to  the  plane  normal  to  that  post.  Then  by  turning  the  instrument  in  both  the  hori- 

*  See  Goldschmidt's  Krystallographische  Winkeltabellen  (432  pp.,  Berlin,  1897). 
9Q  ™TT«a«e  a-?£ les  rec*ulre(i  bT  his,  gystem  f<*  all  known  species.  See  also  Zs.  Kryst., 
wnrV  </  -11  The.same  author's  atlas  der  Krystallformen,  1913  et  seq.,  is  a  monumental 
work  giving  all  previously  published  crystal  figures  together  with  a  discussion  of  the  forms 
ooserveu  upon  tnem. 


MEASUREMENT   OF   THE    ANGLES   OF   CRYSTALS 


159 


zpntal  and  vertical  planes  this  surface  is  brought  into  the  proper  position  to  reflect  the 
signal  into  the  telescope,  see  position  I,  Fig.  382.  The  horizontal  angle  of  this  position  is 
noted.  Then  the  vertical  circle  is  turned  through  an  angle  of  180°.  This  brings  the 
reflecting  surface  into  the  position  indicated  by  the  dotted  lines  in  the  figure.  In  order 
to  again  bring  this  surface  back  to  its  reflecting  position  the  vertical  circle  with  the  post 
h  must  be  moved  in  the  horizontal  plane  until  the  position  II  is  reached.  The  horizontal 
reading  of  this  position  is  also  noted.  The  angle  midway  between  these  two  readings  is 
the  polar  position  desired.  That  is,  when  the  post  h  lies  in  the  direction  of  the  broken 
line  P-B  a  plane  normal  to  its  axis  would  reflect  a  beam  of  light  from  the  collimator  into 
the  telescope.  This  position  constitutes  the  zero  position  of  the  horizontal  circle  from 
which  the  p  angles  are  measured. 

The  method  used  to  adjust  a  crystal  upon  the  instrument  so  that  it  will  occupy  the 
proper  position  for  measurement  will  vary  with  the  character  of  the  crystal.  A  few  illus- 
trations follow.  1.  //  the  crystal  has  a  basal  plane  at  right  angles  to  a  prism  zone.  The 
crystal  is  mounted  upon  the  post  h  so  that  the  faces  of  the  prism  zone  lie  as  nearly  as  pos- 
sible parallel  to  the  axis  of  the  post  or  the  basal  plane  as  nearly  as  possible  normal  to  it. 
Then  the  instrument  is  moved  until  the  reading  of  the  horizontal  circle  agrees  with  the 
polar  position  already  determined.  Then  by  means  of  the  tipping  screws  the  crystal  is 
moved  until  the  reflection  from  the  basal  plane  is  center  ed  upon  the  cross-hairs  of  the  tele- 
scope. If  the  adjustments  have  been  accurately  made  the  signal  will  remain  stationary 
while  the  vertical  circle  is  revolved.  Next  the  horizontal  circle  is  moved  through  an  angle 
of  90°.  This  will  bring  the  reflections  from  the  faces  of  the  prism  zone  into  the  telescope. 
If  the  pinacoid  010  is  present  the  vertical  circle  is  turned  until  the  reflected  signal  from  this 
face  falls  on  the  horizontal  cross-hair.  The  reading  of  the  vertical  circle  under  these  con- 
ditions establishes  the  position  of  the  meridian  from  which  the  </>  angles  are  measured. 
If  the  pinacoid  010  is  not  present  it  is  usually  possible  to  determine  its  theoretical  position 
from  the  position  of  other  faces  in  the  prism  zone  or  in  the  zone  between  010  and  100. 
2.  //  there  is  no  basal  plane  present  upon  the  crystal  but  a  good  prism  zone.  Under  these  cir- 
cumstances the  horizontal  circle  is  turned  until  it  is  exactly  90°  away  from  its  determined 
polar  angle  and  then  the  crystal  adjusted  by  means  of  the  tipping  scr  ews  until  the  signals 
from  the  faces  of  the  prism  zone  all  fall  on  the  vertical  cross-hair  as  the  vertical  circle  of 
the  goniometer  is  turned.  3.  //  neither  basal  plane  or  prism  zone  is  available  but  there  are 
two  or  more  faces  present  which  are  equally  inclined  to  a  theoretical  basal  plane.  First  adjust 
the  crystal  as  nearly  as  possible  in  the  proper  position  and  then  obtaining  reflections  from 
these  faces  note  the  horizontal 
circle  reading  in  each  case. 
Take  an  average  of  these  read- 
ings and  adding  or  subtracting 
this  angle  from  the  polar  angle 
of  the  horizontal  scale  place 
the  instrument  in  this  position. 
Then  by  tipping  the  crystal 
try  to  bring  it  into  such  a 
position  that  all  of  these  faces 
will  successively  reflect  the  sig- 
nal into  the  telescope  as  the 
vertical  circle  is  turned.  The 
operation  may  have  to  be  re- 
peated two  or  three  times  before 
the  final  adjustment  is  made. 
If  the  angle  between  the  inclined 
faces  and  the  theoretical  base 
is  known  the  instrument  can 
be  set  in  the  proper  position 
at  once  and  the  crystal 
brought  into  adjustment  very 
quickly.  Other  problems  wil 
arise  in  practice  but  their 
solution  will  be  along  similar  lines  to  those  suggested  above.  It  may  frequently  happen 
that  more  than  one  method  of  adjustment  may  be  used  with  a  given  crystal.  In  that ,  rase 


H  6010 
[0=0°;  p=90° 


120 

43° 24;  P«90 


in  all  possible  ways  before  making  the  measurements. 


160 


CRYSTALLOGRAPHY 


After  these  adjustments  have  been  completed  the  crystal  is  turned  about  both  the 
horizontal  and  vertical  planes  so  that  each  face  upon  it  successively  reflects  the  signal 
into  the  telescope.  The  horizontal  and  vertical  readings  are  made  in  each  case.  The 
forms  present  can  then  be  readily  plotted  in  either  the  stereographic  or  gnomonic  projec- 
tions. Fig.  383  shows  how  the  forms  of  a  simple  crystal  of  topaz  could  be  plotted  in  the 
stereographic  projection  from  the  <f>  and  p  angles  obtained  from  it  —  the  two  circle  goni- 
ometer measurements.  For  each  face  the  vertical  circle  angle,  <£,  is  plotted  on  the  divided 
circle,  the  position  of  6(010)  giving  the  zero  point  while  the  horizontal  circle  angle  is  plotted 
on  a  radial  line  from  the  center  of  the  projection,  the  position  of  c(001)  giving  its  zero  point. 


COMPOUND  OR  TWIN   CRYSTALS 

233.  Twin  Crystals.  —  Twin  crystals  are  those  in  which  one  or  more 
parts  regularly  arranged  are  in  reverse  position  with  reference  to  the  other 
part  or  parts.  They  often  appear  externally  to  consist  of  two  or  more  crystals 
symmetrically  united,  and  sometimes  have  the  form  of  a  cross  or  star.  They 
also  exhibit  the  composition  in  the  reversed  arrangement  of  part  of  the  faces, 


384 


386 


Thenardite 


Columbite 


Fluorite 


in  the  striae  of  the  surface,  and  in  re-entering  angles;  in  certain  cases  the 
compound  structure  can  only  be  surely  detected  by  an  examination  in  polar- 
ized light.  The  above  figures  (Figs.  384-386)  are  examples  of  typical  kinds  of 
twin  crystals,  and  many  others  are  given  on  the  pages  following. 

To  illustrate  the  relation  of  the  parts  in  a  twin  crystal,  Figs.  387,  388  are 
given.  Fig.  387  shows  a  regular  octahedron  divided  into  halves  by  a  plane 
parallel  to  an  octahedral  face.  If  now  the  lower  half  be  supposed  to  be  re- 
volved 180°  about  an  axis  normal  to  this  plane,  the  twinned  octahedron  of 
Fig.  388  results.  This  is  a  common  type  of  twin  in  the  isometric  system, 
and  the  method  here  employed  to  describe  the  position  of  the  parts  of  the 
crystal  to  one  another  is  applicable  to  nearly  all  twins. 

234.  Distinction  between  Twinning  and  Parallel  Grouping.  —  It  is 
important  to  understand  that  crystals,  or  parts  of  crystals,  so  grouped  as  to 
occupy  parallel  positions  with  reference  to  each  other  —  that  is,  those  whose 
similar  faces  are  parallel  — are  not  called  twins;  the  term  is  applied  only 
where  the  crystals  or  parts  of  them  are  united  in  their  reversed  position  in 
accordance  with  some  deducible  mathematical  law.  Thus  Fig.  389,  which 
represents  a  cluster  of  partial  crystals  of  analcite,  is  a  case  of  parallel 
grouping  simply  (see  Art.  252);  but  Fig.  407  illustrates  twinning,  and  this  is 


COMPOUND   OR   TWIN   CRYSTALS 


161 


true  of  Fig.  416  also.     Since  though  in  these  cases  the  axes  remain  parallel 
the  similar  faces  (and  planes  of  symmetry)  are  reversed  in  position. 

235.  Twinning-Axis.  —  The  relative  position  of  the  parts  of  a  twinned 
crystal  can  be  best  described  as  just  explained,  by  reference  to  that  line  or 
axis  called  the  twinning-axis,  a  revolution  of  180°  about  which  would  serve  to 


388 


Twinned  Octahedron 


Analei'te 


bring  the  twinned  part  parallel  to  the  other,  or  in  other  words,  which  would 
cause  one  of  the  parallel  parts  to  take  a  twinned  position  relatively  to  the  other. 

The  twinning-axis  is  always  a  possible  crystalline  line  —  that  is,  either 
a  crystallographic  axis  or  the  normal  to  some  possible  face  on  the  crystal, 
usually  one  of  the  common  fundamental  forms. 

It  is  not  to  be  supposed  that  ordinary  twins  have  actually  been  formed  by 
such  a  revolution  of  the  parts  of  crystals,  for  all  twins  (except  those  of  second- 
ary origin,  see  Art  242)  are  the  result  of  regular  molecular  growth  or  enlarge- 
ment, like  that  of  the  simple  crystal.  This  reference  to  a  revolution,  and  an 
axis  of  revolution,  is  only  a  convenient  means  of  describing  the  forms. 

In  certain  rare  cases,  particularly  of  certain  pseudo-hexagonal  species,  a 
revolution  of  60°  or  120°  about  a  normal  to  the  base  has  been  assumed  to 
explain  the  complex  group  observed. 

236.  T winning-Plane.  —  The  plane  normal  to  the  axis  of  revolution  is 
called  the  twinning-plane.     The  axis  and  plane  of  twinning  bear  the  same 
relation  to  both  individuals  in  their  reversed  position;   consequently,  in  the 
majority  of  cases,  the  twinned  crystals  are  symmetrical  with  reference  to  the 
twinning-plane. 

The  twinning-plane  is,  with  rate  exceptions,  parallel  to  a  possible  occurring 
face  on  the  given  species,  and  usually  one  of  the  more  frequent  or  fundamental 
forms.  The  exceptions  occur  only  in  the  triclinic  and  monoclinic  systems, 
where  the  twinning-axis  is  sometimes  one  of  the  oblique  crystallographic  axes, 
and  then  the  plane  of  twinning  normal  to  it  is  obviously  not  necessarily  a 
crystallographic  plane;  this  is  conspicuously  true  in  albite. 

237.  Composition-Plane.  —  The  plane  by  which  the  reversed  crystals 
are  united  is  the  composition-plane.     This  and  the  twinning-plane  very  com- 
monly coincide;   this  is  true  of  the  simple  example  given  above  (Fig.  388), 
where  the  plane  about  which  the  revolution  may  be  conceived  to  take  place 
(normal  to  the  twinning-axis)  and  the  plane  by  which  the  semi-individuals  are 
united  are  identical.     When  not  coinciding,  the  two  planes  are  generally  at 
right  angles  to  each  other  —  that  is,  the  composition-plane  is  parallel  to  the 
axis  of  revolution.     Examples  of  this  are  given  below.     Still  again,  where  the 


162  CRYSTALLOGRAPHY 

crystals  are  not  regularly  developed,  and  where  they  interpenetrate,  the  con- 
tact surface  may  be  interrupted,  or  may  be  exceedingly  irregular.  In  such 
cases  the  axis  and  plane  of  twinning  have,  as  always,  a  definite  position,  but 
the  composition-plane  loses  its  significance. 

Thus  in  quartz  twins  the  interpenetrating  parts  have  often  no  rectilinear 
boundary,  but  mingle  in  the  most  irregular  manner  throughout  the  mass, 
showing  this  composite  irregularity  by  abrupt  variations  in  the  character  of 
the  surfaces.  This  irregular  internal  structure,  found  in  many  quartz  crystals, 
even  the  common  kinds,  is  well  brought  out  by  means  of  polarized  light;  also 
by  etching  with  hydrofluoric  acid. 

The  composition-plane  has  sometimes  a  more  definite  signification  than  the 
twinning-plane.     This  is  due  to  the  fact  that  in  many  cases,  whereas  the  former 
is  fixed,  the  twinning-axis  (and  twinning-plane)  maybe  exchanged 
390          for  another  line  (and  plane)  at  right  angles  to  each,  respectively, 
— 7v    since  a  revolution  about  the  second  axis  will  also  satisfy  the 
*  c   '     '  conditions  of  producing  the  required  form.     An  example  of  this 
is  furnished  by  Fig.  390,  of  orthoclase;  the  composition-plane 
is  here  fixed  —  namely,  parallel  to  the  crystal  face,  6(010). 
But  the  axis  of  revolution  may  be  either  (1)  parallel  to  this 
face  and  normal  to  a (100),  which    is    then  consequently  the 
twinning-plane,  though  the  axis  does  not    coincide  with  the 
crystallographic  axis;  or  (2)  the  twinning-axis  may  be  taken  as 
__     coinciding  with  the  vertical  axis,  and  then  the  twinning-plane 
Orthoclase     normal  to  it  is  not  a  crystallographic  face.     In  other  simpler 
cases,  also,  the  same  principle  holds  good,  generally  in  con- 
sequence of  the  possible  mutual  interchange  of  the  planes  of  twinning  and 
composition.     In  most  cases  the  true  twinning-plane  is  evident,  since  it  is 
parallel  to  some  face  on  the  crystal  of  simple  mathematical  ratio. 

238.  An  interesting  example  of  the  possible  choice  between  two  twinning-axes  at  right 
angles  to  each  other  is  furnished  by  the  species  staurolite.  Fig.  439  shows  a  prismatic  twin 
from  Fannin  Co.,  Ga.  The  measured  angle  for  bb  was  70°  30'.  The  twinning-axis  deduced 
from  this  may  be  normal  to  the  face  (230),  which  would  then  be  the  twinning-plane.  Or, 
instead  of  this  axis,  its  complementary  axis  at  right  angles  to  it  may  be  taken,  which  would 
equally  well  produce  the  observed  form.  Now  in  this  species  it  happens  that  the  faces,  130 
and  230  (over  100),  are  almost  exactly  at  right  angles  with  each  other,  and,  according  to  the 
latter  supposition,  130  becomes  the  twinning-plane,  and  the  axis  of  revolution  is  normal  to 
it.  Hence,  either  230  or  130  may  be  the  twinning-plane,  either  supposition  agreeing  closely 
with  the  measured  angle  (which  could  not  be  obtained  with  great  accuracy).  The  former 
method  of  twinning  (tw.  pi.  230)  conforms  to  the  other  twins  observed  on  the  species,  and 
hence  it  may  be  accepted.  What  is  true  in  this  case,  however,  is  not  always  true,  for  it 
will  seldom  happen  that  of  the  two  complementary  axes  each  is  so  nearly  normal  to  a  face 
of  the  crystal.  In  most  cases  one  of  the  two  axes  conforms  to  the  law  in  being  a  normal 
to  a  possible  face,  and  the  other  does  not,  and  hence  there  is  no  doubt  as  to  which  is  the 
true  twinning-axis. 

Another  interesting  case  is  that  furnished  by  columbite.  The  common  twins  of  the 
species  are  similar  to  Fig.  385,  p.  160,  and  have  e(021)  as  the  twinning-plane;  but  twins 
also  occur  like  Fig.  434,  p.  169,  where  the  twinning-plane  is  g(023).  The  two  faces,  021 
and  023,  are  nearly  at  right  angles  to  each  other,  but  the  measured  angles  are  in  this  case 
sufficiently  exact  to  prove  that  the  two  kinds  cannot  be  referred  to  one  and  the  same  law. 

239.  Contact-  and  Penetration-Twins.  —  In  contact-twins,  when  nor- 
mally formed,  the  two  halves  are  simple  connate,  being  united  to  each  other 
by  the  composition-plane;  they  are  illustrated  by  Figs.  385,  388,  etc.  In 
actual  crystals  the  two  parts  are  seldom  symmetrical,  as  demanded  by 
theory,  but  one  may  preponderate  to  a  greater  or  less  extent  over  the  other; 


COMPOUND   OR   TWIN    CRYSTALS 


163 


in  some  cases  only  a  small  portion  of  the  second  individual  in  the  reversed 
position  may  exist.  Very  great  irregularities  are  observed  in  nature  in  this 
respect.  Moreover,  the  re-entering  angles  are  often  obliterated  by  the  abnor- 
mal developments  of  one  or  other  of  the  parts,  and  often  only  an  indistinct  line 
on  some  of  the  faces  marks  the  division  between  the -two  individuals. 

Penetration-twins  are  those  in  which  two  or  more  complete  crystals  inter- 
penetrate, as  it  were  crossing  through  each  other.  Normally,  the  crystals  have 
a  common  center,  which  is  the  center  of  the  axial  system  for  both ;  practically, 
however,  as  in  contact-twins,  great  irregularities  occur. 

Examples  of  twins  of  this  second  kind  are  given  in  the  annexed  figures, 
Figs.  386  and  391  of  fluorite,  Fig.  392  of  tetrahedrite,  and  Fig.  393  of  chabazite. 
Other  examples  occur  in  the  pages  following,  as,  for  instance,  of  the  species 
staurolite  (Figs.  438-441),  the  crystals  of  which  sometimes  occur  in  nature 
with  almost  the  perfect  symmetry  demanded  by  theory.  It  is  obvious  that 
the  distinction  between  contact-  and  penetration-twins  is  not  of  great  import- 
ance, and  the  line  cannot  always  be  clearly  drawn  between  them. 


392 


393 


Fluorite 


Tetrahedrite 


Chabazite 


240.  Paragenic  and  Metagenic  Twins.  —  The  distinction  of  paragenic  and  metagenic 
twins  belongs  rather  to  crystallogeny  than  crystallography.  Yet  the  forms  are  often  so 
obviously  distinct  that  a  brief  notice  of  the  distinction  is  important. 

In  ordinary  twins,  the  compound  structure  had  its  beginning  in  a  nucleal  compound 
molecule,   or  was  compound    in    its  very  origin;    and  whatever 
394  inequalities  in  the  result,  these  are  only  irregularities  in  the  devel- 

opment from  such  a  nucleus.  But  in  others,  the  crystal  was  at 
first  simple;  and  afterwards,  through  some  change  in  itself  or  in 
the  condition  of  the  material  supplied  for  its  increase,  received  new 
layers,  or  a  continuation,  in  a  reversed  position.  This  mode  ot 
twinning  is  metagenic,  or  a  result  subsequent  to  the  origin  of  the 
crystal;  while  the  ordinary  mode  is  paragenic.  One  form  ot  it  is 
illustrated  in  Fig.  394.  The  middle  portion  had  attained  a  length  of 
half  an  inch  or  more,  and  then  became  geniculated  simultaneously 
at  either  extremity.  These  geniculations  are  often  repeated  in 
rutile,  and  the  ends  of  the  crystal  are  thus  bent  into  one  another, 
and  occasionally  produce  nearly  regular  prismatic  forms. 

This  metagenic  twinning  is  sometimes  presented  by  the  successive 
layers  of  deposition  in  a  crystal,  as  in  some  quartz  crvstals,  especia 
amethyst,  the  inseparable  layers,  exceedingly  thin,  being  of  oppos 
kinds.     In    a  similar   manner,  crystals   of   the  triclmic  feldspars, 

by  oscillatory  composition, 


Rutile 
albite,  etc., 


_-  ™.,  are  often  made  up  of  thin  plates  parallel  to  6(010)   by  osc 
and  the  face  c(001),  accordingly,  is  finely  striated  parallel  to  the  edge 

241.  Repeated  Twinning,  Polysynthetic  and  Symmetrical.  —  In  the 
preceding  paragraph  one  case  of  repeated  twinning  has  been  mentioned,  that 
of  the  feldspars;  it  is  a  case  of  parallel  repetition  or  parallel  grouping  in  re- 
versed position  of  successive  crystalline  lamellae.  This  kind  of  twinning  is 


164 


CRYSTALLOGRAPHY 


often  called  polysynthetic  twinning,  the  lamellae  in  many  cases  being  extremely 
thin,  and  giving  rise  to  a  series  of  parallel  lines  (striations)  on  a  crystal  face  or 
a  surface  of  cleavage.  The  triclinic  feldspars  show  in  many  cases  polysyn- 
thetic twinning  and  not  infrequently  on  both  c(001)  and  6(010),  cf.  p.  172. 
It  is  also  observed  with  magnetite  (Fig.  474) ,  pyroxene,  barite,  etc. 

Another  kind  of  repeated  twinning  is  illustrated  by  Figs.  395-400,  where 
the  successively  reversed  individuals  are  not  parallel.  In  these  cases  the  axes 
may,  however,  lie  in  a  zone,  as  the  prismatic  twins  of  aragonite,  or  they  may 
be  inclined  to  each  other,  as  in  Fig.  397  of  staurolite  In  all  such  cases  the 
repetition  of  the  twinning  tends  to  produce  circular  forms,  when  the  angle 
between  the  two  axial  systems  is  an  aliquot  part  of  360°  (approximately). 
Thus  six-rayed  twinned  crystals,  consisting  of  three  individuals  (hence  called 
trillings),  occur  with  chrysoberyl  (Fig.  395),  or  cerussite  (Fig.  396),  or  staurolite 
(Fig.  397),  since  three  times  the  angle  of  twinning  in  each  case  is  not  far  from 
360°.  Again,  five-fold  twins,  or  fivelings,  occur  in  the  octahedrons  of  gold  and 


397 


Spinel 


Rutile 


Phillipsite 


spinel  (Fig  398),  since  5  X  70°  32'  =  360°  (approx.).  Eight-fold  twins,  or 
eigktlings,  of  rutile  (Figs.  399,  413)  occur,  since  the  angle  of  the  axes  in  twinned 
position  goes  approximately  eight  times  in  360°. 

Repeated  twinning  of  the  symmetrical  type  often  serves  to  give  the  com- 
pound crystal  an  apparent  symmetry  of  higher  grade  than  that  of  the  simple 
individual,  and  the  result  is  often  spoken  of  as  a  kind  of  pseudo-symmetry 
(Art.  20) ,  cf.  Fig.  431  of  aragonite,  which  represents  a  basal  section  of  a 
pseudo-hexagonal  crystal.  Fig.  400  of  phillipsite  (cf.  Figs.  452-454)  is  an  inter- 


EXAMPLES   OF   IMPORTANT   METHODS   OF   TWINNING 


165 


esting  case,  since  it  shows  how  a  multiple  twin  of  a  monoclinic  crystal  may 
simulate  an  isometric  crystal  (dodecahedron). 

Compound  crystals  in  which  twinning  exists  in  accordance  with  two  laws 
at  once  are  not  of  common  occurrence;  an  excellent  example  is  afforded  by 
staurolite,  Fig.  441.  They  have  also  been  observed  with  albite,  orthoclase, 
and  in  other  cases. 

242.  Secondary  Twinning.  —  When  there  is  reason  to  believe  that  the 
twinning  has  been  produced  subsequently  to  the  original  formation  of  the 
crystal,  or  crystalline  mass,  as,  for  example,  by  pressure,  it  is  said  to  be 
secondary.     Thus  the  calcite  grains  of  a  crystalline  limestone  often  show  such 
secondary  twinning  lamellae.     The  same  are  occasionally  observed  (||c,  001) 
in  pyroxene  crystals.     Further,  the  poly  synthetic  twinning  of  the  triclinic 
feldspars  is  often  secondary  in  origin.     This  subject  is  further  discussed  on  a 
later  page,  where  it  is  also  explained  that  in  certain  cases  twinning  may  be 
produced  artificially  in  a  crystal  individual  —  e.g.,  in  calcite  (see  Art.  282). 

EXAMPLES  OF  IMPORTANT  METHODS  OF  TWINNING 

243.  Isometric  System.  —  With  few  exceptions  the  twins  of  the  normal 
class  of  this  system  are  of  one  kind,  the  twinning-axis  an  octahedral  axis,  and 
the  twinning-plane  consequently  parallel  to  an  octahedral  face;  in  most  cases, 
also,  the  latter  coincides  with  the  composition-plane.     Fig.  388,  p.   161,* 

401  402  403 


Galena  Hauynite  Sodalite 

shows  this  kind  as  applied  to  the  simple  octahedron;  it  is  especially  common 
with  the  spinel  group  of  minerals,  and  is  hence  called  in  general  a  spinel-twin. 

*  It  will!  be  noted  that  here  and  elsewhere  the  letters  used  to  designate  the  faces  on 
the  twinned  parts  of  crystals  are  distinguished  by  a  subscript  line. 


166 


CRYSTALLOGRAPHY 


Fig.  401  is  a  similar  more  complex  form;  Fig.  402  shows  a  cube  twinned  by  this 
method,  and  Fig.  403  represents  the  same  form  but  shortened  in  the  direction 
of  the  octahedral  axis,  and  hence  having  the  anomalous  aspect  of  a  triangular 
pyramid.  All  these  cases  are  contact-twins. 

Penetration-twins,  following  the  same  law,  are  also  common.     A  simple 
case  of  fluorite  is  shown  in  Fig.  391,  p.  163;   Fig.  404  shows  one  of  galena; 
Fig.  405  is  a  repeated  octahedral  twin  of  haiiynite,  and 
Fig.  406  a  dodecahedral  twin  of  sodalite. 

244.  In  the  pyritohedral  class  of  the  isometric  system 
penetration-twins  ot  the  type  shown  in  Fig.  407  are 
common  (this  form  of  pyrite  is  often  called  the  iron 
cross).  Here  the  cubic  axis  is  the  twinning-axis,  and 
obviously  such  a  twin  is  impossible  in  the  normal 
class. 

Figs.  408  and  409  show  analogous  forms  with  par- 
allel axes  for  crystals  belonging  to  the  tetrahedral 
class.  The  peculiar  development  of  Fig.  408  of 
tetrahedrite  is  to  be  noted.  Fig.  410  is  a  twin  of  the 
ordinary  spinel  type  of  another  tetrahedral  species,  sphalerite;  with  it, 
complex  forms  with  repeated  twinning  are  not  uncommon  and  sometimes 
polysynthetic  twin  lamellae  are  noted. 


Pyrite 


408 


409 


410 


Tetrahedrite 


Eulytite 


Sphalerite 


245.  Tetragonal  System.  —  The  most  common  method  is  that  where 
the  twinning-plane  is  parallel  to  a  face  of  the  pyramid,  e(101) .  It  is  especially 
characteristic  of  the  species  of  the  rutile  group  —  viz.,  rutile  and  cassiterite: 


411 


413 


Cassiterite  Zircon  Rutile 

also  similarly  the  allied  species  zircon.     This  is  illustrated  in  Fig.  411,  and 


EXAMPLES   OF   IMPORTANT  METHODS   OF   TWINNING 


167 


again  in  Fig.  412.  Fig.  413  shows  a  repeated  twin  of  rutile,  the  twinning 
according  to  this  law;  the  vertical  axes  of  the  successive  six  individuals  lie 
in  a  plane,  and  an  inclosed  circle  is  the  result.  Another  repeated  twin  of  rutile 
according  to  the  same  law  is  shown  in  Fig.  399;  here  the  successive  vertical 
axes  form  a  zigzag  line;  Fig.  414  shows  an  analogous  twin  of  hausmannite. 
Another  kind  of  twinning  with  the  twinning-plane  parallel  to  a  face  of  the 
pyramid  (301)  is  shown  in  Fig.  415. 

246.  In  the  pyramidal  class  of  the  same  system  twins  of  the  type  of  Fig. 
416  are  not  rare.  Here  the  vertical  axis,  c,  is  the  twinning-axis;  such  a  crystal 
may  simulate  one  of  the  normal  class. 


414 


415 


416 


Hausmannite 


Rutile 


Scheelite 


417 


In  chalcopyrite,  of  the  sphenoidal  class,  twinning  with  a  face  of  the  unit 
pyramid,  /(111),  as  the  twinning-plane  is  common  (Fig.  417).  As  the  angles 
differ  but  a  small  fraction  of  a  degree  from  those  of  a 
regular  octahedron,  such  twins  often  resemble  closely 
spinel-twins.  The  face  6(101)  may  also  be  a  twinning- 
plane  and  other  rarer  types  have  been  noted. 

247.  Hexagonal  System.  —  In  the  hexagonal  divis- 
ion of  this    system    twins  are  rare.     An  example  is 
furnished  by  pyrrhotite,  Fig.  418,  where  the  twinning- 
plane  is  the  pyramid  (1011),  the  vertical  axes  of  the 
individual  crystals  being  nearly  at  right  angles  to  each 
other  (since  0001  A  1011  =  45°  8'). 

248.  In   the  species  belonging  to    the  trigonal  or 


Chalcopyrite 


rhombokedral  division,  twins  are  common.  Thus  the 
twinning-axis  may  be  the  vertical  axis,  as  in  the 
contact-twins  of  Figs.  419  and  420,  or  the  penetration- 
twin  of  Fig.  393.  Or  the  twinning-plane  may  be 
the  obtuse  rhombohedron  e(0112),  as  in  Fig. 
421,  the  vertical  axes  crossing  at  angles  of  127  2 
and  52i°.  Again,  the  twinning-plane  may  be 
r(10ll)  as  in  Figs.  422-425,  the_  vertical  axes 
nearly  at  right  angles  (90f°);  or  (0221),  as  in  Fig. 
426,  the  axes  inclined  53f°  and  126|  . 


Pvrrhotite 


5.  tne  axes  inclined  004     auu   j.^4  . 

In  the  trapezohedral  class,  the  species  quartz   shows  several  methods 
twinning.     In  Fig.  427  the  twinning-plane  is  the  pyramid  {(1122},  the  axes 
crossing  at  angles  of  84|°  and  95i°-     In  Fig.  428  the  twmmng-axis  is  c,  the 


168 


CRYSTALLOGRAPHY 


axes  hence  parallel,  the  individuals  both  right-  or  both  left-handed  but  un- 
symmetrical,  r(]0ll)  then  parallel  to  and  coinciding  with  2(0111).     The  re- 


420 


421 


422 


Figs.  419-426,  Calcite 

suiting  forms,  as  in  Fig.  428,  are  mostly  penetration-twins,  and  the  parts  are 
often  very  irregularly  united,  as  shown  by  dull  areas  (z)  on  the  plus  rhombo- 
hedral  face  (r);  otherwise  these  twins  are  recognized  by  pyro-electrical 
phenomena.  In  Fig.  429  the  twinning-plane  is  a(1120)  — the  Brazil  law  — 
the  individuals  respectively  right-  and  left-handed  and  the  twin  symmetrical 
with  reference  to  an  a-face;  these  are  usually  irregular  penetration-twins;  in 
these  twins  r  and  r,  also  z  and  z,  coincide  These  twins  often  show,  in  con- 
427  428  429 


Figs.  427-429,  Quartz 

verging  polarized  light,  the  phenomenon  of  Airy's  spirals.     It  may  be  added 
that  pseudo-twins  of  quartz  are  common  —  that  is,  groups  of  crystals  which 


EXAMPLES   OF   IMPORTANT   METHODS   OF   TWINNING 


169 


430 


431 


nearly  conform  to  some  more  or  less  complex  twinning  law,  but  where  the 
grouping  is  nevertheless  only  accidental 

249.  Orthorhombic  System.  —  In  the 
orthorhombic  system  the  commonest 
method  of  twinning  is  that  where  the 
twinning-plane  is  a  face  of  a  prism  of  60°, 
or  nearly  60°.  This  is  well  shown  with  the 
species  of  the  aragonite  group.  In  accord- 
ance with  the  principle  stated  in  Art.  241, 
the  twinning  after  this  law  is  often 
repeated,  and  thus  forms  with  pseudo- 
hexagonal  symmetry  result.  Fig.  430 
shows  a  simple  twin  of  aragonite;  Fig.  431  \ 
shows  a  basal  section  of  an  aragonite  triplet 
which  although  it  resembles  a  hexagonal 


Aragonite 


prism  reveals  its  twinned  character  by  the  striations  on  the  basal  plane  and 
by  irregularities  on  its  composite  prism  faces  due  to  the  fact  that  the  pris- 
matic angle  is  not  exactly  60°.  With  witherite  (and  bromlite),  apparent 
hexagonal  pyramids  are  common,  but  the  true  complex  twinning  is  revealed 
in  polarized  light,  as  noted  later. 

Twinning  of  the  same  type,  but  where  a  dome  of  60°  is  twinning-plane, 
is  common  with  arsenopyrite  (tw.  pi.  e(101)),  as  shown  in  Figs.  432,  433;  also 

434 


Arsenopyrite  Columbite 

Fig.  434  of  columbite,  but  compare  Fig.  385  and  remarks  in  Art  238,     Another 
example  is  given  in  Fig.  395  of  alexandrite  (chrysoberyl) .     Chrysolite,  man- 
435  436  437 


Marcasite 


Arsenopyrite 


ganite,  humite,  are  other  species  with  which  this  kind  of  twinning  is  common. 
Another  common  method  of  twinning  is  that  where  the  twinning  is  parallel 


170 


CRYSTALLOGRAPHY 


to  a  face  of  a  prism  of  about  70J°,  as  shown  in  Fig.  435.     With  this  method 
symmetrical  fivelings  not  infrequently  occur  (Figs.  436,  437). 

The  species  staurolite  illustrates  three  kinds  of  twinning.  In  Fig.  438  the 
twinning-plane  is  (032),  and  since  (001  A  032)  =  45°  41',  the  crystals  cross 
nearly  at  right  angles.  In  Fig.  439  the  twinning-plane  is  the  prism  (230).  In 
Fig.  440  it  is  the  pyramid  (232) ;  the  crystals  then  crossing  at  angles  of  about 
60°,  stellate  trillings  occur  (see  Fig.  397),  and  indeed  more  complex  forms.  In 
Fig.  441  there  is  twinning  according  to  both  (032)  and  (232). 

440 


Staurolite 


441 


Staurolite 


Struvite 


In  the  hemimorphic  class,  twins  of  the  type  shown  in  Fig.  442,  with  c(001) 
as  the  twinning-plane,  are  to  be  noted. 

250.  Mpnoclinic  System.  —  In  the  monoclinic  system,  twins  with  the  ver- 
tical axis  as  twinning-axis  are  common ;  this  is  illustrated  by  Fig.  443  of  augite 
(pyroxene),  Fig.  444  of  gypsum,  and  Fig.  445  of  orthoclase  (see  also  Fig.  390, 

443  444  445 


Augite 


Gypsum 


y 

Orthoclase 


p.  162).     With  the  latter  species  these  twins  are  called  Carlsbad  twins  (because 
common  in  the  trachyte  of  Carlsbad,  Bohemia) ;  they  may  be  contact-twins 


EXAMPLES   OF   IMPORTANT   METHODS   OF   TWINNING 


171 


(Fig.  390),  or  irregular  penetration-twins  (Fig.  445).     In  Fig.  390  it  is  to  be 
noted  that  c  and  x  fall  nearly  in  the  same  plane. 

In  Fig.  446,  also  of  orthoclase,  the  twinning-plane  is  the  clinodome  (021), 
and  since  (001  A  021)  =  44°  56^',  this  method  of  twinning  yields  nearly 
square  prisms.  These  twins  are  called  Baveno  twins  (from  a  prominent 
locality  at  Baveno,  Italy) ;  they  are  often  repeated  (Fig.  447).  In  Fig.  448  a 


446 


447 


448 


Orthoclase 

Manebach  twin  is  shown;  here  the  twinning-plane  is  c(001).  Other  rarer 
types  of  twinning  have  been  noted  with  orthoclase.  Polysynthetic  twinning 
with  c(001)  as  twinning-plane  i&  common  with  pyroxene  (cf.  Fig.  461,  p.  173). 
Twins  of  the  aragonite-chrysoberyl  type  are  not  uncommon  with  mono- 
clinic  species,  having  a  prominent  60°  prism  (or  dome),  as  in  Fig.  449.  Stellate 
twins  after  this  law  are  common  with  chondrodite  and  clinohumite.  An 
analogous  twin  of  pyroxene  is  shown  in  Fig.  450;  here  the  pyramid  (122)  is  the 
twinning-plane,  and  since  (010  A  122)  =  59°  21',  the  crystals  cross  at  angles 
of  nearly _60°;  further,  the  orthopinacoids  fall  nearly  in  a  common  zone,  since 
(100  A  122)  =  90°  9'.  In  Fig.  451  the  twinning-plane  is  the  orthodome 


449 


450 


461 


Wolframite 


Pyroxene 


Pyroxene 


(101)  Phillipsite  and  harmotome  exhibit  multiple  twinning,  and  the  crystals 
often  show  pseudo-symmetry.  Fig.  452  shows  a  cruciform  fourling  with 
c(001)  as  twinning-plane,  the  twinning  shown  by  the  stnations  on  the  side  face. 
This  is  compounded  in  Fig.  453  with  twinning-plane  (Oil),  making  nearly 
square  prisms,  and  this  further  repeated  with  ra(110)  as  twinning-plane 


172 


CR  YST  ALLO  GR  APH  Y 


yields  the  form  in  Fig.  454,  or  even  Fig.  400,  p.  164,  resembling  an  isometric 
dodecahedron,  each  face  showing  a  fourfold  striation. 

452  453  454 


Phillipsite 

251.  Triclinic  System.  —  The  most  interesting  twins  of  the  triclinic 
system  are  those  shown  by  the  feldspars.  Twinning  with  6(010)  as  the 
twinning-plane  is  very  common,  especially  polysynthetic  twinning  yielding 
thin  parallel  lamellae,  shown  by  the  striations  on  the  face  c  (or  the  correspond- 
ing cleavage-surface),  and  also  clearly  revealed  in  polarized  light.  This  is 
known  as  the  albite  law  (Figs.  455,  456).  Another  important  method  (Fig. 
457)  is  that  of  the  pericline  law;  the  twinning-axis  is  the  crystallographic 
axis  b.  Here  the  twins  are  united  by  a  section  (rhombic  section)  shown  in  the 
figure  and  further  explained  under  the  feldspars.  Polysynthetic  twinning  after 
this  law  is  common,  and  hence  a  cleavage-mass  may  show  two  sets  of  striations, 
one  on  the  surface  parallel  to  c(001)  and  the  other  on  that  parallel  to  6(010). 
The  angle  made  by  these  last  striations  with  the  edge  001/010  is  character- 
istic of  the  particular  triclinic  species,  as  noted  later. 

455  456  457 


Albite 

Twins  of  albite  of  other  rarer  types  also  occur,  and  further  twins  similar 
458  to  the  Carlsbad,  Baveno,  and  Manebach  twins  of  ortho- 

clase.     Fig.  458  shows  twinning  according  to  both  the 
albite  and  Carlsbad  types. 

REGULAR  GROUPING  OF  CRYSTALS 

252.  Parallel  Grouping.  —  Connected  with  the  sub- 
ject of  twin  crystals  is  that  of  the  parallel  position  of 
associated  crystals  of  the  same  species,  or  of  different 
species. 

Crystals  of  the  same  species  occurring  together  are 
very  commonly  in  parallel  position.  In  this  way  large 


Albite 


EXAMPLES   OF   IMPORTANT   METHODS   OF   TWINNING 


173 


459 


460 


crystals,  as  of  calcite,  quartz,  fluorite,  are  sometimes  buiJt  up  of  smaller 
individuals  grouped  together  with  corresponding  faces  parallel.  This 
parallel  grouping  is  often  seen  in  crystals  as  they  lie  on  the  supporting 
rock.  On  glancing  the  eye  over  a  surface  covered  with  crystals  a  reflection 
from  one  face  will  often  be  accompanied  by  reflections  from  the  corres- 
ponding face  in  each  of  the  other  crystals,  showing  that  the  crystals  are 
throughout  similar  in  their  positions. 

With  many  species,  complex  crystalline  forms  result  from  the  growth  of 
parallel  partial  crystals  in  the 
direction  of  the  crystallographic 
axes,  or  axes  of  symmetry.  Thus 
dendritic  forms,  resembling  branch- 
ing vegetation,  often  of  great  del- 
icacy, are  seen  with  gold,  copper, 
argentite,  and  other  species,  espe- 
cially those  of  the  isometric  sys- 
tem. This  is  shown  in  Fig.  459 
(ideal),  and  again  in  Fig.  460, 
where  the  twinned  and  flattened 
cubes  (cf.  Fig.  403,  p.  165)  are 
grouped  in  directions  corresponding 
to  the  diagonals  of  an  octahedral  Co 

face  which  is  the  twinning-plane. 

253.  Parallel  Grouping  of  Unlike  Species.  —  Crystals  of  different  spe- 
cies often  show  the  same  tendency  to  parallelism  in  mutual  position.  This  is 
true  most  frequently  of  species  which  are  more  or  less  closely  similar  in  form 
and  composition.  Crystals  of  albite,  implanted  on  a  surface  of  orthoclase, 

are  sometimes  an  example  of 
this;  crystals  of  amphibole  and 
pyroxene  (Fig.  461),  of  zircon 
and  xenotime  (Fig.  462),  of  va- 
rious kinds  of  mica,  are  also  at 
times  observed  associated  in  par- 
allel position. 

The  same  relation  of  position 
also  occasionally  occurs  where 
there  is  no  connection  in  composi- 
tion, as  the  crystals  of  rutile 
on  tabular  crystals  of  hematite, 
the  vertical  axes  of  the  former 
coinciding  with  the  horizontal 
Amphibole  enclosing  Xenotime  enclosing  zircon  axes  of  the  latter.  Crystals  of 
pyroxene  in  parallel  in  parallel  position  calcite  have  been  observed  whose 

position  rhombohedral  faces  had  a  series 

of  quartz  crystals  upon  them,  all  in  parallel  position;  sometimes  three 
such  quartz  crystals,  one  on  each  rhombohedral  face,  entirely  envelop 
the  calcite,  and  unite  with  re-entering  angles  to  form  pseudo-twins  (rather 
trillings)  of  quartz  after  calcite.  Parallel  growths  of  the  sphenoidal  chalcopyr- 
ite  upon  the  tetrahedral  sphalerite  are  common,  the  similarity  in  crystal 
structure  of  the  two  species  controlling  the  position  of  the  crystals  of  chal- 
copyrite. 


461 


462 


174 


CRYSTALLOGRAPHY 


IRREGULARITIES  OF  CRYSTALS 

254.  The  laws  of  crystallization,  when  unmodified  by  extrinsic  causes, 
should  produce  forms  of  exact  geometrical  symmetry,  the  angles  being  not 
only  equal,  but  also  the  homologous  faces  of  crystals  and  the  dimensions  in  the 
directions  of  like  axes.     This  symmetry  is,  however,  so  uncommon  that  it  can 
hardly  be  considered  other  than  an  ideal  perfection.     The  various  possible 
kinds  of  symmetry,  and  the  relation  of  this  ideal  geometrical  symmetry  to  the 
actual  crystallographic  symmetry,  have  been  discussed  in  Arts.  14  and  18  et 
seq.     Crystals  are  very  generally  distorted,  and  often  the  fundamental  forms 
are  so  completely  disguised  that  an  intimate  familiarity  with  the  possible 
irregularities  is  required  in  order  to  unravel  their  complexities.     Even  the 
angles  may  occasionally  vary  rather  widely. 

The  irregularities  of  crystals  may  be  treated  under  several  heads:  1, 
Variations  of  form  and  dimensions;  2,  Imperfections  of  surface;  3,  Varia- 
tions of  angles;  4,  Internal  imperfections  and  impurities. 

1.    VARIATIONS   IN  THE   FORMS   AND   DIMENSIONS 
OF   CRYSTALS 

255.  Distortion  in  General.  —  The  variations  in  the  forms  of  crystals, 
or,  in  other  words,  their  distortion,  may  be  irregular  in  character,  certain  faces 
being  larger  and  others  smaller  than  in  the  ideal  geometrical  solid.     On  the 
other  hand,  it  may  be  symmetrical,  giving  to  the  distorted  form  the  symmetry 
of  a  group  or  system  different  from  that  to  which  it  actually  belongs.     The 
former  case  is  the  common  rule,  but  the  latter  is  the  more  interesting. 

256.  Irregular  Distortion.  —  As  stated  above  and  on  p.  13,  all  crystals 
show  to  a  greater  or  less  extent  an  irregular  or  accidental  variation  from  the 
ideal  geometrical  form.     This  distortion,  if  not  accompanied  by  change  in 
the  interfacial  angles,  has  no  particular  significance,  and  does  not  involve  any 
deviation  from  the  laws  of  crystallographic  symmetry.     Figs.  463,  464  show 
distorted  crystals  of  quartz ;  they  may  be  compared  with  the  ideal  form,  Fig. 
284,  p.  113.     Fig.  465  is  an  ideal  and  Fig.  466  an  actual  crystal  of  lazulite. 


463 


464 


465 


466 


Quartz 


Lazulite 


The  correct  identification  of  the  forms  on  a  crystal  is  rendered  much  more  difficult 

because  ol  this  prevailing  distortion,  especially  when  it  results  in  the  entire  obliteration  of 

urtain  laces  by  the  enlargement  of  others.     In  deciphering  the  distorted  crystalline  forms 

it  must  be  remembered  that  while  the  appearance  of  the  crystals  may  be  entirely  altered, 

e  intertacial  angles  remain  the  same;  moreover,  like  faces  are  physically  alike  —  that  is 


IRREGULARITIES   OF   CRYSTALS 


175 


alike  in  degree  of  luster,  in  striations,  and  so  on.     Thus  the  prismatic  faces  of  quartz  show 
almost  always  characteristic  horizontal  striations. 

In  addition  to  the  variations  in  form  which  have  just  been  described,  still 
greater  irregularities  are  due  to  the  fact  that,  in  many  cases,  crystals  in  nature 
are  attached  either  to  other  crystals  or  to  some  rock  surface,  and  in  consequence 
of  this  are  only  partially  developed.  Thus  quartz  crystals  are  generally 
attached  by  one  extremity  of  the  prism,  and  hence  have  only  one  set  of  pyra- 
midal faces;  perfectly  formed  crystals,  having  the  double  pyramid  complete, 
are  rare. 

257.  Symmetrical  Distortion.  —  The  most  interesting  examples  of  the 
symmetrical  distortion  of  crystalline  forms  are  found  among  crystals  of  the 
isometric  system.  An  elongation  in  the  direction  of  one  cubic  axis  may  give 
the  appearance  of  tetragonal  symmetry,  or  that  in  the  direction  of  two  cubic 
axes  of  orthorhombic  symmetry;  while  in  the  direction  of  an  octahedral  axis 
a  lengthening  or  shortening  gives  rise  to  forms  of  apparent  rhombohedral 
symmetry.  Such  cases  are  common  with  native  gold,  silver,  and  copper. 

A  cube  lengthened  or  shortened  along  one  axis  becomes  a  right  square  prism,  and  if 
varied  in  the  direction  of  two  axes  is  changed  to  a  rectangular  prism.  Cubes  of  pyrite, 
galena,  fluorite,  etc.,  are  often  thus  distorted.  It  is  very  unusual  to  find  a  cubic  crystal 
that  is  a  true  symmetrical  cube.  In  some  species  the  cube  or  octahedron  (or  other  iso- 
metric form)  is  lengthened  into  a  capillary  crystal  or  needle,  as  happens  in  cuprite  and  pyrite. 

An  octahedron  flattened  parallel  to  a  face  —  that  is,  in  the  direction  of  a  trigonal  sym- 
metry axis  is  reduced  to  a  tabular  crystal  resembling  a  rhombohedral  crystal  with  basal 
plane  (Fig.  467).  If  lengthened  in  the  same  direction  (i.e.  along  line  A-B,  Fig.  468),  to  the 
obliteration  of  the  terminal  octahedral  faces,  it  becomes  an  acute  rhombohedron. 

When  an  octahedron  is  extended  in  the  direction  of  a  line  between  two  opposite  edges, 


467 


468 


469 


470 


Distorted  Octahedrons 
471  472 


473 


Distorted  Dodecahedrons 


or  that  of  a  binary  symmetry  axis,  it  has  the  general  form  of  a  recftan^laf,oct^he(}f.onj 
still  farther  extended,  as  in  Fig.  469,  it  resembles  a  combination  of  two  orthorhombic  d 
(spinel,  fluorite,  magnetite). 


n 
domes 


176  CRYSTALLOGRAPHY 

The  dodecahedron  lengthened  in  the  direction  of  a  trigonal  symmetry  axis  becomes  a 
six-sided  prism  with  three-sided  summits,  as  in  Fig.  470.  If  shortened  in  the  same  direc- 
tion, it  becomes  a  short  prism  of  the  same  kind  (Fig.  471).  Both  resemble  rhombohedral 
forms  and  are  common  in  garnet.  When  lengthened  in  the  direction  of  one  of  the  cubic 
axes,  the  dodecahedron  becomes  a  square  prism  with  pyramidal  summits  (Fig.  472),  and 
shortened  along  the  same  axis  it  is  reduced  to  a  square  octahedron,  with  truncated  angles 
(Fig.  473). 

The  trapezohedron  elongated  in  the  direction  of  an  octahedral  (trigonal)  axis  assumes 
rhombohedral  (trigonal)  symmetry. 

If  the  elongation  of  the  trapezohedron  takes  place  along  a  cubic  axis,  it  becomes  a  double 
eight-sided  pyramid  with  four-sided  summits;  or  if  these  summit  planes  are  obliterated 
by  a  farther  extension,  it  becomes  a  complete  eight-sided  double  pyramid. 

Similarly  the  trisoctahedron,  tetrahexahedron  and  hexoctahedron  may  show  distortion 
of  the  same  kind.  Further  examples  are  to  be  found  in  the  other  systems. 

2.     IMPERFECTIONS   OF   THE  SURFACES  [OF   CRYSTALS 

258.  Striations  Due  to  Oscillatory  Combinations.  —  The  parallel  lines 
or  furrows  on  the  surfaces  of  crystals  are  called  strice  or  striations,  and  such 
surfaces  are  said  to  be  striated. 

Each  little  ridge  on  a  striated  surface  is  inclosed  by  two  narrow  planes 
more  or  less  regular.  These  planes  often  correspond  in  position  to  different 
faces  of  the  crystal,  and  these  ridges  have  been  formed  by  a  continued 
oscillation  in  the  operation  of  the  causes  that  give  rise,  when  acting  uninter- 
ruptedly, to  enlarged  faces.  By  this  means,  the  surfaces  of  a  crystal  are 
marked  in  parallel  lines,  with  a  succession  of  narrow  planes  meeting  at  an 
angle  and  constituting  the  ridges  referred  to. 

This  combination  of  different  planes  in  the  formation  of  a  surface  has  been 
termed  oscillatory  combination.  The  horizontal  striations  on  prismatic 
crystals  of  quartz  are  examples  of  this  combination,  in  which  the  oscillation 
has-  taken  place  between  the  prismatic  and  rhombohedral  faces.  Thus 
crystals  of  quartz  are  often  tapered  to  a  point,  without  the  usual  pyramidal 
terminations. 

Other  examples  are  the  striations  on  the  cubic  faces  of  pyrite  parallel  to 
the  intersections  of  the  cube  with  the  faces  of  the 
pyritohedron;  also  the  striations  on  magnetite  due 
to  the  oscillation  between  the  octahedron  and  do- 
decahedron. Prisms  of  tourmaline  are  very  com- 
monly bounded  vertically  by  three  convex  surfaces, 
owing  to  an  oscillatory  combination  of  the  faces  in 
the  prismatic  zone. 

259.  Striations  Due  to  Repeated  Twinning.  —  The 
striations  of  the    basal   plane   of   albite  and  other 
triclinic  feldspars,  also  of  thex  rhombohedral  surfaces 
of  some  calcite,  have  been  explained  in  Art.  241  as 
Magnetite  due  to  polysynthetic  twinning.     This  is  illustrated  by 

Fig.  474  of  magnetite  from  Port  Henry,  N.  Y.  (Kemp.) 
260.  Markings  from  Erosion  and  Other  Causes.  —  The  faces  of  crys- 
tals are  often  uneven,  or  have  the  crystalline  structure  developed  as  a  con- 
sequence of  etching  by  some  chemical  agent.  Cubes  of  galena  are  frequently 
thus  uneven,  and  crystals  of  lead  sulphate  (anglesite)  or  lead  carbonate  (cerus- 
site)  are  sometimes  present  as  evidence  with  regard  to  the  cause.  Crystals 
of  numerous  other  species,  even  of  corundum,  spinel,  quartz,  etc.,  sometimes 
show  the  same  result  of  partial  change  over  the  surface  —  often  the  incipient 


IRREGULARITIES   OF   CRYSTALS 


177 


stage  in  a  process  tending  to  a  final  removal  of  the  whole  crystal.  Interesting 
investigations  have  been  made  by  various  authors  on  the  action  of  solvents 
on  different  minerals,  the  actual  structure  of  the  crystals  being  developed  in 
this  way.  This  method  of  etching  is  fully  discussed,  with  illustrations  in 
another  place  (Art.  286). 

The  markings  on  the  surfaces  of  crystals  are  not,  however,  always  to  be 
ascribed  to  etching.  In  most  cases  such  depressions,  as  well  as  the  minute 
elevations  upon  the  faces  having  the  form  of  low  pyramids  (so-called  vicinal 
prominences) ,  are  a  part  of  the  original  molecular  growth  of  the  crystal,  and 
often  serve  to  show  the  successive  stages  in  its  history.  They  may  be  imper- 
fections arising  from  an  interrupted  or  disturbed  development  of  the  form,  the 
perfectly  smooth  and  even  crystalline  faces  being  the  result  of  completed 
action  free  from  disturbing  causes.  Examples  of  the  markings  referred  to 
occur  on  the  crystals  of  most  minerals,  and  conspicuously  so  on  the  rhombo- 
hedral  faces  of  quartz. 

Faces  of  crystals  are  often  marked  with  angular  elevations  more  or  less 
distinct,  which  are  due  to  oscillatory  combination.  Octahedrons  of  fluorite 
are  common  which  have  for  each  face  a  surface  of  minute  cubes,  proceeding 
from  an  oscillation  between  the  cube  and  octahedron.  Sometimes  an  examina- 
tion of  such  a  crystal  shows  that  though  the  form  is  apparently  octahedral, 
there  are  no  octahedral  faces  present  at  all.  Other  similar  cases  could  be 
mentioned. 

Whatever  their  cause,  these  minute  markings  are  often  of  great  importance 
as  revealing  the  true  molecular  symmetry  of  the  crystal.  For  it  follows  from 
the  symmetry  of  crystallization  that  like  faces  must  be  physically  alike  — 
that  is,  in  regard  to  their  surface  character;  it  thus  often  happens  that  on  all 
the  crystals  of  a  species  from  a  given  locality,  or  perhaps  from  all  localities,  the 
same  planes  are  etched  or  roughened  alike.  There  is  much  uniformity  on 
the  faces  of  quartz  crystals  in  this  respect. 

261.  Curved  surfaces  may  result  from  (a)  oscillatory  combination; 
or  (6)  some  independent  molecular  condition  producing  curvatures  in  the 
laminae  of  the  crystal ;  or  (c)  from  a  mechanical  cause. 

Curved  surfaces  of  the  first  kind  have  been  already  mentioned  (Art.  258). 
A  singular  curvature  of  this  nature  is  seen  in  Fig.  475,  of  calcite;  in  the  lower 


476 


476 


Calcite 


Diamond 


Beryl 


part  traces  of  a  scalenohedral  form  are  apparent  which  was  in  oscillatory  com- 
bination with  the  prismatic  form. 


178  CRYSTALLOGRAPHY 

Curvatures  of  the  second  kind  sometimes  have  all  the  faces  convex.  This 
is  the  case  in  crystals  of  diamond  (Fig.  476),  some  of  which  are  almost  spheres. 
The  mode  of  curvature,  in  which  all  the  faces  are  equally  convex,  is  less 
common  than  that  in  which  a  convex  surface  is  opposite  and  parallel  to  a 
corresponding  concave  surface.  Rhombohedrons  of  dolomite  and  siderite  are 
usually  thus  curved.  The  feathery  curves  of  frost  on  windows  and  the 
flagging-stones  of  pavements  in  winter  are  other  examples.  The  alabaster 
rosettes  from  the  Mammoth  Cave,  Kentucky,  are  similar.  Stibnite  crystals 
sometimes  show  very  remarkable  curved  and  twisted  forms. 

A  third  kind  of  curvature  is  of  mechanical  origin.  Sometimes  crystals 
appear  as  if  they  had  been  broken  transversely  into  many  pieces,  a  slight 
displacement  of  which  has  given  a  curved  form  to  the  prism.  This  is  common 
in  tourmaline  and  beryl.  The  beryls  of  Monroe,  Conn.,  often  present  these 
interrupted  curvatures,  as  represented  in  Fig.  477. 

Crystals  not  infrequently  occur  with  a  deep  pyramidal  depression  occupy- 
ing the  place  of  each  plane,  as  is  often  observed  in  common  salt,  alum,  and 
sulphur.  This  is  due  in  part  to  their  rapid  growth. 

3.     VARIATIONS   IN  THE   ANGLES   OF  CRYSTALS 

262.  The  greater  part  of  the  distortions  described  in  Arts  256,  257 
occasion  no  change  in  the  interfacial  angles  of  crystals.     But  those  imper- 
fections that  produce  convex,  curved,  or  striated  faces  necessarily  cause  such 
variations.     Furthermore,  circumstances  of  heat  or  pressure  under  which 
the  crystals  were  formed  may  sometimes  have  resulted  not  only  in  distortion 
of  form,  but  also  some  variation  in  angle.     The  presence  of  impurities  at  the 
time  of  crystallization  may  also  have  a  like  effect. 

Still  more  important  is  the  change  in  the  angles  of  completed  crystals 
which  is  caused  by  subsequent  pressure  on  the  matrix  in  which  they  were 
formed,  as,  for  example,  the  change  which  may  take  place  during  the  more  or 
less  complete  metamorphism  of  the  inclosing  rock. 

The  change  of  composition  resulting  in  pseudomorphous  crystals  (see 
Art.  273)  is  generally  accompanied  by  an  irregular  change  of  angle,  so  that 
the  pseudomorphs  of  a  species  vary  much  in  angle. 

In  general  it  is  safe  to  affirm  that,  with  the  exception  of  the  irregularities 
arising  from  imperfections  in  the  process  of  crystallization,  or  from  the  sub- 
sequent changes  alluded  to,  variations  in  angles  are  rare,  and  the  constancy 
of  angle  alluded  to  in  Art.  11  is  the  universal  law. 

In  cases  where  a  greater  or  less  variation  in  angle  is  observed  in  the  crystals 
of  the  same  species  from  different  localities,  the  cause  for  this  can  usually  be 
found  in  a  difference  of  chemical  composition.  In  the  case  of  isomorphous 
compounds  it  is  well  known  that  an  exchange  of  corresponding  chemically 
equivalent  elements  may  take  place  without  a  change  of  form,  though  usually 
accompanied  with  a  slight  variation  in  the  fundamental  angles. 

The  effect  of  heat  upon  the  form  of  crystals  is  alluded  to  in  Art.  433. 

4.     INTERNAL  IMPERFECTIONS   AND   INCLUSIONS 

263.  The  transparency  of  crystals  is  often  destroyed  by  disturbed  crystal- 
lization;   by  impurities  taken  up  from  the  solution  during  the  process  of 
crystallization;   or,  again,  by  the  presence  of  foreign  matter  resulting  from 


IRREGULARITIES   OF   CRYSTALS  179 

partial  chemical  alteration.  The  general  name,  inclusion,  is  given  to  any 
foreign  body  inclosed  within  the  crystal,  whatever  its  origin.  These  inclusions 
are  extremely  common;  they  may  be  gaseous,  liquid,  or  solid;  visible  to  the 
unaided  eye  or  requiring  the  use  of  the  microscope. 

Rapid  crystallization  is  a  common  explanation  of  inclusions.  This  is 
illustrated  by  quartz  crystals  containing  large  cavities  full  or  nearly  full  of 
water  (in  the  latter  case,  these  showing  a  movable  bubble);  or,  they  may 
contain  sand  or  iron  oxide  in  large  amount.  In  the  case  of  calcite,  crystalliza- 
tion from  a  liquid  largely  charged  with  a  foreign  material,  as  quartz  sand,  may 
result  in  the  formation  of  crystals  in  which  the  impurity  makes  up  as  much 
as  two-thirds  of  the  whole  mass;  this  is  seen  in  the  famous  Fontainebleau 
limestone,  and  similarly  in  that  from  other  localities. 

264.  Liquid  and  Gas  Inclusions.  —  Attention  was  early  called  by 
Brewster  to  the  presence  of  fluids  in  cavities  in  certain  minerals,  as  quartz, 
topaz,  beryl,  chrysolite,  etc.  In  later  years  this  subject  has  been  thoroughly 
studied  by  Sorby,  Zirkel,  Vogelsang,  Fischer,  Rosenbusch,  and  others.  The 
nature  of  the  liquid  can  often  be  determined,  by  its  refractive  power,  or  by 
special  physical  test  (e.g.,  determination  of  the  critical  point  in  the  case  of 
CO2),  or  by  chemical  examination.  In  the  majority  of  cases  the  observed 
liquid  is  simply  water;  but  it  may  be  the  salt  solution  in  which  the  crystal  was 
formed,  and  not  infrequently,  especially  in  the  case  of  quartz,  liquid  carbon 
dioxide  (CO2),  as  first  proved  by  Vogelsang.  These  liquid  inclusions  are 
marked  as  such,  in  many  cases,  by  the  presence  in  the  cavity  of  a  movable 
bubble  of  gas.  Occasionally  cavities  contain  two 
liquids,  as  water  and  liquid  carbon  dioxide,  the 
latter  then  inclosing  a  bubble  of  the  same  sub- 
stance as  gas  (cf.  Fig.  478).  Interesting  exper- 
iments can  be  made  with  sections  showing  such 
inclusions  (cf.  literature,  p.  181).  The  mixture 
of  gases  yielded  by  smoky  quartz,  meteoric  iron, 
and  other  substances,  on  the  application  of  heat, 
has  been  analyzed  by  Wright. 

In  some  cases  the  cavities  appear  to  be  empty; 
if  they  then  have  a  regular  form  determined  by 
the  crystallization  of  the  species,  they  are  often 
called  negative  crystals.  Such  cavities  are  com- 
monly of  secondary  origin,  as  remarked  on  a  later  Beryllonite 
•pase. 

265.  Solid  Inclusions.  —  The  solid  inclusions  are  almost  infinite  in 
their  variety.  Sometimes  they  are  large  and  distinct,  and  can  be  referred  to 
known  mineral  species,  as  the  scales  of  gothite  or  hematite,  to  which  the 
peculiar  character  of  aventurine  feldspar  is  due.  Magnetite  is  a  very  common 
impurity  in  many  minerals,  appearing,  for  example,  in  the  Pennsbury  mica; 
quartz  is  also  often  mechanically  mixed,  as  in  staurolite  and  gmelinite 
the  other  hand,  quartz  crystals  very  commonly  inclose  foreign  material,  such 
as  chlorite,  tourmaline,  rutile,  hematite,  asbestus,  and  many  other  minerals. 
(Cf.  also  Arts.  266,  267.)  ,  , , 

The  inclusions  may  consist  of  a  heterogeneous  mass  of  material;   << 
granitic  matter  seen  in  orthoclase  crystals  in  a  porphyntic  granite;   or  the 
feldspar,  quartz,  etc.,  sometimes  inclosed  in  large  coarse  crystals  of  beryl  or 
spodumene,  occurring  in  granite  veins. 


180 


CRYSTALLOGRAPHY 


266.  Microlites,  Crystallites.  —  The  microscopic  crystals  observed  as 
inclusions  may  sometimes  be  referred  to  known  species,  but  more  generally 
their  true  nature  is  doubtful.  The  term  microlites,  proposed  by  Vogelsang, 
is  often  used  to  designate  the  minute  inclosed  crystals;  they  are  generally  of 
needlelike  form,  sometimes  quite  irregular,  and  often  very  remarkable  in  their 
arrangement  and  groupings;  some  of  them  are  exhibited  in  Fig.  484  and  Fig. 
485,  as  explained  below.  Where  the  minute  individuals  belong  to  known 
species  they  are  called,  for  example,  feldspar  microlites,  etc. 

Crystallites  is  an  analogous  term  used  by  Vogelsang  to  cover  those  minute 
forms  which  have  not  the  regular  exterior  form  of  crystals,  but  may  be  con- 
sidered as  intermediate  between  amorphous  matter  and  true  crystals.  Some 
of  the  forms  are  shown  in  Figs.  479-483;  they  are  often  observed  in  glassy 
volcanic  rocks,  and  also  in  furnace-slags.  A  series  of  names  has  been  given  to 
varieties  of  crystallites,  such  as  globulites,  margarites,  etc.  Trichite  and 
belonite  are  names  introduced  by  Zirkel;  the  former  name  is  derived  from 
i£,  hair;  trichites,  like  that  in  Fig.  483,  are  common  in  obsidian. 


479 


480 


481 


482 


Crystallites 

The  microscopic  inclusions  may  also  be  of  an  irregular  glassy  nature;  this 
kind  is  often  observed  in  crystals  which  have  formed  from  a  molten  mass,  as 
lava  or  the  slag  of  an  iron  furnace. 

267.  Symmetrically  Arranged  Inclusions.  —  In  general,  while  the  solid 
inclusions  sometimes  occur  quite  irregularly  in  the  crystals,  they  are  more 
generally  arranged  with  some  evident  reference  to  the  symmetry  of  the  form, 
or  external  faces  of  the  crystals.  Examples  of  this  are  shown  in  the  following 


484 


486 


Augite  (Zirkel) 


Leucite  (Zirkel) 


Garnet  inclosing  quartz 
(Heddle) 

figures.     Fig.  484  exhibits  a  crystal  of  augite,  inclosing  magnetite,  feldspar 
and  nephelite  microlites,  etc.     Fig.  485  shows  a  crystal  of  leucite,  a  species 


IRREGULARITIES   OF   CRYSTALS 


181 


whose  crystals  very  commonly  inclose  foreign  matter, 
tion  of  a  crystal  of  garnet,  containing  quartz. 


Fig.  486  shows  a  sec 


487 


488 


Andalusite 

Another  striking  example  is  afforded  by  andalusite  (Fig.  487),  in  which  the 
inclosed  carbonaceous  impurities  are  of  considerable  extent  and  remarkably 
arranged,  so  as  to  yield  symmetrical  figures  of  various  forms.  Staurolite 
occasionally  shows  analogous  carbonaceous  impurities  symmetrically  dis- 
tributed. 

The  magnetite  common  as  an  inclusion  in  muscovite,  alluded  to  above, 
is  always  symmetrically  disposed,  usually  parallel   to 
the  directions  of  the  percussion-figure  (Fig.  491,  p.  189). 
The  asterism  of  phlogopite  is  explained  by  the  presence 
of  symmetrically  arranged  inclusions  (cf,  Art,  368). 


Fig.  488  shows  an  interesting  case  of  symmetrically  arranged 
inclusions  due  to  chemical  alteration.  The  original  mineral, 
spodumene,  from  Branchville,  Conn.,  has  been  altered  to  a 
substance  apparently  homogeneous  to  the  eye,  but  found 
under  the  microscope  to  have  the  structure  shown  in  Fig.  488. 
Chemical  analysis  proves  the  base  to  be  albite  and  the  inclosed 
hexagonal  mineral  to  be  a  lithium  silicate  (LiAlSO4)  called 
eucryptite.  It  has  not  yet  been  identified  except  in  this 
form. 

LITERATURE 


Eucryptite  in  Albite 


Some  of  the  most  important  works  on  the  subject  of  microscopic  inclusions  are  referred 
to  here;  for  a  fuller  list  of  papers  reference  may  be  made  to  the  work  of  Rosenbusch  (1904) ; 
also  that  of  Zirkel  and  others  mentioned  on  pp.  3  and  4. 

Brewster.  Many  papers,  published  mostly  in  the  Philosophical  Magazine,  and  the 
Edinburgh  Phil.  Journal,  from  1822-1856. 

Blum,  Leonhard,  Seyfert,  and  Sochting.  Die  Einschlusse  von  Mineralien  in  krystalli- 
sirten  Mineralien.  Haarlem,  1854.  (Preisschrift.) 

Sorby.  On  the  microscopical  structure  of  crystals,  etc.  Q.  J.  G.  Soc.,  14,  453,  1858 
(and  other  papers). 

Sorby  and  Butler.  On  the  structure  of  rubies,  sapphires,  diamonds,  and  some  other 
minerals.  Proc.  Roy.  Soc.,  No.  109,  1869. 

Reusch.     Labradorite.     Pogg.  Ann.,  120,  95,  1863. 

Vogelsang.     Labradorite.     Arch.  Neerland,  3,  32,  1868. 

Fischer.  Kritische-microscopische  mineralogische  Studien.  Freiburg  in  Br.,  64  pp., 
1869;  Ite  Fortsetzung,  64  pp.,  1871;  2te  Forts.,  96  pp.,  1873 

Kosmann.     Hypersthene.  Jahrb.  Min.,  532,  1869;  501,  1871. 

Schrauf.     Labradorite.     Ber.  Ak.  Wien,  60  (1)  996,  1869. 

Vogelsang.     Die  Krystalliten.     175  pp.,  Bonn,  1875. 

Vogelsang  and  Geissler.  Ueber  die  Natur  der  Flussigkeitsemschlusse  in  gewissen 
Mineralien.  Pogg.  Ann,  137,  56,  257,  1869 

Hartley.  Liquid  CO2  in  cavities,  etc.  J.  Chem.  Soc.,  1,  137;  2,  237,  1876,  1,  241,  2, 
271,  1877;  also,  Proc.  Roy.  Soc,  26,  137,  150,  1877  _ 

Gumbel.     Enhydros.     Ber.  Ak.  Miinchen,  10,  241,  1880;  11,  321,  1881. 

Hawes.     Smoky  quartz  (CO.).     Am.  J.  Sc    21,203,  1881 

A.  W.  Wright.     Gases  in  smoky  quartz.     Am  J.  fee,  21,  209,  l? 

Rutley.     Notes  on  Crystallites.     Mm.  MM.,  t,  2W-,  18M. 

Vater.     Das  Wesen  der  Krystalliten,  Zs.  Kr,  27,  505,  189b. 


182  CEYSTALLOGBAPHY 


CRYSTALLINE  AGGREGATES 

268.  The  greater  part  of  the  specimens  or  masses  of  minerals  that  occur 
may  be  described  as  aggregations  of  imperfect  crystals.     Many  specimens 
whose  structure  appears  to  the  eye  quite  homogeneous,  and  destitute  internally 
of  distinct  crystallization,  can  be  shown  to  be  composed  of  crystalline  grains. 
Under  the  above  head,  consequently,  are  included  all  the  remaining  varieties 
of  structure  among  minerals. 

The  individuals  composing  imperfectly  crystallized  individuals  may  be: 

1.  Columns,  or  fibers,  in  which  case  the  structure  is  columnar  or  fibrous. 

2.  Thin  lamince,  producing  a  lamellar  structure. 

3.  Grains,  constituting  a  granular  structure. 

269.  Columnar  and  Fibrous  Structure.  —  A  mineral  possesses  a  col- 
umnar structure  when  it  is  made  up  of  slender  columns,  as  some  amphibole. 
When  the  individuals  are  flattened  like  a  knife-blade,  as  in  cyanite,  the  struc- 
ture is  said  to  be  bladed. 

The  structure  again  is  called  fibrous  when  the  mineral  is  made  up  of  fibres, 
as  in  asbestus,  also  the  satin-spar  variety  of  gypsum.  The  fibres  may  or  may 
not  be  separable.  There  are  many  gradations  between  coarse  columnar  and 
fine  fibrous  structures.  Fibrous  minerals  have  often  a  silky  luster. 

The  following  are  properly  varieties  of  columnar  or  fibrous  structure : 

Reticulated:  when  the  fibers  or  columns  cross  in  various  directions  and 
produce  an  appearance  having  some  resemblance  to  a  net. 

Stellated:  when  they  radiate  from  a  center  in  all  directions  and  produce 
star-like  forms.  Ex.  stilbite,  wavellite. 

Radiated,  divergent:  when  the  crystals  radiate  from  a  center  without 
producing  stellar  forms.  Ex.  quartz,  stibnite. 

270.  Lamellar  Structure.  —  The    structure   of  a   mineral    is   lamellar 
when  it  consists  of  plates  or  leaves.     The  laminae  may  be  curved  or  straight, 
and  thus  give  rise  to  the  curved  lamellar  and  straight  lamellar  structure.     Ex. 
wollastonite  (tabular  spar),  some  varieties  of  gypsum,  talc,  etc.     If  the  plates 
are  approximately  parallel  about  a  common  center  the  structure  is  said  to  be 
concentric.     When  the  laminae  are  thin  and  separable,  the  structure  is  said  to 
be  foliaceous  or  foliated.     Mica  is  a  striking  example,  and  the  term  micaceous 
is  often  used  to  describe  this  kind  of  structure. 

271.  Granular  Structure.  —  The  particles  in  a  granular  structure  differ 
much  in  size.     When  coarse,  the  mineral  is  described  as  coarse-granular;  when 
fine,  fine-granular;  and  if  not  distinguishable  by  the  naked  eye,  the  structure  is 
termed  impalpable.     Examples  of  the  first  may  be  observed  in  granular  crys- 
talline limestone,  sometimes  called  saccharoidal;  of  the  second,  in  some  varie- 
ties of  hematite;  of  the  last,  in  some  kinds  of  sphalerite. 

The  above  terms  are  indefinite,  but  from  necessity,  as  there  is  every  degree 
of  fineness  of  structure  among  mineral  species,  from  perfectly  impalpable, 
through  all  possible  shades,  to  the  coarsest  granular.  The  term  phanero-crys- 
talline  has  been  used  for  varieties  in  which  the  grains  are  distinct,  and  crypto- 
crystalline  for  those  in  which  they  are  not  discernible,  although  an  indistinct 
crystalline  structure  can  be  proved  by  the  microscope. 

Granular  minerals,  when  easily  crumbled  in  the  fingers,  are  said  to  be  friable. 
f  -272.  Imitative  Shapes.  —  The  following  are  important  terms  used  in 
describing  the  imitative  forms  of  massive  minerals. 


CRYSTALLINE   AGGREGATES  183 

Reniform:  kidney-shaped.  The  structure  may  be  radiating  or  concentric 
Ex.  hematite. 

Botryoidal:  consisting  of  a  group  of  rounded  prominences.  The  name  is 
derived  from  the  Greek  Corpus,  a  bunch  of  grapes.  Ex.  limonite,  chalcedony 
prehnite. 

Mammillary:  resembling  the  botryoidal,  but  composed  of  larger  promi- 
nences. Ex.  malachite. 

Globular:  spherical  or  nearly  so;  the  globules  may  consist  of  radiating 
fibres  or  concentric  coats.  When  attached,  as  they  usually  are,  to  the  surface 
of  a  rock,  they  are  described  as  implanted  globules. 

Nodular:  in  tuberose  forms,  or  having  irregular  protuberances  over  the 
surface. 

Amygdaloidal:    almond-shaped,  applied  often  to  a  rock  (as  diabase)  con- 
taining almond-shaped  or  sub-globular  nodules. 

Coralloidal:  like  coral,  or  consisting  of  interlaced  flexuous  branchings  of  a 
white  color,  as  in  the  variety  of  aragonite  called  flos  ferri. 

Dendritic:  branching  tree-like,  as  in  crystallized  gold.  The  term  den- 
drites  is  used  for  similar  forms  even  when  not  crystalline,  as  in  the  dendrites 
of  manganese  oxide,  which  form  on  surfaces  of  limestone  or  are  inclosed  in 
"moss-agates." 

Mossy:  like  moss  in  form  or  appearance. 

Filiform  or  Capillary:  very  slender  and  long,  like  a  thread  or  hair;  con- 
sists ordinarily  of  a  succession  of  minute  crystals.  Ex.  millerite. 

Acicular:  slender  and  rigid,  like  a  needle.     Ex.  stibnite. 

Reticulated:  net-like.     See  Art.  269. 

Drusy:  closely  covered  with  minute  implanted  crystals.     Ex.  quartz. 

Stalactitic:  when  the  mineral  occurs  in  pendent  columns,  cylinders,  or 
elongated  cones.  Stalactites  are  produced  by  the  percolation  of  water,  hold- 
ing mineral  matter  in  solution,  through  the  rocky  roofs  of  caverns.  The 
evaporation  of  the  water  produces  a  deposit  of  the  mineral  matter,  and  grad- 
ually forms  a  long  pendent  cylinder  or  cone.  The  internal  structure  may  be 
imperfectly  crystalline  and  granular,  or  may  consist  of  fibres  radiating  from 
the  central  column,  or  there  may  be  a  broad  cross-cleavage.  The  most  famil- 
iar example  of  stalactites  is  afforded  by  calcite.  Chalcedony,  gibbsite, 
limonite,  and  some  other  species,  also  present  stalactitic  forms. 

The  term  amorphous  is  used  when  a  mineral  has  not  only  no  crystalline 
form  or  imitative  shape,  but  does  not  polarize  the  light  even  in  its  minute 
particles,  and  thus  appears  to  be  destitute  wholly  of  a  crystalline  structure 
internally,  as  most  opal.  Such  a  structure  is  also  called  colloid  or  jelly-like, 
from  the  Greek  /coXXa  (see  p.  8),  for  glue.  The  word  amorphous  is  from  a 
privative,  and  M°P</>??,  shape. 


273.  Pseudomorphous  Crystals.  —  Every  mineral  species  has,  when 
distinctly  crystallized,  a  definite  and  characteristic  form.  Occasionally, 
however,  crystals  are  found  that  have  the  form,  both  as  to  angles  and  general 
habit,  of  a  certain  species,  and  yet  differ  from  it  entirely  in  chemical  composi- 
tion. Moreover,  it  is  often  noted  in  such  cases  that,  though  in  outward  form 
complete  crystals,  in  internal  structure  they  are  granular,  or  waxy,  and  have 
no  regular  cleavage.  Even  if  they  are  crystalline  in  structure  the  optical 
characters  do  not  conform  to  those  required  by  the  symmetry  of  the  faces. 


1 84  CR  YSTALLO  GR  APH  Y 

Such  crystals  are  called  pseudomorphs,  and  their  existence  is  explained  by 
the  assumption,  often  admitting  of  direct  proof,  that  the  original  mineral  has 
been  changed  into  the  new  compound;  or  it  has  disappeared  through  some 
agency,  and  its  place  been  taken  by  another  chemical  compound  to  which  the 
form  does  not  belong.  In  all  these  cases  the  new  substance  is  said  to  be  a 
pseudomorph  after  the  orginal  mineral. 

Common  illustrations  of  pseudomorphous  crystals  are  afforded  by  mala- 
chite in  the  form  of  cuprite,  limonite  in  the  form  of  pyrite,  barite  in  the  form  of 
quartz,  etc.  This  subject  is  further  discussed  in  the  chapter  on  Chemical 
Mineralogy. 


PART  II.    PHYSICAL  MINERALOGY 


274.  The   PHYSICAL   CHARACTERS  of  minerals  fall  under  the  following 
heads : 

I.  Characters  depending  upon  Cohesion  and  Elasticity  —  viz.,  cleavage, 
fracture,  tenacity,  hardness,  elasticity,  etc. 

II.  Specific  Gravity,  or  the  Density  compared  with  that  of  water. 

III.  Characters  depending  upon  Light — viz.,  color,  luster,  degree  of  trans- 
parency, special  optical  properties,  etc. 

IV.  Characters  depending  upon  Heat  — viz.,  heat-conductivity,  change  of 
form  and  of  optical  characters  with  change  of  temperature,  fusibility,  etc. 

V.  Characters  depending  upon  Electricity  and  Magnetism. 

VI.  Characters  depending  upon  the  action  of  the  senses — viz.,  taste, 
odor,  feel. 

275.  General  Relation  of  Physical  Characters  to  Molecular  Structure.— 
It  has  been  stated  on  pp.  7,  8  that  the  geometrical  form  of  a  crystallized  min- 
eral is  the  external  evidence  of  the  internal  molecular  structure.     A  full 
knowledge  in  regard  to  this  structure,  however,  can  only  be  obtained  by 
the  study  of  the  various  physical  characters  included  in  the  classes  enumerated 
above. 

Of  these  characters,  the  specific  gravity  merely  gives  indication  of  the 
atomic  mass  of  the  elements  present,  and  further,  of  the  state  of  molecular 
aggregation.  The  first  of  these  points  is  illustrated  by  the  high  specific 
gravity  of  compounds  of  lead;  the  second,  by  the  distinction  observed,  for 
example,  between  carbon  in  the  form  of  the  diamond,  with  a  specific  gravity 
of  3' 5,  and  the  same  chemical  substance  as  the  mineral  graphite,  with  a  specific 
gravity  of  only  2. 

All  the  other  characters  (except  the  relatively  unimportant  ones  of  Class 
VI)  in  general  vary  according  to  the  direction  in  the  crystal;  in  other  words 
they  have  a  definite  orientation.  For  all  of  them  it  is  true  that  directions 
which  are  crystallographically  identical  have  like  physical  characters. 

In  regard  to  the  converse  proposition  —  viz.,  that  in  all  directions  crystal- 
lographically dissimilar  there  may  be  a  variation  in  the  physical  characters,  an 
important  distinction  is  to  be  made.  This  proposition  holds  true  for  all 
crystals,  so  far  as  the  characters  of  Class  I  are  concerned;  that  is,  those 
depending  upon  the  cohesion  and  elasticity,  as  shown  in  the  cleavage,  hard- 
ness, the  planes  of  molecular  gliding,  the  etching-figures,  etc.  It  is  also  true 
in  the  case  of  pyro-electricity  and  piezo-electricity. 

It  does  not  apply  in  the  same  way  with  respect  to  the  characters  which 
involve  the  propagation  of  light  (and  radiant  heat),  the  change  of  volume  with 
change  of  temperature;  further,  electric  radiation,  magnetic  induction,  etc. 

185 


186  PHYSICAL   MINERALOGY 

Thus,  although  it  will  be  shown  that  the  optical  characters  of  crystals  are 
in  agreement  in  general  with  the  symmetry  of  their  form,  they  do  not  show 
all  the  variations  in  this  symmetry.  It  is  true,  for  example,  that  all  directions 
are  optically  similar  in  a  crystal  belonging  to  any  class  under  the  isometric 
system;  but  this  is  obviously  not  true  of  its  molecular  cohesion,  as  may  be 
shown  by  the  cleavage.  Again,  all  directions  in  a  tetragonal  crystal  at  right 
angles  to  the  vertical  axis  are  optically  similar;  but  this  again  is  not  true  of 
the  cohesion.  These  points  are  further  elucidated  under  the  description  of 
the  special  characters  of  each  group. 


I.  CHARACTERS  DEPENDING  UPON  COHESION  AND 

ELASTICITY 

\ 

276.  Cohesion,  Elasticity.  —  The  name  cohesion  is  given  to  the  force  of 

attraction  existing  between  the  molecules  of  one  and  the  same  body,  in  con- 
sequence of  which  they  offer  resistance  to  any  influence  tending  to  separate 
them,  as  in  the  breaking  of  a  solid  body  or  the  scratching  of  its  surface. 

Elasticity  is  the  force  which  tends  to  restore  the  molecules  of  a  body  back 
into  their  original  position,  from  which  they  have  been  disturbed,  as  when  a 
body  has  suffered  change  of  shape  or  of  volume  under  pressure. 

The  varying  degrees  of  cohesion  and  elasticity  for  crystals  of  different 
minerals,  or  for  different  directions  in  the  same  crystal,  are  shown  in  the 
prominent  characters:  cleavage,  fracture,  tenacity,  hardness;  also  in  the 
gliding-planes,  percussion-figures  or  pressure-figures,  and  the  etching-figures. 

277.  Cleavage.  —  Cleavage  is  the  tendency  of  a  crystallized  mineral  to 
break  in  certain  definite  directions,  yielding  more  or  less  smooth  surfaces. 
It  obviously  indicates  a  minimum  value  of  cohesion  in  the  direction  of  easy 
fracture  —  that  is,  normal  to  the  cleavage-plane  itself.     The  cleavage  parallel 
to  the  cubic  faces  of  a  crystal  of  galena  is  a  familiar  illustration.     An  amor- 
phous body  (p.  8)  necessarily  can  show  no  cleavage. 

As  stated  in  Art.  31,  the  consideration  of  the  molecular  structure  of 
crystals  shows  that  a  cleavage-plane  must  be  a  direction  in  which  the  mole- 
cules are  closely  aggregated  together;  while  normal  to  this  the  distance 
between  successive  layers  of  molecules  must  be  relatively  large,  and  hence  this 
last  is  the  direction  of  easy  separation.  It  further  follows  that  cleavage  can 
exist  only  parallel  to  some  possible  face  of  a  crystal,  and,  further,  that  this 
must  be  one  of  the  common  fundamental  forms.  Hence  in  cases  where  the 
choice  in  the  position  of  the  axes  is  more  or  less  arbitrary  the  presence  of 
cleavage  is  properly  regarded  as  showing  which  planes  should  be  made  funda- 
mental. Still  again,  cleavage  is  the  same  in  all  directions  in  a  crystal  which 
are  crystallographically  identical. 

Cleavage  is  defined,  (1)  according  to  its  direction,  as  cubic,  octahedral, 
rhomobohedral,  basal,  prismatic,  etc.  Also,  (2)  according  to  the  ease  with 
which  it  is  obtained,  and  the  smoothness  of  the  surface  yielded.  It  is  said  to 
be  perfect  or  eminent  when  it  is  obtained  with  great  ease,  affording  smooth, 
lustrous  surfaces,  as  in  mica,  topaz,  calcite.  Inferior  degrees  of  cleavage  are 
spoken  of  as  distinct,  indistinct  -or  imperfect,  interrupted,  in  traces,  difficult. 
These  terms  are  sufficiently  intelligible  without  further  explanation.  It  may 
be  noticed  that  the  cleavage  of  a  species  is  sometimes  better  developed  in  some 
of  its  varieties  than  in  others. 


CHARACTERS   DEPENDING   UPON   COHESION   AND   ELASTICITY       187 

278.  Cleavage  in  the  Different  Systems.  —  (1)  In  the  ISOMETRIC  SYSTEM,  cleavage 
is  cubic,  when  parallel  to  the  faces  of  the  cube;   this  is  the  common  case,  as  illustrated  by 
galena  and  halite,     it  is  also  often  octahedral  —  that  is,  parallel  to  the  octahedral  faces  as 
with  fluonte  and  the  diamond.     Less  frequently  it  is  dodecahedral,  or  parallel  to  the  faces 
of  the  rhombic  dodecahedron,  as  with  sphalerite. 

In  the  TETRAGONAL  SYSTEM,  cleavage  is  often  basal,  or  parallel  to  the  basal  plane,  as 
with  apophylhte;  also  prismatic,  or  parallel  to  one  (or  both)  of  the  square  prisms  as  with 
rutile  and  wernerite;  less  frequently  it  is  pyramidal,  or  parallel  to  the  faces  of  the  square 
pyramid,  as  with  scheelite. 

In  the  HEXAGONAL  SYSTEM,  cleavage  is  usually  either  basal,  as  with  beryl,  or  prismatic, 
parallel  to  one  of  the  six-sided  prisms,  as  with  nephelite;  pyramidal  cleavage,  as  with 
pyromorphite,  is  rare  and  imperfect. 

In  the  RHOMBOHEDRAL  DIVISION,  besides  the  basal  and  prismatic  cleavages  rhombo- 
hedral  cleavage,  parallel  to  the  faces  of  a  rhombohedron,  is  also  common,  as  with  calcite 
and  the  allied  species. 

In  the  ORTHORHOMBIC  SYSTEM,  cleavage  parallel  to  one  or  more  of  the  pinacoids  is 
common.  Thus  it  is  basal  with  topaz,  and  in  all  three  pinacoidal  directions  with  anhydrite. 
Prismatic  cleavage  is  also  common,  as  with  barite;  in  this  case  the  arbitrary  position 
assumed  in  describing  the  crystal  may  make  this  cleavage  parallel  to  a  "horizontal  prism," 
or  dome. 

In  the  MONOCLINIC  SYSTEM,  cleavage  parallel  to  the  clinopinacoid,  is  common,  as  with 
orthoclase,  gypsum,  heulandite  and  euclase;  also  basal,  as  with  the  micas  and  orthoclase, 
or  parallel  to  the  orthopinacoid;  also  prismatic,  as  with  amphibole.  Less  frequently 
cleavage  is  parallel  to  a  hemi -pyramid,  as  with  gypsum. 

In  the  TRICLINIC  SYSTEM,  it  is  usual  and  proper  to  so  select  the  fundamental  form  as  to 
make  the  cleavage  directions  correspond  with  the  pinacoids. 

279.  In  some  cases  cleavage  which  is  ordinarily  not  observed  may  be  developed  by  a 
sharp  blow  or  by  sudden  change  of  temperature.     Thus,  quartz  is  usually  conspicuously 
free  from  cleavage,  but  a  quartz  crystal  heated  and  plunged  into  cold  water  often  shows 
planes  of  separation  *  parallel  to  both  the  +  and  —  rhombohedrqns  and  to  the  prism  as 
well.     Similarly,  the  prismatic  cleavage  of  pyroxene  is  observed  with  great  distinctness  in 
thin  sections,  made  by  grinding,  while  not  so  readily  noted  in  large  crystals. 

When  the  cleavage  is  parallel  to  a  closed  form  —  that  is,  when  it  is  cubic,  octahedral, 
dodecahedral,  or  rhombohedral  (also  pyramidal  in  the  tetragonal,  hexagonal,  and  ortho- 
rhombic  systems)  —  solids  resembling  crystals  may  often  be  broken  out  from  a  single 
crystalline"  individual,  and  all  the  fragments  have  the  same  angles.  It  is,  in  general,  easy 
to  distinguish  such  a  cleavage  form,  as  a  cleavage  octahedron  of  fluorite,  from  a  true 
crystal  by  the  splintery  character  of  the  faces  of  the  former. 

280.  Cleavage  and  Luster.  —  The  face  of  a  crystal  parallel  to  which  there  is  perfect 
cleavage  often  shows  a  pearly  luster  (see  p.  249),  due  to  the  partial  separation  of  the  crystal 
into  parallel  plates.     This  is  illustrated  by  the  basal  plane  of  apophyllite.  the  clinopina- 
coid of  stilbite  and  heulandite.     An  iridescent  play  of  colors  is  also  often  seen,  as  with 
calcite,    when  the  separation  has  been  sufficient  to  produce  the  prismatic  colors  by 
interference. 

281.  Gliding-planes.  —  Closely  related  to  the  cleavage  directions  in 
their  connection  with  the  cohesion  of  the  molecules  of  a  crystal  are  the  gliding- 
planes,  or  directions  parallel  to  which  a  slipping  of  the  molecules  may  take 
place  under  the  application  of  mechanical  force,  as  by  pressure. 

This  may  have  the  result  of  simply  producing  a  separation  into  layers  in 
the  given  direction,  or,  on  the  other  hand,  and  more  commonly,  there  may  be 
a  revolution  of  the  molecules  into  a  new  twinning-position,  so  that  secondary 
twinning-lamellce  are  formed. 

Thus,  if  a  crystal  of  halite,  or  rock  salt,  be  subjected  to  gradual  pressure 
in  the  direction  of  a  dodecahedral  face,  a  plane  of  separation  is  developed 
normal  to  this  and  hence  in  the  direction  of  another  face  of  the  same  form. 
There  are  six  such  directions  of  molecular  slipping  and  separation  in  a  crystal 
of  this  substance.  Certain  kinds  of  mica  of  the  biotite  class  often  show 

*  Lehmann  (Zs.  Kr.,  11,  608,  1886)  and  Judd  (Min.  Mag.,  8,  7,  1888^  regard  these  as 
gliding-planes  (see  Art.  281). 


188 


PHYSICAL   MINERALOGY 


Biotite 


pseudo-crystalline  faces,  which  are  undoubtedly  secondary  in  origin  —  that 
is,  have  been  developed  by  pressure  exerted  sub- 
sequently to  the  growth  of  the  crystal  (cf.  Fig.  489). 

In  stibnite,  the  base,  c(001),  normal  to  the  plane  of  perfect 
cleavage,  is  a  gliding-plane.  Thus  a  slipping  of  the  molecules 
without  their  separation  may  be  made  to  take  place  by 
pressure  in  a  plane  (||c)  normal  to  the  direction  of  perfect 
cleavage  (||6).  A  slender  prismatic  crystal  supported  near 
the  ends  and  pressed  downward  by  a  dull  edge  is  readily  bent, 
or  knicked,  in  this  direction  without  the  parts  beyond  the 
support  being  affected. 

282.  Secondary  Twinning.  -  -  The  other  case 
mentioned  in  the  preceding  article,  where  molecular 
slipping  is  accompanied  by  a  half -re  volution  (180°) 
of  the  molecules  into  a  new  twinning-position  (see  p.  160  et  seq.)jis  well  illus- 
trated by  calcite.  Pressure  upon  a  cleavage-fragment  may  result  in  the  forma- 
tion of  a  number  of  thin  lamella  in  twinning-position  to  the  parent  mass,  the 
twinning-plane  being  the  obtuse  negative  rhombohedron,  0(0112).  Second- 
ary twinning-lamellaB  similar  to  these  are  often  observed  in  natural  cleavage- 
masses  of  calcite,  and  particularly  in  the  grains  of  a  crystalline  limestone,  as 
observed  in  thin  sections  under  the  microscope. 

Secondary  twinning-lamellse  may  also  be  produced  (and  are  often  noted  in 
nature)   in  the  case  of  the  triclinic  feldspars,  pyroxene, 
barite,  etc.     A  secondary   lamellar    structure   in   quartz 
has    been    observed    by    Judd,    in    which    the    lamellae 
consisted  of  right-handed  and  left-handed  portions. 

By  the  proper  means  a  complete  calcite  twin  may  be  artificially 
produced  by  pressure.  Thus,  if  a  cleavage-fragment  of  prismatic 
form,  say  fr-8  mm.  in  length  and  3-6  mm.  in  breadth,  be  placed 
with  the  obtuse  edge  on  a  firm  horizontal  support,  and  pressed  by 
the  blade  of  an  ordinary  tableknife  on  the  other  obtuse  edge  (at  a, 
Fig.  490),  the  result  is  that  a  portion  of  the  crystal  is  reversed  in 
position,  as  if  twinned  parallel  to  the  plane  (0112)  which  in  the 
figure  lies  in  a  vertical  position.  If  skillfully  done,  the  twinning 
surface  is  perfectly  smooth,  and  the  re-entrant  angle  corresponds 
exactly  with  that  required  by  theory. 


490 


Artificial  Twinning 
in  Calcite 


283.  Parting.  —  The   secondary   twinning-planes   described   are    often 
directions  of  an  easy  separation  —  conveniently  called  parting  —  which  may 
be  mistaken  for  cleavage.*     The  basal  parting  of  pyroxene  is  a  common 
example  of  such  pseudo-cleavage;   it  was  long  mistaken  for  cleavage.     The 
basal  and  rhombohedral  (1011)  and  the  less  distinct  prismatic  (1120)  parting 
of  corundum;   the  octahedral  parting  of  magnetite  (cf.  Fig.  474,  p.  176),  are 
other  examples. 

An  important  distinction  between  cleavage  and  parting  is  this :  parting  can 
exist  only  in  certain  definite  planes —  that  is,  on  the  surface  of  a  twinning-lamel- 
la  —  while  the  cleavage  may  take  place  in  any  plane  having  the  given  direction. 

284.  Percussion-figures.  —  Immediately   connected   with  the   gliding- 
planes  are  the  figures  —  called  percussion-figures  f  —  produced  upon  a  crystal 

*  The  lamellar  structure  of  a  massive  mineral,  without  twinning,  may  also  be  the  cause 
of  a  fracture  which  can  be  mistaken  for  cleavage. 

t  The  percussion-figures  are  best  obtained  if  the  crystal  plate  under  investigation  be 
supported  upon  a  hard  cushion  and  a  blow  be  struck  with  a  light  hammer  upon  a  steel  rod 
the  slightly  rounded  point  of  which  is  held  firmly  against  the  surface. 


CHARACTERS   DEPENDING   UPON    COHESION   AND   ELASTICITY      189 


section  by  a  blow  or  pressure  with  a  suitable  point.  In  such  cases,  the  method 
described  serves  to  develop  more  or  less  well-defined  cracks  whose  orientation 
varies  with  the  crystallographic  direction  of  the  surface.  Thus  upon  the 
cubic  face  of  a  crystal  of  halite  a  four-rayed,  star-shaped  figure  is  produced 
with  arms  parallel  to  the  diagonals  —  that  is,  parallel  to 
the  dodecahedral  faces.  On  an  octahedral  face  a  three- 
rayed  star  is  obtained. 

The  percussion-figures  in  the  case  of  the  micas  have 
been  often  investigated,  and,  as  remarked  later,  they  form 
a  means  of  fixing  the  true  orientation  of  a  cleavage-plate 
having  no  crystalline  outlines.  The  figure  (Fig.  491)  is 
here  a  six-rayed  star  one  of  whose  branches  is  parallel  to 
the  clinopinacoid  (6),  the  others  approximately  parallel 
to  the  intersection  edges  of  the  prism  (m)  and  base  (c).* 

Pressure  upon  a  mica  plate  produces  a  less  distinct  six-rayed  star^diagonal 
to  that  just  named;  this  is  called  a  pressure-figure. 

285.  Solution-planes.  —  In  the  case  of  many  crystals,  it  is  possible  to  prove  the  ex- 
istence of  certain  directions,  or  structure-planes,  in  which  chemical  action  takes  place  most 
readily  —  for  example,  when  a  crystal  is  under  great  pressure.  These  directions  of  chemi- 
cal weakness  have  been  called  solution-planes.  They  often  manifest  themselves  by  the 
presence  of  a  multitude  of  oriented  cavities  of  crystalline  outline  (so-called  negative  crystals) 
in  the  given  direction. 

These  solution-planes  in  certain  cases,  as  shown  by  Judd,  are  the  same  as  the  directions 
of  secondary  lamellar  twinning,  as  is  illustrated  by  calcite.  Connected  with  this  is  the 
schillerization  (see  Art.  369),  observed  in  certain  minerals  in  rocks  (as  diallage,  schillerspar). 

286.  Etching-figures.  —  Intimately  connected  with  the  general  sub- 
jects here  considered,  of  cohesion  in  relation  to  crystals,  are  the  figures  pro- 
duced by  etching  on  crystalline  faces;  these  are  often  called  etching-figures. 
This  method  of  investigation,  developed  particularly  by  Baumhauer,  is  of  high 
importance  as  revealing  the  molecular  structure  of  the  crystal  faces  under 
examination,  and  therefore  the  symmetry  of  the  crystal  itself. 

The  etching  is  performed  mostly  by  solvents,  as  by  water  in  some  cases, 
more  generally  the  ordinary  mineral  acids,  or  caustic  alkalies,  also  by  steam  at 
a  high  pressure  and  hydrofluoric  acid;  the  last  is  especially  powerful  in  its 
action,  and  is  used  frequently  with  the  silicates.  The  figures  produced  are  in 

the  majority  of  cases  angular  depressions, 
such  as  low  triangular  or  quadrilateral 
pyramids,  whose  outlines  may  run  par- 
allel to  some  of  the  crystalline  edges. 
In  some  cases  the  planes  produced  can  be 
referred  to  occurring  crystallographic 
faces.  They  appear  alike  on  similar 
faces  of  crystals,  and  hence  serve  to 
distinguish  different  forms,  perhaps  in 
appearance  identical,  as  the  two  sets  of 
faces  in  the  ordinary  double  pyramid  of 
quartz;  so,  too,  they  reveal  the  corn- 
Quartz,  right-  Quartz,  left-  pound  twinning-structure  common  on 
handed  crystal  handed  crystal  some  crystals,  as  quartz  and  aragonite. 

*  Cf.  Walker,  Am.  J.  Sc.,  2,  5,  1896,  and  G.  Friedel,  Bull.  Soc.  Min.,  19,  18,  1896. 
Walker  found  the  angle  opposite  6(010)  (x  in  Fig.  491)  to  be  53°  to  56°  for  muscovite,  59° 
for  lepidolite,  60°  for  biotite,  and  61°  to  63°  for  phlogopite. 


492 


493 


190 


PHYSICAL   MINERALOGY 


Further,  their  form  in  general  corresponds  to  the  symmetry  of  the 
group  to  which  the  given  crystal  belongs.  They  thus  reveal  the  trape- 
zohedral  symmetry  of  quartz  and  the  difference  between  a  right-handed  and 
left-handed  crystal  (Figs.  492,  493);  the  distinction  between  calcite  and 
dolomite  (Figs.  496,  497) ;  the  distinctive  character  of  apatite,  pyromorphite, 
etc.;  the  hemimorphic  symmetry  of  calamine  and  nephelite  (cf.  Fig.  237, 
p.  102),  etc.;  they  also  prove  by  their  form  the  monoclinic  crystallization  of 
muscovite  and  other  micas  (Fig.  495). 

Fig.  494  shows  the  etching-figures  formed  on  a  basal  plane  (cleavage)  of  topaz  by  fused 
caustic  potash;  Fig.  495,  those  on  a  cleavage-plate  of  muscovite  by  hydrofluoric  acid;  Fig. 
496,  upon  a  rhombohedral  face  of  calcite,  and  Fig.  497,  on  one  of  dolomite  by  dilute  hydro- 
chloric acid. 


494 


495 


497 


Topaz 


Muscovite 


Calcite 


499 


Dolomite 
500 


Spangolite 

The  shape  of  the  etching-figures  may  vary  with  the  same  crystal  with  the  nature  of  the 
solvent  employed,  though  their  symmetry  remains  constant.     For  example,  Fig.  498  shows 

the  figures  obtained  with  spangolite 

601  502  by  the   action    of   sulphuric   acid, 

Fig.  499  by  the  same  diluted,  and 
Fig.  500  by  hydrochloric  acid  of 
different  degrees  of  concentration. 


Of  the  same  nature  as 
the  etching-figures  artificially 
produced,  in  their  relation  to 
the  symmetry  of  the  crystal, 
are  the  markings  of  ten  observed 
on  the  natural  faces  of  crys- 
tals. These  are  sometimes 
secondary,  caused  by  a  natural 

,,  etching  process,  but  are  more 

rften  an  irregularity  in  the  crystalline  development  of  the  crystal.  The 
inverted  triangular  depressions  often  seen  on  the  octahedral  faces  of  diamond 
crystals  are  an  example.  Fig.  501  shows  natural  depressions,  rhombohedral 
C h1aracter'  observed  on  corundum  crystals  from  Montana  (Pratt).  Fig. 
shows  a  twin  crystal  of  fluorite  with  natural  etching-figures  (Pirsson)  - 


Corundum 


Fluorite 


CHARACTERS   DEPENDING   UPON    COHESION   AND    ELASTICITY       191 

these  are  minute  pyramidal  depressions  whose  sides  are  parallel  to  the  faces 
of  the  trapezohedron  (311). 

287.  Corrosion  Forms.  —  If  the  etching  process  spoken  of  in  the  pre- 
ceding article  —  whether  natural  or  artificial  —  is  continued,  the  result  may 
be  to  destroy  the  original  crystalline  surface  and  to  substitute  for  it  perhaps  a 
multitude  of  minute  elevations,  more  or  less  distinct;   or,  further,  new  faces 
may  be  developed,  the  crystallographic  position  of  which  can  often  be  deter- 
mined, though  the  symbols  may  be  complex.     The  mere  loss  of  water  in  some 
cases  produces  certain  corrosive  forms. 

Penfield  subjected  a  sphere  of  quartz  (from  a  simple  right-handed  individual)  to  the 
prolonged  action  of  hydrofluoric  acid.  It  was  found  that  it  was  attacked  rapidly  in  the 
direction  of  the  vertical  axis,  but  barely  at  all  at  the  -\-  extremities  of  the  horizontal  axes. 
Figs.  503,  504  show  the  form  remaining  after  the  sphere  had  been  etched  for  seven  weeks; 
Fig.  503  is  a  basal  view;  Fig.  504,  a  front  view;  the  circle  shows  the  original  form  of  the 
sphere,  the  dotted  hexagon  the  position  of  the  axes. 

288.  Fracture.  —  The  term  fracture  is  used  to  define  the  form  or  kind 
of  surface  obtained  by  breaking  in  a  direction  other  than  that  of  cleavage  in 
crystallized  minerals,  and  503 

in  any  direction  in  mas- 
sive minerals.  When 
the  cleavage  is  highly 
perfect  in  several  direc- 
tions, as  the  rhombo- 
hedral  cleavage  of  calcite, 
fracture  is  often  not 
readily  obtainable. 

Fracture  is  defined  as  : 

(a)  Conchoidal;  when 
a    mineral    breaks    with  Etched  Sphere  of  Quartz 

SS?dS"1ftl^S3tod  from  the  resemblance  of  the  concavity  to  the  valve 
of  a  shell,  from  concha,  a  shell.  This  is  well  illustrated  by  obsidian,  also  by 
flint.  If  the  resulting  forms  are  small,  the  fracture  is  said  to  be  smaK-con- 
choidal-  if  only  partially  distinct,  it  is  subconchoidal. 

(6)  aL«,when  the  surface  of  fracture,  though  rough  with  numerous 
small  elevations  and  depressions,  still  approximates  to  a  plane  surface. 

(c)  Uneven;  when  the  surface  is  rough  and  entirely  irregular,  t 

°f  ™f  Hackf  when  the  elevations  are  sharp  or  jagged;  broken  iron. 

SffitS^i^t1,*^  by  the  re- 
sista'nc^  wSnaesmooth  surface  offers  to  abrasion.     V*&*£ 
determined  by  observing  the  comparative  ease  or  difficulty  with 

that  of  talc  impressible 


by   he  fingeaa,  to  that  ofthe  diamond.     To 
this  character,  a  scale  of  hardness  was  introduced  by 


scale  of  Mohs  is  now  universally  accepted. 


192  PHYSICAL   MINERALOGY 

1.  Talc.  6.  Orthoclase. 

2.  Gypsum  7.  Quartz. 

3.  Caltite.  8.  Topaz. 

4.  Fluorite.  9.  Corundum. 

5.  Apatite.  10.  Diamond. 

Crystalline  varieties  with  smooth  surfaces  should  be  taken  so  far  as 
possible. 

If  the  mineral  under  examination  is  scratched  by  the  knife-blade  as  easily 
as  calcite  its  hardness  is  said  to  be  3;  if  less  easily  than  calcite  and  more  so 
than  fluorite  its  hardness  is  3' 5.  In  the  latter  case  the  mineral  in  question 
would  be  scratched  by  fluorite  but  would  itself  scratch  calcite.  It  need 
hardly  be  added  that  great  accuracy  is  not  attainable  by  the  above  methods, 
though,  indeed,  for  purposes  of  the  determination  of  minerals,  exactness  is 
quite  unnecessary. 

It  should  be  noted  that  minerals  of  grade  1  have  a  greasy  feel  to  the  hand; 
those  of  grade  2  are  easily  scratched  by  the  finger-nail;  those  of  grade  3  are 
rather  readily  cut,  as  by  a  knife;  of  grade  4,  scratched  rather  easily  by  the 
knife;  grade  5,  scratched  with  some  difficulty;  grade  6,  barely  scratched  by  a 
knife,  but  distinctly  by  a  file  —  moreover,  they  also  scratch  ordinary  glass. 
Minerals  as  hard  as  quartz  (H.  =  7),  or  harder,  scratch  glass  readily  but  are 
little  touched  by  a  file;  the  few  species  belonging  here  are  enumerated  in 
Appendix  B;  they  include  all  the  gems. 

290.  Sclerometer.  —  Accurate  determinations  of  the  hardness  of  min- 
erals can  be  made  in  various  ways,  one  of  the  best  being  by  use  of  an  instru- 
ment called  a  sclerometer.  The  mineral  is  placed  on  a  movable  carriage,  with 
the  surface  to  be  experimented  upon  horizontal ;  this  is  brought  in  contact  with 
a  steel  point  (or  diamond  point),  fixed  on  a  support  above;  the  weight  is  then 
determined  which  is  just  sufficient  to  move  the  carriage  and  produce  a  scratch 
on  the  surface  of  the  mineral. 

By  means  of  such  an  instrument  the  hardness  of  the  different  faces  of  a 
given  crystal  has  been  determined  in  a  variety  of  cases.  It  has  been  found 
that  different  faces  of  a  crystal  (e.g.,  cyanite)  differ  in  hardness,  and  the  same 
face  may  differ  as  it  is  scratched  in  different  directions.  In  general,  differ- 
ences in  hardness  are  noted  only  with  crystals  which  show  distinct  cleavage; 
the  hardest  face  is  that  which  is  intersected  by  the  plane  of  most  complete 
cleavage.  Further,  of  a  single  face,  which  is  intersected  by  cleavage-planes, 
the  direction  perpendicular  to  the  cleavage-direction  is  the  softer,  those 
parallel  to  it  the  harder. 

This  subject  has  been  investigated  by  Exner  (p.  194),  who  has  given  the  form  of  the 
cwrves  of  hardness  for  the  different  faces  of  many  crystals.  These  curves  are  obtained  as 
follows:  the  least  weight  required  to  scratch  a  crystalline  surface  in  different  directions, 
for  each  10°  or  15°,  from  0°  to  180°,  is  determined  with  the  sclerometer;  these  directions 
are  laid  off  as  radii  from  a  center,  and  the  length  of  each  is  made  proportional  to  the  weight 
fixed  by  experiment  —  that  is,  to  the  hardness  thus  determined;  the  line  connecting  the 
extremities  of  these  radii  is  the  curve  of  hardness  for  the  given  face. 

The  following  table  gives  the  results  obtained  *  (see  literature)  in  comparing  the  hard- 
ness of  the  minerals  of  the  scale  from  corundum,  No.  9,  taken  as  1000,  to  gypsum,  No.  2. 
Pfaff  used  the  method  of  boring  with  a  standard  point,  the  hardness  being  determined  by 
the  number  of  rotations;  Rosiwal  used  a  standard  powder  to  grind  the  surface,  Jaggar 
employed  his  micro-scle  rometer,  the  method  being  essentially  a  modification  of  that  of 

*  The  numbers  are  here  given  as  tabulated  by  Jaggar. 


CHARACTERS   DEPENDING    UPON    COHESION   AND    ELASTICITY      193 

Pfaff.  By  means  of  this  instrument  he  is  able  to  test  the  hardness  of  the  minerals  present 
in  a  thin  section  under  the  microscope.  Measurements  of  absolute  hardness  have  also  been 
made  by  Auerbach.  Holmquist  has  recently  made  many  hardness  tests  by  the  grinding 
method.  His  results  with  regard  to  the  minerals  of  the  scale  of  hardness  agree  fairly  well 
with  those  ot  Rosiwal  given  below  but  show  considerable  discrepancies  with  the  results 
obtained  by  the  other  methods.  He,  like  Rosiwal,  finds  that  topaz  is  lower  in  the  scale 
than  quartz. 

Pfaff,  1884  Rosiwal,  1892  Jaggar,  1897 

9.  Corundum 1000  1000  1000 

8.  Topaz 459  138  152 

7.  Quartz 254  149  40 

6.  Orthoclase 191  287  25 

5.  Apatite :...  53'5  6'20  1'23 

4.  Fluorite 37'3  470  75 

3.  Calcite 15'3  2'68  '26 

2.  Gypsum 12'03  '34  '04 

291.  Relation  of  Hardness  to  Chemical  Composition.  —  Some  general  facts  of  impor- 
tance can  be  stated  *  in  regard  to  the  connection  between  the   hardness   of   a   mineral 
and  its  chemical  composition. 

1.  Compounds  of  the  heavy  metals,  as  silver,  copper,  mercury,  lead,  etc.,  are  soft,  their 
hardness  seldom  exceeding  2 '5  to  3. 

Among  the  compounds  of  the  common  metals,  the  sulphides  (arsenides)  and  oxides  of 
iron  (also  of  nickel  and  cobalt)  are  relatively  hard  (e.g.,  for  pyrite  H.  =  6  to  6'5;  for 
hematite  H.  =  6,  etc.);  here  belong  also  columbite,  iron  niobate;-  tantalite,  iron  tantalate; 
wolframite,  iron  tungstate. 

2.  The  sulphides  are  mostly  relatively  soft  (except  as  noted  in  1),  also  most  of  the 
carbonates,  sulphates,  and  phosphates. 

3.  Hydrous  salts  are  relatively  soft.    This  is  most  distinctly  shown  among  the  silicates 
—  e.g.,  compare  the  feldspars  and  zeolites. 

4.  The  conspicuously  hard  minerals  are  found  chiefly  among  the  oxides  and  silicates; 
many  of  them  are  compounds  containing  aluminium  —  e.g.,  corundum,  diaspore,  chryso- 
beryl,  and  many  alumino-silicates.     Outside  of  these  the  borate,  boracite,  is  hard  (H.  =  7); 
also  iridosmine. 

On  the  relation  of  hardness  to  specific  gravity,  see  Art.  302. 

292.  Practical  Suggestions.  —  Several  points  should  be   regarded    hi    the    trials   of 
hardness: 

(1)  If  the  mineral  is  slightly  altered,  as  is  often  the  case  with  corundum,  garnet,  etc., 
the  surface  may  be  readily  scratched  when  this  would  be  impossible  with  the  mineral  itself; 
a  trial  with  an  edge  of  the  latter  will  often  give  a  correct  result  in  such  a  case. 

(2)  A  mineral  with  a  granular  surface  often  appears  to  be  scratched  when  the  grains 
have  been  only  torn  apart  or  crushed. 

(3)  A  relatively  soft  mineral  may  leave  a  faint  white  ridge  on  a  surface,  as  of  glass, 
which  can  be  mistaken  for  a  scratch  if  carelessly  observed. 

(4)  A  crystal,  as  of  quartz,  is  often  slightly  scratched  by  the  edge  of  another  of  the  same 
species  and  like  hardness. 

(5)  The  scratch  should  be  made  in  such  a  way  as  to  disfigure  the  specimen  as  little  as 
possible. 

293.  Tenacity.  —  Minerals  may  be  either  brittle,  sectile,  malleable,  or 
flexible. 

(a)  Brittle;    when  parts  of  a  mineral  separate  in  powder  or  grains  on 
attempting  to  cut  it,  as  calcite. 

(b)  Sectile;    when  pieces  may  be  cut  off  with  a  knife  without  falling  to 
powder,  but  still  the  mineral  pulverizes  under  a  hammer.     This  character  is 
intermediate  between  brittle  and  malleable,  as  gypsum. 

(c)  Malleable;   when  slices  may  be  cut  off,  and  these  slices  flattened  out 
under  a  hammer;  native  gold,  native  silver. 

*  See  further  in  Appendix  B. 


194  PHYSICAL   MINERALOGY 

(d)  Flexible;  when  the  mineral  will  bend  without  breaking,  and  remain 
bent  after  the  bending  force  is  removed,  as  talc. 

The  tenacity  of  a  substance  is  properly  a  consequence  of  its  elasticity. 

294.  Elasticity.  —  The  elasticity  of  -a  solid  body  expresses  at  once  the 
resistance  which  it  makes  to  a  change  in  shape  or  volume,  and  also  its  tendency 
to  return  to  its  original  shape  when  the  deforming  force  ceases  to  act.  If  the 
limit  of  elasticity  is  not  passed,  the  change  in  molecular  position  is  proportional 
to  the  force  acting,  and  the  former  shape  of  volume  is  exactly  resumed;  if 
this  limit  is  exceeded,  the  deformation  becomes  permanent,  a  new  position  of 
molecular  equilibrium  having  been  assumed;  this  is  shown  in  the  phenomena 
of  gliding-planes  and  secondary  twinning,  already  discussed.  The  magni- 
tude of  the  elasticity  of  a  given  substance  is  measured  by  the  coefficient  of 
elasticity,  or,  better,  the  coefficient  of  restitution.  This  is  denned  as  the  rela- 
tion, for  example,  between  the  elongation  of  a  bar  of  unit  section  to  the  force 
acting  to  produce  this  effect;  similarly  of  the  bending  or  twisting  of  a  bar. 
The  subject  was  early  investigated  acoustically  by  Savart;  in  recent  years, 
Voigt  and  others  have  made  accurate  measures  of  the  elasticity  of  many  sub- 
stances and  of  the  crystals  of  the  same  substance  in  different  directions. 
The  elasticity  of  an  amorphous  body  is  the  same  in  all  directions,  but  it  changes 
in  value  with  change  of  crystallographic  direction  in  all  crystals. 

The  distinction  between  elastic  and  inelastic  is  often  made  between  the 
species  of  the  mica  group  and  allied  minerals.  Muscovite,  for  example,  is 
described  as  "  highly  elastic/'  while  phlogopite  is  much  less  so.  In  this  case 
it  is  not  true  in  the  physcial  sense  that  muscovite  has  a  high  value  for  the 
coefficient  of  elasticity;  its  peculiarity  lies  rather  in  the  fact  that  its  elasticity 
is  displayed  through  unusually  wide  limits. 

LITERATURE 
Hardness 

Seebeck.     Sklerometer.     Programm  d.  Coin  Realgymnasiums,  1833. 

Franz.     Pogg.,  80,  37,  1850. 

Grailich  u.  Pekarek.     Ber.  Ak.  Wien,  13,  410,  1854. 

Pfaff.     Mesosklerometer.     Ber.  Ak.  Munchen,  13,  55,  1883. 

Sohncke.     Halite.     Pogg.,  137,  177,  1869. 

Exner.  Ueber  die  Harte  der  Krystallflachen,  166  pp.  Vienna,  1873  (Preisschrift 
Wiener.  Akad.). 

Auerbach.     Wied.  Ann.,  43,  61,  1891;  45,  262,  277,  1892;  68,  357,  1896. 

Rosiwal.     Verb.  G.  Reichs.,  475,  1896. 

T.  A.  Jaggar,  Jr.     Microsclerometer.     Am.  J.  Sc.,  4,  399,  1897. 

Schroeder  van  der  Kolk.  Ueber  Harte  in  Verland  mit  Spaltbarkeit,  Verb.  Ak.  Am- 
sterdam, 8,  1901. 

Holmquist.  Ueber  den  Relativen  Abnutzungswiderstand  der  Mineralien  der  Harte- 
skala.  Geol.  For.  Forh.,  33,  281,  1911.  Die  Schleifharte  der  Feldspathe,  ibid.,  36,  401, 
1914.  Die  Hartestufe,  4-5,  ibid.,  38,  501,  1916. 

Etching-figures,  etc. 

Goldschmidt  and  Wright.  Ueber  Aetzfiguren,  Lichtfiguren  und  Losungskorper.  With 
exhaustive  references  to  the  literature.  N.  Jb.  Min.  Beil-Bd.,  17,  355-390,  1903. 

Gliding-planes,  Secondary  Twinning,  etc. 


)be,"  halite,  calcite.     Pogg.  Ann.,  132,  441,  1867.     Mica,  ibid., 
136,  130,  632,  1869.     Gypsum,  ibid.,  p.  135.     Ber.  Ak.,  Berlin,  440,  1873. 

~   61\  vSoMfe'     Pogg<  Ann-'  138>  337'  1869>  Zs"  G-  Ges->  26»  137»  1874-     Galena, 

L.,  1,  L6&, 


SPECIFIC    GRAVITY   OR   RELATIVE    DENSITY  195 

Baumhauer.     Calcite.     Zs.  Kr.,  3,  588,  1879. 
1  7™  898     Caldte>  augite>  stibnite>  etc.     Jb.  Min.,  1,  32,  1883;  2, 13,  1883.     Also  ibid., 

LiJ*  ^  JU?d<     Solution-planes   etc.     Q.  J.  G.  Soc.,  41,  374,  1885;   Min.  Mag.,  7,  81, 
1887.     Structure  planes  of  corundum,  Min.  Mag.,  11,  49   1895 
Voigt.     See  below. 

Elasticity 

Savart.     Ann.  Ch.  Phys.,  40,  1,  113,  1829;  also  in  Pogg.  Ann.,  16,  206,  1829. 

Neumann.     Pogg.  Ann.,  31,  177,  1834. 

Angstrom.     Pogg.  Ann.,  86,  206,  1852. 

Baumgarten.     Calcite.     Pogg.  Ann.,  152,  369,  1874. 

Groth.     Halite.     Pogg.  Ann.,  157,  115,  1876. 

Coromilas.     Gypsum,  mica.     Inaug.  Diss.,  Tubingen,  1877  (Zs.  Kr.,  1,  407,  1877) 

Reusch.     Ice.     Wied.  Ann.,  9,  329,  1880. 

Klang.     Fluorite.     Wied.  Ann.,  12,  321,  1881. 

Koch.     Halite,  sylvite.     Wied.  Ann.,  18,  325,  1883. 

Beckenkamp.     Alum.     Zs.  Kr.,  10,  41,  1885. 

Voigt.  Pogg.  Ann.,  Erg.  Bd.,  7,  1,  177,  1876.  Wied.  Ann.,  38,  573,  1889.  Calcite, 
39,  412,  1890.  Dolomite,  ibid.,  40,  642,  1890.  Tourmaline,  ibid.,  41,  712,  1890;  44,  168 
1891.  Also  papers  in  Nachr.  Ges.  Wiss.  Gottingen. 

Tutton.     The  Elasmometer.     Crystalline  Structure  and  Chemical  Constitution,  1910. 


II.   SPECIFIC  GRAVITY  OR  RELATIVE  DENSITY 

295.  Definition  of  Specific  Gravity.  —  The  specific  gravity  of  a  mineral 
is  the  ratio  of  its  density  *  to  that  of  water  at  4°  C.  (39'2°  F.).  This  relative 
density  may  be  learned  in  any  case  by  comparing  the  ratio  of  the  weight  of  a 
certain  volume  of  the  given  substance  to  that  of  an  equal  volume  of  water; 
hence  the  specific  gravity  is  often  defined  as:  the  weight  of  the  body  divided  by 
the  weight  of  an  equal  volume  of  water. 

The  statement  that  the  specific  gravity  of  graphite  is  2,  of  corundum  4,  of 
galena  7'5,  etc.,  means  that  the  densities  of  the  minerals  named  are  2,  4,  and 
7'5,  etc.,  times  that  of  water;  in  other  words,  as  familiarly  expressed,  any 
volume  of  them,  a  cubic  inch  for  example,  weighs  2  times,  4  times,  7*5  times, 
etc.,  as  much  as  a  like  volume,  a  cubic  inch,  of  water. 

Strictly  speaking,  since  the  density  of  water  varies  with  its  expansion  or 
contraction  under  change  of  temperature,  the  comparison  should  be  made  with 
water  at  a  fixed  temperature,  namely  4°  C.  (39'2°  F.),  at  which  it  has  its  maxi- 
mum density.  If  made  at  a  higher  temperature,  a  suitable  correction  should 
be  introduced  by  calculation.  Practically,  however,  since  a  high  degree  of 
accuracy  is  not  often  called  for,  and,  indeed,  in  many  cases  is  impracticable  to 
attain  in  consequence  of  the  nature  of  the  material  at  hand,  in  the  ordinary 
work  of  obtaining  the  specific  gravity  of  minerals  the  temperature  at  which 
the  observation  is  made  can  safely  be  neglected.  Common  variations  of  tem- 
perature would  seldom  affect  the  value  of  the  specific  gravity  to  the  extent  of 
one  unit  in  the  third  decimal  place. 

*  The  density  of  a  body  is  strictly  the  mass  of  the  unit  volume.  Thus  if  a  cubic  centi- 
meter of  water  (at  its  maximum  density,  4°  C.  or  39'2°  F.)  is  taken  as  the  unit  of  mass,  the 
density  of  any  body  —  as  gold  —  is  given  by  the  number  of  grams  of  mass  (about  19)  in  a 
cubic  centimeter;  in  this  case  the  same  number,  1.9,  gives  the  relative  density  or  specific 
gravity.  If,  however,  a  pound  is  taken  as  the  unit  of  mass,  and  the  cubic  foot  as  the  unit  of 
volume,  the  mass  of  a  cubic  foot  of  water  is  62'5  Ibs.,  that  of  gold  about  1188  Ibs.,  and  the 
specific  gravity  is  the  ratio  of  the  second  to  the  first,  or,  again,  19. 


196 


PHYSICAL   MINERALOGY 


For  the  same  reason,  it  is  not  necessary  to  take  into  consideration  the  fact 
that  the  observed  weight  of  a  fragment  of  a  mineral  is  less  than  its  true  weight 
by  the  weight  of  air  displaced. 

Where  the  nature  of  the  investigation  calls  for  an  accurate  determination 
of  the  specific  gravity  (e.g.,  to  four  decimal  places),  no  one  of  the  precautions 
in  regard  to  the  purity  of  material,  exactness  of  weight-measurement,  temper- 
ature, etc.,  can  be  neglected.*  The  accurate  values  spoken  of  are  needed  in 
the  consideration  of  such  problems  as  the  specific  volume,  the  relation  of  molec- 
ular volume  to  specific  gravity,  and  many  others. 

296.  Determination  of  the  Specific  Gravity  by  the  Balance.  —  The 
direct  comparison  by  weight  of  a  certain  volume  of  the  given  mineral  with  an 
equal  volume  of  water  is  not  often  practicable.  By  making  use,  however,  of 
a  familiar  principle  in  hydrostatics,  viz.,  that  a  solid  immersed  in  water,  in 
consequence  of  the  buoyancy  of  the  latter,  loses  in  weight  an  amount  which  is 
equal  to  the  weight  of  an  equal  volume  of  the  water  (that  is,  the  volume  it  dis- 
places) —  the  determination  of  the  specific  gravity  becomes  a  very  simple 
process. 

The  weight  of  the  solid  in  the  air  (w)  is  first  determined  in  the  usual  man- 
ner;  then  the  weight  in  water  is  found  (w')]    the  difference  between  these 
weights  —  that  is,  the  loss  by  immersion  (w  —  wf)  —  is  the  weight  of  a  volume 
505  of  water  equal  to  that  of  the  solid ;  finally,  the  quotient  of 

the  first  weight  (w)  by  that  of  the  equal  volume  of  water 
as  determined  (w  —  w')  is  the  specific  gravity  (G). 
Hence, 

w 


.   w  —  w' 

A  common  method  of  obtaining  the  specific  gravity  of 
a  firm  fragment  of  a  mineral  is  as  follows:  First  weigh 
the  specimen  accurately  on  a  good  chemical  balance. 
Then  suspend  it  from  one  pan  of  the  balance  by  a  horse- 
hair, silk  thread,  or,  better  still,  by  a  fine  platinum  wire, 
in  a  glass  of  water  conveniently  placed  beneath,  and  take 
the  weight  again  with  the  same  care;  then  use  the  results 
as  above  directed.  The  platinum  wire  may  be  wound 
around  the  specimen,  or  where  the  latter  is  small  it  may 
be  made  at  one  end  into  a  little  spiral  support. 

297.  The  Jolly  Balance.  —  Instead  of  using  an  ordin- 
ary balance  and  determining  the  actual  weight,  the  spiral 
balance  of  Jolly,  shown  in  Fig.  505,  maybe  conveniently 
employed;  this  is  also  suitable  when  the  mineral  is  in  the 
form  of  small  grains.  The  instrument  consists  of  a  spiral 
spring  at  the  lower  end  of  which  are  suspended  two  pans 

for'spedSfGravitv  or  ^  baskets>  '  and  d,  Fig.  505.  Upon  the  movable 
stand -B  rests  a  beaker  filled  with  water.  When  in  adjust- 
ment for  reading  this  stand  has  such  a  position  that  the  pan  d  is  immersed  in 
the  water  while  c  hangs  above  it.  Upon  the  upright  A  there  is  a  mirror  upon 
which  is  marked  a  scale.  The  position  of  the  balance  at  any  time  is  obtained 
by  so  placing  the  eye  that  the  bead,  m,  and  its  reflection  in  the  mirror  coincide 


Spring  or 
Jolly  Balance 


*  Cf.  Earl  of  Berkeley  in  Min.  Mag.,  11,  64,  1895. 


SPECIFIC   GRAVITY   OR   RELATIVE   DENSITY 


197 


and  then  reading  the  position  of  the  top  of  the  bead  upon  the  scale.  The  first 
step  in  the  operation  consists  in  getting  the  position  of  the  spring  alone,  having 
the  pan  d  immersed  in  the  water  in  the  beaker.  Let  this  reading  be  represented 
by  n.  The  mineral  whose  specific  gravity  is  to  be  determined  is  then  placed 
on  the  pan  or  basket,  c,  and  the  platform  B  raised  until  d  is  properly  immersed 
in  the  water.  The  position  of  the  bead  m  is  again  read.  Let  this  value  be 
represented  by  NI.  If  from  N\  be  subtracted  the  number  n,  expressing  the 
amount  to  which  the  scale  is  stretched  by  the  weight  of  spring  and  pans  alone, 
the  difference  will  be  proportional  to  the  weight  of  the  mineral.  Next,  the 
mineral  is  placed  in  the  lower  pan,  d,  immersed  in  the  water,  and  again  the 
corresponding  scale  number,  Nz,  read.  The  difference  between  these  readings 
(Ni  —  Nz)  is  a  number  proportional  to  the  loss  of  weight  in  water.  The 
specific  gravity  is  then 

Nj-n  . 


It  is  obviously  necessary  to  have  the  wires  supporting  the  lower  pan  immersed 
to  the  same  depth  in  the  case  of  each  of  the  three  determinations.  If  care  is 
taken  the  specific  gravity  can  be  obtained  accurately  to  two  decimal  places. 

298.  The  Beam  Balance.  —  A  beam  balance  described  by  Penfield  is 
another  very  simple  and  quite  accurate  device  for  measuring  the  specific 
gravity.  It  is  illustrated  in  Fig.  506,  which  will  make  clear  its  essential  parts. 
The  beam  is  so  balanced  by  a  weight  on  its  shorter  end  that  it  is  very  nearly 
in  equilibrium  when  the  lower  pan  is  immersed  in  water.  An  exact  balance 
is  then  obtained  by  the  small  rider  d.  When  the  beam  is  once  balanced  this 
rider  is  kept  stationary  and  its  position  disregarded  in  the  subsequent  readings. 
The  mineral  is  first  placed  in  the  upper  pan  and  the  beam  balanced  by  another 
rider  of  such  a  weight  that  its  position  will  be  near  the  outer  end  of  the  beam. 

506 


Beam  Balance  for  Specific  Gravity,  £th  Natural  Size  (after  Penfield) 

The  position  of  this  rider  is  then  read  from  the  scale  engraved  upon  the  beam. 
Let  this  value  be  equal  to  Ni.  The  mineral  is  next  transferred  to  the  lower 
pan  and  the  beam  again  brought  into  balance  by  moving  this  same  rider  back. 
The  second  reading  may  be  represented  by  N2.  The  formula  for  obtaining  the 
specific  gravity  is  now: 

n  Nl       . 

=  N^^"2 

299.   Pycnometer.  —  If  the  mineral  is  in  the  form  of  grains  or  small 
fragments,  the  specific  gravity  may  be  obtained  by  use  of  the  pycnometer. 


198  PHYSICAL  MINERALOGY 

This  is  a  small  bottle  (Fig.  507)  having  a  stopper  which  fits  tightly  and  ends  in 
a  tube  with  a  very  fine  opening.     The  bottle  is  filled  with  distilled  water,  the 
stopper  inserted,  and  the  overflowing  water  carefully  removed 
607  with  a  soft  cloth  and  then  weighed.     The  weight  of  the  water 

is  obviously  the  difference  between  this  last  weight  and  that 
of  the  bottle  and  mineral  together,  as  first  determined.  The 
mineral  whose  density  is  to  be  determined  is  also  weighed. 
Lastly  the  bottle  is  weighed  with  the  mineral  in  it  and  filled 
with  water  as  described  above.*  The  weight  of  the  water 
displaced  by  the  mineral  is  obviously  the  difference  between 
this  last  weight  and  that  of  the  bottle  filled  with  water  plus 
the  weight  of  the  mineral.  The  specific  gravity  of  the  min- 
eral is  equal  to  its  weight  alone  divided  by  the  weight  of  the 
equal  volume  of  water  thus  determined.  Where  this  method 

is  followed  with  sufficient  care,  especially  avoiding  any  change 

Pycnometer       of   temperature   in   the   water,   the   results  may  be  highly 

accurate. 

If  the  mineral  forms  a  porous  mass,  it  may  be  first  reduced  to  powder,  but 
it  is  to  be  noted  that  it  has  been  shown  by  Rose  that  chemical  precipitates 
have  uniformly  a  higher  density  than  belongs  to  the  same  substance  in  a  less 
finely  divided  state.  This  increase  of  density  also  characterizes,  though  to  a 
less  extent,  a  mineral  in  a  fine  state  of  mechanical  subdivision.  It  is  explained 
by  the  condensation  of  the  water  on  the  surface  of  the  powder. 

300.  Use  of  Liquids  of  High  Density.  —  It  is  often  found  convenient 
both  in  the  determination  of  the  specific  gravity  and  in  the  mechanical  separa- 
tion of  fragments  of  different  specific  gravities  (e.g.,  to  obtain  pure  material 
for  analysis,  or  again  in  the  study  of  rocks)  to  use  a  liquid  of  high  density  — 
that  is,  a  so-called  heavy  solution.  One  of  these  is  the  solution  of  mercuric 
iodide  in  potassium  iodide,  called  the  Sonstadt  or  Thoulet  solution.  When 
made  with  care  it  has  a  maximum  density  of  nearly  3 '2,  which  by  dilution 
may  be  lowered  at  will. 

A  second  solution,  often  employed,  is  the  Klein  solution,  the  borotungstate 
of  cadmium,  having  a  maximum  density  of  3*6.  This  again  may  be  lowered 
at  will  by  dilution,  observing  certain  necessary  precautions.  Still  a  third 
solution  of  much  practical  value  is  that  proposed  by  Brauns,  methylene  iodide, 
which  has  a  specific  gravity  of  3*324.  A  number  of  other  solutions,  more  or  less 
practical,  have  also  been  suggested.!  When  one  of  these  liquids  is  to  be  used 
for  the  determination  of  the  specific  gravity  of  fragments  of  a  certain  mineral 
it  must  be  diluted  until  the  fragments  just  float  and  the  specific  gravity  then 
obtained,  most  conveniently  by  the  Westphal  balance  (Art.  301). 

When,  on  the  other  hand,  the  liquid  is  to  be  used  for  the  separation  of  the 
fragments  of  two  or  more  minerals  mixed  together,  the  material  is  first  reduced 
to  the  proper  degree  of  fineness,  the  dust  and  smallest  fragments  being  sifted 
out,  then  it  is  introduced  into  the  solution  and  this  diluted  until  one  con- 
stituent after  another  sinks  and  is  removed.  For  the  convenient  application 

*  Care  should  be  taken  to  prevent  air-bubbles  being  included  among  the  mineral 
particles.  This  may  be  accomplished  by  placing  the  bottle  under  an  air-pump  and  ex- 
hausting the  air  or  by  suspending  the  bottle  for  a  short  time  in  a  beaker  filled  with  boiling 
water  and  then  allowing  it  to  cool  again  before  weighing. 

t  Johannsen,  Manual  of  Petrographic  Methods,  p.  519  et  seq.,  gives  in  detail  an  account 
of  the  various  solutions,  the  methods  of  their  preparation,  etc. 


SPECIFIC    GRAVITY   OR   RELATIVE    DENSITY  199 

of  this  method  a  suitable  tube  is  called  for  and  certain  precautions  must  be 
observed;  compare  the  papers  noted  in  the  literature  (p.  200),  especially  one 
by  Penfield. 

301.  Westphal's  Balance. -The  Westphal  balance  is  conveniently  used  to  determine 

^A.SPQen^C  gi?  Y  ?ia  qm<??  nnd  5ence  °j  a  mineral  when  a  heavy  solution  is  employed 
(Art.  300).  It  consists  essentially  of  a  graduated  steelyard  arm,  upon  which  the  weights 
in  the  form  of  riders  are  placed.  These  must  be  so  adjusted  that  the  sinker  is  freely  sus- 
pended m  the  given  liquid  while  the  index  at  the  end  points  to  the  zero  of  the  scale  and 
shows  that  the  arm  is  horizontal  (cf.  Johannsen,  p.  533).  The  graduation  usually  allows 
of  the  specific  gravity  being  read  off  directly  without  calculation. 

302.  Relation  of  Density  to  Hardness,  Chemical  Composition,  etc.— The  density  or 
specific  gravity,  of  a  solid  depends,  first,  upon  the  nature  of  the  chemical  substances  which 
it  contains,  and,  second,  upon  the  state  of  molecular  aggregation. 

Thus,  as  an  illustration  of  the  first  point,  all  lead  compounds  have  a  high  density 
(G.  =  about  6),  since  lead  is  a  heavy  metal,  or,  chemically  expressed,  has  a  high  atomic 
weight  (206'4).  Similarly,  barium  sulphate,  barite,  has  a  specific  gravity  of  4'5,  while  for 
calcium  sulphate  or  anhydrite  the  value  is  only  2'95  {atomic  weight  for  barium  137  for 
calcium  about  40). 

On  the  other  hand,  while  aluminium  is  a  metal  of  low  density  (G.  =  2'5  and  atomic 
weight  =  27),  its  oxide,  corundum,  has  a  remarkably  high  density  (G.  =  4)  and  is  also  very 
hard  (H.  =  9).  Again,  carbon  (atomic  weight  =  12)  has  a  high  density  in  the  diamond 
(G.  =  3'5)  and  low  in  graphite  (G.  =  2);  also,  the  first  is  hard  (H.  =  10),  the  second  soft 
(H.  =  1'5).  In  these  and  similar  cases  the  high  density  signifies  great  molecular  aggrega- 
tion, and  hence  it  is  natural  that  it  should  be  accompanied  by  great  hardness  and  resistance 
to  the  attack  of  acids. 

As  bearing  upon  this  point,  it  is  to  be  noted  that  the  density  of  many  substances  is 
altered  by  fusion.  Again,  the  same  mineral  in  different  states  of  molecular  aggregation 
may  differ  (but  only  slightly)  in  density.  Furthermore,  minerals  having  the  same  chemical 
composition  have  sometimes  different  densities,  corresponding  to  the  different  crystalline 
forms  in  which  they  appear.  Thus  in  the  case  of  calcium  carbonate  (CaCO3),  calcite  has 
G.  =  27,  aragonite  has  G.  =  2'9. 

303.-  Average  Specific  Gravities.  —  It  is  to  be  noted  that  among  minerals  of  NON- 
METALLIC  LUSTER  the  average  specific  gravity  ranges  from  2'6  to  3.  Here  belong  quartz 
(2'66),  calcite  (27),  the  feldspars  (2'6-275),  rmiscovite  (2'8).  A  specific  gravity  of  2'5  or 
less  is  low,  and  is  characteristic  of  soft  minerals,  and  often  those  which  are  hydrous  (e.g., 
gypsum,  G.  =  2'3).  The  common  species  fluorite,  tourmaline,  apatite,  vesuvianite,  amphi- 
bole,  pyroxene,  and  epidote  lie  just  above  the  limit  given,  namely,  3'0  to  3'5.  A  specific 
gravity  of  3'5  or  above  is  relatively  high,  and  belongs  to  hard  minerals  (as  corundum,  see 
Art.  302),  or  to  those  containing  a  heavy  metal,  as  compounds  of  strontium,  barium,  also 
iron,  tungsten,  copper,  silver,  lead,  mercury,  etc. 

With  minerals  of  METALLIC  LUSTER,  the  average  is  about  5  (here  belong  pyrite,  hematite, 
etc.),  while  if  below  4  it  is  relatively  low  (graphite  2,  stibnite  4'5);  if  7  or  above,  relatively 
high  (as  galena,  7 '5). 

Tables  of  minerals  arranged  according  to  their  specific  gravity  are  given  in  Appendix  B. 

304.  Constancy  of  Specific  Gravity.  —  The  specific  gravity  of  a  mineral  species  is  a 
character  of  fundamental  importance,  and  is  highly  constant  for  different  specimens  of  the 
same  species,  if  pure,  free  from  cavities,  solid  inclusions,  etc.,  and  if  essentially  constant  in 
composition.     In  the  case  of  many  species,  however,  a  greater  or  less  variation  exists  in  the 
chemical  composition,  and  this  at  once  causes  a  variation  in  specific  gravity.     The  different 
kinds  of  garnet  illustrate  this  point;    also  the  various  minerals  intermediate  between  the 
tantalate  of  iron  (and  manganese)  and  the  niobate,  varying  from  G.  =  7'3  to  G.  =  5'3. 

305.  Practical  Suggestions.  —  It  should  be  noted  that  the  determination  of  the  specific 
gravity  has  little  value  unless  the  fragment  taken  is  pure  and  is  free  from  impurities,  internal 
and  external,  and  not  porous.     Care  must  be  taken  to  exclude  air-bubbles,  and  it  will  often 
be  found  well  to  moisten  the  surface  of  the  specimen  before  inserting  it  in  the  water,  and 
sometimes  boiling  (or  the  use  of  the  air-pump)  is  necessary  to  free  it  from  air.     If  it  absorbs 
water  this  latter  process  must  be  allowed  to  go  on  till  the  substance  is  fully  saturated.     No 
accurate  determinations  can  be  made  unless  the  changes  of  temperature  are  rigorously 
excluded  and  the  actual  temperature  noted. 

In  a  mechanical  mixture  of  two  constituents  in  known  proportions,  when  the  specific 
gravity  of  the  whole  and  of  one  are  known,  that  of  the  other  can  be  readily  obtained.  This 
method  is  often  important  in  the  study  of  rocks. 


200  PHYSICAL   MINERALOGY 

It  is  to  be  noted  that  the  hand  may  be  soon  trained  to  detect  a  difference  of  specific 
eravitv  if  like  volumes  are  taken,  even  in  a  small  fragment  —  thus  the  difference  between 
calcite  or  albite  and  barite,  even  the  difference  between  a  small  diamond  and  a  quartz 
crystal,  can  be  detected. 

LITERATURE.  —  Specific  Gravity 
General: 

Beudant.     Pogg.  Ann.,  14,  474,  1828. 

Jenzsch.     Pogg.  Ann.,  99,  151,  1856. 

Jolly.     Ber.  Ak.  Miinchen,  1864,  162. 

Gadolin.     Pogg.,  106,  213,  1859. 

G.  Rose.     Pogg.  Ann.,  73,  1;  75,  403,  1848. 

Scheerer.     Pogg.  Ann.,  67,  120,  1846. 

Schroder.     Pogg.  Ann.,  106,  226,  1859.     Jb.  Min.,  561,  932,  1873;   399,  1874,  etc. 

Tschermak.     Ber.  Ak.  Wien,  47  (1),  292,  1863. 

Websky.  Die  Mineralien  nach  den  fur  das  specifische  Gewicht  derselben  angenom- 
menen  und  gefundenen  Werthen.  170  pp.  Breslau,  1868. 

Use  of  Heavy  Solutions,  etc.: 

Sonstadt.     Chem.  News,  29,  127,  1874. 
Thoulet.     Bull.  Soc.  Min.,  2,  17,  189,  1879. 
Breon.     Bull.  Soc.  Min.,  3,  46,  1880. 
Goldschmidt.     Jb.  Min.,   Beil.-Bd.,  1,  179,  1881. 
D.  Klein.     Bull.  Soc.  Min.,  4,  149,  1881. 
Rohrbach.    Jb.  Min.,  2,  186,  1883. 
Gisevius.     Inaug.  Diss.,  Bonn.,  1883. 
Brauns.     Jb.  Min.,  2,  72,  1886;  1,  213,  1888. 
Retgers.     Jb.  Min.,  2,  185,  1889. 
Salomon.     Jb.  Min.,  2,  214,  1891. 
Penfield.     Am.  J.  Sc.,  50,  446,  1895. 
Merwin.     Am.  J.  Sc.,  32,  425,  1911. 


III.   CHARACTERS  DEPENDING  UPON   LIGHT 
GENERAL  PRINCIPLES   OF   OPTICS 

306.  Before  considering  the  optical  characters  of  minerals  in  general,  and 
more  particularly  those  that  belong  to  the  crystals  of  the  different  systems,  it 
is  desirable  to  review  briefly  some  of  the  more  important  principles  of  optics 
upon  which  the  phenomena  in  question  depend. 

For  a  fuller  discussion  of  the  optics  of  crystals,  special  reference  is  made  to  the  works 
of  Groth  (translation  by  Jackson),  Liebisch,  Mallard,  Duparc  and  Pearce,  Rosenbusch 
(translation  by  Iddings),  Iddings,  Johannsen,  Winchell,  mentioned  on  p.  3  also  to  the 
various  advanced  text-books  of  Physics. 

307.  The  Nature  of  Light.  —  Light  is  now  considered  to  be  an  electro- 
magnetic phenomenon  due  to  a  periodicJvariation  in  the  energy  given  off  by 
vibrating  electrons.     This  energy  is  transmitted  by  a  series  of  periodic  changes 
that  show  all  the  characters  of  ordinary  wave  phenomena.     The  light  waves, 
as  they  are  commonly  called,  possess  certain  short  wave-lengths  that  are  of  the 
correct  magnitude  to  affect  the  optic  nerves.     Other  similar  waves  with  longer 
or  shorter  wave-lengths  belong  to  the  same  class  of  phenomena.     Immediately 
beyond  the  violet  end  of  the  visible  spectrum  come  the  so-called  "  ultra- 
violet" waves  with  still  shorter  wave-lengths  and  on  beyond  these  we  have 
the  X-rays  and  the  " gamma"  rays  produced  by  radium.     Of  the  waves 
having  greater  lengths  than  those  of  light  waves  we  have  the  waves  that  give 


CHARACTERS   DEPENDING   UPON   LIGHT  201 

rise  to  the  sensation  of  heat  and  the  Hertzian  waves  used  in  wireless  All  of 
these  vibrations,  while  varying  enormously  in  their  wave-lengths,  belong  to 
the  same  order  of  phenomena  and  obey  the  same  laws.  The  proportion  that 
the  section  of  the  series  which  produces  the  effect  of  light  bears  to  the  whole 
may  be  strikingly  shown  when  we  say  that  if  ordinary  white  light  is  broken  up 
into  a  spectrum  a  yard  long  and  this  then  considered  to  be  extended  on  either 
end  so  as  to  include  all  known  electro-magnetic  waves  the  entire  spectrum 
would  be  over  five  million  miles  in  length. 

The  transmission  of  light  through  interstellar  space,  through  liquids  and 
transparent  solids,  has  for  some  time  been  explained  by  the  assumption  that 
a  medium,  called  the  luminiferous  ether,  pervades  all  space,  including  the 
intermodular  space  of  material  bodies.  In  this  medium  the  vibrations  of 
light  waves  are  assumed  to  take  place.  For  the  purposes  of  the  present  work, 
however,  it  is  unnecessary  to  consider  closely  the  exact  nature  of  light  or  the 
mode  of  its  transmission.  It  will  assist  greatly,  however,  in  obtaining  a  clear 
idea  of  the  behavior  of  light  in  crystals  if  we  assume  that  light  waves  are  me- 
chanical in  nature  and  consist  of  periodic  vibrations  in  an  all-prevailing  ether. 

308.  Wave-motion  in  General.  —  A  familiar  example  of  wave-motion 
is  given  by  the  series  of  concentric  waves  which  on  a  surface  of  smooth  water 
go  out  from  a  center  of  disturbance,  as  the  point  where  a  pebble  has  been 
dropped  in.     These  surface-waves  are  propagated  by  a  motion  of  the  water- 
particles  which  is  transverse  to  the  direction  in  which  the  waves  themselves 
travel;   this  motion  is  given  from  each  particle  to  the  next  adjoining,  and  so 
on.     Thus  the  particles  of  water  at  any  one  spot  oscillate  up  and  down,* 
while  the  wave  moves  on  as  a  circular  ridge  of  water  of  constantly  increasing 
diameter,  but  of  diminishing  height.     The  ridge  is  followed  by  a  valley, 
indeed  both  together  properly  constitute  a  wave  in  the  physical  sense.     This 
compound  wave  is  followed  by  another  wave  and  another,  until  the  original 
impulse  has  exhausted  itself. 

Another  familiar  kind  of  wave-motion  is  illustrated  by  the  sound-waves 
which  in  the  free  air  travel  outward  from  a  sonorous  body  in  the  form  of 
concentric  spheres.  Here  the  actual  motion  of  the  layers  of  air  is  forward 
and  back  —  that  is,  in  the  direction  of  propagation  of  the  sound  —  and  the 
effect  of  the  transfer  of  this  impulse  from  one  layer  to  the  next  is  to  give  rise 
alternately  to  a  condensed  and  rarefied  shell  of  air,  which  together  constitute 
a  sound-wave  and  which  expand  in  spherical  waves  of  constantly  decreasing 
intensity  (since  the  mass  of  air  set  in  motion  continually  increases).  Sound- 
waves, as  of  the  voice,  may  be  several  feet  in  length,  and  they  travel  at  a  rate 
of  1120  feet  per  second  at  ordinary  temperatures. 

309.  It  is  important  to  understand  that  in  both  the  cases  mentioned,  as  in 
every  case  of  free  wave-motion,  each  point  on  a  given  wave  may  be  considered 
as  a  center  of  disturbance  from  which  a  system  of  new  waves  tend  to  go  out. 
These  individual  wave-systems  ordinarily  destroy  each  other  except  so  far  as 
the  onward  progression  of  the  wave  as  a  whole  is  concerned.     This  is  further 
discussed  and  illustrated  in  its  application  to  light-waves  (Art  312  and  Figs. 
509,  510). 

In  general,  therefore,  a  given  wave  is  to  be  considered  as  the  resultant  of 
all  these  minor  wave-systems.  If,  however,  a  wave  encounters  an  obstacle  in 
its  path,  as  a  narrow  opening  (i.e.,  one  narrow  in  comparison  with  the  length 

*  Strictly  speaking,  the  path  of  each  particle  approximates  closely  to  a  circle. 


202  PHYSICAL   MINERALOGY 

of  the  wave)  or  a  sharp  edge,  then  the  fact  just  mentioned  explains  how  the 
waves  seem  to  bend  about  the  obstacles,  since  new  waves  start  from  them  as 
centers.  This  principle  has  an  important  application  in  the  case  of  light- 
waves, explaining  the  phenomena  of  diffraction  (Art.  331). 

310.  Still  another  case  of  wave-motion  may  be  mentioned,  since  it  is  particularly  help- 
ful in  giving  a  correct  apprehension  of  light-phenomena.  If  a  long  rope,  attached  at  one 
end,  be  grasped  at  the  other,  a  quick  motion  of  the  hand,  up  or  down,  will  give  rise  to  a  half 
wave-form  —  in  one  case  a  crest,  in  the  other  a  trough  —  which  will  travel  quickly  to  the 
other  end  and  be  reflected  back  with  a  reversal  in  its  position;  that  is,  if  it  went  forward 
as  a  hill-like  wave,  it  will  return  as  a  trough.  If,  just  as  the  wave  has  reached  the  end.  a 
second  like  one  be  started,  the  two  will  meet  and  pass  in  the  middle,  but  here  for  a  brief 
interval  the  rope  is  sensibly  at  rest,  since  it  feels  two  equal  and  opposite  impulses.  This 
will  be  seen  later  to  be  a  case  of  the  simple  interference  of  two  like  waves  opposed  in  phase. 

Again,  a  double  motion  of  the  hand,  up  and  down,  will  produce  a  complete  wave,  with 
crest  and  trough,  as  the  result,  and  this  again  is  reflected  back  as  in  the  simpler  case.  Still 
again,  if  a  series  of  like  motions  are  continued  rhythmically  and  so  timed  that  each  wave 
is  an  even  part  of  the  whole  rope,  the  two  systems  of  equal  and  opposite  waves  passing  in 
the  two  directions  will  interfere  and  a  system  of  so-called  stationary  waves  will  be  the 
result,  the  rope  seeming  to  vibrate  in  segments  to  and  fro  about  the  position  of  equilibrium. 

Finally,  if  the  end  of  the  rope  be  made  to  describe  a  small  circle  at  a  rapid,  uniform, 
rhythmical  rate,  a  system  of  stationary  waves  will  again  result,  but  now  the  vibrations  of 
the  string  will  be  sensibly  in  circles  about  the  central  line.  This  last  case  will  be  seen  to 
roughly  indicate  the  kind  of  transverse  vibrations  by  which  the  waves  of  circularly  polar- 
ized light  are  propagated,  while  the  former  case  represents  the  vibrations  of  waves  of  what 
is  called  plane-polarized  light. 

All  these  cases  of  waves  obtained  with  a  rope  deserve  to  be  carefully  considered  and 
studied  by  experiment,  for  the  sake  of  the  assistance  they  give  to  an  understanding  of  the 
complex  phenomena  of  light-waves. 

311.  Light-waves.  —  In  the  discussion  that  follows,  in  order  to  make 
the  explanations  simpler  and  clearer,  light  waves  have  been  treated  as  if  they 
consisted  of  mechanical  disturbances  in  a  material  medium  called  the  ether. 

The  vibrations  in  the  ether  caused  by  the  transmission  of  a  light  wave 
take  place  in  directions  transverse  to  the  direction  of  the  movement  of  the 
wave.  These  oscillations  have  the  following  characters.  When  an  ether  par- 
ticle is  set  vibrating  it  moves  from  its  original  position  with  gradually  decreas- 
ing velocity  until  the  position  of  its  maximum  displacement  is  reached.  Then 
with  gradually  increasing  velocity  it  returns  to  its  original  position  and  since 
it  is  moving  without  friction  it  will  continue  in  the  same  direction  on  past  this 
point.  Its  velocity  will  then  again  diminish  until  it  has  reached  a  displace- 
ment equal  but  opposite  in  direction  to  its  first  swing,  when  it  will  start  back 
on  its  course  and  repeat  the  oscillation.  The  varying  velocity  of  such  an 
oscillation  would  be  the  same  as  that  shown  by  a  particle  moving  around  a 
circle  with  uniform  speed  if  the  particle  was  observed  in  a  direction  lying  in  the 
plane  of  the  circle.  Under  these  conditions  the  particle  would  appear  to  move 
forward  and  backward  along  a  straight  line  with  constantly  changing  velocity. 
Such  a  motion  is  called  simple  harmonic  motion. 

The  motion  of  one  ether  particle  is  communicated  to  another  and  so  on, 
each,  in  order,  falling  a  little  behind  in  the  time  of  its  oscillation.  Conse- 
quently, while  the  individual  particles  move  only  back  and  forth  in  the  same 
line  the  wave  disturbance  moves  forward.  If,  at  a  given  instant  of  time,  the 
positions  of  successive  particles  in  their  oscillations  are  plotted,  a  curve,  such 
as  shown  in  Fig.  508,  will  be  formed.  Such  a  curve  is  known  as  a  harmonic 
curve.  The  oscillatory  motion  of  the  particles  in  a  light  wave  is  called  a 
periodic  motion  since  it  repeats  itself  at  regular  intervals.  The  maximum  dis- 


CHARACTERS   DEPENDING   UPON    LIGHT 


203 


D 


placement  of  a  particle  from  its  original  position  of  rest  is  called  the  amplitude 

of  the  wave  (distance  C-D,  Fig.  508).     The  phase  of  a  particle  at  a  given 

instant  is  its  position  in 

the     vibration     and     the  608 

direction    in    which   it  is 

moving.  /^ 

The  distance  between    /— 
any  particle  and  the  next   / 
which  is  in  a  like  position  r — 

—  i.e.,  of  like  phase,  as  A   \ 

and  B  —  is  the  wave-length;     \~  j\l  I/ 

and  the  time  required  for 

this  completed  movement  Harmonic  Curve 

is  the   time   of   vibration, 

or  vibration-period.  The  wave-system  therefore  travels  onward  the  distance 
of  one  wave-length  in  one  vibration-period.  The  intensity  of  the  light  varies 
with  the  amplitude  of  the  vibration,  and  the  color,  as  explained  in  a  later  ar- 
ticle, depends  upon  the  length  of  the  waves;  the  length  of  the  violet  waves  is 
about  one-half  the  length  of  the  red  waves. 

In  ordinary  light  the  transverse  vibrations  are  to  be  thought  of  as  taking 
place  in  all  planes  about  the  line  of  propagation.  In  the  above  figure,  vibra- 
tions in  one  plane  only  are  represented ;  light  that  has  only  one  direction  of 
transverse  vibration  is  said  to  be  plane-polarized. 

Light-waves  have  a  very  minute  length,  only  0'000023  of  an  inch  for  the 
yellow  sodium  flame,  and  they  travel  with  enormous  velocity,  186,000  miles 
per  second  in  a  vacuum;  thus  light  passes  from  the  sun  to  the  earth  in  about 
eight  minutes.  The  vibration-period,  or  time  of  one  oscillation,  is  conse- 
quently extremely  brief;  it  is  given  by  dividing  the  distance  traveled  by  light 
in  one  second  by  the  number  of  waves  included.* 

312.  Wave-front.  —  In  an  isotropic  medium,  as  air,  water,  or  glass  — 
that  is,  one  in  which  light  would  be  propagated  in  all  directions  about  a  lumi- 
nous point  with  the  same  velocity  —  the  waves  are  spherical  in  form.  The 
wave-front  is  the  continuous  surface,  in  this  case  spherical,  which  includes  all 
particles  that  commence  their  vibration  at  the  same  moment  of  time.  Obvi- 
ously the  curvature  of  the  wave-front  diminishes  as  the  distance  of  the  source 
of  light  increases,  and  when  the  light  comes  from  an  indefinitely  great  distance 
(as  the  sun)  the  wave-front  becomes  sensibly  a  plane  surface.  Such  waves  are 
usually  called  plane  waves.  These  cases  are  illustrated  by  Figs.  509  and  510. 
In  Fig.  509  the  luminous  point  is  supposed  to  be  0,  and  the  medium  being 
isotropic,  il  is  obvious  that  the  wave-front,  as  ABC  .  .  .  G,  is  spherical.  It  is 
also  made  clear  by  this  figure  how,  as  briefly  stated  in  Art.  309,  the  resultant 
of  all  the  individual  impulses  which  go  out  from  the  successive  points,  as 
A,  B,  C,  etc.,  as  centers,  form  a  new  wave-front,  abc  .  .  .  g,  concentric  with 
ABC  G.  In  Fig.  510  the  luminous  body  is  supposed  to  be  at  a  great  dis- 

*  "On  account  of  the  tremendous  speed  at  which  light  travels  the  rapidity  of  vibration, 
or  "frequency  "  of  light  as  it  passes  through  a  fixed  point,  is  extremely  great.  About  eight 
hundred  trillion  waves  of  violet  light  would  pass  through  such  a  point  in  a  second.  Ine 
extreme  brevity  of  the  interval  of  time  required  for  the  passage  of  a  single  wave  of  this 
sort  may  perhaps  be  realized  better  when  it  is  said  that  one  eight-hundred-trillionth  of  a 
second  is  a  vastly  smaller  part  of  a  second  than  a  second  is  of  the  whole  of  historic  time. 
Comstock  and  Troland,  "The  Nature  of  Matter  and  Electricity,  p.  157. 


204 


PHYSICAL   MINERALOGY 


tance,  so  that  the  wave-front  AB  . 
609 


F  is  a  plane  surface.  Here  also  the 
individual  impulses  from  A,  B,  etc., 
unite  to  form  the  wave-front  ab  . . .  / 
parallel  to  AB  .  .  .  F. 

313.  Light-ray.  —  The  study  of 
light-phenomena  is,  in  certain  cases, 
facilitated  by  the  conception  of  a 
light-ray,  a  line  drawn  from  the 
luminous  point  to  the  wave-front, 
and  whose  direction  is  taken  so  as 
to  represent  that  of  the  wave  itself. 

510 


A 

V 

a  > 

B 

Y 

b  ^ 

C 

/v 
y 

D 

V 
\A 

d^ 

E 

x\ 
J 

1 

F 

\ 

A 

f    . 

/ 

/ 


In  Fig.  509  OA,  OB,  etc.,  are  diverging  light-rays,  and  in  Fig.  510 
OA,  OB,  etc.,  are  parallel  light-rays.  In  both  these  cases,  where 
the  medium  is  assumed  to  be  isotropic,  the  light-ray  is  normal  to  the  wave- 
front.  This  is  equivalent  to  saying  that  the  light-wave  moves  onward  in  a 
direction  normal  to  the  wave-front. 

It  must  be  understood  that  the  " light-ray"  has  no  real  existence  and  is 
to  be  taken  only  as  a  convenient  method  of  representing  the  direction  of 
motion  of  the  light-waves  under  varying  conditions.  Thus  when  by  appro- 
priate means  (e.g.,  the  use  of  lenses)  the  curvature  of  the  wave-front  is  altered 
—  for  example,  if  from  being  a  plane  surface  it  is  made  sharply  convex  —  then 
the  light-rays,  at  first  parallel,  are  said  to  be  made  to  diverge.  Again,  if  the 
convex  wave-front  is  made  plane,  the  diverging  light-rays  are  then  said  to  be 
made  parallel. 

314.  Wave-length.  Color.  White  Light.  —  Notwithstanding  the  very 
small  length  of  the  waves  of  light,  they  can  be  measured  with  great  precision. 
The  visual  part  of  the  waves  going  out  from  a  brilliantly  incandescent  body, 
as  the  glowing  carbons  of  an  electric  arc-light,  may  be  shown  to  consist  of 
waves  of  widely  varying  lengths.  They  include  red  waves  whose  length  is 

0*0007604  mm.  ( about  •    nAA  of  an  inch  )  and  waves  whose  length  constantly 
\          oy,uuu  / 

diminishes  without  break,  through  the  orange,  yellow,  green,  and  blue  to  the 
violet,  whose  minimum  length  (0'0003968  mm.)  is 'about  half  of  that  of  the 
red.  The  colo  of  light  is  commonly  said  to  depend  upon  its  wave-length  and 
will  be  so  spoken  of  here.  This  is  not  strictly  true,  however,  because,  since 
the  velocity  of  light  varies  with  the  medium  through  which  it  is  traveling 


CHARACTERS   DEPENDING   UPON   LIGHT  205 


constant  under  all  conditions,  it  follows 
mpL  ^ave;1,engt.h  of  "fht  of  the  same  color  must  be  different  in  different 
media.  It  is,  therefore,  rather  the  frequency  with  which  the  light  waves  reach 
the  eye  tLat  determines  the  color  sensation.  Commonly  a  given  color  t 
produced  by  the  combination  of  several  different  wave-lengths  of  light  It  I 
strictly  monochromatic  only  when  it  corresponds  to  one  definite  wave-length 
this  is  nearly  true  of  the  bright-yellow  sodium  line,  though  strictly  TpeS 
this  consists  of  two  sets  of  waves  of  slightly  different  lengths. 

The  effect  of  white  light"  is  obtained  if  all  the  waves  from  the  red  to  the 
violet  come  together  to  the  eye  simultaneously;  for  this  reason  a  piece  of 
platinum  at  a  temperature  of  1500°  C.  appears  " white  hot" 

The  radiation  from  the  sources  named,  either  the  sun,  the 
electric  carbons  or  the  glowing  platinum,  includes  also  longer  waves 
which  do  not  affect  the  eye,  but  which,  like  the  light-waves,  produce  the 
effect  of  sensible  heat  when  received  upon  an  absorbing  surface,  as  one  of  lamp- 
black. There  are  also,  particularly  in  the  radiation  from  the  sun,  waves 
shorter  than  the  violet  which  also  do  not  affect  the  eye.  The  former  are 
called  infra-red,  the  latter 
ultra-violet  waves. 

The  brightness  of  light 
depends  upon  the  am- 
plitude of  its  vibrations 
and  varies  directly  as  the 
square  of  this  distance. 

315.  Complementary 
Colors.  -  -  The  sensation 
of  white  light  mentioned 
above    is     also    obtained 

when  to  a  given  color —  ^ \r     \^   \,<    \^  ^X M 

,  i  .  T        1  "*    V  *•*   x  n  *  T"* /T* 

that    is,    light-waves     of 

given     wave-length  -  -  is 

combined  a  certain  other 

so  -  called     complementary 

color.   Thus  certain  shades 

of    pink   and    green    combined,  as   by   the   rapid   rotation   of   a   card   on 

which  the    colors   form  segments,  produce  the  effect  of  white.     Blue  and 

yellow  of  certain  shades  are  also  complementary.     For  every  shade  of  color  in 

the  spectrum  there  is  another  one  complementary  to  it  in  the  sense  here 

defined.     The  most  perfect  illustration  of  complementary  colors  is  given  by 

the  examination  of  sections  of  crystals  in  polarized  light,  as  later  explained. 

316.  Reflection.  —  When   light- waves   come   to  the   boundary   which 
separates  one  medium  from  another,  as  a  surface  of  water,  or  glass  in  air, 
they  are,  in  general,  in  part  reflected  or  returned  back  into  the  first  medium. 

The  reflection  of  light-waves  is  illustrated  by  Figs.  511  and  512.  In  Fig. 
511,  MM  is  the  reflecting  surface  —  here  a  plane  surface  —  and  the  light- 
waves have  a  plane  wave-front  (Abcde);  in  other  words,  the  light-rays 
(OA,  Ob,  etc.)  are  parallel.  It  is  obvious  that  the  wave-front  meets  the  sur- 
face first  at  A  and  successively  from  point  to  point  to  E.  These  points  are  to 
be  regarded  as  the  centers  of  new  wave-systems  which  unimpeded  would  be 
propagated  outward  in  all  directions  and  at  a  given  instant  would  have 
traveled  through  distances  equal  to  the  lines  Aa',  Bb' ,  etc.  Hence  the  com- 


206 


PHYSICAL   MINERALOGY 


mon  tangent  fghkE  to  the  circular  arcs  drawn  with  these  radii  from  A,  B, 
etc.,  represents  the  direction  of  the  new  or  reflected  wave-front.     But  geomet- 


512 


rically  the  angle  eAE  is 
equal  to  fEA,  or  the  in- 
cident and  reflected  wave- 
fronts  make  equal  angles 
with  the  reflecting  surface. 
If  NA  is  a  normal  at  A, 
the  angle  OAN  -  -  called 
the  angle  of  incidence  —  is 
equal  to  NAF,  the  angle 
of  reflection.  Hence  the 
familiar  law: 

The  angle  of  incidence  is 
equal  to  the  angle  of  reflec- 
tion. 

Furthermore,  the  "  in- 
cident and  reflected  rays" 
both  lie  in  the  same  plane 
with  the  normal  .to  the 
reflecting  surface. 

In  Fig.  512,  where  the  luminous  point  is  at  0,  the  waves  going  out  from  it 
will  meet  the  plane  mirror  MM  first  at  the  point  A  and  successively  at  points, 
as  B,  C,  D,  etc.,  farther  away  to  the  right  (and  left)  of  A.  Here  also  it  is  easy 
to  show  that  all  the  new  impulses,  which  have  their  centers  at  A,  B,  C,  etc., 
must  together  give  rise  to  a  series  of  reflected  waves  whose  center  is  at  0',  at  a 
distance  equally  great  from  MM  measured  on  a  normal  to  the  surface 
(OA  =  O'A}. 

Now  the  lines  OA,  OB,  etc.,  which  are  perpendicular  to  the  wave-front, 
represent  certain  incident  light-rays,  and  the  eye  placed  in  the  direction  BE, 
CF,  etc.,  will  see  the  luminous  point  as  if  at  0'  .  It  follows  from  the  construc- 
tion of  the  figure  and  can  be  proved  by  experiment  that  if  BN,  CN',  etc.,  are 
normals  to  the  mirror  the  angles  of  incidence,  OBN,  OCN'  ',  etc.,  are  equal  to 
the  angles  of  reflection,  NBE,  N'CF,  etc.,  respectively.  Hence  the  above  law 
applies  to  this  case  also. 

If  the  reflecting  surface  is  not  plane,  but,  for  example,  a  concave  surface, 
as  that  of  a  spherical  or  parabolic  mirror,  there  is  a  change  in  the  curvature  of 
the  wave-front  after  reflection,  but  the  same  law  still  holds  true. 

The  proportion  of  the  reflected  to  the  incident  light  increases  with  the  smoothness  of 
the  surface  and  also  as  the  angle  of  incidence  diminishes.  The  intensity  of  the  reflected 
light  is  a  maximum  for  a  given  surface  in  the  case  of  perpendicular  incidence  (OA,  Fig.  512). 

If  the  surface  is  not  perfectly  polished,  diffuse  reflection  will  take  place,  and  there  will 
be  no  distinct  reflected  ray.  It  is  the  diffusely  reflected  light  which  makes  the  reflected 
surface  visible;  if  the  surface  of  a  mirror  were  absolutely  smooth  the  eye  would  see  the 
reflected  body  in  it  only,  not  the  surface  itself.  Optically  expressed,  the  surface  is  to  be 
considered  smooth  if  the  distance  between  the  scratches  upon  it  is  considerablv  less  (say 
one-fourth)  than  the  wave-length  of  light. 

317.  Refraction.  —  When  light  passes  from  one  medium  into  another 
there  is,  in  general,  an  increase  or  decrease  in  its  velocity,  and  this  commonly 
results  in  the  phenomenon  of  refraction  —  that  is,  a  change  in  the  direction  of 
propagation.  The  principles  applicable  here  can  be  most  easily  shown  in  the 


CHARACTERS   DEPENDING   UPON    LIGHT 


207 


513 


case  of  light-waves  with  a  plane  wave-front,  as  shown  in  Fig  513  —  that  is 
where  the  light-rays  OA,  OB,  etc.,  are  parallel.  Suppose,  for  example,  that 
a  light-wave,  part  of  whose  wave- 
front  is  Abcde,  passes  from  air 
obliquely  into  glass,  in  which  its 
velocity  is  about  two-thirds  as 
great  as  it  was  in  the  air  and 
suppose  the  surface  of  the  glass  to 
be  plane.  At  the  moment  that  the 
ray  0-A  enters  the  glass  the  ray 
0-E  has  reached  the  point  e. 
During  the  time  that  the  latter 
ray  travels  from  e  to  E,  the  ray 
0-A  will  have  advanced  in  the 
glass  a  distance  equal  to  %e-E,  or 
to  some  point  on  an  arc  having  this 
distance  as  a  radius  (A-f).  In  the 
same  way  during  the  time  ray  0-E 
passes  from  the  point  p  to  E,  ray 
0-B  will  have  traveled  in  the  glass  the  distance  B-g,  equal  to 
f  p-E.  In  this  way  arcs  may  be  drawn  about  each  one  of  the  points  A,  B, 
C,  etc.,  and  the  position  of  the  new  wave-front  in  the  glass  determined  by  their 
common  tangent,  Ekhgf.  It  is  seen  that  there  is  a  change  of  direction  in  the 
wave-front,  or  otherwise  stated,  in  the  light-ray,  the  magnitude  of  which 
depends  on  the  ratio  between  the  light-velocities  in  the  two  media,  and,  as 
discussed  later,  also  upon  the  wave-length  of  the  light.  The  light-ray  is  here 
said  to  be  broken  or  refracted,  and  for  a  medium  like  glass,  optically  denser 
than  air  (i.e.,  with  a  lower  value  of  the  light- velocity),  the  refraction  is  toward 
the  perpendicular  with  the  angle  of  refraction,  r,  smaller  than  the  angle  of 
incidence,  i.  In  the  opposite  case  —  when  light  passes  into  an  optically 
rarer  medium  —  the  refraction  is  away  from  the  perpendicular  and  the  angle 
of  refraction  is  larger  than  that  of  incidence  (Art.  323). 

318.  Refractive  Index.  —  It  is  obvious  from  the  figure  that  whatever 
the  direction  of  the  wave-front  —  that  is,  of  the  light-rays  —  relatively  to  the 
given  surface,  the  ratio  of  eE  to  Af,  which  determines  the  direction  of  the  new 
wave-front  (i.e.,  the  direction  of  a  refracted  ray,  AF)  is  constant.  This  ratio 

y 
is  equal  to  —  where  V  is  the  value  of  the  light-velocity  for  the  first  medium 

(here  air)  and  v  for  the  second  (as  glass).     This  constant  ratio  is  commonly 
represented  by  n  and  is  known  as  the  index  of  refraction.     Therefore 

eE 


In  Fig.  513,  by  construction, 

/  eAE  =  /  i     and     /  AEf  =  /  r. 

Al  eE 

Also, 


Therefore, 


sn 
sin  r 


and 

eE_ 

AE  =  eE 
Af  Af 
AE 


208 


PHYSICAL   MINERALOGY 


sin  ^  , 

The  law  of  refraction  then  is  given  by  the  expression,  n  =  -    - ,  or  may  be 

olll   / 

formulated  as  follows: 

The  sine  of  the  angle  of  incidence  bears  a  constant  ratio  to  the  sine  of  the 
angle  of  refraction. 

In  the  case  of  light  passing  from  air  into  crown  glass  this  ratio  is  found  to 

3in  ^  =  T608,  and    this    number  consequently   gives   the  value   of   the 


be, 

sin  r 

refractive    index,  or 
514 


for    this    kind 


of    glass. 

The  above  relation  holds  true  for 
any  wave-system  of  given  wave- 
length in  passing  from  one  medium 
into  another,  whatever  the  wave- 
front  or  shape  of  the  bounding  sur- 
face. In  Fig.  514  the  luminous 
point  is  at  0,  and  it  can  be  readily 
shown  that  the  new  wave-front 
propagated  in  the  second  me- 
dium (of  greater  optical  density) 
has  a  flattened  curvature  and 
corresponding  to  this  a  center 

at  0'   f  where  ^4^  =  — ).     Here  the 


OA        v 

incident  rays  OB,  OC,  are  re- 
fracted at  J3*and  C,  the  correspond- 
ing refracted  rays  being  BE  and  CF. 
For  this  case  also  the  relation  holds 
good, 


n 


sin  i 
sinr 


sin  i 
sin  r 


-, ,  etc. 


If  the  bounding  surface  is  not  plane  but  curved,  as  in  lenses,  there  is  a 
change  in  the  curvature  of  the  wave-front  in  the  second  medium,  but  the 

simple  law,  n  =  -  —  >  holds  true  here  also,  so  long  as  the  medium  is  isotropic. 

The  relation  between  wave-length  and  refractive  index  is  spoken  of  in 
Art.  328. 

319.  Relation  of  Refractive  Index  to  Light- velocity.  —  The  discussion 
of  the  preceding  article  shows  that  if  n  is  the  refractive  index  of  a  given  sub- 
stance for  waves  of  a  certain  length,  referred  to  air,  V  the  velocity  in  air  and  v 
the  velocity  in  the  given  medium,  then 

V 

n  =  —• 

v 

For  two  media  whose  indices  are  n\  and  nz  respectively,  it  consequently  follows 
that 

n\  _  v%  t 
nz       v\ 


CHARACTERS   DEPENDING   UPON   LIGHT  209 

Therefore,  The  indices  of  refraction  of  two  given  media  for  a  certain  wave- 
length are  inversely  proportional  to  their  relative  light-velocities. 

In  other  words,  if  the  velocity  of  light  in  air  is  taken  as  equal  to  1  and 
the  velocity  of  the  same  light  is  found  to  be  one  half  as  great  when  passing 
through  a  given  substance,  the  index  of  refraction,  or  n,  of  that  substance 
when  referred  to  air  (n  =  TO)  will  be  equal  to  2*0. 

320.  Principal  Refractive  Indices.  —  The  refractive  index  has,  as 
stated,  a  constant  value  for  every  substance,  referred,  as  is  usual,  to  air  (or 
it  may  be  to  a  vacuum).  In  regard  to  solid  media,  it  is  evident  from  Art. 
318  and  will  be  further  explained  later  that  those  which  are  isotropic,  viz., 
amorphous  substances  and  crystals  of  the  isometric  system,  can  have  but  a 
single  value  of  this  index.  Crystals  of  the  tetragonal  and  hexagonal  systems 
have,  as  later  explained,  two  principal  refractive  indices,  e  and  co,  corresponding 
to  the  velocities  of  light-propagation  in  certain  definite  directions  in  them. 
Further,  all  orthorhombic,  monoclinic,  and  triclinic  crystals  have  similarly 
three  principal  indices,  a,  |S,  7.  In  the  latter  'cases  of  so-called  anisotropic 
media,  the  mean  refractive  index  is  taken,  namely,  as  the  arithmetical  mean 


321.  Effect  of  Index  of  Refraction  upon  Luster,  etc.  —  The  luster  and 
general  appearance  of  a  transparent  substance  depend  largely  upon  its  refrac- 
tive index.  For  instance  the  peculiar  aspect  of  the  mineral  cryolite,  by  means 
of  which  it  is  usually  possible  to  readily  identify  the  substance,  is  due  to  its 
low  index  of  refraction.  If  cryolite  is  pulverized  and  the  powder  poured  into 
a  test  tube  of  water  it  will  disappear  and  apparently  go  into  solution.  It  is 
quite  insoluble,  however,  but  becomes  invisible  in  the  water  because  its  index 
of  refraction  (about  1*34)  is  near  that  of  water  (T335).  The  light  will  travel 
with  practically  the  same  velocity  through  the  cryolite  as  through  the  water 
and  consequently  suffer  little  reflection  or  refraction  at  the  surfaces  between 
the  two.  On  the  other  hand  powdered  glass  with  a  higher  index  of  refraction 
than  that  of  water  appears  white  under  the  same  conditions  because  of  the 
reflection  of  light  from  the  surfaces  of  the  particles. 

Substances  having  an  unusually  high  index  of  refraction  have  an  appear- 
ance which  it  is  hard  to  define,  and  which  is  generally  spoken  of  as  an  adaman- 
tine luster.  .This  kind  of  luster  may  be  best  comprehended  by  examining 
specimens  of  diamond  (n  =  2*419)  or  of  cerussite  (n  =  1*98).  They  have  a 
flash  and  quality,  sometimes  almost  a  metallic  appearance,  which  is  not 
possessed  by  minerals  of  a  low  refractive  index.  Compare,  for  example,  spec- 
imens of  cerussite  and  fluorite  (n  =  1'434).  The  usual  index  of  refraction  for 
minerals  may  be  said  to  range  not  far  from  1*55,  and  gives  to  minerals  a  luster 
which  has  been  termed  vitreous.  Quartz,  feldspar,  and  halite  show  good 
examples  of  vitreous  luster. 

Below  is  given  a  list  of  common  minerals  arranged  according  to  their  indices 
of  refraction.  For  minerals  other  than  those  of  the  isometric  system  the 
average  value  (as  defined  in  the  preceding  article)  is  given  here. 

Water  ...........  1  '  335  Muscovite  .......  1  582 

Fluorite  .........  1'434  Beryl  ...........  1'582 

Orthoclase  .......  1523  Calcite  ..........  T601 

Gypsum  .........  1'524  Topaz  ...........  1622 

Quartz  ..........  1  "547  Tremolite  .......  1  '622 


210  PHYSICAL   MINERALOGY 

Dolomite  ........  1626  Anglesite  ........  T884 

Aragonite  .......  1  633  Zircon  ...........  1  952 

Apatite  .........  1  633  Cerussite  ........  T  986 

Barite  ...........  1640  Cassiterite  .......  2'029 

Diopside  ........  T  685  Sulphur  ..........  2'077 

Cyanite  ..........  1'723  Sphalerite  ........  2369 

Epidote  ..........  1750  Diamond  ........  2  419 

Corundum  .......  1  765  Rutile  ...........  2  711 

Almandite  .......  1*810  Cuprite  ..........  2849 

Malachite  ........  1  '  880  Cinnabar  ........  2  969 

322.  Relations  between  Chemical  Composition,  Density,  and  Refractive  Index.  —  That 
definite  relations  exist  between  the  chemical  composition  of  a  substance,  its  specific  gravity, 
and  its  index  of  refraction,  has  been  conclusively  shown  in  many  cases.  With  the  plagio- 
clase  feldspar  group,  for  instance,  the  variation  in  composition  which  the  different  members 
show  is  accompanied  by  a  direct  variation  in  density  and  refractive  index.  Attempts 
have  been  made  to  express  these  relations  in  the  form  of  mathematical  statements. 
The  two  most  satisfactory  expressions  are  the  one  proposed  by  Gladstone  and  Dale,* 

l-^  —  =  constant,  and  the   one    proposed    independently   by    Lorentz  f   and   Lorenz,t 

n2  ~     •  -.  =  constant.     In  these  n  is  equal  to  the  mean  refractive  index  and  d  to  the  density. 

These  were  originally  proposed  for  use  with  gases  and  solutions  and  for  these  bodievS  have 
been  found  to  serve  about  equally  well.  When  attempts  are  made,  however,  to  apply  them 
to  crystalline  solids  the  results  are  at  the  best  only  approximate.  §  This  is  probably  because 
the  formulas  do  not  take  into  consideration  the  modifications  that  the  crystal  structure 
must  introduce. 

323.   Total  Reflection.     Critical  Angle.  —  In   regard   to   the    principle 
stated  in  Art.  318  and  expressed  by  the  equation  n  =  -   —  ,  two  points  are  to  be 

noted.     First,  if  the  angle  i  =  0°,  then  sin  i  —  0,  and  obviously  also  r  =  0;  in 
other  words,  when  the  ray  of  light  (as  OA,  Fig.  514)  coincides  with  the  per- 
pendicular, no  change  of  direction  takes  place,  the  ray  proceeds  onward  (AD) 
into  the  second  medium  without  deviation,  but  with  a  change  of  velocity. 
Again,  if  the  angle  i  =  90°,  then  sin  i  =  1,  and  the  equation  above  becomes 

n  =  -  —  or  sin  r  =  -.     Asn  has  a  fixed  value  for  every  substance,  it  is  obvi- 
sin  T  7i 

ous  that  there  will  also  be  a  corresponding  value  of  the  angle  r  for  the  case 
mentioned.  From  the  above  table  it  is  seen  that  for  water,  sin  r  =  VT^H 

1   OOO 


r  =  48°  31';  for  crown  glass  (n  =  1'608),  sin  r  =  and  r  =  38°  27';  for 

diamond,  sin  r  =  ^r—  -  and  r  =  24°  25'. 


This  fact,  that  for  each  substance  at  a  particular  value  of  the  angle  r~the 
angle  i  becomes  equal  to  90°,  has  an  important  bearing  on  the  behavior  of 
light  when  it  is  passing  from  an  optically  denser  into  an  optically  rarer  medium. 

*  Phil.  Trans.,  153,  317,  1863. 
t  Wiedem.  Ann.,  9,  641,  1880. 
J  Wiedem.  Ann.,  11,  70,  1880. 

§  E.  S.  Larsen,  Am.  Jour.  Sci.,  28,  263,  1909.  See  also  Cheneveau,  Ann.  Chem.  Phys., 
12)  145,  '28  J,  1907. 


CHARACTERS   DEPENDING   UPON   LIGHT 


211 


515 
B 


In  Fig.  515  we  may  assume  that  light  rays  coming  from  various  directions 

meet  the  surface  between  a  block  of  glass  and  the  air  at  the  point  A.     Light 

traveling  along  the  path  O-A  will 

pass  out   into  the  air  without  a 

change  in  its  direction  but  with  an 

increase    in    its    velocity.       If    it 

emerges    from    the    glass    at  any 

other  angle  than  90°  the  ray  on 

entering  the  air  will  be  bent  away 

from   the   perpendicular    and   the 

angle  of  deviation  will  vary  with 

the  angle  at  which  the  ray  touched 

the  surface  and  with  the  index  of 

refraction  of  the  glass.     The  same 

law  holds  true  in  this  case  as  in 

the  case  of  a  ray  entering  from  the 

air, 


except  that  the  formula  nows  reads  n  =  — — . ,  where  r  =  the  angle  the  ray  in 

szn  v 

air  makes  with  the  normal  to  the  surface  and  i  =  the  angle  that  the  ray  makes 
within  the  glass  to  the  same  normal.  In  Fig.  515  the  ray  C-A  will  pass  out 
into  the  air  along  the  line  A-D.  But  the  angle  i  for  the  ray  E-A  =  38°  27' 
and,  as  shown  in  the  preceding  paragraph,  for  glass,  where  n  =  1*608,  the 
angle  r  in  the  air  will  be  90°  and  the  ray  will  travel  along  the  surface  of  the 
glass  in  the  direction  A-F.  Consequently  any  ray,  such  as  G-A,  which  meets 
the  surface  of  the  glass  at  an  angle  greater  than  38°  27',  will  be  unable  to  pass 
out  into  the  air  and  will  suffer  total  reflection  at  the  surface,  passing  back  into 
the  glass  in  the  direction  A-G',  with  angle  GAG  =  angle  GAG'.  The  angle 
at  which  total  reflection  takes  place  for  any  substance  is  known  as  its  critical 


The  phenomenon  of  total  reflection  is  taken  advantage  of  in  the  cutting 
of  gem  stones.  According  to  common  practice  such  a  stone  is  cut  with  a  flat 
surface  on  top  and  with  a  number  of  inclined  facets  on  the  bottom.  The 
light  that  enters  the  stone  from  above  is  in  a  large  measure  totally  reflected 
from  the  sloping  planes  below  and  comes  back  to  the  eye  through  the  stone. 
The  amount  of  light  reflected  in  this  way  and  the  consequent  brilliancy  of  the 
gem  increases  with  its  index  of  refraction.  Two  stones  cut  exactly  alike,  one 
from  diamond  and  the  other,  perhaps,  from  quartz,  would  have  very  different 


516 


517 


Total  Reflection  in  Fluorite  n  =  1.43       Total  Reflection  in  Diamond  n  =  2.42 

appearances  due  to  this  difference  in  the  amount  of  light  totally  reflected  from 
their  lower  facets.     This  principle  is  illustrated  in  Figs.  516  and  517.     They 


212 


PHYSICAL   MINERALOGY 


represent  cross  sections  of  two  hemispheres  cut,  one  from  fmorite  and  the 
other  from  diamond.  It  is  assumed  that  light  from  all  directions  is  focused 
on  the  center  of  the  plane  surface  of  each  hemisphere.  All  the  light  that  meets 
this  surface  at  an  angle  greater  than  the  critical  angle  for  the  mineral  will  be 
totally  reflected  back  through  the  spherical  surface.  The  shaded  areas  of  the 
figures  show  the  amount  of  light  in  each  case  that  would  be  so  reflected  and 
clearly  illustrate  the  optical  difference  between  the  two  substances. 

324.  Effect  of  Index  of  Refraction  upon  Microscopic  Phenomena.  —  In 
the  study  of  minerals,  especially  in  thin  sections  under  the  microscope,  varia- 
tions in  the  index  of  refraction  give  effects  which  are  of  importance.  In  Fig. 
518  let  it  be  assumed  that  L  is  the  objective  lens  of  a  compound  microscope, 
and  that  the  instrument  is  exactly  focused  upon  a  point  O,  Fig.  518,  A.  If 
now  we  imagine  that  a  section  of  some  mineral  of  mean  index  of  refraction  is 

518 


; — Cover  glass 
br~~Section  in  balsam 
A-Glass  slide 


placed  under  the  lens,  Fig.  518,  B,  the  point  O'  will  now  be  in  focus,  or  as  in 
Fig.  518,  C,  where  the  mineral  is  supposed  to  have  a  high  index  of  refraction, 
the  focus  will  be  at  O".  Thus  it  is  that  with  two  sections  of  equal  thickness 
and  with  the  lens  in  the  same  position,  one  looks  deeper  into  the  mineral  of 
higher  index  of  refraction.  Consequently,  when  there  are  two  minerals  in 
the  same  section,  the  one  having  a  high  and  the  other  a  low  index  of  refraction 
(for  example,  a  crystal  of  zircon,  n  =  1.95,  embedded  in  quartz,  n  =  1.55),  the 
one  having  the  higher  index  of  refraction  will  apparently  have  the  greater 
thickness  and  will  appear  to  stand  up  in  relief  above  the  surface  of  the  mineral 
of  lower  index.  The  apparent  relief  is  furthermore  augmented  by  other 
properties  to  be  explained  below. 

In  preparing  thin  sections  of  minerals  or  rocks  for  study  with  the  micro- 
scope the  process,  in  brief,  is  to  make  first  a  flat  surface  upon  the  mineral  or  rock 
by  grinding  it  upon  a  plate  supplied  with  some  abrasive.  This  flat  surface  is 
then  cemented  to  a  piece  of  glass  by  means  of  Canada  balsam  and  the  re- 
mainder of  the  mineral  is  ground  away  until  only  a  thin  film  remains,  which  in 
the  best  rock  sections  is  not  over  0'03  mm.  in  thickness.  The  section  is  finally 
embedded  in  balsam,  n  about  1'54,  and  over  it  a  thin  cover  glass  is  laid.  In 


CHARACTERS   DEPENDING   UPON   LIGHT  213 

the  preparation  of  a  section  the  surfaces  are  not  polished,  hence,  from  the 
nature  of  the  abrasive,  they  must  be  pitted  and  scratched  and  it  may  be 
assumed  that  in  cross  section  such  a  preparation  would  be  somewhat  as  repre- 
sented in  Fig.  518,  D.  When  a  thin  section  is  examined  under  the  microscope 
the  light  enters  the  section  from  below,  having  been  reflected  up  into  the 
microscope  tube  by  an  inclined  mirror.  Before  it  reaches  the  section  it  will 
have  passed  through  a  nicol  prism  and  through  a  slightly  converging  lens.  Let 
it  be  assumed  that  the  mineral  at  a,  Fig.  518,  D,  is  one  of  mean  refractive 
index.  The  convergent  light  entering  the  section  will  pass  with  little  or  no 
refraction  from  the  mineral  into  the  balsam  because  their  refractive  indices 
are  nearly  alike.  Hence  the  roughness  of  the  surface  of  the  section  is  not 
apparent  and  the  mineral  appears  as  if  polished.  If  there  is  a  crack,  as  at  6, 
so  much  light  penetrates  it  that  it  is  scarcely  visible  when  the  convergent 
lens  is  close  to  the  object,  but  when  the  latter  is  lowered,  and  especially  when 
the  light  is  restricted  by  the  use  of  an  iris  diaphragm  inserted  into  the  micro- 
scope tube,  the  nearly  parallel  rays  of  light  will  suffer  some  total  reflection 
along  the  line  of  the  crack  and  so  make  it  visible.  On  the  other  hand,  if  the 
mineral  has  a  high  index  of  refraction  there  will  be  innumerable  places  all  over 
the  section  where  the  surfaces  are  so  inclined  that  the  light  will  suffer  total 
reflection  in  attempting  to  pass  from  the  optically  dense  mineral  into  the  rarer 
balsam.  Hence  the  uneven  surface  of  the  section  due  to  its  grinding  is  plainly 
visible.  This  effect  is  more  pronounced  if  the  convergent  lens  is  lowered. 
The  cracks  that  may  exist  in  a  mineral  of  high  index  of  refraction  are  for  the 
same  reasons  much  more  distinct  than  in  a  mineral  of  low  index.  Further, 
if  a  mineral  of  high  index  of  refraction  is  embedded  in  one  of  low,  c,  Fig.  518, 
D,  there  will  be  places  along  its  outer  edge  where  total  reflection  will  take  place, 
thus  causing  its  outline  to  be  dark  and  distinct.  This  effect  combined  with 
the  roughened  aspect  of  the  surface  and  the  apparent  increase  in  thickness, 
as  described  in  the  preceding  paragraph,  all  tend  to  make  a  mineral  of  high 
index  of  refraction  stand  out  conspicuously  in  relief. 

325.  Determination  of  the  Indices  of  Refraction  of  Mineral  Grains 
under  the  Microscope.  —  The  considerations  of  the  preceding  article  sug- 
gest a  means  of  determining  the  indices  of  refraction  of  mineral  grains  under 
the  microscope.  If  a  grain  is  immersed  in  a  liquid  of  known  index  of  refrac- 
tion it  is  possible  to  determine  whether  it  has  a  higher  or  lower  index  of 
refraction  than  the  liquid  and  by  the  use  of  a  series  of  liquids  of  varying 
refractive  indices  it  is  possible  to  determine  with  considerable  accuracy  the 
index  of  refraction  of  the  mineral.  A  list  of  liquids  *  in  common  usejfor  such 
purposes,  with  their  indices  of  refraction  is  given  below. 

Mixtures  of  refined  petroleum  oils  and  turpentine — 1  450-1  '475 

Turpentine  and  ethylene  bromide  or  clove  oil 1  480-1 '  535 

Clove  oil  and  a-monobromnaphthalene 1  540-1 '  635 

Petroleum  oils  and  a-monobromnaphthalene 1  475-1 '  650 

a-monobromnaphthalene  and  methylene  iodide 1'  650-1 '  740 

Sulphur  dissolved  in  methylene  iodide 1  740-1  790 

Mixtures   of   methylene    iodide   with   iodides   of   antimony, 

arsenic  and  tin,  also  sulphur  and  iodof orm  (see  Merwin) ...     1  740-1  870 

Methylene  iodide  and  arsenic  trisulphide  (see  Merwin) 1  740-2  280 

Resin-like  substances  formed  from  mixtures  of  piperine  and 

*  Wright,  Methods  of  Petrographic-Microscopic  Research,  p.  98;  Merwin,  Jour.  Wash. 
Acad.  Sc.,  3,  35,  1913. 


214 


PHYSICAL   MINERALOGY 


the  tri-iodides  of  arsenic  and  antimony.     These  fuse  easily 
and  mineral  grains  can  be  thus  embedded  in  a  thin  film  of  the 

material 1  '680-2 '  10 

The  indices  of  refraction  of  the  test  liquids  can  be  determined  either  b 
the  use  of  the  total  refractometer  or  by  filling  a  hollow  glass  prism  with  th 
liquid  and  using  the  metho'ds  employed  with  ordinary  mineral  prisms,  se 
Art.  327. 

A  series  of  these  liquids  should  be  prepared  which  for  most  purposes  migh 
conveniently  show  differences  in  the  indices  of  the  different  liquids  of  0*01 
For  more  exacting  work  smaller  differences  betw.een  the  indices  of  the  member 
of  the  series  would  be  of  advantage.  If  these  are  kept  in  well  stopperei 
bottles  and  are  protected  from  the  light  they  will  show  very  little  change  ove 
considerable  periods  of  time.  It  is  advisable,  however,  to  check  their  indice 
at  least  once  a  year. 

The  mineral  to  be  studied  should  be  broken  down  into  uniform  sma] 
grains.  (0'05  mm.  is  usually  a  good  diameter)  and  then  a  few  grains  place< 
upon  a  glass  slide.  A  drop  of  liquid  with  a  known  index  of  refraction  is  the] 
placed  upon  the  grains  and  the  whole  covered  with  a  thin  cover  glass.  Whei 
a  mineral  grain  is  immersed  in  a  liquid  of  closely  the  same  index  of  refractio] 
it  loses  its  sharpness  of  outline  and  if  the  mineral  is  colorless  and  the  corre 
spondence  of  the  two  indices  exact  it  will  quite  disappear.  Certain  tests 
however,  are  commonly  used  to  determine  the  relative  indices  of  the  minera 
and  the  liquid  which  with  proper  care  can  distinguish  differences  as  small  a 
O'Ol  or  with  practice  and  especial  care  as  small  as  O'OOl.  To  make  these  test 
the  condenser  below  the  microscope  stage  should  be  lowered  and,  if  the  instru 
ment  has  a  sub-stage  iris  diaphragm,  this  should  be  partly  closed.  Unde: 
these  conditions  the  obliquity  of  the  light  is  reduced  and  only  a  small  penci 
of  light  composed  of  nearly  parallel  rays  enters  the  section.  Let  Fig.  511 

represent  a  mineral  grair 
illuminated  in  this  way  wher 
immersed  in  a  liquid  o1 
higher  index  of  refraction 
The  light  rays  as  the} 
pass  from  the  mineral  intc 
the  higher  refracting  liquic 
above  will  be  bent  awa^ 
from  the  perpendicular.  In 
the  opposite  case,  Fig.  520, 
where  the  mineral  has  the 
higher  index  the  reverse  wil] 
be  true  and  the  light  rays 
will  be  bent  toward  the 
perpendicular.  This  will 
produce  in  one  case  a 
brighter  illumination  of  the 
borders  of  the  mineral  grain 
of  its.  center.  This  dif- 


519 


520 


Grain  with  Low  Refractive  Grain  with  High  Refractive 
Index  immersed  in  Liquid  Index  immersed  in  Liquid 
of  High  Refractive  Index  of  Low  Refractive  Index 


and  in  the  other  a  brighter  illumination  _  _  __.  _0  ^ 
ference  in  illumination  is,  however,  commonly  so  slight  as  to  be  cer- 
tainly detected  only  with  difficulty.  The  so-called  Becke  Test  is  commonly 
used  under  these  circumstances.  This  consists  in  focusing  upon  the  grain 
with  a  high  power  objective  and  then  slowly  raising  or  lowering  the  micro- 


CHARACTERS   DEPENDING   UPON    LIGHT  215 

scope  tube.  In  the  case  illustrated  by  Fig.  519,  when  the  tube  is  raised,  a 
narrow  line  of  light  will  be  seen  to  move  outward  from  the  mineral,  while 
when  the  tube  is  lowered  this  line  will  move  inward.  In  the  case  illustrated 
in  Fig.  520  the  opposite  conditions  will  prevail.  A  convenient  rule  to  remem- 
ber is  that  when  the  microscope  tube  is  raised  the  Becke  line  will  move  toward  the 
material  of  higher  refractive  index  and  when  the  tube  is  lowered  this  line  will 
move  toward  the  material  of  lower  index.  This  makes  a  very  satisfactory  and 
quite  delicate  test  for  distinguishing  differences  in  refractive  indices.  Some- 
times two  lines  will  appear  moving  in  opposite  directions  and  it  may  be  diffi- 
cult to  decide  which  is  the  Becke  line.  This  is  usually  obviated  by  lowering 
the  condenser  or  decreasing  the  aperture  in  the  iris  diaphragm.  For  the  use 
of  the  Becke  test  in  rock  sections,  see  Art.  326. 

The  test  upon  mineral  grains  immersed  in  a  liquid  may  also  be  made  by 
means  of  oblique  illumination.     An  oblique  pencil  of  rays  may  be  obtained 
most  conveniently  by  placing  a  pencil,  a  finger,  or  a  piece  of  cardboard  between 
the  reflecting  mirror  and  the  polarizer  in  such  a  way  as  to  darken  one-half  of 
the  field  of  vision.     The  best  results  will  be  obtained  by  the  use  of  an  objective 
of  medium  magnifying  power.     When  a  mineral  grain  is  viewed  under  these 
conditions  it  will  be  noted  that  one  of  its  edges  is  more  brightly  illuminated 
than    the     other.      With     the     condenser 
lens    lowered    and    mineral    with   a  lower 
index    of   refraction   than    the   liquid,  the 
bright  edge  of   the  mineral  will   be  away 
from    the    shadow,  while    if    the    mineral 
has  a  higher    index    than    the    liquid   the 
bright  edge  will  be  on  the  side  toward  the 
shadow.        These     conditions     are     pre- 
sented    in     Fig.    521,    where    L    and  H 
represent    grains  with  indices  respectively 
lower    and     higher    than     the     liquid    in 
which   they   are   immersed.     If    the    con- 
denser lens   is   raised    effects    exactly   op- 
posite  to   those   described   above   will   be 
noted.      It    is    wise,  at    first    at    least,  to 
test    the    apparatus    used    by    observing 
mineral  fragments  of  known  indices  and  taking  note  of  the  effects  produced. 

Commonly  the  liquids  used  have  a  higher  dispersion  than  the  mineral  to 
be  tested.  In  other  words  the  liquid  will  have  distinctly  different  indices  of 
refraction  for  red  and  for  blue  light.  If  the  mineral  should  have  an  index 
intermediate  between  those  for  red  and  blue  light  in  the  liquid  the  grain 
when  illuminated  in  oblique  light  will  show  colored  borders.  With  the  con- 
denser lens  lowered  the  edge  of  the  mineral  next  to  the  shadow  will  be  colored 
an  orange-red  while  the  edge  away  from  the  shadow  will  be  pale  blue.  If  the 
amount  of  the  dispersion  in  the  liquid  (i.e.,  the  difference  between  the  indices 
for  blue  and  red  light)  is  not  too  great  this  effect  gives  very  closely  the  refrac- 
tive index  of  the  mineral. 

It  should  be  pointed  out  here  that  all  minerals,  except  those  of  the  isometric 
system,  show  different  indices  of  refraction  depending  upon  the  crystal  direc- 
tion in  which  the  light  is  passing  through  the  mineral.  Consequently  un- 
orientated  grains  of  a  mineral,  unless  it  belongs  to  the  isometric  system,  will 
show  a  variation  in  the  refractive  indices  depending  upon  their  position  on 


Darker  >/\ 

....  .      (    L      ^Brighter 


216 


PHYSICAL   MINERALOGY 


522 


12   11   10 


7   8   9654    3  2 


the  slide.  Sometimes  it  is  possible  to  determine  the  crystal  orientation  of  a 
grain  due  to  some  significant  cleavage  or  structure  and  so  obtain  the  index 
for  some  particular  crystal  direction,  but  ordinarily  all  that  can  be  determined 
is  the  mean  index  of  refraction  of  the  mineral. 

326.  The  Becke  Test  in  Rock  Sections.  —  The  Becke  test  can  be  often 
used  in  a  rock  section  to  determine  the  relative  indices  of  refraction  of  two 
different  minerals  lying  in  contact  with  each  other.     Their  contact  plane  should 
be  nearly  vertical  in  order  to  give  clear  results.     The  position  of  this  plane 
can  be  determined  by  focusing  on  the  surface  of  the  section  and  then  when 
the  microscope  tube  is  lowered  note  whether  or  not  the  position  of  the  dividing 
line  between  the  two  minerals  remains  stationary  or  moves.     If  it  remains 
stationary  or  moves  only  a  little,  the  dividing  plane  is  vertical  or  nearly  so. 
Under  these  conditions  assume  that  the  cone  of  light  entering  from  below  is 
focused  at  point  O,  Fig.  522,  lying  on  the  dividing  plane  between  L  (mineral 
with  lower  index)  and  H  (mineral  with  higher  index).     The  light  rays  1-6 

passing  as  they  do  from 
a  mineral  of  lower  index 
into  one  of  higher  will 
suffer  no  total  reflection 
and  all  emerge  from  the 
section  on  the  side  of  H. 
On  the  other  hand,  rays 
7-12  attempting  to  pass 
from  H  to  L  will  only  in 
part  pass  across  the 
dividing  plane  while  the 
others  will  be  totally 
reflected  and  add  them- 
selves to  rays  1-6  on  the 
side  of  H.  H  will  there- 
fore show  a  brighter 
illumination  than  L.  In 
this  case  also  when  the 
tube  of  the  microscope  is 
raised  the  Becke  line  will 
be  seen  moving  toward 
the  mineral  of  higher 
index  or  when  the  tube  is 
lowered  toward  that  of 

lower  index.     The  best  results  will  be  obtained  by  using  an  objective  of  high 

magnification  and  the  condenser  lens  must  be  lowered. 

327.  Determination  of  the  Index  of  Refraction  by  Means  of  Prisms  or 
Plates.  —  For  the  more  accurate  determination  of  the  indices  of  refraction  of 
minerals  a  natural  or  cut  prism  or  plate  of  the  mineral  is  used.     In  all  cases, 
except  minerals  of  the  isometric  system,  the  prism  or  plate  used  must  have  a 
certain  crystallographic  orientation.     This  matter,  however,  will  be  discussed 
when  the  optical  characters  of  such  minerals  are  given.     For  the  present,  we 
will  assume  that  the  mineral  whose  index  of  refraction  is  to  be  determined  is 
isometric  in  its  crystallization.     There  are  two  chief  methods  of  determining 
the  index  of  refraction  by  the  use  of  a  prism. 

1.  The  Method  of  Perpendicular  Incidence.  —  This  method,  although  not 


12     3456 


CHARACTERS    DEPENDING   UPON   LIGHT 


217 


the  one  most  generally  employed,  is  an  excellent  one  to  become  acquainted 
with,  as  it  may  be  used  to  advantage  in  some  cases  and  from  it  the  formula 
necessary  for  making  the  calculations  is  readily  derived.     It  is  necessary  to 
have  a  prism  of  the  mineral  which  has  two 
plane  surfaces  meeting  at  a  small  angle. 

This  angle  should  be  small  enough  so  that 
the  light  may  pass  freely  through  the  prism 
and  not  suffer  any  total  reflection  as  it 
attempts  to  pass  out  into  the  air.  For  in- 
stance with  fluorite  in  which  n  =  1*434,  the 
prism  angle  must  be  less  than  44°  12',  for  at  a 
this  angle  total  reflection  would  take  place. 
For  a  mineral  of  higher  index  the  angle 
would  have  to  be  smaller  still,  as  with  dia- 
mond, n  =  2 '4 19,  where  total  reflection 
would  take  place  at  24°  24'.  On  the  other 
hand,  more  accurate  results  will  be  obtained  Refraction  of  Light  through  a  Prism 
if  the  prism  angle  is  fairly  near  to  the  limit  Method  of  Perpendicular  Incidence 
for  the  mineral  being  used.* 

Let  Fig.  523  represent  the  cross  section  of  such  a  prism.  Let  a-b  represent 
a  ray  of  light  striking  the  face  of  this  prism  at  90°  incidence.  It  will  suffer 
no  deviation  in  its  path  on  entering  the  prism  but  will  proceed  with  somewhat 
diminished  velocity  until  it  reaches  c.  In  passing  out  of  the  prism  at  this  point, 
from  a  denser  to  a  rarer  medium,  the  light  will  be  deflected  away  from  the 
normal  to  the  surface,  P-P',  making  a. deviation  5  in  the  direction  o-d.  The 
data  necessary  for  the  calculation  of  the  index  of  refraction  under  these 
conditions  are  the  angle  of  the  prism,  a,  and  that  of  the  deviation  in 
the  path  of  the  light,  5.  It  is  easy  to  see  from  the  figure  that  a  and  a'  are 
equal,  for  they  are  both  parts  of  right-angled  triangles  having  the  angle 
bP'c  in  common,  and  a"  is  equal  to  a!  because  they  are  opposite  angles.  The 
angle  of  incidence,  as  defined  in  Art.  317,  is  equal  to  a  +  8  and  the  angle  of 

refraction  is  equal  to  a.     Therefore  the  usual  formula  -    -  —  n  becomes  here 

sin  r 

Sm  .a          =  n.     In  order  to  make  a  determination  of  the  index  of  refraction, 
sin  a 

therefore,  it  is  necessary  to  measure  these  two  angles,  a  and  5. 

The  prism  is  mounted  on  a  one-circle  reflection  goniometer  and  its  angle 
a  measured  in  the  same  way  as  an  angle  upon  a  crystal.  The  instrument  is 
then  adapted  to  the  uses  of  a  refractometer.  For  this  purpose  it  is  necessary 
to  note  that  the  telescope  and  vernier  are  both  fastened  to  the  outer  rim  of  the 
instrument  and  move  together.  The  graduated  circle  being  clamped,  the 
telescope  tube  is  first  moved  to  the  position  T',  Fig.  524,  so  that  the  rays  from 
the  collimator  tube,  C,  passing  the  edge  of  the  prism,  cause  the  light  signal  to 
fall  on  the  vertical  cross-hair  of  the  telescope.  The  inner  Circle  being  clamped 
the  telescope  is  next  moved  through  an  arc  of  exactly  60°  to  position  T"  and 
then  clamped.  Next  the  prism  is  turned  to  the  first  position  so  that  the 
light  from  C  is  reflected  from  its  right-hand  face  and  the  signal  s  falls  on  the 
cross-hair  of  T".  In  this  position  the  normal,  N,  to  the  prism  face,  must  bisect 
the  angle  between  the  axes  of  C  and  T".  The  prism  is  now  turned  through 
an  angle  of  exactly  60°  to  its  second  position,  which  brings  the  normal  AT 
exactly  in  line  with  the  axis  of  the  collimator  tube.  When  this  has  been 


218 


PHYSICAL  MINERALOGY 


accomplished  the  graduated  circle  is  securely  clamped.     The  telescope  may 


524 


now  be  undamped  and 
moved  without  altering  the 
position  of  the  prism,  and 
somewhere  between  T'  and 
T"  a  position  T'"  will  be 
found  where  the  refracted 
ray  falls  on  the  cross-hair 
of  the  telescope.  The  move- 
ment of  the  telescope  from 
the  position  T"'  back  to 
T'  gives  the  angle  of  devia- 
tion, or  5,  of  the  light 
ray  that  has  been  refracted 
by  the  prism.  In  practice 
it  is  well  to  repeat  the 
measurements  both  of  a  and 
d  several  times  and  to 
go  through  all  the  opera- 
tions of  shifting  the  posi- 
tions of  the  prism  and 
telescope.  If  white  light  is 
used  for  illumination  the 
refracted  ray  seen  at  T"f 
will  appear  as  a  narrow 
spectrum.  To  make  an 
exact  determination  a  mono- 
chromatic light  (sodium  light 
is  best)  must  be  employed. 

2.    The  Method  of  Min- 
imum  Deviation.  -  -  This  is 
the    method    that   is   most 
of   refraction    by  the  use   of 


525 


Determination  of  Index  of  Refraction 
Method  of  Perpendicular  Incidence 

generally  employed  for  determining  indices 
prisms.  It  depends  upon 
the  principle  that  when  a 
beam  of  light,  abed,  Fig. 
525,  traverses  a  prism  in  such 
a  way  that  the  angles  i  and  i' 
are  equal,  the  beam  suffers 
the  minimum  amount  of 
deviation  in  its  path  of  any 
possible  course  through  the 
prism.  This  fact  may  be 
proven  empirically  by  experi- 
mentation on  the  refrac- 
tometer.  In  order  to  make 
a  determination,  the  angle  a 
of  the  prism  is  first  measured 
on  the  goniometer.  The 
angle  of  the  prism  with  this 
method  may  be  considerably  larger  than  when  the  method  of  perpendicular 


526 


CHARACTERS   DEPENDING   UPON   LIGHT  219 

incidence  is  used. 

in  the  position  &.  _,  W110 

telescope  undamped  and  moved  until 
the  refracted  ray  appears  in  it.  Now, 
turn  the  central  post  with  the  prism 
on  it  toward  the  left  and  follow  the  signal 
with  the  telescope.  The  position  of 
minimum  deviation  is  soon  reached, 
when,  on  turning  the  prism,  the  signal 
seems  to  remain  stationary  for  a  moment 
and  then  moves  away  to  the  right, 
no  matter  in  which  direction  the  prism  is 
turned.  A  little  practice  is  needed 
to  determine  exactly  the  position  of  min- 
imum deviation  and  the  measurement 
should  be  made  in  a  monochromatic 
light.  When  the  telescope  is  properly 
placed  at  this  point  the  graduated  circle 
is  clamped  and  the  telescope  turned 
until  the  direct  signal  from  the  collimator 
tube  is  fixed  upon  the  vertical  cross- 
hair. The  angle  between  these  two 
positions  of  the  telescope  is  the  same  as 
the  angle  of  deviation,  or  5.  The  for- 
mula for  making  the  necessary  calcu- 
lation from  these  measurements  follows  very  simply  from  a  comparison  of 
Figs.  525  and  523.  It  may  be  imagined  that  Fig.  525  is  composed  of  two 
prisms  like  Fig.  523  placed  back  to  back.  This  results  in  doubling  the  angles 
a  and  5  so  that  the  formula  now  becomes 


sn 


8) 


sn  -J-a 

3.  The  Method  of  Total  Reflection.  —  This  method  is  based  upon  the  prin- 
ciple that  light  cannot  always  pass  from  an  optically  dense  into  an  optically 
rarer  medium  but  at  a  certain  angle,  known  as  the  critical  angle,  will  suffer 
total  reflection.  The  critical  angle  for  any  substance  varies  with  the  index  of 
refraction  of  that  substance  as  explained  in  Art.  323.  Consequently  if  we 
can  measure  this  critical  angle  we  can  calculate  the  index  of  refraction  of  the 
substance.  This  method  is  particularly  useful  because  the  measurement 
can  be  made  upon  a  single  polished  surface,  which  may  be  quite  small  in  area. 
This  measurement  is  made  by  means  of  an  instrument,  known  as  the  Total 
Refractometer,  a  description  of  which  will  be  found  in  Art.  352.  The  essential 
feature  of  this  instrument  is  a  hemisphere  of  glass  with  a  known,  high  index 
of  refraction.  The  upper  surface  of  the  hemisphere  is  plane  and  should  be 
accurately  adjusted  in  a  horizontal  position.  The  mineral  to  be  tested  may 
be  of  any  shape  provided  that  some  surface  upon  it  has  been  ground  plane 
and  polished.  A  drop  of  some  liquid  of  high  index  of  refraction  is  placed  be- 
tween the  surface  of  the  glass  hemisphere  and  the  flat  surface  of  the  mineral. 
This  serves  to  unite  the  two  substances  and  dispel  the  thin  layer  of  air  that 
would  otherwise  separate  them.  The  liquid  should  have  an  index  of  refraction 
intermediate  between  that  of  the  glass  and  that  of  the  mineral.  As  the  liquid 


220 


PHYSICAL   MINERALOGY 


lies  between  the  two  substances  in  the  form  of  a  thin  film  with  parallel  surfaces 
whatever  optical  effect  it  has  upon  the  light  as  it  enters  will  be  balanced  by 
the  opposite  effect  as  the  light  leaves  the  film.  So  the  optical  effect  of  the 
liquid  can  be  ignored.  Fig.  527  represents  a  cross  section  of  such  a  hemi- 
sphere with  a  mineral  plate  resting  upon  it.  Let  it  be  now  supposed  that  by 
means  of  a  mirror  a  beam  of  monochromatic  light  is  thrown  upon  the  apparatus 
from  the  direction  of  X.  Rays  1  and  2  will  suffer  partial  refraction  at  the 
527  dividing  plane  between  the 

glass  and  the  mineral  to  rays 
1'  and  2'  and  also  partial 
reflection  to  rays  1"  and  2". 
Ray  3  strikes  the  mineral  at 
the  critical  angle  for  the 
combination  of  the  glass  and 
mineral  and  will  in  part  be 
refracted  at  a  90°  angle  and 
emerge  as  ray  3',  just  grazing 
the  surface  of  the  hemisphere. 
The  greater  part  of  ray  3  will 
however  be  reflected  as  ray  3". 
Beyond  this  point,  all  the  light 
must  be  totally  reflected,  thus 
4  to  4".  If  the  optical 
axis  of  a  telescope  is  now 
brought  to  the  direction  3", 
what  appears  to  be  a  marked 
One  side  will  be  illuminated  by  the 


Determination  of  Index  of  Refraction 
Method  of  Total  Reflection,  I. 


528 


shadow  will  appear  in  the  field  of  vision. 

total  reflection  of  all  rays  beyond  those  of  the  critical  angle  while  the  other 
side  will  be  distinctly  darker  since 
here  a  considerable  amount  of 
the  light  passed  out  into  the 
mineral.  The  angle  between  the 
position  of  the  shadow  and  the 
normal  to  the  surface  of  the 
hemisphere,  /*,  Fig.  527,  will  be 
the  critical  angle  for  the  combina- 
tion of  glass  and  mineral.  As  the 
index  of  refraction  of  the  glass  is 
known  it  is  possible  to  calculate 
what  the  index  of  refraction  of  the 
mineral  must  be.  If  the  mineral 
plate  is  transparent  enough  so 
that  light  may  pass  through 
it  into  the  glass  hemisphere 
another  method  of  illumination 
may  be  used,  as  illustrated 
Fig.  528.  The  reflecting 


m 
mirror 


Determination  of  Index  of  Refraction 
Method  of  Total  Reflection,  II. 


is  so  arranged  that  the  light  comes  from  the  direction  X.  Rays  1  and  2  will 
be  refracted  to  1'  and  2'  and  3  which  just  grazes  the  surface  to  3'.  Beyond 
this  point  no  light  will  pass  into  the  hemisphere  and  a  telescope  placed  with 
its  axis  along  the  line  3'  will  show  in  its  field  a  dark  shadow.  The  contrast 


CHARACTERS   DEPENDING    UPON    LIGHT  221 

between  the  light  and  dark  portions  of  the  field,  by  this  method  of  illumination, 
is  much  stronger  than  by  the  one  first  described.  The  telescope  is  so  placed 
that  the  line  of  the  shadow  exactly  divides  the  angle  between  the  diagonal 
cross-hairs  of  the  eyepiece.  The  telescope  is  attached  to  a  graduated  circle 
from  which  the  angle  M  can  be  directly  read.  With  each  of  these  instruments 
comes  ordinarily  a  table  giving  the  indices  of  refraction  corresponding  to  the 
different  possible  values  of  ju.  This  table  can  easily  be  converted  into  a  curve 
plotted  on  co-ordinate  paper  in  such  a  way  that  the  index  of  refraction  for  a 
particular  angle  can  be  read  at  a  glance.  Further,  the  calculation  can  be  made 
having  given  the  index  of  refraction  of  the  glass  of  the  hemisphere  and  the 
value  of  fji  for  a  special  mineral  plate.  Let  n'  equal  the  index  of  refraction  of 
the  glass  of  the  hemisphere  and  //  the  critical  angle  measured;  then  the  index 
of  refraction  of  the  mineral,  n,  =  sin  ju  X  n'.* 

328.  Dispersion.  —  Thus  far  the  change  in  direction  which  light  suffers  in 
reflection  and  refraction  has  alone  been  considered.     It  is  further  true  that 
the  amount  of  refraction  differs  for  light  of  different  wave-lengths,  being 
greater  for  blue  than  for  red.     In  consequence  of  this  fact,  if  ordinary  light  be 
passed  through  a  prism,  as  in  Fig.  525,  it  will  not  only  be  refracted,  but  it  will 
also  suffer  dispersion  or  be  separated  into  its  component  colors,  thus  forming 
the  prismatic  spectrum. 

This  variation  for  the  different  colors  depends  directly  upon  their  wave- 
lengths; the  red  waves  are  longer,  their  transverse  vibrations  are  slower,  and 
it  may  be  shown  to  follow  from  this  that  they  suffer  less  change  of  velocity 
on  entering  the  new  medium  than  the  violet  Waves,  which  are  shorter  and 
whose  velocity  of  transverse  vibration  is  greater.  Hence  the  refractive  index 
for  a  given  substance  is  greater  for  blue  than  for  red  light.  The  following 
are  values  of  the  refractive  indices  for  diamond  determined  by  Schrauf  : 

2-40845  red  (lithium  flame). 

2*41723  yellow  (sodium  flame). 

2*42549  green  (thallium  flame). 

329.  Spectroscope.  —  The  instrument  most   commonly  used  for  the 
analysis  of  the  light  by  dispersion  is  familiar  to  all  as  the  spectroscope.     There 

*  The  derivation  of  this  formula  follows.     From  the  ordinary  law  for  the  index  of  re- 

n-  But  when  the  critical  angle  h 


reached  i  =  90°  and  sin  i  —  1.     Therefore  we  may  substitute  and  have 

n  =  --  =  -  -,  or  velocity  of  light  in  mineral  =  -  .     Further,  we  may  derive 

velocity  of  light  in  mineral  n 

in  the  same  svay  for  the  highly  refracting  glass  of  the  hemisphere  whose  refractive  index, 

n1,  is  known,  the  expression,  velocity  of  light  in  glass  =  —  .     Further,  we  have  in  the  case 

of  the  light  attempting  to  pass  from  the  glass  (optically  denser  medium)  into  the  mineral 
the  expression, 

velocity  of  light  in  mineral  _  sin  90° 

velocity  of  light  in  glass         sin  /x   (measured  on  instrument). 
By  substituting  this  becomes 

n  _  sin  90°  _     1 
1         sin  n        sin  n 
n' 

or  —  -  =  —     or    n  =  sin  /n  X  »'• 

sin  M       n 


222  PHYSTCAL   MINERALOGY 

are  a  number  of  varieties  of  spectroscopes  made,  the  simplest  of  which  consists 
of  a  glass  prism  mounted  at  the  center  of  the  instrument  with  two  tubes 
pointing  away  from  it.  The  light  from  the  given  source  is  received  through 
a  narrow  slit  in  the  end  of  one  tube  and  made  to  fall  as  a  plane-wave  (that  is, 
as  a  "  pencil  of  parallel  rays  ")  upon  one  surface  of  a  prism  at  the  center.  The 
light  is  dispersed  by  its  passage  through  the  prism  and  the  spectrum  produced 
is  viewed  through  a  suitable  telescope  at  the  end  of  the  second  tube. 

If  the  light  from  an  incandescent  solid  —  which  is  ''white  hot"  (Art.  314) 
—  is  viewed  through  the  spectroscope,  the  complete  band  of  colors  of  the 
spectrum  is  seen  from  the  red  through  the  orange,  yellow,  green,  blue,  to  the 
violet.  If,  however,  the  light  from  an  incandescent  vapor  is  examined,  it  is 
found  to  give  a  spectrum  consisting  of  bright  lines  (or  bands)  only,  and  these 
in  a  definite  position  characteristic  of  it  —  as  the  yellow  line  (double  line)  of 
sodium  vapor;  the  more  complex  series  of  lines  and  bands,  red,  yellow,  and 
green,  characteristic  of  barium;  the  multitude  of  bright  lines  due  to  iron 
vapor  (in  the  intensely  hot  electric  arc),  and  so  on. 

330.  Absorption.  —  Of  the  light  incident  upon  the  surface  of  a  new 
medium,  not  only  is  part  reflected  (Art.  316)  and  part  transmitted  and  re- 
fracted (Art.  317),  but,  in  general,  part  is  also  absorbed  at  the  surface  and  part 
also  during  the  transmission.  Physically  expressed,  absorption  in  this  case 
means  the  transformation  of  the  ether-waves  into  sensible  heat,  that  is,  into 
the  motion  of  the  molecules  of  the  body  itself. 

The  color  of  a  body  gives  an  evidence  of  this  absorption.  Thus  a  sheet  of 
red  glass  appears  red  to  the  eye  by  transmitted  light,  because  in  the  trans- 
mission of  the  light-waves  through  it,  it  absorbs  all  except  those  which  to- 
gether produce  the  effect  of  red.  For  the  same  reason  a  piece  of  jasper 
appears  red  by  reflected  light,  because  it  absorbs  part  of  the  light-waves  at  the 
surface,  or,  in  other  words,  it  reflects  only  those  which  together  give  the 
effect  of  this  particular  shade  of  red. 

Absorption  in  general  is  selective  absorption;  that  is,  a  given  body  absorbs 
particular  parts  of  the  total  radiation,  or,  more  definitely,  waves  of  a  definite 
wave-length  only.  Thus,  if  transparent  pieces  of  glass  of  different  colors  are 
held  in  succession  in  the  path  of  the  white  light  which  is  passing  into  the 
spectroscope,  the  spectrum  viewed  will  be  that  due  to  the  selective  absorption 
of  the  substance  in  question.  A  layer  of  blood  absorbs  certain  parts  of  the 
light  so  that  its  spectrum  consists  of  a  series  of  absorption  bands.  Certain 
rare  substances,  as  the  salts  of  didymium,  etc.,  have  the  property  of  selective 
absorption  in  a  high  degree.  In  consequence  of  this,  a  section  of  a  mineral 
containing  them  often  gives  a  characteristic  absorption  spectrum. 

This  latter  property  may  be  made  use  of  in  testing  certain  minerals,  more 
especially  those  that  contain  the  rare  earths  or  uranium.  These  give  char- 
acteristic absorption  bands  in  the  spectrum.  They  may  be  tested  by  passing 
a  strong  white  light  through  a  thin  section  of  the  mineral  and  observing  the 
resulting  spectrum  by  means  of  a  direct  vision  spectroscope.  Often  a  better 
result  will  be  obtained  by  illuminating  the  surface  of  the  mineral  and  testing 
the  reflected  light  for  absorption  bands.  The  light  will  have  sufficiently 
penetrated  the  mineral  before  reflection  to  have  had  some  of  it  absorbed. 
These  tests  can  be  made  best  by  some  sort  of  a  microspectroscope,  which 
will  give  a  clear  spectrum  superimposed  upon  a  scale  of  wave-lengths.* 

*'••  For  details  of  this  method  of  testing  minerals  see  Wherry.  Smithsonian  Misc.  Coll.. 
66,  No.  5,  1915. 


CHARACTERS   DEPENDING   UPON   LIGHT  223 

The  dark  lines  of  the  solar  spectrum,  of  which  the  so-called  Fraunhofer 
lines  are  the  most  prominent,  are  due  to  the  selective  absorption  exerted  by 
the  solar  atmosphere  upon  the  waves  emitted  by  the  much  hotter  incandescent 
mass  of  the  sun. 

331.  Diffraction.  —  When  monochromatic  light  is  made  to  pass  through 
a  narrow  slit,  or  by  the  sharp  edge  of  an  opaque  body,  it  suffers  diffraction,  and 
there  arise,  as  may  be  observed  upon  an  appropriately  placed  screen,  a  series 
of  dark  and  light  bands,  growing  fainter  on  the  outer  limits.     Their  presence 
is  explained  (see  Arts.  335,  336)  as  due  to  the  interference,  or  mutual  reaction, 
of  the  adjoining  systems  of  waves  of  light,  that  is,  the  initial  light-waves, 
and  further,  those  which  have  their  origin  at  the  edge  or  sides  of  the  slit  in 
question.     It  is  essential  that  the  opening  in  the  slit  should  be  small  as  com- 
pared with  the  wave-length  of  the  light.     If  ordinary  light  is  employed, 
the  phenomena  are  the  same,  and  for  the  same  causes,  except  that  the  bands 
are  successive  colored  spectra. 

Diffraction  spectra,  explained  on  the  principles  alluded  to,  are  obtained  from  diffraction 
gratings.  These  gratings  consist  of  a  series  of  extremely  fine  parallel  lines  (say,  15,000  or 
20,000  to  an  inch)  ruled  with  great  regularity  upon  glass,  or  upon  a  polished  surface  of 
speculum  metal.  The  glass  grating  is  used  with  transmitted,  and  the  speculum  grating 
with  reflected,  light;  the  Rowland  grating  of  the  latter  kind  has  a  concave  surface.  Each 
grating  gives  a  number  of  spectra,  of  the  first,  second,  third  order,  etc.  These  spectra 
have  the  advantage,  as  compared  with  those  given  by  prisms,  that  the  dispersion  of  the 
different  colors  is  strictly  proportional  to  the  wave-length. 

332.  Double  Refraction.  —  As  implied  in  Art.  320,  all  crystallized  sub- 
stances may  be  divided  into  two  principal  optical  classes,  viz. :   isotropic,  in 
which  light  has  the  same  velocity  no  matter  what  the  direction  of  its  propaga- 
tion, and  anisotropic,  in  which  the  velocity  of  light  in  general  varies  with  the 
direction   of   propagation.     The   anisotropic   class  is  further  divided  into 
uniaxial,  which  includes  crystals  of  the  tetragonal  and  hexagonal  systems,  and 
biaxial,  which  includes  crystals  of  the  orthorhombic,  monoclinic,  and  triclinic 
systems.     The  characters  of  these  various  optical  classes  will  be  explained 
in  detail  further  on. 

In  the  discussion  of  Art.  317,  applying  to  isotropic  media,  it  was  shown  that 
light-waves  passing  from  one  medium  into  another,  which  is  also  isotropic, 
suffer  simply  a  change  in  wave-front  in  consequence  of  their  change  in  velocity. 
In  anisotropic  media,  however,  which  include  all  crystals  but  those  of  the 
isometric  system,  there  are,  in  general,  two  wave-systems  propagated  with 
different  velocities  and  only  in  certain  limited  cases  is  it  true  that  the  light- 
ray  is  normal  to  the  wave-front.  This  subject  cannot  be  adequately  explained 
until  the  optical  properties  of  these  media  are  fully  discussed,  but  it  must  be 
alluded  to  here  since  it  serves  to  explain  the  familiar  fact 
that,  while  with  glass,  for  example,  there  is  only  one 
refracted  ray,  many  other  substances  give  two  refracted  rn — 
rays,  or,  in  other  words,  show  double  refraction.  I 

The  most  familiar  example  of  this  property  is  fur-       / 


nished  by  the  mineral  calcite,  also  called  on  account 

of    this    property  "doubly-refracting   spar."     If  mnop 

(Fig.  529)  be  a  cleavage  piece  of  calcite,  and  a  ray  of 

light   meets   it    at    b,  it  will,  in    passing    through,  be 

divided  into  two  rays,  be,  bd.     For  this  reason,  a  dark 

spot    or    a   line    seen    through     a    piece    of    calcite    ordinarily    appears 

double.     As  implied  above,  the  same  property  is  enjoyed  by  all  crystallized 


224  PHYSICAL  MINERALOGY 

minerals,  except  those  of  the  isometric  system.  The  wide  separation  of  the 
two  refracted  rays  by  calcite,  which  makes  the  phenomenon  so  striking,  is  a 
consequence  of  the  large  difference  in  the  values  of  its  indices  of  refraction;  in 
other  words,  as  technically  expressed,  it  is  due  to  the  strength  of  its  double 
refraction,  or  its  birefringence. 

333.  Double  refraction  also  takes  place  in  the  anisotropic  media  just 
mentioned,  in  the  majority  of  cases,  even  when  the  incident  light  is  perpen- 
dicular to  the  surface.     If  the  medium  belongs  to  the  uniaxial  class  (see  p.  253, 
et  seq.),  one  of  the  rays  always  retains  its  initial  direction  normal  to  the  sur- 
face;  but  the  other,  except  in  certain  special  cases,  is  more  or  less  deviated 
from  it.     With  a  biaxial  substance,  further,  both  rays  are  usually  refracted  and 
bent  from  their  original  direction.     In  the  case  of  both  uniaxial  and  biaxial 
media,  however,  it  is  still  true  that  the  normal  to  the  wave-front  remains  unre- 
fracted  with  perpendicular  incidence. 

334.  Interference  of  Waves  in  General.  —  The  subject  of  'the  inter- 
ference of  light-waves,  alluded  to  in  Art.  331,  requires  detailed  discussion.     It 
is  one  of  great  importance,  since  it  serves  to  explain  many  common  and  beauti- 
ful phenomena  in  the  optical  study  of  crystals. 

Referring  again  to  the  water-waves  spoken  of  in  Art.  308,  it  is  easily 
understood  that  when  two  wave-systems,  going  out,  for  example,  from  two 
centers  of  disturbance  near  one  another,  come  together,  if  at  a  given  point 
they  meet  in  the  same  phase  (as  crest  to  crest),  the  result  is  to  give  the  particle 
in  question  a  double  amplitude  of  motion.  On  the  other  hand,  if  at  any  point 
the  two  wave-systems  come  together  in  opposite  phases,  that  is,  half  a  wave- 
length apart,  the  crest  of  one  corresponding  to  the  trough  of  the  other,  they 
interfere  and  the  amplitude  of  motion  is  zero.  Under  certain  conditions, 
therefore,  two  sets  of  waves  may  unite  to  form  waves  of  double  amplitude;  on 
the  other  hand,  they  may  mutually  interfere  and  destroy  each  other.  Obvi- 
ously an  indefinite  number  of  intermediate  cases  lie  between  these  extremes. 
What  is  true  of  the  waves  mentioned  is  true  also  of  sound-waves  and  of  wave- 
motion  in  general.  A  very  simple  case  of  interference  was  spoken  of  in  con- 
nection with  the  discussion  of  the  waves  carried  by  a  long  rope  (Art.  310). 

335.  Interference  of  Light-waves.  —  Interference  phenomena  can  be 
most  satisfactorily  studied  in  the  case  of  light-waves.     The  extreme  cases  are 
as  follows:  If  two  waves  of  like  length  and  intensity,  and  propagated  in  the 
same  direction,  meet  in  the  same  phase,  they  unite  to  form  a  wave  of  double 
intensity  (double  amplitude).     This,  as  stated  in  Art.  311,  will  cause  an 
increase  in  the  intensity  of  the  light.     If,  however,  the  waves  differ  in  phase 
by  half  a  wave-length,  or  an  odd  multiple  of  this,  they  interfere  and  extinguish 
each  other  and  no  light  results.     For  other  relations  of  phase  they  are  also 
said  to  interfere,  forming  a  new  resultant  wave,  differing  in  amplitude  from 
each  of  the  component  waves.     In  the  above  cases  monochromatic  light- waves 
were  assumed  (that  is,  those  of  like  length).     If  ordinary  white  light  is  used 
interference  for  certain  wave-lengths  may  result  with  the  consequent  sub- 
traction of  the  corresponding  color  from  the  white  light  and  so  give  rise  to 
various  spectrum  colors. 

336.  Illustrations  of  Interference.  —  A  simple  illustration  is  afforded  by 
the  bright  colors  of  very  thin  films  or  plates,  as  a  film  of  oil  on  water,  a  soap- 
bubble,  and  like  cases,.     To  understand  these,  it  is  only  necessary  to  remember 
that  the  incident  light-waves  are  reflected  in  part  from  the  upper  and  in  part 
from  the  lower  surface  of  the  film  or  plate.     The  rays  that  are  reflected  from 


CHARACTERS    DEPENDING   UPON    LIGHT 


225 


531 


the  under  surface  of  the  very  thin  film  (see  Fig.  530)  having  traveled  a  greater 
distance  and  with  a  different  velocity  will,  when  they  unite  with  those  rays 
reflected  from  the  upper  surface,  show  in 
general  a  different  phase.  For  some  partic- 
ular wave-length  of  light  this  difference  is 
likely  to  be  exactly  a  half  wave-length  or 
some  odd  multiple  of  this  amount  and  so  the 
corresponding  color  will  be  eliminated 
(assuming  that  ordinary  white  light  is  being 
used)  and  its  complementary  color  will  be 
seen.  It  is  to  be  noted  that  the  phenom- 
ena of  interference  by  reflection  are  some- 
what complicated  by  the  fact  that  there  is 
a  reversal  of  phase  (that  is,  a  loss  of 
half  a  wave-length)  at  the  surface  that 
separates  the  medium  of  greater  optical  density  from  the  rarer  one. 
Hence  the  actual  relation  in  phase  of  the  two  reflected  rays,  as  AC,  BD  (sup- 
posing them  of  the  same  wave-length)  is  that  determined  by  the  retardation. 

due  to  the  greater  length  of  path  trav- 
ersed by  BD,  together  with  the  loss  of  a 
A  half  wave-length  due  to  the  reversal 

of  phase  spoken  of.  As  shown  in  the 
figure,  there  are  also  two  transmitted  waves  which  also  interfere  in  like  manner. 
A  plano-convex  lens  of  long  curvature,  resting  on  a  plane  glass  surface 
(Fig.  531),  and  hence  separated  from  it,  except  at  the  center,  by  a  film  of  air 
of  varying  thickness,  gives  by  reflected  monochromatic  light  a  dark  center  and 
about  this  a  series  of  light  and  dark  rings,  called  Newton's  rings.  The  dark 
center  is  due  to  the  interference  of  the  incident  and  reflected  waves,  the 
later  half  a  wave-length  behind  the  former.  The  light  rings  correspond 
to  the  distances  where  the  two  sets  of  reflected  waves  meet  in  the  same 
phase,  that  is  (noting  the  explanation  above)  where  the  retardation  of  those 
having  the  longer  path  is  a  half  wave-length  or  an  odd  multiple  of  this  (JX, 
fX,  fX,  etc.).  Similarly  the  dark  rings  fall  between  these  and  correspond  to 
the  points  where  the  two  waves  meet  in  opposite  phase,  the  retardation  being 
a  wave-length  or  an  even  multiple  of  this.  The  rings  are  closer  together  with 
blue  than  with  red  because  of  the  smaller  wave-length  of  blue  light.  In  each 
of  the  cases  described  the  ring  is  properly  the  intersection  on  the  plane  surface 
of  the  cone  of  rays  of  like  retardation. 

In  ordinary  white  light  we  get,  instead  of  the  alternate  light  and  dark  rings 
described  above,  a  series  of  colored  bands.  If  the  illumination  was  originally 
by  sodium  light  the  position  of  the  dark  rings  indicates  where  light  for  that 
particular  wave-length  has  been  extinguished  through  interference.  When 
white  light  is  used  the  conditions  in  respect  to  its  component  having  the 
yellow  sodium-light  wave-length  have  not  changed  and  this  light  will  still  be 
eliminated  at  the  same  points,  but  now,  instead  of  dark  rings,  we  get  rings  having 
the  complementary  color  blue.  If  our  original  illumination  was  by  means  of 
a  red  light  the  dark  rings  would  have  had  different  positions  from  those  pro- 
duced in  sodium  light.  And  again  when  white  light  is  used  red  light  is  elim- 
inated at  those  points  and  its  complementary  color  shows.  In  this  way  we 
obtain  a  series  of  colored  rings,  each  showing  the  successive  colors  of  the 
spectrum.  The  series  of  the  spectrum  colors  are  repeated  a  number  of  times 


226 


PHYSICAL  MINERALOGY 


due  to  successive  interferences  produced  by  differences  of  phase  of  J,  1J,  2|, 
etc.,  wave-lengths.  The  different  series  are  distinguished  as  of  the  first, 
second,  third,  etc.,  order;  for  a  given  color,  as  red,  may  be  repeated  a  number 
of  times.  The  interference  rings  for  different  colored  lights  are  not  evenly 
spaced,  the  rings  shown  in  blue  light  being,  for  instance,  closer  together  than 
for  red.  Consequently  after  three  or  four  repetitions  of  the  spectrum  bands 
the  different  interference  rings  begin  to  overlap  one  another  and  the  resulting 
colors  become  fainter  and  less  pure.  Ultimately  this  overlapping  becomes 
so  general  that  the  effect  of  color  is  lost  and  white  light,  the  so-called  white  of 
the  higher  orders,  is  shown. 

Another  most  satisfactory  illustration  of  the  interference  of  light-waves  is  given  by 
means  of  the  diffraction  gratings  spoken  of  in  Art.  331. 

Other  cases  of  the  composition  of  two  systems  of  light-waves  will  be  con- 
sidered after  some  remarks  on  polarized  light. 

337.  Polarization  and  Polarized  Light.  —  Ordinary  light  is  propagated 
by  transverse  vibrations  of  the  ether  which  may  take  place  in  any  direction  as 
long  as  it  is  at  right  angles  to  the  line  of  propagation.  The  direction  of  vibra- 
tion is  constantly  changing  and  the  resulting  disturbance  of  the  ether  is  a 
complex  one.  A  ray  of  ordinary  light  will  be  symmetrical,  therefore,  only  to 
the  line  of  its  propagation. 

Plane-polarized  light,  on  the  other  hand,  as  stated  briefly  in  Art.  311,  is 
propagated  by  ether-vibrations  which  take  place  in  one  plane  only.  The 
change  by  which  ordinary  light  is  converted  into  a  polarized  light  is  called 
polarization,  and  the  plane  at  right  angles  to  the  plane  of  transverse  vibration 
is  called  the  plane  of  polarization* 

Polarization  may  be  accomplished  (1)  by  reflection  and  by  single  refrac- 
tion, and  (2)  by  double  refraction. 

Polarization  by  Reflection  and  Single  Refraction.  —  In  general, 

light  which  has  suffered  reflection 
from  a  surface  like  that  of  polished 
glass  is  more  or  less  completely  po- 
larized; that  is,  the  reflected  waves 
are  propagated  by  vibrations  to  a 
large  extent  limited  to  a  single  plane, 
viz.,  (as  assumed)  the  plane  normal 
to  the  plane  of  incidence,  which  last 
is  hence  the  plane  of  polarization. 
Furthermore,  in  this  case,  the  light 
transmitted  and  refracted  by  the 
reflecting  medium  is  also  in  like 
manner  partially  polarized;  that  is, 
the  vibrations  are  more  or  less  limited 
to  a  single  plane,  in  this  case  a  plane  at 
right  angles  to  the  former  and  hence 
coinciding  with  the  plane  of  incidence. 
For  instance,  in  Fig.  532,  let  a-b  rep- 
resent an  incident  light  ray  in  which 
the  vibrations  are  taking  place  in  all  possible  transverse  directions  as  represented 

>  *  It  is  necessary  to  keep  clear  the  distinction  between  the  plane  of  polarization  and  the 
plane  in  which  the  vibrations  take  place.  All  ambiguity  is  avoided  by  speaking  uniformly 
of  the  vibration-plane  of  the  light. 


338. 


532 


CHARACTERS  DEPENDING  UPON  LIGHT 


227 


by  the  arrows,  x-x,  y-y,  and  z-z.  When  this  ray  strikes  the  polished  surface 
at  6  light  with  vibrations  parallel  to  x-x  will  be  reflected  along  b-c  and 
other  vibrations  near  to  x-x  in  direction  will  be  shifted  to  this  direction  so 
that  the  reflected  ray  will  be 
largely  polarized.  In  a  similar 
manner  the  light  having  z-£ 
vibrations  will  enter  the 
transparent  substance  as  the 
refracted  ray  b-d  and  other 
vibrations  will  be  shifted  to 
this  direction  so  that  the  re- 
fracted ray  is  also  largely 
polarized  and  in  a  plane  at  right 
angles  to  that  of  the  reflected 
ray.  Light  reflected  from  a 
polished  and  transparent  sur- 
face  is  not  completely 
polarized  but  there  is 


Brewster's  Law 

an    angle    of    incidence     for    every    substance 

at  which  the  amount  of  polarization  will  be  at  its  maximum.  This  will  hap- 
pen, as  illustrated  in  Fig.  533,  when  the  angle  between  the  reflected  and 
refracted  rays  A B  and  AC  equals  90°.  It  is  evident  from  a  consideration  of 

the  figure  that  the  angle  r  is  the  complement  of  i\  hence  the  formula  ?    -  =  n 

becomes  in  this  case 

sin  i 

— :  =  tan  i  =  n. 
cos  ^ 

This  law,  established  by  Brewster,  may  be  stated  as  follows : 

The  angle  of  incidence  for  maximum  polarization  is  that  angle  whose  tangent 
is  the  index  of  refraction  of-the  reflecting  substance.  For  crown  glass  this  angle 
is  about  57°  (see  Fig.  533) .  If  light  suffers  repeated  reflections  from  a  series 
of  thin  glass  plates,  the  polarization  is  more  complete,  though  its  intensity  is 
weakened.  Metallic  surfaces  polarize  the  light  very  slightly. 

339.  Polarization    by    Double    Refraction.  —  When    light    in   passing 
through  a  crystalline  medium  is  doubly  refracted  (Art.  332)  or  divided  into 
two  sets  of  waves,  it  is  always  true  that  both  are  completely  polarized  and  in 
planes  at  right  angles  to  each  other.     This  subject  can  only  be  satisfactorily 
explained  after  a  full  discussion  of  the  properties  of  anisotropic  crystalline 
media,  but  it.  may  be  alluded  to  here  since  this  principle  gives  the  most  satis- 
factory method  of  obtaining  polarized  light.     For  this  end  it  is  necessary  that 
one  of  the  two  wave-systems  should  be  extinguished,  so  that  only  that  one 
due  to  a  single  set  of  vibrations  is  transmitted.     This  is  accomplished  by 
natural  absorption  in  the  case  of  tourmaline  plates  and  by  artificial  means  in 
the  nicol  prisms  of  calcite. 

340.  Polarized     Light    by    Absorption.  —  Light     passing    through    a 
strongly  colored  but  transparent  thin  section  of  a  tourmaline  crystal  —  the 
section  being  cut  parallel  to  the  vertical  crystallographic  axis  —  will  be  almost 
completely  polarized.     This  can  be  easily  demonstrated  in  the  following  way. 
Select  a  polished  floor  surface,  or  a  table  top  and  stand  in  such  a  position  that 
light  from  a  window  is  reflected  from  the  polished  wood  to  the  eye.     Look  at 
this  reflected  light  through  the  tourmaline  section,  holding  it  first  with  the 


228  PHYSICAL   MINERALOGY 

direction  'of  the  c  crystal  axis  in  a  horizontal  position  and  then  turning  the 
section  until  the  c  axis  becomes  vertical.  The  light  passing  into  the  tour- 
maline section  is  in  considerable  part  polarized  through  its  reflection  from 
the  wood  surface  and  possesses  a  horizontal  vibration  direction.  It  will  be 
noted  that  when  the  c  axis  of  the  tourmaline  is  horizontal  the  section  readily 
transmits  light  but  when  this  axis  is  vertical  the  section  becomes  practically 
opaque.  The  crystal  structure  of  the  tourmaline  is  such  that  light  entering 
it  is  broken  up  into  two  rays  (i.e.,  it  is  doubly  refracted),  one  of  which  has  its 
vibrations  parallel  to  the  c  axis,  while  the  vibrations  of  the  other  lie  in  the 
plane  of  the  horizontal  crystal  axes.  From  the  foregoing  experiment  it  is 
obvious  that  the  light  vibrating  parallel  to  the  c  axis  is  readily  transmitted  by 
the  crystal  but  that  the  other  ray,  vibrating  in  the  horizontal  axial  plane,  is 
almost  completely  absorbed.  Under  these  conditions  it  is  clear  that  the  trans- 
mitted light  belongs  almost  wholly  to  one  ray,  the  vibrations  of  which  take 
place  in  a  single  direction.  In  other  words,  the  light  transmitted  by  such  a 
tourmaline  section  is  polarized. 

If  two  such  sections  of  tourmaline  are  available  it  is  instructive  to  make 
the  following  experiment  with  them.  Place  them  together,  first  with  their 
c  axes  parallel  to  each  other,  and  then  turn  one  section  upon  the  other  until 
these  axes  are  at  right  angles  to  each  other.  In  the  first  case,  the  light  comes 
through  the  sections  because  the  vibration  planes  of  the  transmitted  rays  in 
the  two  sections  are  parallel  to  each  other.  In  the  second  case,  all  light  is 
cut  off  because  now  these  two  vibration  planes  are  at  right  angles  to  each 
other,  the  light  that  did  get  through  the  first  section  being  wholly  absorbed 
in  the  second. 

341.  Polarized  Light  by  Double  Refraction.  —  Calcite,  as  already  stated 
in  Art.  332,  possesses  in  an  unusual  degree  the  power  to  doubly  refract  light. 
If  we  take  a  cleavage  block  of  clear  calcite  (Iceland  spar)  and  look  at  an  image 
through  it,  such  as  a  dot  or  line  drawn  on  a  piece  of  paper,  the  image  will  appear 
double.  If  we  take  a  card  and  make  in  it  a  pinhole,  place  the  card  upon 
one  face  of  a  cleavage  rhombohedron  and,  looking  through  the  calcite,  hold 
it  up  against  a  source  of  light,  we  will  observe  two  bright  dots.  Now  if  we 
look  in  the  same  way  at  the  light  reflected  from  a  polished  wooden  surface, 
as  described  in  the  preceding  article,  we  will  find  that  when  a  line  bisecting 
the  acute  angles  of  the  rhombic  face  of  the  cleavage  block  is  horizontal  one  of 
these  images  is  bright  while  the  other  is  almost  invisible.  If  we  then  turn 
the  block  so  that  the  line  bisecting  the  obtuse  angles  of  the  rhombic  face  is 
horizontal  the  first  image  will  fade  while  the  second  becomes  bright.  Remem- 
bering that  the  light  reflected  from  the  polished  wooden  surface  is  largely 
polarized  with  a  horizontal  vibration  direction,  it  becomes  evident  from  this 
experiment  that  the  two  rays  into  which  the  light  is  broken  up  in  passing 
through  the  calcite  are  polarized  and  that  their  planes  of  vibration  are  at 
right  angles  to  each  other  and  respectively  bisect  the  angles  of  the  rhombic 
face  of  the  cleavage  block.  As  the  double  refraction  of  calcite  is  strong,  it 
follows  that  the  indices  of  refraction  of  the  two  rays  show  considerable  differ- 
ences. This  fact  is  taken  advantage  of  in  constructing  a  prism  from  calcite 
in  such  a  way  as  to  wholly  eliminate  one  of  these  rays  and  so,  as  only  the  other 
ray  can  come  through  the  prism,  effectively  polarizing  the  light  that  emerges. 

The  prism  referred  to  above  is  called  the  Nicol  Prism  or  simply  the  nicol. 
A  full  explanation  of  the  nicol  cannot  be  made  at  this  time,  as  there  would  be 
required  a  knowledge  of  the  optical  properties  of  hexagonal  crystals,  but  a 


CHARACTERS    DEPENDING   UPON    LIGHT 


229 


535 


description  may  be  given  enabling  one  to  understand  its  construction  and 

uses.     In  Fig.  534  is  represented  a  cleavage  rhombohedron  of  calcite  with  its 

edges  vertical.     Let  d  represent  a  point  of  light  underneath  the  rhombo- 
hedron.    Light  coming  from  d  will  be  broken  into  two  rays  whose  paths 

through  the  rhombohedron  are  shown 

by  the  lines  o  and  e.     As  shown  above, 

these  two    rays    are    polarized,    with 

vibration  directions   as  indicated  .by 

the  double  arrows  in  the  top  view  in 

Fig.  534.     In  the  construction  of   a 

nicol,  the  top  and  bottom  surfaces  of 

such   a    cleavage    rhombohedron  are 

ground    and    polished   so    that    they 

make  angles  of  68°  with  the  vertical 

edges.     Then  the  block  is  cut  in  two 

along  the  diagonal  a-/,  as  shown  in 

Fig.   535.     These  two  surfaces,  after 

being  polished,  are  cemented  together 

by  means  of  a  thin  layer  of  Canada 

balsam.     Let  us  assume  that  a  ray  of 

light  enters  the  prism  from  below,  as 

shown  in  Fig.  535.     It  is  broken  up 

into  the   rays  o  and   e.     The  ray  o 

travels  with  the  slower  velocity,  has 
therefo're  the  higher  index  of  refraction, 
and  shows  a  greater  deviation  from 

the  original  path.     The  Canada  balsam  Nico1  Prism 

has  a  lower  index  of  refraction  than  ray  a,  which,  therefore,  when  it  strikes  the 
layer  of  balsam,  is  attempting  to  pass  from  an  optically  dense  into  a  rarer 
medium.  The  construction  of  the  prism  is  such  that  this  ray  meets  the  layer  of 
balsam  at  an  angle  greater  than  the  critical  angle  for.  this  optical  combination 
and  suffers  therefore  total  reflection  toward  the  side  of  the  prism,  and  will 
be  absorbed  by  whatever  fastening  holds  the  nicol.  The  second  ray  e 
passes  through  the  prism  with  almost  no  deviation  from  its  original  course. 
Its  index  of  refraction  and  that  of  the  Canada  balsam  are  nearly  the  same, 
hence  the  ray  suffers  almost  no  deflection  at  this  point  and  passes  out  of  the 
upper  face  of  the  prism.  The  light,  therefore,  that  emerges  from  a  nicol 
belongs  wholly  to  one  ray  and  is  all  vibrating  parallel  to  the  shorter  diagonal 
of  the  rhombic  end  surface.  It  should  be  noted,  however,  that  some  prisms 
are  made  in  a  different  way  and  that  the  above  statement  concerning  the 
plane  of  vibration  of  the  light  emerging  from  the  prism  may  not  always  hold 
true.  It  is  always  wise  to  test  the  plane  of  vibration  of  a  nicol  by  looking 
through  it  at  the  floor  or  a  table  top  as  previously  described.  The  prism  will 
show  bright  when  its  plane  of  vibration  is  horizontal,  thus  corresponding  to 
the  plane  of  vibration  of  the  reflected  light. 

342.  Polariscope.  Polarizer.  Analyzer.  —  The  combination  of  two 
nicols,  or  other  polarizing  contrivances,  between  which  transparent  mineral 
sections  may  be  examined  in  polarized  light  is  called,  in  general,  a  polariscope; 
the  common  forms  of  which  are  described  later.  In  any  polariscope  the  lower 
prism,  or  other  contrivance,  which  polarizes  the  light  given  from  the  outside 
source  is  called  the  polarizer;  the  upper  prism  is  the  analyser.  If  these  prisms 


230 


PHYSICAL   MINERALOGY 


have  their  vibration-planes  at  right  angles  to  each  other,  they  are  said  to  be 
crossed;  the  incident  light  polarized  by  the  polarizer  will  then  be  extinguished 
by  the  analyzer;  briefly,  under  these  conditions  it  is  said  to  suffer  extinction. 
343.  Interference  of  Plane-polarized  Waves.  Interference  Colors.  — 
When  sections  of  doubly  refracting  minerals  are  examined  in  polarized  light 
certain  interference  effects  are  commonly  obtained  that  are  of  great  impor- 
tance. As  shown  in  Art.  341,  calcite  when  it  doubly  refracts  light  also  polarizes 
the  two  rays  and  in  planes  that  are  at  right  angles  to  each  other.  In  general, 
this  is  true  of  sections  of  doubly  refracting  minerals.  Consider,  then,  what 
takes  place  when  a  general  section  of  a  doubly  refracting  mineral  is  placed  in 
a  polariscope  between  the  polarizer  and  analyzer  the  planes  of  vibration  of 
which  are  at  right  angles  to  each  other.  In  Fig.  536  let  the  rectangular  out- 
line represent  such  a  section.  The  double  arrows  marked  o  and  e  show  the 
two  possible  directions  of  vibration  of  light  in  the  section.  The  direction 
P-P'  represents  the  plane  of  vibration  of  light  which  emerges  from  the  polar- 
izer below  and  A- A'  shows  the  direction  in  which  light  must  vibrate  when  it 
emerges  from  the  analyzer  above.  In  the  first  case  to  be  considered  the 
directions  o  and  e  are  taken  as  parallel  to  P-P'  and  A- A'  respectively.  The 
light  that  enters  the  section  from  below  must  all  vibrate  parallel  to  the  direc- 
tion P-P'.  It  enters  the  mineral  section  and  must  vibrate  there  as  the  ray 
labeled  o.  There  will  be  no  ray  in  the  mineral  vibrating  parallel  to  the  direc- 
tion e,  as  a  vibration  parallel  to  o  cannot  be  resolved  into  another  at  right 
angles  to  it.  The  light  will  leave  the  section,  therefore,  still  vibrating  parallel 
to  P-P'  and  enter  the  analyzer  above.  It  will,  however,  be  entirely  reflected 
in  the  analyzer  at  the'layer  of  balsam  since  only  light  vibrating  parallel  to  A- A', 
which  is  at  right  angles  to  P-P',  can  emerge  from  the  analyzer.  Consequently, 
when  such  a  section  has  its  planes  of  vibration  parallel  to  those  of  the  polar- 
izer and  analyzer,  the  section  will  appear  dark.  The  same  reasoning  holds 
true  when  the  section  is  turned  to  a  position  at  90°  from  the  first.  Con- 
sequently with  such  a  section  there  are  four  positions  at  90°  to  each  other 
in  which  it  appears  dark  during  its  complete  rotation  upon  the  stage  of  the 
polariscope.  At  such  positions  the  section,  is  said  to  be  extinguished. 


636 


537 

A' 


538 


-P'    P 


Next  consider  what  happens  when  the  vibration  directions  of  the  section 
are  at  oblique  angles  to  those  of  the  polarizer  and  analyzer.  In  Fig.  537 
let  o  and  e  represent  the  directions  of  vibration  in  a  section  which  makes  some 
oblique  angle. with  the  directions  P-P'  and  A- A'.  In  Fig.  538A  let  the  line 
P-P'  represent  the  direction  and  amplitude  of  the  vibration  of  the  light  enter- 


CHARACTERS   DEPENDING   UPON    LIGHT  231 

ing  the  mineral  section  having  come  through  the  polarizer  below.  The  light 
must  vibrate  in  the  mineral  in  directions  parallel  to  o  and  e,  Fig.  537.  The 
vibration  P-P'  will  therefore  be  resolved  into  two  vibrations  at  right  angles 
to  each  other  which  will  be  parallel  respectively  to  o  and  e.  In  Fig.  538A  the 
lines  o  and  e  representing  the  direction  and  amplitudes  of  such  vibrations  are 
found  by  the  application  of  the  principle  of  the  parallelogram  of  forces.  The 
two  rays  emerge  from  the  mineral  section  vibrating  in  these  two  planes  and 
enter  the  analyzer  above.  Since  the  planes  of  vibration  in  the  analyzer  are 
parallel  to  A- A'  and  P-P'  these  two  rays  o  and  e  will  resolve  each  into  two 
new  rays  which  will  vibrate  now  parallel  to  A-A'  and  P-P'.  The  two  rays 
labeled  P  and  P'  in  Fig.  5385  will  be  absorbed  by  the  analyzer  but  the  rays 
marked  A  and  A'  will  emerge  and  meet  the  eye.  The  section  in  this  position, 
therefore,  will  be  illuminated.  Consequently  the  section  will  be  illuminated 
in  all  possible  positions  in  which  the  directions  of  vibration  of  the  light  in  the 
mineral  make  inclined  angles  with  the  directions  of  vibration  of  the  polarizer 
and  analyzer.  It  is  easy  to  prove  that  this  illumination  will  be  at  its  maxi- 
mum when  the  angle  between  the  directions  o  and  e  and  A-A'  and  P-P'  is 
45°.  In  addition  to  being  illuminated,  the  section,  if  thin,  will  also  be  colored. 
This  interference  color,  as  it  is  called,  of  mineral  sections  when  examined  in 
a  polariscope,  now  needs  explanation. 

The  amount  of  refraction  which  any  ray  of  light  suffers  on  entering  a 
mineral  depends  upon  two  things,  namely,  the  angle  of  incidence  at  which  the 
light  enters  and  the  index  of  refraction  of  the  mineral.  In  the  case  of  a  doubly 
refracting  mineral  we  have  a  light  ray  entering  the  section  at  a  given  angle  of 
incidence  and  then  being  broken  up  into  two  polarized  rays  which  have  differ- 
ent angles  of  refraction  and  so  travel  different  paths.  Consequently  the 
indices  of  refraction  for  these  rays  must  be  different  and  from  this  it  follows 
that  the  two  rays  must  have  different  velocities  and  will  therefore  emerge 
from  the  mineral  in  different  phases.  Light  waves  having  different  phases 
will  in  a  greater  or  less  degree  interfere  with  each  other  and  in  case  of  light  of 
certain  wave-lengths,  i.e.,  light  of  some  particular  color,  the  interference  may 
lead  to  extinguishment  of  that  particular  wave-length.  If  one  particular 
color  is  subtracted  in  this  way  from  white  light  the  result  will  be  to  produce 
the  complementary  color  and  under  such  conditions  the  section  will  no  longer 
be  white  but  colored.  The  color  of  thin  sections  of  minerals  when  seen  under 
the  polariscope  is  known  as  their  interference  color.  To  develop  this  subject 
further  use  will  be  made  of  an  accessory  of  the  microscope  known  as  the 
Quartz  Wedge. 

The  Quartz  Wedge  consists  simply  of  a  very  thin  tapering  wedge  the  faces 
of  Which  are  approximately  parallel  to  the  prism  of  a  quartz  crystal.  It  is 
mounted  on  a  narrow  glass  plate,  Fig.  539,  A.  The  plate  is  generally  marked 
with  the  letter  Q  (quartz)  and  with  an  arrow.  If  the  wedge  is  cut,  as  is 
usually  the  case,  with  its  longer  direction  at  right  angles  to  the  vertical  axis 
of  a  quartz  crystal,  the  arrow  is  marked  X  (or  a),  which  indicates  that  of  the 
two  directions  of  vibration  of  light  in  the  wedge  the  one  which  is  parallel  to 
this  direction  is  that  of  the  ray  which  is  propagated  with  greater  velocity. 
Some  wedges  are  cut  with  their  longer  direction  parallel  to  the  vertical 
axis  of  quartz,  and  the  arrow  in  this  case  would  be  marked  Z  (or  c),  which 
indicates  that  this  is  the  direction  of  vibration  of  the  slower  ray.  It  is  abso- 
lutely essential  that  the  optical  orientation  of  the  wedge  be  known. 

The  quartz  wedge  furnishes  a  prismatic  section  of  varying  thickness  and 


232 


PHYSICAL  MINERALOGY 


of  known  orientation  and  may  be  used  to  study  the  effects  of  polarized  light 
on  plates  (short  sections  of  the  wedge)  of  different  thicknesses.  Take  the 
simplest  form  of  polariscope,  a  combination  of  polarizer  and  analyzer  without 


539 

A 


r 

± 

1     + 

H- 

+ 

4 

P 

X**— 

-«e 

!     i 

:                       ! 
i                       ! 

Q 

Quartz  Wedge 

lenses,  and  arrange  it  so  that  the  vibration  planes  of  the  instrument  are  crossed. 
Illuminate  with  ordinary  light  and  on  the  stage  of  the  instrument  place  a 
quartz  wedge  with  its  X  direction  parallel  to  the  plane  of  vibration  of  the 
polarizer.  The  light  in  entering  the  quartz  will  vibrate  parallel  to  the  X 
direction  and  without  changing  its  plane  of  vibration  will  pass  through  the 
quartz  and  up  into  the  upper  nicol  where  it  will  suffer  total  reflection.  Hence 
the  wedge  in  this  position  will  appear  dark  throughout  its  length.  A  similar 
result  will  be  obtained  when  the  X  direction  of  the  wedge  is  placed  parallel 
to  the  vibration  plane  of  the  analyzer.  But  if  the  wedge  is  turned  so  that  its 
X  direction  makes  an  angle  of  about  45°  with  the  plane  of  vibration  of  the 
polarizer  the  wedge  will  exhibit  a  series  of  beautiful  interference  colors, 
arranged  in  transverse  bands,  the  nature  of  which  will  be  discussed  in  a  later 
paragraph.  If  the  wedge  is  turned  from  this  45°  position  the  colors  become 
less  and  less  brilliant  as  the  position  of  extinction  is  neared.  i 

As  preliminary  to  another  experiment,  paste  a  narrow  strip  of  paper, 
P-P,  Fig.  539,  B,  on  the  top,  but  to  one  side,  of  a  quartz  wedge.  Place  this 
on  the  stage  of  a  polariscope  (without  lenses)  and  illuminate  with  diffused 
sodium  light.  When  the  wedge  is  examined  under  these  conditions  it  will  be 
found  that  it  shows  extinction  when  its  vibration  directions  are  parallel  to 
those  of  the  polariscope  but  at  the  45°  position  it  will  show  transverse  dark 
bands  upon  a  yellow  field.  The  number  of  these  bands  will  depend  upon  the 
thickness  of  the  wedge;  usually  there  will  be  two  or  three,  although  for  this 
experiment  it  is  interesting  to  have  a  longer  and  proportionally  thicker  wedge 
than  those  commonly  supplied,  so  as  to  have  more  bands  appearing.  Mark 
on  the  strip  of  paper  the  position  of  each  band,  as  illustrated  in  Fig.  539,  B  and 
number  them,  starting  at  the  band  nearest  the  thinner  end  of  the  wedge.  The 
number  1  band  marks  the  place  where  the  faster  of  the  two  rays,  into  which 
the  quartz  breaks  up  the  sodium  light,  has  gained  exactly  one  wave  length  in 
its  phase  over  the  slower  ray.  At  the  point  marked  2  the  gain  is  two  wave- 
lengths, etc. 

In  explaining  the  phenomenon  just  described,  reference  is  made  to  Fig. 
540  in  which  it  is  assumed  that  P-P'  is  the  plane  of  the  polarizer  and  A- A1 


CHARACTERS    DEPENDING   UPON    LIGHT 


233 


is  the  plane  of  the  analyzer,  and  a  quartz  wedge  is  between  them  at  such  an 
angle  that  the  direction  of  the  vertical  crystal  axis  lies  parallel  to  C-C'.  If  we 
explain  the  action  of  light  in  the  wedge  in  a  purely  mechanical  way  we  may  say, 
let  the  amplitude  of  vibration  of  an  ether  particle  before  the  light  has  entered 
the  wedge  be  represented  in  the  figure  by  the  line  0-p.  The  vibration  may  be 
likened  to  that  of  a  pendulum',  swinging  back  and  forth  from  p  to  p'.  If  the 
impact,  or  disturbance,  of  an  ether  particle  is  communicated  to  the  ether 
particles  of  the  quartz  when  it  is  at  0  at  the  middle  of  an  oscillation  from 
p  to  p',  there  will  result  two  disturbances,  one  to  r  parallel  to  C-C'  and  the 
other  to  s  at  right  angles  thereto.  The  amplitude  of  the  vibrations  repre- 
sented by  0-r  and  0-s  are  determined  by  the  parallelogram  of  forces,  as  indi- 
cated by  the  dotted  lines  in  the  figure.^  During  the  passage  of  these  two  rays 
through  the  quartz  the  one  whose  vibrations  are  represented  by  s-s'  travels 
the  faster  and  it  is  assumed  that  the  thickness  of  the  quartz  wedge  at  the  place 
under  consideration  is  such  that,  on  emerging,  this  ray  is  just  one  wave-length 
ahead  of  the  one  whose  vibrations  are  parallel  to  r-r'.  Now,  when  one  ray  is 
exactly  one  wavelength  ahead  of  another  (it  may  be  two,  three  or  any  exact 
number  of  wavelengths)  the  conditions  are  such,  that,  at  the  middle  of  the 
vibration,  when  an  ether  particle  of  the  ray  s-s'  is  just  starting  from  0  to  s, 
an  ether  particle  of  the  ray  r-r'  will  be  just  starting  from  0  to  r.  Now  con- 
sider the  effects  produced  by  the  simultaneous  impacts  in  the  directions  0  to 
s  and  0  to  r  upon  the  ether  particles  of  the  calcite  constituting  the  analyzer. 
A*  vibration  from  s'  to  s  acting  at  0  will  displace  the  ether  particles  of  the 
calcite  to  a  and  a'.  Likewise  a  vibration  from  r'  to  r  acting  at  0  will  displace 
the  ether  particles  to  p  and  p'.  Two  of  these  resulting  disturbances,  namely 
0-<j'  and  0-p',  are  easily  disposed  of,  for  being  in  the  plane  P-P'  their  effects 
cannot  pass  beyond  the  layer  of  Canada  balsam  in  the  nicol.  The  other  dis- 
turbances 0-ff  and  0-p  are  both  in  the  plane  A- A'  and  can  emerge  from  the 
nicol,  but  since  the  ether  particles  at  Oare  acted  upon  simultaneously  by  forces 
of  equal  magnitude  acting  in  opposite  directions  no  disturbance  can  take 
place  and  under  these  conditions  the  section  is  dark.  From  the  above  it 


540 


641 


\ 


P\ 


follows  that,  when  a  section  of  a  doubly  refracting  mineral  is  observed  be- 
tween crossed  nicols  with  its  vibration  planes  making  some  oblique  angle 


234 


PHYSICAL   MINERALOGY 


with  the  vibration  planes  of  the  nicols,  complete  interference  will  take  place 
for  some  particular  wave-length  of  light  whenever  the  two  polarized  rays 
corresponding  to  this  color  emerge  from  the  section  in  the  same  phase. 

It  is  well  to  consider  next  the  effects  that  result  when,  with  the  planes  of 
vibration  of  the  nicols  crossed,  light  travels  through  such  thicknesses  of  the 
quartz  wedge  that  one  ray  gains  -J-,  f ,  or  some  other  half  wave-length  over  the 
second  ray.  Let  it  be  supposed,  Fig.  541,  that  at  0,  the  middle  of  an  oscilla- 
tion from  p  to  p',  the  impact  is  communicated  to  the  ether  particles  of  a 
quartz  section  the  vertical  crystal  axis  of  which  lies  parallel  to  the  direction 
C—Cr.  There  will  result  two  disturbances  in  the  quartz,  one  from  0  to  r  and 
the  other  from  0  to  s.  After  traversing  the  section  the  phases  of  the  two  rays 
differ  by  one  half  wave-length  so  that  when  the  direction  of  the  first  oscilla- 
tion is  from  0  to  r,  that  of  the  other  will  be  from  0  to  sf.  The  impulse  0-r 
gives  rise  in  the  analyzer  to  two  disturbances  0-p  and  0-p'.  The  impulse 
0-s'  results  in  the  two  displacements  O-a-  and  0-a'.  Of  these  disturbances 
0-p'  and  0-a'  do  not  extend  beyond  the  layer  of  Canada  balsam  of  the  analyzer, 
while  0-p  and  0-a,  both  of  equal  magnitude  and  vibrating  in  the  plane  A- A', 
are  additive  and  give  rise  to  a  disturbance  and  the  sensation  of  light.  Hence, 
in  the  experiment  with  the  quartz  wedge  in  sodium  light,  there  are  areas  of 
light  between  the  dark  bands,  Fig.  539,  B. 

An  instructive  experiment  with  the  wedge  should  also  be  tried  with 
sodium  light  illumination  but  with  the  planes  of  vibration  of  the  polari- 
scope  parallel  to  each  other  instead  of  crossed  as  in  the  previous  cases. 
If  light  traverses  such  a  thickness  of  quartz  that,  on  emerging,  one  ray 
has  gained  one  half  of  a  wave-length  over  the  other  the  conditions  up  to 
the  time  the  vibrations  enter  the  analyzer  will  be  the  same  as  in  the 
previous  case.  The  vibrations,  however,  which  can  now  pass  through 
the  analyzer  result,  Fig.  542,  from  the  disturbances  0-p'  and  0-a',  and  these 
acting  on  an  ether  particle  in  opposite  directions  but  with  unequal  force  would 
produce  a  disturbance  in  the  direction  0-p'  and,  therefore,  give  rise  to  the 
sensation  of  light.  A  wedge  with  the  direction  of  the  vertical  crystal  axis 
about  parallel  to  C-C'  will  appear  yellow  throughout  its  entire  length.  This 
will  not  be  the  case,  however,  if  the  wedge  is  turned  so  that  the  vertical  axis 


542 


543 


makes  an  angle  of  45    with  the  plane  of  polarization,  Fig.  543,  for  then  the 
forces  acting  upon  an  ether  particle  at  0  are  0-p'  and  0-a,  which,  being  equal 


CHARACTERS   DEPENDING   UPON   LIGHT  235 

and  in  opposite  directions,  will  neutralize  each  other  and  therefore  will  not 
produce  any  sensation  of  light.  A  wedge  in  the  45°  position  will  therefore 
show  a  series  of  dark  bands,  the  first,  starting  from  the  thin  end  of  the  wedge, 
being  where  one  ray  has  gained  J  wave-length,  the  second  where  it  has  gained 
j  wave-lengths,  etc.,  over  the  second  ray.  In  Fig.  539,  B,  the  positions  of  the 
bands  in  this  experiment  are  indicated  by  the  crosses  marked  on  the  strip  of 
paper  pasted  upon  one  side  of  the  quartz  wedge.  The  lines  and  crosses  on 
this  paper  strip  indicating  gains  of  whole  and  one  half  wave-lengths  for  yellow 
light  may  now  serve  as  starting  points  for  further  considerations. 

For  the  next  experiment  use  a  microscope  with  crossed  nicols,  a  number  3  or 
4  objective,  and  illuminate  with  ordinary  light;  place  the  wedge  in  the  45° 
position  and  focus  on  that  part  of  it  opposite  the  first  line  drawn  on  the  paper 
strip  The  field  will  show  at  its  center  a  blue  color,  about  at  the  point  where 
it  is  beginning  to  merge  into  red.  A  moment's  consideration  will  indicate 
what  this  color  really  is.  It  is  a  mixture  of  all  colors  of  the  spectrum  except 
yellow.  That  this  is  the  case  may  be  proved  by  analyzing  the  blue  by  means 
of  a  small  direct-vision  spectroscope.  This  will  show  a  spectrum  through 
which  runs  a  dark  band  between  the  red  and  green,  that  is,  where  the  yellow 
would  normally  appear.  The  blue  of  the  wedge  at  this  point  is  therefore  the 
complement  of  yellow,  which  has  been  made  to  disappear  by  interference. 
Next  focus  the  microscope  on  the  wedge  opposite  the  second  line.  Here  the 
color  will  be  nearly  a  sky  blue,  with  perhaps  a  tinge  of  green.  Upon  analysis 
with  the  spectroscope  again  a  dark  band  will  be  found  in  the  yellow,  this  time 
due  to  interference  brought  about  by  a  difference  in  phase  of  two  wave-lengths 
for  sodium  light.  Proceeding  next  to  opposite  the  third  line  the  color  will 
be  found  to  be  a  light  green,  which  on  analysis  shows  a  band  where  yellow 
should  occur  and  a  perceptible  shortening  of  the  spectrum,  especially  by  cut- 
ting off  the  extreme  blue  and  violet.  Opposite  the  fourth  line  the  color  would 
be  a  very  pale  green  which  upon  analysis  with  the  spectroscope  would  show 
two  dark  bands,  one  in  the  yellow  and  another  in  the  blue.  The  pale  green 
color  is  therefore  due  to  a  mixture  of  red,  green,  and  violet.  If,  in  the  original 
experiment  the  wedge  had  been  illuminated  by  a  monochromatic  blue  light 
it  would  have  been  found  at  the  thicker  end  of  the  wedge,  where  the  fourth 
band  for  yellow  light  was  located,  there  would  have  been  a  fifth  band  for  the 
blue  light.  Consequently  the  interference  color  at  this  point  of  the  wedge  is 
equivalent  to  white  light  from  which  both  yellow  and  blue  have  been  sub- 
tracted. If  a  wedge  of  extra  length  was  available  for  study  it  would  have  been 
noted  that  opposite  the  eighth  band  for  sodium  light  the  color  showing,  when 
the  wedge  is  studied  in  the  polarizing  microscope,  was  white.  This  upon 
analysis  would  show  a  spectrum  crossed  by  bands  in  the  red,  yellow,  green,  and 
blue.  In  other  words,  in  traversing  the  thickness  of  the  quartz  at  this  point, 
the  faster  ray  has  gained  for  red  seven  wave-lengths  over  the  slower  ray,  for 
yellow  eight,  for  green  nine,  for  blue  ten.  The  white  polarization  effect 
seen  when  looking  at  this  point  with  the  microscope  is  known  as  white  of  the 
higher  order.  It  is  a  mixture  of  the  several  primary  colors  of  the  spectrum, 
some  portions  of  all  of  which  are  present  and  combine  to  give  the  effect  of  white. 

It  is  important  to  study  carefully  the  polarization  colors  of  the  quartz 
wedge  under  the  microscope,  using  Fig.  544  as  a  guide.  It  will  be  noted  that 
the  colors  occur  in  general  in  the  following  order  as  the  thickness  of  the  quartz 
increases :  violet,  blue,  green,  yellow,  orange,  red.  This  sequence  of  colors  is 
repeated  quite  distinctly  three  times  and  then  as  the  thicker  end  of  the  wedge 


PHYSICAL   MINERALOGY 


236 

is  approached  the  colors  become  fainter  and  not  so  clear.     This  series  of 
interference  colors  is  divided  into  orders  as  indicated  in  Fig.  544.     It  is  to  be 


544 


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Third  Order  i-A.  Fourth  Order  -A-  Higher  Ordere- 


>-  First  Order  -A^  Second  Order 

Interference  Colors  with  Quartz  Wedge 

noted  that  at  the  very  thin  end  of  the  wedge  before  any  interference  can  have 
taken  place  the  color  is  white.  Also  the  thicker  end  of  the  wedge  is  white 
because  here  there  is  an  overlapping  of  the  various  points  of  interference  of 
the  different  colors.  The  thickness  of  the  wedge  at  the  different  points  is 
given  in  millimeters  in  Fig.  544. 

344.  Sensitive  Tint.  —  Among  the  accessories  of  the  polarizing  micro- 
scope is  a  thin  plate  of  gypsum  mounted  between  two  plates  of  glass.    It  is 
commonly  marked  S.  T.  and  also  with  an  arrow  marked  either  X  (o)  or  Z  (c), 
indicating  respectively  the  direction  of  vibration  of  the  faster  or  slower  ray. 
If  this  is  placed  on  the  microscope  stage  in  the  45°  position  with  the  nicols 
crossed,  the  interference  color  shown  is  reddish  violet,  the  same  as  that  close 
to  the  red  of  the  first  order  of  the  quartz  wedge.     It  is  an  interesting  experi- 
ment to  first  put  a  quartz  wedge  under  the  microscope  and  focus  on  the  red- 
violet,  just  beyond  the  red  of  the  first  order  and  then  cover  it  with  the  sensi- 
tive tint  arranged  in  such  a  way  that  its  X  direction  is  at  right  angles  to  the 
X  direction  of  the  quartz  wedge.     The  resulting  color  will  be  gray.     The 
explanation  of  this  is  simple.     Whatever  gain  the  faster  ray  had  made  over  the 
slower  in  passing  through  the  quartz  has  been  overcome  or  neutralized  by 
passing  through  a  layer  of  gypsum  of  opposite  optical  orientation- and  of  suit- 
able thickness  to  produce  the  same  interference  as  the  quartz.     The  name 
Sensitive  Tint  is  given  to  this  gypsum  plate  because  a  slight  increase  of  the 
double  refraction  which  it  shows  will  give  a  blue  color  while  a  corresponding 
slight  decrease  will  change  the  color  to  yellow.      Numerous  uses  of  the  sensi- 
tive tint  will  be  given  in  subsequent  articles. 

345.  Interference  Colors  of  Mineral  Sections.  —  The  interference  col- 
ors of  mineral  sections  depend  upon  three  things. 

1.  On  the  strength  of  the  birefringence  of  the  mineral,  or  in  other  words 
upon  the  amount  of  double  refraction  that  the  mineral  shows.     The  greater 
the  birefringence  the  higher  the  order  of  interference  color,  the  other  influenc- 
ing factors  remaining  constant. 

2.  The  thickness  of  the  section.     The  thicker  the  section  the  greater  will 
be  the  amount  of  double  refraction  and  consequently  the  higher  the  order  of 
the  interference  color. 


CHARACTERS   DEPENDING   UPON   LIGHT  237 

3.  The  crystallographic  orientation  of  the  section.  This  will  be  explained 
later  when  the  optical  characters  of  the  different  crystal  systems  are  described 

346.  Determination  of  the  Order  of  the  Interference  Color  of  a  Min- 
eral Section.  —  It  is  often  important  to  determine  to  which  order  (see  last 
paragraph  of  Art.  343)  the  interference  color  of  a  given  section  belongs.     If, 
as  is  often  the  case,  the  section  has  somewhere  a  tapering  wedge-like  edge,  the 
successive  bands  of  color  shown  there  can  be  counted  and  the  order  of  the 
color  of  the  surface  of  the  section  determined.     In  other  words  the  order  of 
the  color  can  be  told  in  the  same  way  as  upon  the  quartz  wedge  itself.     If 
such  an  edge  cannot  be  found  the  quartz  wedge  is  used  as  described  below. 

Suppose  a  certain  mineral  section  showed  an  interference  color  of  orange- 
red  and  it  was  desired  to  ascertain  whether  this  color  belonged  to  the  first  or 
second  order.  Under  the  microscope  with  crossed  nicols  find  a  position  of 
extinction  of  the  section  and  then  turn  it  upon  the  stage  of  the  microscope 
through  an  angle  of  45°.  By  doing  this  the  vibration  directions  of  the  section 
are  brought  into  such  a  position  that  they  make  angles  of  45°  with  the  vibra- 
tion directions  of  the  polarizer  and  analyzer.  Then  insert  above  the  section 
and  below  the  analyzer  a  quartz  wedge,  the  optical  orientation  of  which  is 
known.  A  slot  running  through  the  microscope  tube  just  above  the  objective 
and  making  an  angle  of  45°  to  the  cross-hairs  is  provided  for  this  purpose. 

Under  these  conditions  there  are  two  possibilities.  Either  the  optical 
orientation  of  the  section  and  the  quartz  wedge  agree;  i.e.,  the  X  direction  of 
the  section  is  parallel  to  the  X  direction  of  the  wedge,  or  these  two  directions 
are  at  right  angles  to  each  other.  The  effect  of  the  introduction  of  the  wedge 
above  the  section  will  be  either  to  increase  or  decrease  the  amount  of  double 
refraction  of  the  light  due  to  the  mineral  section.  If  the  double  refraction  is 
increased,  the  optical  effect  will  be  as  if  the  mineral  section  had  been  thickened 
and  in  this  case  its  interference  color  will  rise  in  its  order.  On  the  other  hand, 
if  the  double  refraction  of  the  light  is  decreased  by  the  introduction  of  the 
quartz  wedge  the  effect  will  be  as  if  the  mineral  section  had  been  thinned  and 
the  interference  color  will  fall  in  its  order.  In  the  first  case  the  red  interfer- 
ence color  of  the  section  would  be  changed  as  the  wedge  is  pushed  in,  first  to 
blue  and  then  to  green.  In  the  second  case  it  would  change  to  orange,  then 
to  yellow  and  green.  Arrange  the  section,  therefore,  so  that  upon  the  intro- 
duction of  the  quartz  wedge  the  interference  color  will  fall  in  its  order.  Then 
gradually  continue  to  push  in  the  wedge,  noting  the  successive  colors  that 
occur  as  the  amount  of  the  double  refraction  is  decreased.  Finally  the  point 
will  be  reached  where  the  thickness  of  the  wedge  will  give  practically  the  same 
amount  of  double  refraction  as  the  mineral  section.  The  two  having  oppo- 
site optical  orientations  the  result  will  be  to  eliminate  all  interference  and  a 
gray  color  of  the  first  order  will  result.  When  this  condition  arises  the  quartz 
wedge  is  said  to  compensate  the  mineral.  By  noting  the  succession  of  colors 
that  occurs  until  this  point  is  reached  the  order  of  the  original  color  of  the 
section  can  be  determined. 

347.  Determination  of  Strength  of  Birefringence.  —  The  birefringence, 
or  amount  of  double  refraction,  varies  with  different  minerals.     It  is  expressed 
numerically  by  a  figure  that  is  the  difference  between  the  greatest  and  least 
indices  of  refraction  of  a  given  mineral.     In  the  case  of  calcite,  for  instance, 
the  index  of  refraction  for  one  ray  is  1'486  and  for  the  other  is  T658.     The 
birefringence  of  calcite  therefore  equals  0'172.     This  is  much  higher  than  for 
most  minerals,  the  strength  of  the  birefringence  of  quartz  being  only  0*0091. 


238 


PHYSICAL   MINERALOGY 


An  accurate  estimation  of  the  strength  of  the  birefringence  of  a  mineral  is  to 
be  made  only  by  determining  the  greatest  and  least  indices  of  refraction.  An 
approximate  determination,  however,  can  often  be  made  in  a  thin  section  under 
the  microscope.  The  order  of  the  interference  color  of  a  section,  as  stated  in 
Art.  345,  varies  with  the  thickness  of  the  mineral,  its  crystallographic  orienta- 
tion and  the  strength  of  its  birefringence.  If  the  first  two  factors  are  known 
the  birefringence  can  be  estimated  by  noting  the  interference  color  of  the' 
section.  Fig.  545  will  aid  in  this  determination.  The  thickness  of  the  sec- 
tion is  shown  in  the  column  at  the  left.  The  strength  of  the  birefringence  is 
expressed  along  the  top  and  right-hand  side  of  the  figure.  Suppose  that  a 
given  section  was  0*03  mm.  in  thickness  and  showed  an  orange-red  interference 
color  of  the  first  order.  By  following  the  diagonal  line  that  crosses  the  hori- 
zontal line  marked  0*03  mm.  at  a  point  lying  in  the  middle  of  the  orange-red 
of  the  first  order  it  will  be  seen  that  the  birefringence  of  the  mineral  must  be 
about  Q'015.  This  method  of  determining  birefringence  is  most  commonly 
used  in  the  case  of  minerals  observed  in  rock  sections.  In  the  case  of  the  best 
rock  sections  the  thickness  of  the  section  is  usually  about  0'03  to  0'04  mm. 
The  thickness  of  the  section  can  also  be  judged  from  the  interference  color 
shown  by  some  known  mineral,  like  quartz  or  feldspar,  which  is  to  be  observed 
in  the  section.  As  the  strength  of  the  birefringence  of  a  mineral  varies  with 
its  crystallographic  orientation  it  is  necessary  always  to  look  over  the  rock 
section  and  use  in  the  observations  that  section  of  the  mineral  which  shows  the 
highest  order  of  interference  color.  The  birefringence  of  a  mineral  is  always 


545 


| 

I 

\    .1 


0.06 
0.05 
0.04 
0.03 
0.02 
0.01 
0.00 


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diii  &-M  § 

o^^dtf'S^S   o 


White  of  higher 
order. 


0.045 
0.050 

0.055 
0.060 
0.065 
0.070 


0.100 
0.120 
0.160 
0.200 
0.300 


Determination  of  the  Strength  of  Birefringence  (after  Pirsson  and  Robinson) 

expressed  as  the  maximum  difference  between  the  indices  of  refraction.     Con- 
sequently, with  a  uniform  thickness,  such  as  is  obtained  in  a  rock  section,  that 


CHARACTERS   DEPENDING   UPON   LIGHT  239 

section  of  a  mineral  which  shows  the  highest  order  of  interference  color  most 
nearly  approaches  the  proper  orientation  for  the  maximum  birefringence. 

The  order  of  the  interference  color  of  a  given  section  is  to  be  determined 
by  the  method  of  compensation  as  explained  in  Art.  346.  Special  quartz 
wedges  are  made  with  scales  upon  them  giving  the  birefringence  produced  by 
the  varying  thicknesses  of  the  wedge.  If  such  a  wedge  is  available  it  is  only 
necessary  to  note  the  birefringence  corresponding  to  that  thickness  of  the 
quartz  which  produced  compensation.  This  will  obviously  equal  the  bire- 
fringence of  the  section  being  tested.  For  a  detailed  description  of  the  various 
wedges  and  compensators  used  for  this  purpose  the  reader  must  be  referred 
to  more  special  text-books.* 

348.  Determination  of  the  Relative  Optical  Character  of  the  Extinc- 
tion Directions  of  any  Section  of  a  Doubly  Refracting  Mineral.  —  It  fre- 
quently becomes  important  to  determine  which  of  the  two  rays  of  light  in  a 
doubly  refracting  mineral  is  being  propagated  with  the  greater  or  less  velocity; 
in  other  words,  to  determine  which  of  the  two  directions  of  vibration  corre- 
sponds to  the  X  and  which  to  the  Z  direction.  Place  the  given  section  under 
the  microscope  with  the  nicols  crossed.  Find  a  position  of  extinction  and  then 
turn  the  section  through  an  arc  of  45°  so  that  its  vibration  directions  make 
that  angle  with  the  planes  of  vibration  of  the  nicols.  If  the  section  in  this 
position  shows  a  strong  color  or  white  of  the  higher  order  the  quartz  wedge  is 
used.  The  optical  orientation  of  the  wedge  must  be  known,  i.e.,  which  are 
its  X  and  Z  directions.  The  wedge  is  then  pushed  through  the  slot  above  the 
objective  lens,  the  thin  end  of  the  wedge  being  introduced  first.  The  vibra- 
tion directions  of  the  wedge  and  the  section  will  now  coincide  and  the  effect 
of  the  gradual  introduction  of  the  wedge  above  the  mineral  will  be  to  slowly 
increase  or  decrease  the  birefringence  due  to  the  section.  The  result  will 
be  to  either  raise  or  lower  the  order  of  the  interference  color  obtained.  If  the 
X  directions  of  the  wedge  and  the  section  coincide  the  effect  will  be  additive 
in  character  and  the  color  will  rise  in  its  order.  If  the  optical  directions  of 
the  two  are  opposed  to  each  other  the  birefringence  is  decreased  and  the  color 
will  fall.  By  noting  which  effect  takes  place  the  X  and  Z  directions  of  the 
section  are  determined. 

In  this  use  of  the  quartz  wedge  the  following  precaution  must  be  observed. 
If  the  section  originally  showed  a  color  of  the  first  order  and  the  wedge  was 
introduced  in  the  opposed  position  the  effect  would  be  to  cause  the  color  to  fall 
rapidly  to  gray  of  the  first  order.  The  optical  effect  of  the  quartz  wedge  would 
thus  quickly  compensate  that  of  the  section.  From  this  point  on  as  the  quartz 
wedge  is  pushed  further  in,  the  optical  effect  of  the  wedge  will  more  and  more 
preponderate  over  that  of  the  section  and  the  interference  colors  will  now 
appear  in  ascending  order.  Under  these  conditions,  if  the  first  effect  of  the 
quartz  wedge  was  overlooked,  a  wrong  deduction  would  be  made.  It  is 
always  best  to  repeat  the  test  with  the  section  rotated  90°  from  the  first  posi- 
tion. The  two  results  should  be  of  opposite  character  and  so  serve  to  confirm 
each  other. 

Frequently  a  thick  section  of  a  mineral  will  show  a  tapering  edge  somewhere 
which  will  show  bands  of  color.  When  the  quartz  wedge  is  introduced  above 
the  section  these  color  bands  will  move,  either  toward  the  center  of  the  section, 

*  See  Johannsen,  Manual  of  Petrographic  Methods;  Wright,  The  Methods  of  Petro- 
graphic-Microscopic  Research. 


240  PHYSICAL   MINERALOGY 

or  go  off  toward  the  edge.  When  the  color  bands  move  up  on  the  section  it 
means  that  the  effect  of  the  quartz  wedge  is  such  that  a  thicker  part  of  the 
section  is  now  showing  the  same  interference  as  a  thinner  part  did  originally. 
In  other  words,  the  result  is  as  if  the  section  had  been  thinned.  If  this  is 
so,  then  the  X  and  Z  directions  of  the  section  and  the  wedge  must  be  opposed 
to  each  other.  On  the  other  hand,  if  the  color  bands  move  off  the  section  it 
means  that  a  thinner  part  of  the  section  is  showing  the  same  interference 
effect  that  a  thicker  portion  did  originally.  The  introduction  of  the  quartz 
wedge  has  in  effect  thickened  the  section  and  therefore  the  similar  optical 
directions  of  the  two  coincide.  This  test  is  particularly  useful  for  determin- 
ing the  X  and  Z  directions  of  deeply  colored  minerals,  as  the  natural  color  of 
the  mineral  may,  over  the  thicker  portion  of  the  section,  completely  mask 
the  interference  color. 

If  a  mineral  section  shows  an  interference  color  of  white  or  gray  of  the  first 
order  the  sensitive  tint  will  give  better  results  than  the  quartz  wedge.  If  the 
similar  optical  directions  of  the  section  and  the  sensitive  tint  coincide  the 
effect  will  be  to  raise  the  color  of  the  sensitive  tint  (red  of  the  first  order)  to 
blue.  On  the  other  hand,  if  the  optical  orientations  of  the  two  are  opposed 
the  color  will  fall  to  yellow.  This  test  can  be  made  to  advantage  only  when 
the  birefringent  effect  of  the  section  is  small  enough  to  just  raise  or  lower  the 
color  of  the  sensitive  tint  respectively  to  blue  or  yellow. 
\  349.  Circularly  and  Elliptically  Polarized  Light.  In  the  preceding 
articles  the  two  interfering  light-rays,  after  emerging  from  the  second  nicol, 
were  assumed  to  be  polarized  in  the  same  plane;  for  them  the  resulting  phe- 
nomena as  indicated  are  comparatively  simple.  If,  however,  two  plane- 
polarized  rays  propagated  in  the  same  direction  have  their  vibration-directions 
at  right  angles  to  each  other,  and  if  they  differ  one-quarter  of  a  wave-length 
(JX)  in  phase  (assuming  monochromatic  light),  then  it  may  be  shown  that 
the  composition  of  these  two  systems  results  in  a  ray  of  circularly  polarized 
light.  Briefly  expressed,  this  is  a  ray  that,  looked  at  end-on,  would  seem  to 
be  propagated  by  ether-vibrations  taking  place  in  circles  about  the  line  of 
transmission.  From  the  side,  the  onward  motion  would  be  like  that  of  a 
screw,  and  either  right-handed  or  left-handed. 

If,  again,  two  light-rays  meet  as  above  described,  with  a  difference  of  phase 
differing  from  JX  (but  not  equal  to  an  even  multiple  of  |X),  then  the  resulting 
composition  gives  rise  to  elliptically  polarized  light,  that  is,  a  light-ray  propa- 
gated by  ether-motions  taking  place  in  ellipses. 

The  above  results  are  obtained  most  simply  by  passing  plane-polarized 
light  through  a  doubly  refracting  medium  of  the  proper  thickness  (e.g.,  a  mica 
plate)  which  is  placed  with  its  vibration-planes  inclined  45°  to  that  of  the 
polarizer.  If  the  thickness  is  such  as  to  give  a  difference  in  phase  of  JX  or  an 
odd  multiple  of  this,  the  light  which  emerges  is  circularly  polarized.  If  the 
phase  differs  from  \\  (but  is  not  equal  to  |X  or  X),  the  emergent  light  is  ellip- 
tically polarized. 

350.  Rotation  of  Plane  of  Polarization.  —  In  the  case  of  certain  doubly 
refracting  crystallized  media  (as  quartz),  and  also  of  certain  solutions,  (as  of 
sugar),  it  can  be  shown  that  the  light  is  propagated  by  two  sets  of  ether- 
vibrations  which  take  place,  not  in  definite  transverse  planes  —  as  in  plane- 
polarized  light  —  but  in  circles;  that  is,  each  ray  is  circularly  polarized,  one 
being  right-handed,  the  other  left-handed.  Further,  of  these  rays,  one  will 
uniformly  gain  with  reference  to  the  other.  The  result  is,  that  if  a  ray  of 


CHARACTERS   DEPENDING   UPON   LIGHT  241 

plane-polarized  light  fall  upon  such  a  medium  (assuming  the  simplest  case,  as 
of  a  section  of  quartz  cut  normal  to  the  vertical  crystal  axis),  it  is  found  that 
the  two  rays  circularly  polarized  within  unite  on  emerging  to  a  plane-polar- 
ized ray,  but  the  plane  of  polarization  has  suffered  an  angular  change  or  rota- 
tion, which  may  be  either  to  the  right  (to  one  looking  in  the  direction  of  the 
ray),  when  the  substance  is  said  to  be  right-handed,  or  to  the  left,  when  it  is 
called  left-handed. 

This  phenomenon  is  theoretically  possible  with  all  crystals  of  a  given 
system  belonging  to  any  of  the  classes  of  lower  symmetry  than  the  normal 
class  which  show  a  plagiohedral  development  of  the  faces  *;  or,  more  simply, 
those  in  which  the  corresponding  right  and  left  (or  +  and  —  )  typical  forms 
are  enantiomorphous  (pp.  71,  112),  as  noted  in  the  chapter  on  crystallography. 
In  mineralogy,  this  subject  is  most  important  with  the  common  species  quartz, 
of  the  rhombohedral-trapezohedral  class,  and  a  further  discussion  of  it  is 
postponed  to  a  later  page  (Art.  394). 


OPTICAL  INSTRUMENTS   AND   METHODS 

351.  Measurement  of  Refractive  Indices.    Refractometer.  —  For  the 

determination  of  the  refractive  indices  of  crystallized  minerals  various  methods 
are  employed.  The  most  accurate  results,  when  suitable  material  is  at  hand, 
may  be  obtained  by  the  ordinary  refractometer.  This  requires  the  observa- 
tion of  the  angle  of  minimum  deviation  (5)  of  a  light-ray  on  passing  through  a 
prism  of  the  given  material,  having  a  known  angle  (a},  and  with  its  edge  cut  in 
the  proper  direction.  The  measurements  of  a  and  5  can  be  made  with  an 
ordinary  refractometer  or  with  the  horizontal  goniometer  described  in  Art. 
231.  For  the  latter  instrument,  the  collimator  is  made  stationary,  being 
fastened  to  a  leg  of  the  tripod  support,  but  the  observing  telescope  with  the 
verniers  moves  freely.  Further,  for  this  object  the  graduated  circle  is  clamped, 
and  the  screw  attachments  connected  with  the  axis  carrying  the  support,  and 
the  vernier  circle  and  observing  telescope  are  loosened.  Light  from  a  mono- 
chromatic source  passes  through  an  appropriate  slit  and  an  image  of  this  is 
thrown  by  the  collimator  upon  the  prism.  With  a  doubly  refracting  substance 
two  images  are  yielded  and  the  angle  of  minimum  deviation  must  be  measured 
for  each ;  the  proper  direction  for  the  edge  of  the  prism  in  this  case  is  discussed 
later.  When  a  and  5  are  known  the  formula  in  Art.  327  is  used. 

352.  Total  Refractometer.  —  The  principle  of  total  reflection  (Art.  323) 
may  also  be  made  use  of  to  determine  the  refractive  index.     No  prism  is  re- 
quired, but  only  a  small  fragment  having  a  single  polished  surface;  this  may 
have  any  direction  with  an  isometric  crystal,  but  in  other  cases  must  have  a 
definite  orientation,  as  described  later.     A  number  of  different  instruments 
have  been  devised  by  means  of  which  indices  of  refraction  may  be  measured 
by  the  use  of  total  reflection.     A  type  widely  used  at  present  is  represented 
in  Fig.  546.     This  particular  instrument  was  made  by  Leiss.     It  consists  of  a 
hemisphere  of  glass  (H)  having  a  high  refractive  index  which  is  mounted  upon 
a  glass  post  through  which  light  may  be  reflected  from  the  mirror  Sp.     The 

*  Of  the  thirty-two  possible  classes  among  crystals,  the  following  eleven  may  be  char- 
acterized by  circular  polarization:  Class  4,  p.  71;  5,  p.  72;  11  and  12,  p.  89;  17,  p.  102; 
22,  p.  112;  23  and  24,  p.  114;  27,  p.  128;  29,  p.  138;  32,  p.  147. 


242 


PHYSICAL   MINERALOGY 


546 


tube  P  contains  a  nicol  prism  so  that  when  a  thin  section  of  a  mineral  is  placed 
upon  the  plane  surface  of  the  hemisphere  it  is  possible  to  obtain  its  optical 
orientation  in  the  same  manner  as  with  the  polarizing  microscope.  The 

polished  mineral  sur- 
face is  placed  upon 
the  plane  surface  of 
H  with  a  film  of 
some  high  refract- 
ing oil  between  them. 
Then  a  beam  of 
light  from  some 
source  of  illumination, 
usually  a  mono- 
chromatic light,  is 
reflected  by  means 
of  the  mirror  Bl  in 
such  a  way  as  to 
produce  a  total  reflec- 
tion shadow  down 
on  the  opposite  side 
of  the  hemisphere. 
For  further  details 
of  the  operation  see 
Art.  327.  The  tel- 
escope F  is  attached 
to  the  disk  V  which 
in  turn  carries  a  scale 
on  its  edge.  The 
telescope  is  moved 
up  or  down  until  the 
line  between  the  light 
and  dark  portions  of 
the  field  lies  on  the 
cross-hairs.  The  angle 
which  is  read  on  the  scale  under  these  conditions  is  the  desired  critical  angle 
for  the  combination  of  the  glass  of  the  hemisphere  and  the  mineral  plate. 
Knowing  this  angle  and  the  index  of  refraction  of  the  glass  of  the  hemisphere 
it  is  possible  to  calculate  the  index  of  refraction  of  the  mineral ;  see  Art.  327. 
Usually  a  table  is  furnished  with  the  total  ref ractometer  by  means  of  which  the 
desired  refractive  index  is  obtained  directly  from  the  value  of  the  measured 
critical  angle.  The  post  carrying  the  glass  hemisphere  may  be  revolved  in 
the  horizontal  plane  and  the  angle  of  rotation  measured  on  the  scale  K.  This 
permits  the  measurement  of  indices  corresponding  to  different  vibration  direc- 
tions in  the  mineral.  L  is  an  eye  lens  which  in  combination  with  the  other 
lenses  of  the  tube  F  makes  a  low  power  microscope,  which  is  used  in  the  pre- 
liminary operations  in  order  to  center  the  mineral  plate,  etc.  In  the  tube  A 
is  an  iris  diaphragm  and  usually  a  small  nicol  prism  that  may  be  pushed  in 
or  out  of  the  tube. 

Fig.  547  represents  a  small  total  refractometer  devised  by  G.  F.  H.  Smith 
which  depends  upon  the  same  principle.  The  mineral  plate  is  placed  upon 
the  glass  surface  shown  on  the  top  of  the  instrument.  The  instrument  is  so 


Total  Refractometer 


CHARACTERS   DEPENDING   UPON   LIGHT 


243 


held  that  light  enters  at  the  forward  end,  and  the  totally  reflected  light  is  sent 
by  means  of  an  inclined  mirror  to  the  eyepiece.     A  scale  is  placed  in  the  instru- 


647 


Smith  Total  Refractometer  (Actual  Size) 


ment  in  such  a  way  that  the  boundary  between  the  light  and  dark  areas  is 
seen  superimposed  upon  it  and  so  yields  directly  the  value  of  the  refractive 
index.  For  rapid  and  approximate  determinations  this  instrument  is  very 
useful. 

353.  Tourmaline  Tongs.  —  A  very  simple  form  of  polariscope  for  con- 
verging light  is  shown  in  Fig.  548;  it  is  convenient  in  use,  but  of  limited  appli- 
cation. Here  the  polarizer  and  analyzer  are  two  tourmaline  plates  such  as 
were  described  in  Art.  340.  They  are  mounted  in  pieces  of  cork  and  held  in 
a  kind  of  wire  pincers.  The  object  to  be  examined  is  placed  between  them  and 
supported  there  by  the  spring  in  the  wire.  In  use  they  are  held  close  to  the 
eye,  and  in  this  position  the  crystal  section  is  viewed  in  converging  polarized 
light,  with  the  result  of  showing  (under  proper  conditions)  the  axial  inter- 
ference-figures (Arts.  .389  and  407) . 


Tourmaline  Tongs 


354.  Polariscope.  Conoscope.  —  The  common  forms  of  polariscopes 
employing  nicol  prisms  are  shown  in  Figs.  549  and  550.*  Fig.  549  represents 
the  instrument  arranged  for  converging  light,  which  is  often  called  a  conoscope. 

The  essential  parts  are  the  mirror  S,  reflecting  the  light,  which  after 
passing  through  the  lens  e  is  polarized  by  the  prism  p.  It  is  then  rendered 
strongly  converging  by  the  system  of  lenses  nn,  before  passing  through  the 
section  under  examination  placed  on  a  plate  at  k.  This  plate  can  be  revolved 

*  These  figures  are  taken  from  the  catalogue  of  Fuess. 


244 


PHYSICAL   MINERALOGY 


through  any  angle  desired,  measured  on  its  circumference.  The  upper  tube 
contains  the  converging  system  oo,  the  lens  t,  and  the  analyzing  prism  q. 
The  arrangements  for  lowering  or  raising  the  tubes  need  no  explanation,  nor 

649  550 


Conoscope 


Polariscope 


indeed  the  special  devices  for  setting  the  vibration-planes  of  the  nicols  at 
right  angles  to  each  other. 

The  accompanying  tube  (Fig.  550)  shows  the  arrangement  for  observations 
in  parallel  light,  the  converging  lenses  having  been  removed. 


CHARACTERS    DEPENDING   UPON    LIGHT 


245 


561 


Fig.  551  represents  in  cross-section  a  simple,  inexpensive  but  quite  efficient 
form  of  polariscope.  The  polarizing  device,  P,  is  in  the  form  of  two  or  three 
thin  glass  sheets,  the  back  of  the  bottom 
one  being  blackened.  These  glass  plates 
are  set  at  the  appropriate  angle  to  secure  the 
maximum  amount  of  polarization  of  the 
light  reflected  from  them  up  through  the 
opening  in  the  stage  K.  M  represents  an 
adjustable  mirror  by  means  of  which  light  is 
reflected  upon  P.  The  analyzer,  A,  is  a 
small  nicol  prism  which  is  held  over  the 
opening  in  the  stage  by  means  of  the  stand- 
ard S.  A  double  series  of  lenses  may  be 
placed  upon  the  stage  of  the  instrument  and 
so  convert  it  into  a  conoscope. 

355.  Polarization -Microscope.  —  The 
investigation  of  the  form  and  optical 
properties  of  minerals  when  in  microscopic 
form  has  been  much  facilitated  by  the 
use  of  microscopes  *  specially  adapted  for 
this  purpose.  First  arranged  with  reference 
to  the  special  study  of  minerals  as  seen  in 
thin  sections  of  rocks,  they  have  now  been  so 
elaborated  as  largely  to  take  the  place  of  the 
older  optical  instruments.  They  not  only 
allow  of  the  determination  of  the  optical 
properties  of  minerals  with  greater  facility, 
but  are  applicable  to  many  cases  where  the  crystals  in  hand  are  far  too  small 
for  other  means. 

A  highly  serviceable  microscope  is  the  Laboratory  Model  made  by  the 
Bausch  and  Lomb  Optical  Co.,  and  illustrated  in  Fig.  552.  The  essential 
arrangements  of  this  instrument  are  as  follows:  The  eyepiece  at  A,  which  is 
removable,  contains  the  cross-hairs  with  an  eye  lens  adjustable  for  focusing 
upon  them.  At  B  is  a  Bertrand  lens  that  slides  in  and  out  of  the  tube,  with 
an  iris  diaphragm  immediately  above  it.  At  C  is  the  analyzer  box  which  slides 
in  and  out  of  the  body  tube.  This  prism  may  be  revolved  through  a  quarter 
turn.  D  is  a  slot  in  the  microscope  tube  with  a  dust-proof  shutter  for  the 
introduction  of  various  accessories,  such  as  the  quartz  wedge,  etc.  At  E  is 
the  nosepiece  which  can  be  centered  by  the  two  screws  which  work  at  right 
angles  in  the  N  and  E  positions.  The  objective  F  is  held  in  place  by  a  spring 
clamp  and  is  quickly  detached.  The  stage,  G,  revolves  and  carries  a  scale 
graduated  into  degrees,  the  attached  vernier  permitting  the  reading  of  angles 
to  one-tenth  degree.  The  substage  at  H  carries  condensing  lenses,  iris  dia- 
phragm and  the  polarizing  prism.  It  can  be  moved  upward  and  downward 
by  means  of  a  screw-head  and  when  at  its  lowest  point  can  be  sprung  to  one 
side,  out  of  the  optical  axis.  The  mirror  at  /  is  adjustable  and  has  both  a 
plane  and  concave  surface.  The  coarse  focusing  adjustment  is  at  J,  while 
the  milled  head  at  K  provides  a  fine  adjustment  by  means  of  which  a  vertical 
movement  of  0'0005  mm.  can  be  read. 

*  For  detailed  descriptions  of  the  polarizing  microscope  and  its  accessories  see  Johannsen, 
Manual  of  Petrographic  Methods;   Wright,  The  Methods  of  Petrographic  Research;  etc. 


Polariscope  (|  natural  size) 


246 


PHYSICAL  MINERALOGY 


356.   The  Research  Model  of  the  Bausch  and  Lomb  microscope  is  illus- 
trated in  Fig.  553.     This  instrument  is  patterned  after  one  described  by 


552 


553 


Petrographical  Microscope 

(Laboratory  Model,  Bausch  and 

Lomb,  |  actual  size) 


Petrographical  Microscope 

(Research  Model,  Bausch  and 

Lomb  j  actual  size) 


Wright  to  whose  papers  reference  is  made  for  a  more  detailed  account.  The 
outstanding  features  of  the  instrument  may  be  briefly  summarized  as  follows : 
It  has  a  large  body-tube  within  which  are  always  contained  the  analyzer  and 
the  Bertrand  lens,  both  when  they  lie  in  or  outside  the  optical  axis  of  the  micro- 
scope. The  two  nicols  may  be  connected  by  means  of  the  upright  bar  and 
rotated  simultaneously  through  an  arc  of  90°.  This  enables  the  measurement 
of  extinction  angles,  etc.,  to  be  made  without  the  necessity  of  revolving  the 
stage  and  the  consequent  difficulty  in  keeping  the  mineral  grain  under  observa- 
tion exactly  centered  in  the  field.  This  bar  carries  verniers  that  lie  against 
the  scale  engraved  upon  the  stage  so  that  the  angle  of  rotation  of  the  nicols 
can  be  accurately  measured.  The  polarizing  prism  can  be  entirely  removed 
from  the  optical  axis.  A  revolvable  carrier  for  a  sensitive  plate  is  attached 
to  the  iris  diaphragm  mount  of  the  substage. 

GENERAL  OPTICAL  CHARACTERS   OF  MINERALS 

357.   There  are  certain  characteristics  belonging  to  all  minerals  alike, 
crystallized  and  non-crystallized,  in  their  relation  to  light.     These  are: 

1.   DIAPHANEITY:  depending  on  the  relative  quantity  of  light  transmitted. 


CHARACTERS   DEPENDING   UPON   LIGHT  247 

2.  COLOR:    depending  on  the  kind  of  light  reflected  or  transmitted,  as 
determined  by  the  selective  absorption. 

3.  LUSTER:  depending  on  the  power  and  manner  of  reflecting  light. 

1.   DIAPHANEITY 

358.  Degrees  of  Transparency.  —  The  amount  of  light  transmitted  by 
a  solid  varies  in  intensity,  or,  in  other  words,  more  or  less  light  may  be  absorbed 
in  the  passage  through  the  given  substance  (see  Art.  330).     The  amount  of 
absorption  is  a  minimum  in  a  transparent  solid,  as  ice,  while  it  is  greatest  in 
one  which  is  opaque,  as  iron.     The  following  terms  are  adopted  to  express  the 
different  degrees  in  the  power  of  transmitting  light : 

Transparent:  when  the  outline  of  an  object  seen  through  the  mineral  is 
perfectly  distinct. 

Subtransparent,  or  semi-transparent:  when  objects  are  seen,  but  the 
outlines  are  not  distinct. 

Translucent:  when  light  is  transmitted,  but  objects  are  not  seen. 

Subtranslucent:  when  merely  the  edges  transmit  light  or  are  translucent. 

When  no  light  is  transmitted,  even  on  the  thin  edges  of  small  splinters,  the 
mineral  is  said  to  be  opaque.  This  is  properly  only  a  relative  term,  since  no 
substance  fails  to  transmit  some  light,  if  made  sufficiently  thin.  Magnetite  is 
translucent  in  the  Pennsbury  mica.  Even  gold  may  be  beaten  out  so  thin  as 
to  be  translucent,  in  which  case  it  transmits  a  greenish  light. 

The  property  of  diaphaneity  occurs  in  the  mineral  kingdom,  from  nearly 
perfect  opacity  to  transparency,  and  many  minerals  present,  in  their  numerous 
varieties,  nearly  all  the  different  degrees. 

2.   COLOR 

359.  Nature  of  Color.  —  As  briefly  explained  in  Art.  314,  the  sensation 
of  color  depends,  in  the  case  of  monochromatic  light,  solely  upon  the  length 
of  the  waves  of  light  which  meet  the  eye.     If  the  light  consists  of  various 
wave-lengths,  it  is  to  the  combined  effect  of  these  that  the  sensation  of 
color  is  due. 

Further,  since  the  light  ordinarily  employed  is  essentially  white  light,  that 
is,  consists  of  all  the  wave-lengths  corresponding  to  the  successive  colors  of  the 
spectrum,  the  color  of  a  body  depends  upon  the  selective  absorption  (see 
Art.  330)  which  it  exerts  upon  the  light  transmitted  or  reflected  by  it.  A 
yellow  mineral,  for  instance,  absorbs  all  the  waves  of  the  spectrum  with  the 
exception  of  those  which  together  give  the  sensation  of  yellow.  In  general, 
the  color  which  the  eye  perceives  is  the  result  of  the  mixture  of  those  waves 
which  are  not  absorbed. 

360.  Streak.  —  The  color  of  the  powder  of  a  mineral  as  obtained  by 
scratching  the  surface  of  the  mineral  with  a  knife  or  file,  or,  still  better,  if  the 
mineral  is  not  too  hard,  by  rubbing  it  on  an  unglazed  porcelain  surface,  is 
called  the  streak.     The  streak  is  often  a  very  important  quality  in  distinguish- 
ing minerals.     This  is  especially  true  with  minerals  having  a  metallic  luster, 
as  defined  in  Art.  364. 

361.  Dichroism;    Pleochroism.  —  The  selective  absorption,  to  which 
the  color  of  a  mineral  is  due,  more  especially  by  transmitted  light,  often  varies 
with  the  crystallographic  direction  in  which  the  light  passes  through  the 
mineral.     It  is  hence  one  of  the  special  optical  characters  depending  upon  the 


248  PHYSICAL   MINERALOGY 

crystallization,  which  are  discussed  later.  Here  belong  dichroism  or  pleochro- 
ism,  the  property  of  exhibiting  different  colors  in  different  crystallographic 
directions  by  transmitted  light.  This  subject  is  explained  further  in  Arts. 
396  and  411. 

302.  Varieties  of  Color.  —  The  following  eight  colors  were  selected  by 
Werner  as  fundamental,  to  facilitate  the  employment  of  this  character  in 
the  description  of  minerals:  white,  gray,  black,  blue,  green,  yellow,  red,  and 
brown. 

(a)  The  varieties  of  METALLIC  COLORS  recognized  are  as  follows: 
1.   Copper-red:     native    copper.  —  2.    Bronze-yellow:     pyrrhotite. —  3.   Brass-yellow: 
chalcopyrite.  —  4.   Gold-yellow:  native  gold.  —  5.   Silver-while:  native  silver,  less  distinct 
in  arsenopyrite.  —  6.   Tin-white:  mercury;  cobaltite.  —  7.    Lead-gray:  galena,  molybdenite. 

—  8.  Steel-gray:  nearly  the  color  of  fine-grained  steel  on  a  recent  fracture;   native  plati- 
num, and  palladium. 

(6)  The  following  are  the  varieties  of  NON-METALLIC  COLORS: 

A.  WHITE.     1.  Snow-white:   Carrara  marble.  —  2.   Reddish  white,  3.    Yellowish  white 
and  4.   Grayish  white:  all  illustrated  by  some  varieties  of  calcite  and  quartz.  —  5.   Greenish 
white:  talc.  —  6.   Milk  white:  white,  slightly  bluish;   some  chalcedony. 

B.  GRAY.     1.   Bluish  gray:  gray,  inclining  to  dirty  blue.  —  2.    Pearl-gray:  gray,  mixed 
with  red  and  blue;    cerargyrite.  —  3.  Smoke-gray:    gray,   with  some  brown;    flint. — 
4.   Greenish  gray:  gray,  with  some  green;  cat's-eye;  some  varieties  of  talc.  —  5.    Yellowish 
gray:  some  varieties  of  compact  limestone.  —  6.   Ash-gray:  the  purest  gray  color;  zoisite. 

C.  BLACK.     1.   Grayish  black:  black,  mixed  with  gray  (without  green,  brown,  or  blue 
tints);  basalt;  Lydian  stone.  —  2.    Velvet-black:   pure  black;   obsidian,  black  tourmaline. 

—  3.   Greenish   black:     augite.  —  4. '  Brownish   black:     brown    coal,    lignite.  —  5.   Bluish 
black:  black  cobalt. 

p.  BLUE.  1.  Blackish  blue:  dark  varieties  of  azurite.  —  2.  Azure-blue:  a  clear  shade 
of  bright  blue;  pale  varieties  of  azurite,  bright  varieties  of  lazulite.  —  3.  Violet-blue:  blue, 
mixed  with  red;  amethyst,  fluorite. —  4.  Lavender-blue:  blue,  with  some  red  and  much 
gray.  —  5.  Prussian-blue,  or  Berlin  blue:  pure  blue;  sapphire,  cyanite.  —  6.  Smalt-blue: 
some  varieties  of  gypsum.  —  7.  Indigo-blue:  blue,  with  black  and  green;  blue  tourmaline. 

—  8.  Sky-blue:  pale  blue,  with  a  little  green;  it  is  called  mountain-blue  by  painters. 

E.  GREEN.     1.    Verdigris-green:  green,  inclining  to  blue;  some  feldspar  (amazon-stone). 

—  2.   Celandine-green:  green,  with  blue  and  gray;  some  varieties  of  talc  and  beryl.     It  is 
the  color  of  the  leaves  of  the  celandine.  —  3.    Mountain-green:    green,  with  much  blue; 
beryl.  —  4.   Leek-green:  green,  with  some  brown;  the  color  of  leaves  of  garlic;   distinctly 
seen  in  prase,  a  variety  of  quartz.  —  5.   Emerald-green:    pure  deep  green;    emerald.  — 
6-.   Apple-green:    light  green  with  some  yellow;    chrysoprase.  —  7.   Grass-green:    bright 
green,  with  more  yellow;  green  diallage.  —  8.    Pistachio-green:  yellowish  green,  with  some 
brown;    epidote.  —  9.   Asparagus-green:   pale  green,  with  much  yellow;    asparagus  stone 
(apatite).  —  10.   Blackish  green:    serpentine.  —  11.    Olive-green:    dark  green,  with  much 
brown  and  yellow;   chrysolite.  —  12.   Oil-green:   the  color  of  olive-oil;   beryl,  pitchstone. 

—  13.   Siskin-green:  light  green,  much  inclining  to  yellow;  uranite. 

F.  YELLOW.     1..  Sulphur-yellow:   sulphur.  —  2.   Straw-yellow:   pale  yellow;   topaz. — 
3.   Wax-yellow:    grayish  yellow  with  some  brown;    sphalerite,  opal.  —  4.   Honey-yellow: 
yellow,  with  some  red  and  brown;    calcite.  —  5.   Lemon-yellow:    sulphur,  orpiment.  — 
6.   Ocher-yellow:  yellow,  with  brown;  yellow  pcher.  —  7.    Wine-yellow:  topaz  and  fluorite. 

—  8.   Cream-yellow:   some  varieties  of  kaolinite.  —  9.   Orange-yellow:   orpiment. 

G.  RED.     1.   Aurora-red:    red,  with  much  yellow;    some  realgar.  —  2.   Hyacinth-red: 
red,  with  yellow  and  some  brown;  hyacinth  garnet.  —  3.   Brick-red:  polyhalite,  some  jas- 
per. —  4.   Scarlet-red:  bright  red,  with  a  tinge  of  yellow;   cinnabar.  —  5.    Blood-red:  dark 
red,  with  some  yellow;    pyrope.  —  6.   Flesh-red:    feldspar.  —  7.   Carmine-red:   pure  red; 
ruby  sapphire.  —  8.    Rose-red:  rose  quartz.  —  9.   Crimson-red:  ruby.  —  10.   Peachblossom- 
red:  red,  with  white  and  gray;  lepidolite.  —  11.   Columbine-red:  deep  red,  with  some  blue; 
garnet.  —  12.   Cherry-red:   dark  red,  with  some  blue  and  brown;   spinel,  some  jasper. — 
13.   Brownish-red:   jasper,  limonite. 

H.  BROWN.  1.  Reddish  brown:  garnet,  zircon.  —  2.  Clove-brown:  brown,  with  red 
and  some  blue;  axinite.  —  3.  Hair-brown:  wood-opal.  —  4.  Broccoli-brown:  brown,  with 
blue,  red,  and  gray;  zircon.  —  5.  Chestnut-brown:  pure  brown.  —  6.  Yellowish  brown: 
jasper.  —  7.  Pinchbeck-brown:  yellowish  brown,  with  a  metallic  or  metallic-pearly  luster; 
several  varieties  of  talc,  bronzite.  —  8.  Wood-brown:  color  of  old  wood  nearly  rotten;  some 


CHARACTERS   DEPENDING   UPON   LIGHT  249 

specimens  of  asbestus- 9.   Liver-brown:    brown,  with  some  gray  and  green;    jasper.  - 
10.   Blackish  brown:  bituminous  coal,  brown  coal. 

3.   LUSTER 

363.  Nature  of  Luster.  —  The  luster  of  minerals  varies  with  the  nature 
5- 1*          surfaces-     A  variation  in  the  quantity  of  light  reflected  produces 
different  degrees  of  intensity  of  luster;  a  variation  in  the  nature  of  the  reflect- 
ing surface  produces  different  kinds  of  luster. 

364.  Kinds  of  Luster.  —  The  kinds  of  luster  recognized  are  as  follows: 

1.  METALLIC:  the  luster  of  the  metals,  as  of  gold,  copper,  iron,  tin. 

In  general,  a  mineral  is  not  said  to  have  metallic  luster  unless  it  is  opaque 
in  the  mmeralogical  sense,  that  is,  it  transmits  no  light  on  the  edges  of  thin 
splinters.  Some  minerals  have  varieties  with  metallic  and  others  with  non- 
metallic  luster;  this  is  true  of  hematite. 

Imperfect  metallic  luster  is  expressed  by  the  term  sub-metallic,  as  illus- 
trated by  columbite,  wolframite.  Other  kinds  of  luster  are  described  briefly 
as  NON-METALLIC. 

2.  NON-METALLIC.     A.   Adamantine:  the  luster  of  the  diamond.     When 
also  sub-metallic,  it  is  termed  metallic-adamantine,  as  cerussite,  pyrargyrite. 

Adamantine  luster  belongs  to  substances  of  high  refractive  index.  This 
may  be  connected  with  their  relatively  great  density  (and  hardness),  as  with 
the  diamond,  also  corundum,  etc. ;  or  because  they  contain  heavy  molecules, 
thus  most  compounds  of  lead,  not  metallic  in  luster,  have  a  high  refractive 
index  and  an  adamantine  luster. 

B.  Vitreous:  the  luster  of  broken  glass.     An  imperfectly  vitreous  luster 
is  termed  sub-vitreous.     The  vitreous  and  sub-vitreous  lusters  are  the  most 
common  in  the  mineral  kingdom.     Quartz  possesses  the  former  in  an  eminent 
degree;  calcite,  often  the  latter. 

C.  Resinous:  luster  of  the  yellow  resins,  as  opal,  and  some  yellow  varieties 
of  sphalerite. 

D.  Greasy:  luster  of  oily  glass.     This  is  near  resinous  luster,  but  is  often 
quite  distinct,  as  nephelite. 

E.  Pearly:   like  pearl,  as  talc,  brucite,  stilbite,  etc.     When  united  with 
sub-metallic,  as  in  hypersthene,  the  term  metallic-pearly  is  used. 

Pearly  luster  belongs  to  the  light  reflected  from  a  pile  of  thin  glass-plates; 
similarly  it  is  exhibited  by  minerals,  which,  having  a  perfect  cleavage,  may  be 
partially  separated  into  successive  plates,  as  on  the  basal  plane  of  apophyllite. 
It  is  also  shown  for  a  like  reason  by  foliated  minerals,  as  talc  and  brucite. 

F.  Silky:  like  silk;  it  is  the  result  of  a  fibrous  structure.     Ex.  fibrous  cal- 
cite, fibrous  gypsum. 

The  different  degrees  and  kinds  of  luster  are  often  exhibited  differently  by 
unlike  faces  of  the  same  crystal,  but  always  similarly  by  like  faces.  For 
example,  the  basal  plane  of  apophyllite  has  a  pearly  luster  wanting  in  the  pris- 
matic faces,  which  have  a  vitreous  luster. 

As  shown  by  Haidinger,  only  vitreous,  adamantine,  and  metallic  luster  belong  to  faces 
perfectly  smooth  and  pure.  In  the  first,  the  refractive  index  of  the  mineral  is  I'S-l'S; 
in  the  second,  l'9-2'5;  in  the  third,  about  2'5.  The  true  difference  between  metallic  and 
vitreous  luster  is  due  to  the  effect  which  the  different  surfaces  have  upon  the  reflected  light; 
in  general,  the  luster  is  produced  by  the  union  of  two  simultaneous  impressions  made  upon 
the  eye.  If  the  light  reflected  from  a  metallic  surface  be  examined  by  a  nicol  prism  (or  the 
dichroscope  of  Haidinger,  Art.  393),  it  will  be  found  that  both  rays,  that  vibrating  in  the 
plane  of  incidence  and  that  whose  vibrations  are  normal  to  it,  are  alike,  each  having  the 


250  PHYSICAL   MINERALOGY 

color  of  the  material,  only  differing  a  little  in  brilliancy;  on  the  contrary,  of  the  light 
reflected  by  a  vitreous  substance,  those  rays  whose  vibrations  are  at  right  angles  to  the 
plane  of  incidence  are  more  or  less  polarized,  and  are  colorless,  while  those  whose  vibrations 
are  in  this  plane,  having  penetrated  somewhat  into  the  medium  and  suffered  some  absorp- 
tion, show  the  color  of  the  substance  itself.  A  plate  of  red  glass  thus  examined  will  show 
a  colorless  and  a  red  image.  Adamantine  luster  occupies  a  position  between  the  others. 

365.  Degrees  of  Luster.  —  The  degrees  of  intensity  of  luster  are  classi- 
fied as  follows: 

1.  Splendent:  reflecting  with  brilliancy  and  giving  well-defined  images,  as 
hematite,  cassiterite. 

2.  Shining:  producing  an  image  by  reflection,  but  not  one  well-defined,  as 
celestite.      • 

3.  Glistening:    affording  a  general  reflection  from  the  surface,  but  no 
image,  as  talc,  chalcopyrite. 

4.  Glimmering:  affording  imperfect  reflection,  and  apparently  from  points 
over  the  surface,  as  flint,  chalcedony. 

A  mineral  is  said  to  be  dull  when  there  is  a  total  absence  of  luster,  as  chalk, 
the  ochers,  kaolin. 

366.  Play  of  Colors.     Opalescence.     Iridescence.  —  The  term  play  of 
colors  is  used  to  describe  the  appearance  of  several  prismatic  colors  in  rapid 
succession  on  turning  the  mineral.     This  property  belongs  in  perfection  to  the 
diamond,  in  which  it  is  due  to  its  high  dispersive  power.     It  is  also  observed 
in  precious  opal,  where  it  is  explained  on  the  principle  of  interference;  in  this 
case  it  is  most  brilliant  by  candle-light. 

The  expression  change  of  colors  is  used  when  each  particular  color  appears 
to  pervade  a  larger  space  than  in  the  play  of  colors  and  the  succession  pro- 
duced by  turning  the  mineral  is  less  rapid.  This  is  shown  in  labradorite,  as 
explained  under  that  species. 

Opalescence  is  a  milky  or  pearly  reflection  from  the  interior  of  a  specimen. 
Observed  in  some  opal,  and  in  cat's-eye. 

Iridescence  means  the  exhibition  of  prismatic  colors  in  the  interior  or  on 
the  surface  of  a  mineral.  The  phenomena  of  the  play  of  colors,  iridescence, 
etc.,  are  sometimes  to  be  explained  by  the  presence  of  minute  foreign  crystals, 
in  parallel  positions;  more  generally,  however,  they  are  caused  by  the  presence 
of  fine  cleavage-lamellae,  in  the  light  reflected  from  which  interference  takes 
place,  analogous  to  the  well-known  Newton's  rings  (see  Art.  336). 

367.  Tarnish.  —  A  metallic  surface  is  tarnished  when  its  color  differs 
from  that  obtained  by  fracture,  as  is  the  case  with  specimens  of  bornite.     A 
surface  possesses  the  steel  tarnish  when  it  presents  the  superficial  blue  color  of 
tempered  steel,  as  columbite.     The  tarnish  is  irised  when  it  exhibits  fixed 
prismatic  colors,  as  is  common  with  the  hematite  of  Elba.     These  tarnish  and 
iris  colors  of  minerals  are  owing  to  a  thin  surface  or  film,  proceeding  from 
different  sources,  either  from  a  change  in  the  surface  of  the  mineral  or  from 
foreign  incrustation;  hydrated  iron  oxide  is  one  of  the  most  common  sources 
of  it  and  produces  the  colors  on  anthracite  and  hematite. 

368.  Asterism.  —  This  name  is  given  to  the  peculiar  star-like  rays  of 
light  observed  in  certain  directions  in  some  minerals.     This  is  seen  by  reflected 
light  in  the  form  of  a  six-rayed  star  in  sapphire,  and  is  also  well  shown  by 
transmitted  light  (as  of  a  small  flame)  with  the  phlogopite  mica  from  South 
Burgess,  Canada.     In  the  former  case  it  is  explained  by  the  presence  of  thin 
twinning-lamellse  symmetrically  arranged.     In  the  other  case  it  is  due  to  the 
presence  of  minute  inclosed  crystals,  also  symmetrically  arranged,  which  are 
probably  rutile  or  tourmaline  in  most  cases.     Crystalline  faces  which  have 


CHARACTERS   DEPENDING   UPON   LIGHT  251 

been  artificially  etched  also  sometimes  exhibit  asterism.  The  peculiar  light- 
figures  sometimes  observed  in  reflected  light  on  the  faces  of  crystals  either 
natural  or  etched,  are  of  similar  nature. 

369.  Schillerization.  —  The  general  term  schiller  is  applied  to  the  pecu- 
liar luster,  sometimes  nearly  metallic,  observed  in  definite  directions  in  certain 
minerals,  as  conspicuously  in  schiller-spar  (an  altered  variety  of  bronzite) 
also  in  diallage,  hypersthene,  sunstone,  and  others.     It  is  explained  by  the 
reflection  either  from  minute  inclosed  plates  in  parallel  position  or  from  the 
surfaces  of  minute  cavities  (negative  crystals)  having  a  common  orientation 
In  many  cases  it  is  due  to  alteration  which  has  developed  these  bodies  (or 
the  cavities)  in  the  direction  of  solution-planes  (see  Art.  285).     The  process 
by  which  it  has  been  produced  is  then  called  schillerization. 

370.  Fluorescence.  —  The  emission  of  light  from  within  a  substance 
while  it  is  being  exposed  to  direct  radiation,  or  in  certain  cases  to  an  electrical 
discharge  in  a  vacuum  tube,  is  called  fluorescence.     It  is  best  exhibited  by 
fluorite,  from  which  the  phenomenon  gained  its  name.     Thus,  if  a  beam  of 
white  light  be  passed  through  a  cube  of  colorless  fluorite  a  delicate  violet  color 
is  called  out  in  its  path.     This  effect  is  chiefly  due  to  the  action  of  the  ultra- 
violet rays,  and  is  connected  with  a  change  of  refrangibility  in  the  transmitted 
light. 

The  electrical  discharge  from  the  negative  pole  of  a  vacuum  tube  calls  out 
a  brilliant  fluorescence  not  only  with  the  diamond,  the  ruby,  and  many  gems, 
but  also  with  calcite  and  other  minerals.  Such  substances  may  continue  to 
emit  light,  or  phosphoresce,  after  the  discharge  ceases. 

371.  Phosphorescence.  —  The  continued  emission  of  light  by  a  sub- 
stance (not  incandescent)  produced  especially  after  heating,  exposure  to  light 
or  to  an  electrical  discharge,  is  called  phosphorescence. 

Fluorite  becomes  highly  phosphorescent  after  being  heated  to  about 
150°  C.  Different  varieties  give  off  light  of  different  colors;  the  chlorophane 
variety,  an  emerald-green  light;  others  purple,  blue,  and  reddish  tints.  This 
phosphorescence  may  be  observed  in  a  dark  place  by  subjecting  the  pulverized 
mineral  to  a  heat  below  redness.  It  may  even  be  produced  by  a  sharp  blow 
with  a  hammer.  Some  varieties  of  white  limestone  or  marble,  after  slight 
heating,  emit  a  yellow  light;  so  also  tremolite,  danburite,  and  other  species. 

The  X-ray  and  ultra-violet  light  will  produce  phosphorescence  in  willemite, 
kunzite,  and  some  diamonds.  The  fact  that  willemite  glows  when  exposed  to 
ultra-violet  light  is  made  use  of  in  testing  the  residues  from  a  willemite  ore  to 
make  certain  the  separation  has  been  complete.  Radium  emanations  cause 
certain  minerals  to  phosphoresce,  as  willemite  and  wurtzite. 

Exposure  to  the  light  of  the  sun  produces  very  apparent  phosphorescence 
with  many  diamonds,  but  some  specimens  seem  to  be  destitute  of  this  power. 
This  property  is  most  striking  after  exposure  to  the  blue  rays  of  the  spectrum, 
while  in  the  red  rays  it  is  rapidly  lost.  A  mixture  of  calcium  sulphide  and 
bismuth  will  phosphoresce  for  a  considerable  period  after  being  exposed  to 
sunlight. 

SPECIAL    OPTICAL    CHARACTERS    BELONGING    TO    CRYSTALS 
OF  THE  DIFFERENT  SYSTEMS 

372.  All  crystallized  minerals  may  be  grouped  into  three  grand  classes, 
which  are  distinguished  by  their  physical  properties,  as  well  as  their  geometri- 
cal form.     These  three  classes  are  as  follows: 


252  PHYSICAL  MINERALOGY 

A.  Isometric  class,  embracing  crystals  of  the  isometric  system,  which  are 
referred  to  three  equal  rectangular  axes. 

B.  Isodiametric  class,  embracing  crystals  of  the  tetragonal  and  hexagonal 
systems.,  referred  to  two,  or  three,  equal  horizontal  axes  and  a  third,  or  fourth, 
axis  unequal  to  them  at  right  angles  to  their  plane.     Crystals  of  this  class  have 
a  fixed  principal  axis  of  crystallographic  symmetry. 

C.  Anisometric  class,  embracing  the  crystals  of  the  orthorhombic,  mono- 
clinic,  and  triclinic  systems,  referred  to  three  unequal  axes.     Crystals  of  this 
class  are  without  a  fixed  axis  of  crystallographic  symmetry. 

373.  Isotropic  Crystals.  —  Of  the  three  classes,  the  ISOMETBIC  CLASS 
includes  all  crystals  which,  with  respect  to  light  and  related  phenomena  involv- 
ing the  ether,  are  isotropic  (from  the  Greek,  signifying  equal  turning) ;  that  is, 
those  which  have  like  optical  properties  in  all  directions.     Their  distinguishing 
characteristic  is  that  light  travels  through  them  with  equal  velocity  in  all 
directions,  provided  their  molecular  equilibrium  is  not  disturbed  by  external 
pressure  or  internal  strain.     If  it  be  imagined  therefore  that  light  starts  from 
a  point  within  an  isotropic  medium  at  a  given  moment  of  time  the  resulting 
wave  surface  will  be  a  sphere. 

It  must  be  emphasized  here,  however,  that  such  a  crystal  is  not  isotropic 
with  reference  to  those  characters  which  depend  directly  upon  the  molecular 
structure  alone,  as  cohesion  and  elasticity.  (See  Art.  275.) 

Further,  amorphous  bodies,  as  glass  and  opal,  which  are  destitute  of  any 
orientated  molecular  structure  —  that  is,  those  in  which  all  directions  are  sensi- 
bly the  same  —  are  also  isotropic,  and  not  only  with  reference  to  light,  but 
also  as  regards  their  strictly  molecular  properties. 

374.  Anisotropic  Crystals ;  Uniaxial  and  Biaxal.  —  Crystals  of  the  ISO- 
DIAMETRIC  and  ANISOMETRIC  CLASSES,  on  the  other  hand,  are  in  distinction 
anisotropic  (from  the  Greek,  signifying  unequal  turning) .     Their  optical  prop- 
erties are  in  general  unlike  in  different  directions,  or,  more  particularly,  the 
velocity  with  which  light  is  propagated  varies  with  the  direction. 

Further,  in  crystals  of  the  isodiametric  class  that  variable  property  of  the 
light-ether  upon  which  the  velocity  of  propagation  depends  remains  constant 
for  all  directions  which  are  normal  to,  or,  again,  for  all  those  equally  inclined 
to,  the  vertical  crystallographic  axis.  In  the  direction  of  this  axis  there  is  no 
double  refraction;  it  is  hence  called  the  optic  axis,  and  the  crystals  of  this 
class  are  said  to  be  uniaxial. 

Crystals  of  the  third  or  anisometric  class  have  more  complex  optical  rela- 
tions requiring  special  explanation,  but  in  general  it  may  be  stated  that  in  them 
there  are  always  two  directions  analogous  in  character  to  the  single  optic  axis 
spoken  of  above;  hence,  these  crystals  are  said  to  be  optically  biaxial. 

A.   ISOMETRIC  CRYSTALS 

375.  It  has  been  stated  that  crystals  of  the  isometric  system  are  optically 
isotropic,  and  hence  light  travels  with  the  same  velocity  in  every  direction  in 
them.     Light  can,  therefore,  suffer  only  single  refraction  in  passing  into  an 
isotropic  medium;    or,  in  other  words,  there  can  be  but  one  value  of  the 
refractive  index  for  a  given  wave-length.     If  this  be  represented  by  n,  while 
V  is  the  velocity  of  light  in  air  and  v  that  in  the  given  medium,  then 

V  V 

n  =  — ,     or    v  =  —  • 
v  n 


CHARACTERS   DEPENDING   UPON   LIGHT  253 

The  wave-front  for  light-waves  propagated  from  any  point  within  such  an 
isotropic  medium  is,  as  already  stated,  a  sphere.  The  sphere,  therefore,  may 
be  taken  to  represent  the  optical  properties  of  an  isotropic  medium.  Sec- 
tions of  a  sphere  normal  to  any  diameter  will  always  be  circles.  These  cir- 
cular sections  with  like  radii  in  all  directions  correspond  to  the  fact  that  the 
optical  character  of  an  isotropic  substance  is  the  same  in  all  directions  normal 
to  the  line  of  light  propagation.  Or,  in  other  words,  light  vibrations  may 
take  place  in  any  direction  normal  to  the  direction  of  transmission;  i.e.,  the 
light  is  not  polarized.  Further  its  velocity  remains  uniform  no  matter  what 
may  be  the  direction  of  its  vibration. 

This  statement  holds  true  of  all  the  classes  of  isometric  crystals.  In  other 
words,  a  crystal  of  maximum  symmetry,  as  fluorite,  and  one  having  the 
restricted  symmetry  characteristic  of  the  tetrahedral  or  pyritohedral  divisions, 
have  alike  the  same  isotropic  character.  Two  of  the  classes,  however,  namely, 
the  plagiohedral  and  the  tetartohedral  classes,  differ  in  this  particular:  that 
crystals  belonging  to  them  may  exhibit  what  has  already  been  defined  (Art. 
350)  as  circular  polarization. 

376.  Behavior  of  Sections  of  Isometric  Crystals  in  Polarized  Light.  — 
In  consequence  of  their  isotropic  character,  isometric  crystals  exhibit  no 
special  phenomena  in  polarized  light.     As  a  section  of  an  isotropic  substance 
(isometric  crystal  or  some  amorphous  material)  has  no  polarizing  or  doubly 
refracting  effect  upon  light  it  does  not  change  at  all  the  character  of  light  that 
enters  it  from  the  polarizer  of  a  polariscope.     Therefore  thin  sections  of  iso- 
tropic media  when  examined  in  a  polariscope  or  polarizing  microscope  with 
the  nicols  crossed  will  appear  dark  in  all  positions.     In  other  words,  they  are 
always  extinguished.     Further,  when  a  colored  mineral  is  examined  without 
the  analyzer  there  will  be  no  change  in  its  color  when  the  section  is  revolved 
with  the  stage  of  the  microscope.     Some  anomalies  are  mentioned  on  a  later 
page,  (Art.  429). 

The  single  refractive  index  of  an  isotropic  substance  may  be  determined 
by  means  of  a  prism  (see  Art.  327)  with  its  edge  cut  in  any  direction  whatever. 

B.   UNI  AXIAL  CRYSTALS 
General  Optical  Relations 

377.  The  crystallographic  and  optical  relations  of  crystals  belonging  to 
crystals  of  the  tetragonal  and  hexagonal  systems  have  already  been  briefly 
summarized  (Art.  374);   it  now  remains  to  develop  their  optical  characters 
more  fully.     This  can  be  done  most  simply  by  making  frequent  use  of  the 
familiar  conception  of  a  light-ray  to  represent  the  character  and  motion  of  the 
light-wave. 

378.  Behavior  of  Light  in  Uniaxial  Minerals.  —  Light  entering  a  uni- 
axial  mineral  is  in  general  broken  up  into  two  rays  which  are  polarized  in  planes 
perpendicular  to  each  other  and  which  travel  with  different  velocities  and 
therefore  have  different  indices  of  refraction.     One  of  the  two  rays  derived 
from  a  single  incident  ray  always  vibrates  in  the  plane  of  the  horizontal  crys- 
tallographic axes.     The  other  ray  vibrates  at  right  angles  to  the  first  and 
always  in  a  vertical  plane  that  includes  the  vertical  crystallographic  axis. 
The  optical  character  of  a  uniaxial  mineral  is  uniform  for  all  directions  lying 
in  the  horizontal  crystallographic  plane  and  therefore  the  ray  whose  vibra- 
tions lie  in  this  plane  will  have  uniform  velocity  no  matter  what  its  direction 


254  PHYSICAL  MINERALOGY 

of  transmission.  This  ray  will  therefore  have  a  single  and  constant  index  of 
refraction,  commonly  designated  by  co.  Since  this  ray  follows  the  usual  law 
as  to  the  constant  ratio  between  the  sines  of  the  angles  of  incidence  and  refrac- 
tion and  in  general  behaves  in  an  ordinary  way  it  is  called  the  ordinary  ray. 
The  ray  which  vibrates  in  a  plane  that  includes  the  vertical  crystallographic 
axis  will  have  the  direction  of  its  vibration  constantly  changing  as  the  direc- 
tion of  its  path  through  the  crystal  changes  and  its  velocity  will  correspond- 
ingly vary.  Its  index  of  refraction  will  therefore  depend  upon  the  direction 
of  its  propagation  and  it  will  not  in  general  obey  the  usual  sine  law.  This 
ray  is  therefore  called  the  extraordinary  ray. 

When  light  travels  in  a  uniaxial  mineral  in  a  direction  parallel  to  the 
vertical  crystallographic  axis,  since  all  its  vibrations  must  take  place  in  the 
horizontal  plane,  it  behaves  wholly  as  the  ordinary  ray  with  a  single  velocity 
and  refractive  index.  There  can  be  no  double  refraction  of  light,  therefore, 
along  this  direction  and  in  this  case  the  mineral  will  behave  like  an  isotropic 
substance.  This  direction  of  no  double  refraction,  coincident  with  the  ver- 
tical crystal  axis,  is  known  as  the  optic  axis  and  as  there  is  only  one  such  direc- 
tion in  this  optical  group  the  latter  is  called  uniaxial.  As  soon  as  the  direc- 
tion of  transmission  becomes  inclined  to  the  vertical  crystal  axis  the  light  is 
doubly  refracted  and  as  the  inclination  increases  the  direction  of  vibration  of 
the  light  of  the  extraordinary  ray  departs  more  and  more  from  the  plane  of 
vibration  of  the  ordinary  ray  with  a  corresponding  change  in  its  velocity  and 
refractive  index.  The  difference  between  the  refractive  indices  of  the  two 
rays  becomes  a  maximum  when  the  light  passes  through  the  mineral  in  a 
horizontal  direction  with  the  direction  of  vibration  of  the  extraordinary  ray 
parallel  to  the  vertical  crystal  axis  —  or  in  other  words  as  divergent  as  possible 
from  the  horizontal  plane.  The  value  of  the  refractive  index  of  the  extra- 
ordinary ray  when  at  its  maximum  difference  from  the  constant  index  of  the 
ordinary  ray  is  the  one  always  quoted  and  is  indicated  by"e.  These  two  indices, 
w  and  e,  are  called  the  principal  indices  of  a  uniaxial  crystal.  A  principal 
section  of  a  uniaxial  crystal  is  a  section  passing  through  the  vertical  axis. 

379.  Positive  and  Negative  Crystals.  —  Uniaxial  crystals  are  divided  into 
two  classes,  depending  upon  whether  the  velocity  of  the  extraordinary  ray  is 
greater  or  less  than  that  of  the  ordinary  ray.     Those  in  which  the  refractive 
index  of  the  ordinary  ray,  co,  is  less  than  that  of  the  extraordinary  ray,  e 
(co  <  e),  are  called  positive.     This  is  illustrated  by  quartz  for  which  (for  yel- 
low sodium  light) : 

co  =  T544.  e  =  1-553. 

On  the  other  hand,  if  e  is  less  than  co  (e  <  co),  the  crystal  is  said  to  be  negative* 
Calcite  is  an  example  for  which  (for  sodium  light) 

co  =  T658.  e  =  1-486. 

Other  examples  are  given  later  (Art.  383) . 

380.  Determination  of  the  Refractive  Indices  in  Uniaxial  Crystals.  — 

The  indices  of  refraction  of  uniaxial  minerals  are  measured  in  much  the  same 

*  It  will  assist  in  remembering  these  relations  to  note  that  the  first  vowel  in  the  words 
positive  and  negative  agrees  with  the  symbol  used  fo*  the  smaller  index  of  refraction  in 
each  case. 


CHARACTERS   DEPENDING   UPON   LIGHT  255 

way  as  in  the  case  of  isotropic  substances.  With  uniaxial  crystals,  however, 
the  prism  or  plate  used  must  have  a  definite  crystallographic  orientation.  If 
a  prism  is  employed  its  edge  should  be  parallel  to  the  optic  axis,  or  in  other 
words  parallel  to  the  vertical  crystal  axis  of  the  mineral.  When  such  a  prism 
is  examined  on  the  refractometer  two  refracted  rays  are  seen,  the  angles  of 
refraction  of  which  can  be  measured  by  either  the  method  of  minimum  devia- 
tion or  perpendicular  incidence  as  described  in  Art.  327.  The  two  rays  are 
polarized,  the  ordinary  ray  vibrating  in  the  horizontal  plane  and  the  extra- 
ordinary ray  vibrating  in  the  vertical  plane,  i.e.,  parallel  to  the  edge  of  the 
prism.  The  plane  of  vibration  of  each  ray  must  be  determined  by  the  use  of 
a  nicol  prism  held  in  front  of  the  eyepiece  of  the  refractometer.  When  the 
plane  of  the  nicol  is  horizontal  the  image  belonging  to  the  ordinary  ray  will  be 
visible  and  when  the  plane  of  the  nicol  is  vertical  only  that  of  the  extraordi- 
nary ray  will  appear.  In  this  way  the  indices  of  the  two  rays  are  determined 
and  the  positive  or  negative  character  of  the  mineral  is  established.  It  is  pos- 
sible to  obtain  these  measurements  in  prisms  with  different  crystallographic 
orientation  but  the  difficulties  attending  their  preparation  are  so  great  that 
such  prisms  are  very  seldom  used. 

If  the  method  of  >total  reflection  is  used  a  single  plate  will  suffice,  provided 
it  lies  either  in  the  prism  zone  of  the  crystal,  or  is  parallel  to  the  basal  plane. 
In  each  case  two  shadows  will  be  observed,  corresponding  in  their  position 
to  the  angles  of  total  reflection  of  the  two  rays:  When  the  plate  is  cut  parallel 
to  a  face  in  the  prism  zone  one  of  these  shadows,  that  belonging  to  the  ordi- 
nary ray,  will  remain  stationary  as  the  plate  is  revolved  on  the  hemisphere  of 
the  total  refractometer  while  the  shadow  of  the  extraordinary  ray  will  vary 
from  being  coincident  with  that  of  the  ordinary  ray  to  a  certain  maximum 
divergence  from  that  position.  This  maximum  difference  in  position,  which 
may  yield  a  greater  or  less  angle  than  that  of  the  ordinary  ray,  depending  upon 
the  optical  character  of  the  mineral,  is  the  angle  corresponding  to  the  true 
value  of  the  refractive  index  of  the  extraordinary  ray.  There  will  be  two 
positions  at  180°  apart  during  the  complete  revolution  of  the  section  at  which 
this  value  may  be  measured.  If  the  plate  was  cut  parallel  to  the  basal  plane 
of  the  crystal  the  two  shadows  would  both  be  stationary  during  such  a  revolu- 
tion and  the  value  of  the  angle  for  both  rays  can  be  measured  in  any  position 
of  the  plate. 

381.  Wave-surface.  —  Remembering  that  the  velocity  of  light-propa- 
gation is  always  inversely  proportional  to  the  corresponding  refractive  index, 
it  is  obvious  that  the  velocity  of  the  ordinary  ray  for  all  directions  in  a 

uniaxial  crystal  must  be  the  same,  being  uniformly  proportional  to  — .     In 

other  words,  supposing  light  originates  at  a  point  within  a  uniaxial  crystal 
the  ordinary  ray  would  travel  out  in  all  directions  with  uniform  velocity  and 
its  wave-front  would  form  a  sphere. 

For  the  extraordinary  ray,  however,  the  velocity  varies  with  the  direction, 

being  proportional  to  -  in  a  horizontal  direction  and  becoming  sensibly  equal 
to  —  when  nearly  coincident  with  the  direction  of  the  vertical  axis.  The 

CO 

law  of  the  varying  change  of  velocity  between  these  values,  -  and  -,  is  given 


256 


PHYSICAL   MINERALOGY 


by  an  ellipse  whose  axes  (OC,  OA,  Figs.  554,  555)  are  respectively  proportional 
to  the  above  values. 

554  555 

c 


00:OA=- 


The  wave-front  of  the  extraordinary  ray  is  then  a  spheroid,  or  an  ellipsoid 
of  revolution  whose  axis  coincides  with  the  vertical  crystallographic  axis, 
that  is,  the  optic  axis.  In  the  direction  of  the  vertical  axis  it  is  obvious  that 
the  wave-fronts  of  the  ordinary  and  extraordinary  rays  will  coincide. 

Figures  556  and  557  represent  vertical  sections  of  the  combined  wave- 


666 


557 


Negative  crystal, 


Positive  crystal,  ox: e. 


surfaces  for  both  "rays.  Fig.  556  gives  that  for  a  negative  crystal  like  calcite 
(e  <  <o),  the  ellipsoidal  wave  surface  of  the  extraordinary  ray  being  outside 
the  spherical  surface  of  the  ordinary  ray;  Fig.  557  that  of  a  positive  crystal 
like  quartz  (co  <  e)  with  the  ellipsoidal  surface  within  that  of  the  sphere. 
Fig.  558  is  an  attempt  to  show  the  relations  of  the  two  wave-fronts  of  a  nega- 
tive crystal  in  perspective  for  a  single  octant.  The  constant  value  of  the 

velocity  of  the  ordinary  ray  (  -  \  whatever  its  direction  in  the  plane  of  Figs. 

556  and  557,  is  expressed  by  the  radius  of  the  circle  (=  OC).  On  the  other 
hand,  the  velocity  of  the  extraordinary  ray  in  the  horizontal  direction  is  given 

by  OA  (-1  while  in  any  oblique  direction,  as  Osr,  Fig.  556  (Ors,  Fig.  557),  it  is 


CHARACTERS   DEPENDING    UPON    LIGHT 
558 


257 


expressed  by  the  length  of  this  line,  becoming  more  and  more  nearly  equal  to 
OC  (  -  J  as  its  direction  approaches  that  of  the  vertical  axis. 

382.  Uniaxial  Indicatrix.  —  The  optical  structure  of  a  uniaxial  crystal 
can  be  represented  by  an  ellipsoid  of  revolution,  called  the  Indicatrix*  from 
which  can  be  obtained  the  directions  of  vibration  and  indices  of  refraction  of 
the  ordinary  and  extraordinary  rays  derived  from  any  single  incident  ray. 
Fig.  559  represents  a  principal  section  of  such  an  ellipsoid  for  an  optically  nega- 
tive crystal ,  the  line  C-C  being  its  axis  of  revolution.  The  axes  of  this  ellip- 
soid are  made  inversely  proportional  to  the  indices  of  refraction  of  the  two 
rays,  co  and  e,  as  follows : 


OC  :  OA  =  -  :  -  or  6 

CO       6 


CO. 


659 


In  this  figure  let  Or  be  a  direction  of  transmis- 
sion of  light.  Let  Vr  and  VR  be  tangents  to 
the  elliptical  surface  at  the  points  r  and  R  and 
OR  be  a  radius  vector  parallel  to  the  tangent 
Vr.  Or  and  OR  form  then  what  are  known 
as  conjugate  radii.  From  the  geometrical 
properties  of  an  ellipse  it  follows  that  the 
area  of  any  parallelogram  with  conjugate 
radii  forming  two  sides,  such  as  ORVr  in  Fig. 
559,  is  constant  and  equal  to  the  area  of  a  par- 
allelogram having  OC  and  OA  as  two  sides. 
Let  RN  be  perpendicular  to  the  extended  line 
Or.  Then  the  area  of  ORVr  will  be  equal  to 
RN'Or.  It  follows  since  RN'Or  =  OA'OC  =  a  constant,  k,  that 

_  OA'OC      J^      .       ~  .         k 
(Jr  —      T-.IT —  T-k-»r »  also 


RN 


RN' 


*  The  Optical  Indicatrix  and  the  Transmission  of  Light  in  Crystals,  by  L.  Fletcher, 
London,  1892. 


258 


PHYSICAL   MINERALOGY 


From  the  last  expression  we  see  that  OA  and  OC  are  inversely  proportional  to 
each  other,  or,  in  other  words,  as  OC  represents  the  minimum  index,  OA  will 
represent  the  corresponding  velocity  of  light  which  will  be  the  maximum  for 
any  transmission  direction  in  the  crystal.  In  the  same  way  Or  and  RN  are 
inversely  proportional  to  each  other,  the  distance  Or  representing  the  velocity 
of  the  extraordinary  ray  traveling  along  that  direction  while  RN  will  represent 
its  refractive  index.  The  line  RN  will  also  give  the  direction  of  vibration  of 
the  extraordinary  ray. 

For  the  radius  vector  Or  there  will  be  another  possible  direction  perpendic- 
ular to  it  and  also  normal  to  the  ellipsoidal  surface.  This  will  be  a  line  from  0 
perpendicular  to  the  principal  section  represented  in  Fig.  559.  This  line  will 
lie  in  the  horizontal  circular  section  of  the  indicatrix  ellipsoid  with  its  length 
equal  to  OA  which  in  turn  is  proportional  to  the  index  of  the  ordinary  ray,  co. 
So  for  a  given  direction  of  transmission  of  light,  such  as  Or,  the  two  lines  that 
are  perpendicular  to  it  and  at  the  same  time  normal  to  the  surface  of  the 
indicatrix  yield  both  the  indices  of  refraction  of  the  two  rays  and  the  directions 
of  their  vibrations. 

If,  however,  the  light  is  passing  parallel  to  the  principal  axis  of  the  indica- 
trix, i.e.,  C-C,  Fig.  559,  there  will  be  an  infinite  number  of  lines  which  are 
perpendicular  to  this  direction  and  at  the  same  time  normal  to  the  surface  of 
the  indicatrix.  These  will  lie  in  the  horizontal  circular  section  of  the  ellip- 
soid and  consequently  will  be  of  a  uniform  length.  From  this  it  is  evident 
that  such  a  transmitted  ray  may  vibrate  in  any  transverse  direction  and  will 
possess  a  single  index  of  refraction  and  velocity.  Along  this  direction,  known 
as  the  optic  axis,  there  will  consequently  be  no  double  refraction  of  the  light. 

383.  Examples  of  Positive  and  Negative  Crystals.  —  The  following  lists  give  promi- 
nent positive  and  negative  uniaxial  crystals,  with  the  values  of  the  refractive  indices,  co  and 
e,  for  each,  corresponding  to  yellow  sodium  light.*  The  difference  between  these,  o>  —  e  or 
e  —  co,  is  also  given;  this  measures  the  birefringence  or  strength  of  the  double  refraction. 

It  may  be  remarked  that  in  some  species  both  +  and  —  varieties  have  been  observed. 
Certain  crystals  of  apophyllite  are  positive  for  one  end  of  the  spectrum  and  negative  for 
the  other,  and  consequently  for  some  color  between  the  two  extremes  it  has  no  double 
refraction.  The  same  is  true  for  some  other  species  (e.g.,  chabazite)  of  weak  double 
refraction. 

NEGATIVE  CRYSTALS 


Proustite. .  2 '979 


Tourmaline  

'638 

Corundum  

•768 

Beryl  

•584 

Vesuvianite 

"720 

Nephelite 

•54? 

Apatite.  .  . 

•634 

2711 
1-486 
1'620 
1-760 
1-578 
1715 
1-538 
1-631 


CO  € 

0-268 
0-172 
0-018 
0-008 
0'006 
0-005 
0-004 
0-003 


POSITIVE  CRYSTALS 


Rutile  

2-616 

2-903 

6  CO 

0'287 

Cassiterite  

1-997 

2-093 

0-096 

Zircon  

1-923 

1-968 

0'045 

Brucite  

1-559 

1-580 

0'021 

Phenacite  

1-654 

1-670 

0'016 

Quartz  

1-544 

1-553 

0'009 

Apophyllite  

1-535 

1-533 

0'002 

Leucite  

1-508 

1-509 

o-ooi 

*  From  tables  by  E.  S.  Larsen. 


CHARACTERS  DEPENDING  UPON  LIGHT 


259 


Examination  of  Uniaxial  Crystals  in  Polarized  Light 

384.  Section  Normal  to  the  Axis  in  Parallel  Polarized  Light.  —  Sup- 
pose a  section  of  a  uniaxial  crystal  to  be  cut  perpendicular  to  the  vertical 
crystallographic  axis.     It  has  already  been  shown  that  light  passing  through 
the  crystal  in  this  direction  suffers  no  double  refraction;  consequently,  such  a 
section  examined  in  parallel  polarized  light  behaves  as  a  section  of  an  isotropic 
substance.     If  the  nicols  are  crossed  it  appears  dark,  or  extinguished,  and  re- 
mains so  when  revolved. 

385.  Section  Parallel  to  the  Axis.  —  A  section  cut  parallel  to  the  verti- 
cal axis,  as  already  explained,,  has  two  directions  of  light- vibration,  one  parallel 
to  this  axis,  that  of  the  extraordinary  ray,  and  the  other  at  right  angles  to  it, 
that  of  the  ordinary  ray.     A  ray  of  light  falling  upon  such  a  section  with 
perpendicular  incidence  is  divided  into  the  two  rays,  ordinary  and  extraor- 
dinary, which  travel  on  in  the  same  path  through  the  crystal,  but  one  of  them 
retarded  relatively  to  the  other.     When  such  a  section  is  examined  in  polar- 
ized light  with  crossed  nicols  it  will  appear  dark,  or  be  extinguished,  when  its 
vibration  directions  lie  parallel  to  the  vibration  directions  of  the  nicols. 
Assume  that  the  section  abed,  Fig.  560,  lies  with  the  direction  of  its  vertical 
crystallographic  axis  parallel  to  P-P,  which  represents  the  vibration  direction 
of  the  polarizer.     The  light  entering  the  section  under  these  conditions  will 
be  vibrating  parallel  to  the  vertical  axis  of  the  crystal  and  will  therefore  pass 
into  the  mineral  wholly  as  the  extraordinary  ray,  there  being  no  vibration 


560 


< 

A 
I 

t 

d 

. 

ft 

c 

r- 

( 

'A 

possible  in  the  direc- 
tion of  the  ordinary 
ray.  The  light  will, 
therefore,  leave  the 
section  with  the  same 
direction  of  vibration 
as  when  it  entered  and 
will  be  entirely  lost  by 
reflection  in  the  an- 
alyzer. If  the  section 
is  turned  at  an  angle 
of  90°,  as  aWd',  Fig. 
560,  similar  conditions 
prevail,  although  in  this  case  the  light  will  vibrate  in  the  section  as  the 
ordinary  ray.  Therefore  in  such  a  section  there  will  be  four  positions  during 
its  complete  revolution  on  the  stage  of  the  polariscope  or  microscope  when  it 
will  be  extinguished. 

If  the  section  stand  obliquely,  as  abed  in  Fig.  561,  it  will  appear  light 
to  the  eye  (and  usually  colored),  for  the  vibrations  parallel  to  P-P  that  have 
passed  through  the  polarizer  have  upon  resolution  a  component  in  the  direc- 
tion of  each  of  the  vibration-planes  of  the  section.  Again,  each  of  these 
components  can  be  resolved  along  the  direction  of  the  vibration-plane  of  the 
upper  nicol,  A- A.  Therefore,  two  rays  will  emerge  from  the  analyzer,  both 
having  the  same  vibration-plane,  but  one  more  or  less  retarded  with  reference 
to  the  other,  the  amount  of  retardation  increasing  with  the  birefringence  and 
the  thickness  of  the  section.  In  general,  therefore,  these  rays  will  interfere, 
and  if  the  thickness  of  the  section  is  sufficient  (and  not  too  great)  it  will 
appear  colored  in  white  light  and,  supposing  the  thickness  uniform,  of  the 
same  color  throughout. 


260  PHYSICAL   MINERALOGY 

386.  Parallel  Extinction.  —  When  the  vibration  directions  of  a  section 
coincide  with  those  of  the  polarizer  and  analyzer,  assuming  them  to  be  crossed, 
the  section  appears  dark  and  it  is  said  to  be  in  the  position  of  extinction.     If  a 
section  extinguishes  when  its  crystallographic  axis  or  axial  plane  is  -parallel  to 
one  of  the  planes  of  vibration  of  the  nicols  it  is  said  to  show  parallel  extinction. 
If,  on  the  other  hand,  no  such  parallelism  exists  between  the  crystallographic 
directions  and  the  directions  of  vibration  in  the  mineral  the  section  is  said  to 
show  inclined  extinction. 

In  the  case  of  uniaxial  minerals,  since  the  vibration  directions  always  lie 
in  some  crystallographic  axial  plane,  all  sections  of  such  minerals  will  show 
parallel  extinction. 

387.  Determination  of  the  Relative  Character  of  the  Extinction  Direc- 
tions of  a  Given  Uniaxial  Mineral.  —  The  relative  characters  of  the  ex- 
tinction directions  of  a  section  of  a  uniaxial  mineral  are  to  be  determined  by 
the  use  of  the  quartz  wedge   or  the  sensitive  tint   as    described  in  Art. 
348.     If  the  orientation  of  the  section  is  known  so  that  it  can  be  told  which  of 
the  directions  of  vibration  belongs  to  the  ordinary  and  which  to  the  extraor- 
dinary ray  the  positive  or  negative  character  of  the  mineral  can  be  determined. 
For  instance,  if  the  ordinary  ray  is  proved  to  be  the  faster  of  the  two  (i.e.,  the 
X  direction)  it  follows  that  its  index  is  the  smaller,  i.e.,  co  <  e,  and  the 
mineral  is  positive. 

388.  Interference  Colors  of  Uniaxial  Minerals.     Birefringence.  —  The 
interference  color  of  any  section  of  a  uniaxial  mineral  depends  upon  the  fol- 
lowing:  first  upon  the  thickness  of  the  section,  second  upon  the  strength  of 
the  double  refraction  of  the  mineral,  i.e.,  its  birefringence,  this  being  measured 
by  the  difference  between  the  indices  of  refraction  of  the  two  rays  in  the  sec- 
tion, and  third  upon  the  crystallographic  orientation  of  the  section.     A  section 
cut  parallel  to  the  basal  plane  shows  no  double  refraction  and  therefore  cannot 
exhibit  any  interference  color.     The  strength  of  the  birefringence,  the  other 
conditions  remaining  uniform,  increases  as  the  inclination  of  the  section  to 
the  basal  plane  increases.     The  highest  birefringence  of  a  given  mineral  is 
therefore  shown  by  its  prismatic  sections. 

The  following  table  *  gives  the  thickness  (in  millimeters)  of  sections  of  a 
few  uniaxial  crystals  which  yield  red  of  the  first  order: 

Birefringence          Thickness  in 
(03  —  e)  or  (e  —  o>)        Millimeters 

Rutile 0-287  0'0019 

Calcite 0172  0'0032 

Zircon 0'062  0*0089 

Tourmaline 0'023  0'0240 

Quartz 0'009  0*0612 

Nephelite 0*004  01377 

Leucite 0*001  0*5510 

Again,  as  another  example,  it  may  be  noted  that  with  zircon  (e  —  co  =  0*062),  a  thick- 
ness of  about  0'009  mm.  gives  red  of  the  first  order;  of  0'017  red  of  the  second  order:  of 
0*026  red  of  the  third  order. 

The  methods  ordinarily  used  to  determine  the  birefringence  of  a  section  (not  J_  c  axis) 
of  a  uniaxial  crystal,  as  also  to  fix  the  relative  value  of  its  two  vibration-directions,  have 
already  been  discussed,  see  Arts.  347  and  348. 

389.  Effects  of  Convergent  Polarized  Light  upon  Sections  of  Uniaxial 
Minerals.     Uniaxial  Interference  Figures.  —  When  certain  sections  of  uni- 

*  See  further,  Rosenbusch  (Mikr.  Phys.  Min.,  1904,  p.  292),  from  whom  these  are  taken. 


CHARACTERS   DEPENDING   UPON   LIGHT 


261 


axial  minerals  are  observed  in  convergent  polarized  light  they  show  what 
are  known  as  interference  figures.  A  symmetrical  interference  figure  is  obtained 
in  uniaxial  minerals  by  allowing  converging  polarized  light  to  pass  through  a 
basal  section  of  the  crystal.  Parallel  polarized  light  entering  such  a  section 
would  suffer  no  double  refraction  and  consequently  give  no  interference.  To 
convert  the  parallel  polarized  light  that  comes  from  the  polarizer  into  con- 
vergent light  a  lens  is  placed  between  the  polarizer  and  the  section.  Under 
these  conditions  a  sharply  converging  cone  of  light  rays  enters  the  section. 
Another  lens  is  placed  above  the  section  to  change  these  oblique  rays  back 
again  into  a  parallel  postion.  Such  an  instrument  is  known  as  a  conoscope 
and  may  be  obtained  by  placing  a  pair  of  lenses  between  the  polarizer  and 
analyzer  of  a  polariscope,  or,  in  case  the  polarizing  microscope  is  used,  the  small 
converging  lens  that  lies  above  the  polarizer  is  swung  into  position  by  a  lever 
and  at  the  same  time  a  small  lens  known  as  the  Bertrand  lens  is  introduced 
into  the  microscope  tube. 

Under  such  conditions  the  light  entering  the  section  is  composed  of  a 
562  converging  system  of  rays  polarized  and 

vibrating  in  the  plane  P-P,  Fig.  562. 
Let  B-B  (Fig.  562,  A)  be  a  vertical 
cross  section  of   the  mineral   section 
along    the    line   B-B,    Fig.   562,    B. 
Consider  any  ray,  as  a,  entering  the 
section.      Since    the    ray    enters    the 
section    obliquely    it    will  be  doubly 
a   refracted   into    the    rays    o    and    e. 
563 


( 

i 

B           oe 

e  o           B 

'  V 

\  I 

The  mineral  being  taken  as  calcite  the  extraordinary  ray  (calcite  being 
negative)  will  have  the  greater  velocity  and  be  least  refracted.  As  the 
light  enters  the  section  in  the  form  of  a  cone  the  traces  of  the  two  rays  as  they 
emerge  from  the  section  will  be  circles,  Fig.  562,  B.  Now  consider  in  a  similar 
case  the  action  of  the  two  rays  a  and  b  or  a'  and  V  (Fig.  563)  upon  each  other. 
Ray  a  on  entering  the  section  is  doubly  refracted  and  polarized  into  the  rays  e 
and  o  which  are  considered  as  emerging  from  the  section  at  the  points  e  and  r. 
Ray  b  also  on  entering  the  section  is  doubly  refracted  and  polarized.  Suppose 
the  extraordinary  ray  derived  from  b  emerges  from  the  section  at  the  same 
point  as  the  ordinary  ray  derived  from  a,  that  is  at  r.  Since  it  travels  with  a 
greater  velocity  the  extraordinary  ray  emerging  at  this  point  will  have 
advanced  in  its  phase  over  that  of  the  ordinary  ray.  In  that  case  they 
would  be  in  a  condition  to  interfere  with  each  other  except  that  they  are 
vibrating  in  planes  perpendicular  to  each  other  and  so  cannot.  The  two  rays 
travel  on,  vibrating  in  planes  at  right  angles  to  each  other  and  maintaining 


262 


PHYSICAL   MINERALOGY 


this  difference  in  phase  until  they  reach  the  upper 'nicol;  there  they  are  each 
resolved  into  rays  vibrating  in  the  plane  A-A,  Fig.  562,  B,  and  are  now  in 
condition  to  interfere  with  each  other.  Let  it  be  assumed  that  the  conditions 
are  right  for  the  extraordinary  ray  to  emerge  from  the  section  just  one  wave- 
length ahead  of  the  ordinary  ray.  Their  components  in  the  upper  nicol  will 
have  opposite  phases  and  therefore  compensate  each  other,  see  Art.  335.  If 
the  section  is  viewed  in  a  monochromatic  light  (for  instance,  sodium  light) 
this  interference  will  result  in  a  black  point.  But  as  these  rays  are  converging 
in  the  form  of  a  cone  they  will  make,  when  they  strike  the  section,  a  circular 
trace  upon  its  surface  and  their  interference  will  result  in  a  dark  ring.  Going 
out  from  the  center  of  the  section  there  will  be  a  succession  of  these  rings 
corresponding  to  the  interference  of  waves  1,  2,  3,  4,  5,  etc.,  wave-lengths 
apart.  As  the  distance  from  the  center  of  the  section  is  increased,  the  paths 

of  the  refracted  rays  in 
the  section  are  lengthened 
and  the  points  of  inter- 
ference are  brought  closer 
together.  This  will  cause 
the  interference  rings  to 
lie  nearer  together  as  the 
distance  from  the  center 
of  the  figure  increases. 

Fig.  564  is  a  top  view 
of  the  section  without 
taking  into  consideration 
the  effects  of  the  upper 
nicol.  Let  the  two  circles 
represent  the  traces  of  the 
emergence  of  the  two  rays 
e  and  o  into  which  one 
incident  conical  ray  is 
divided ;  e,  being  the  least 
refracted  (for  calcite),  will 
be  the  inner  one.  The 
plane  of  vibration  of  e 
is  always  parallel  to  some  plane  passing  through  the  vertical  axis 
of  the  crystal,  therefore  the  trace  of  its  plane  of  vibration  upon 
the  surface  of  the  section  will  always  be  in  a  radial  direction.  The  plane  of 
vibration  of  o  is  at  right  angles  to  that  of  the  extraordinary  ray  and  parallel 
to  the  horizontal  axes  of  the  crystal,  therefore  the  trace  of  its  plane  of  vibra- 
tion upon  the  surface  of  the  section  will  always  be  in  a  tangential  direction, 
see  Fig.  564.  Along  the  line  P-P,  Fig.  564,  only  light  vibrating  in  a  radial 
plane  or  that  of  the  extraordinary  ray  can  come  through  the  section,  since  the 
light  entering  the  section  cannot  be  resolved  into  the  vibrations  of  the  ordinary 
ray.  The  intensity  and  direction  of  vibration  of  the  light  that  emerges  from 
the  section  along  the  line  P-P  is  represented  by  the  double  arrow  on  that  line. 
Along  the  line  A-A,  since  the  light  entering  the  section  is  still  vibrating  in 
the  plane  P-P,  all  the  light  passing  through  the  section  must  vibrate  as  the 
ordinary  ray.  It  is  evident,  therefore,  that  along  these  two  directions,  P-P 
and  A-A  the  plane  of  vibration  of  the  light  is  not  changed  by  passage  through 
the  section  and  consequently  such  light  will  be  completely  absorbed  in  the 


CHARACTERS   DEPENDING    UPON    LIGHT  263 

upper  nicol.  In  this  way  dark  brushes  will  be  formed  along  the  lines  P-P 
and  A- A.  A  dark  spot  will  also  be  formed  in  the  center  of  the  field  because 
any  light  entering  the  section  at  this  point  must  enter  in  the  direction  of  the 
optic  axis  and  therefore  will  not  be  doubly  refracted  and  consequently  will 
also  be  absorbed  in  the  analyzer. 

Now  consider  point  B,  Fig.  564,  which  lies  45°  away  from  P  and  A.  Here 
the  directions  of  vibration  of  e  and  o  would  be  equally  inclined  to  the  planes  of 
vibration  of  the  polariscope,  A-A  and  P-P.  Light  striking  the  section  at  B 
would  be  vibrating  in  the  plane  P-P  but  by  resolution  a  component  vibrating 
in  the  direction  B-B  would  come  through  the  section  as  the  ray  e;  in  the  same 
manner  a  component  vibrating  in  a  direction  at  right  angles  to  B-B  would 
emerge  as  o.  The  intensities  and  directions  of  vibration  of  these  two  rays  at 
this  point  are  represented  by  the  double  arrows.  When  these  rays  meet  the 
analyzer  above  they  would  again  each  be  resolved  and  their  components 
which  vibrate  in  the  plane  A-A  would  emerge  from  the  analyzer.  In  this  way 
it  is  seen  that,  except  at  the  special  points  where  complete  interference  takes 
place,  light  will  result  in  the  interference  figure  at  all  points  away  from  the 
center  of  the  figure  and  from  the  lines  P-P 
and  A-A.  From  the  consideration  of  Fig. 
564  it  is  evident  that  the  greatest  amount 
of  light  will  come  through  the  section  at 
the  45°  points,  such  as  B.  When  viewed 
in  monochromatic  light,  therefore,  the 
interference  figure  consists  of  a  series  of 
concentric  dark  and  light  rings  crossed  by  a 
vertical  and  a  horizontal  dark  brush  in- 
tersecting in  the  center  of  the  field  of  the 
microscope,  like  Fig.  565. 

If  a  basal  section  of  a  uniaxial  mineral 
while  in  the  conoscope  is  viewed  in  daylight 
colored  rings  will  take  the  place  of  the  light 
and  dark  rings  observed  in  the  monochro- 
matic light.  The  change  will  be  like  that  Uniaxial  Interference  Figure 
shown  by  the  quartz  wedge  in  the  similar 
case  described  in  Art.  343.  Where  the  first  few  dark  rings  near 
the  center  of  the  figure  were  formed  by  the  interference  of  rays 
having  the  wave-length  of  sodium,  light  colored  rings  will  result  in  the  daylight 
illumination.  These  rings  will  be  composed  of  all  the  components  of  white 
light  with  the  yellow  of  sodium  subtracted.  The  other  colors  are  obtaind  in 
a  similar  manner  by  the  elimination  though  interference  of  some  particular 
wave-length  of  light.  While  the  interference  figure  when  illuminated  in  the 
monochromatic  light  showed  a  large  number  of  distinct  black  rings  in  day- 
light, the  corresponding  colored  rings  are  limited  in  number  and  their  colors, 
gradually  becoming  fainter  as  the  distance  from  the  center  of  the  figure 
increases,  finally  merge  into  the  white  of  the  higher  order.  This  is  due  to  the 
overlapping  of  the  interference  rings  of  the  various  colors  in  the  same  manner 
as  observed  in  the  quartz  wedge,  see  Art.  343.  The  interference  figure 
viewed  in  daylight  will  of  course  retain  the  black  cross  and  center  since  these 
are  due  to  the  cutting  out  of  all  the  light  by  the  analyzer  and  are  not  the  result 
of  interference. 

The  distance  of  each  successive  ring  from  the  center  of  the  interference 


264 


PHYSICAL   MINERALOGY 


figure  obviously  depends  upon  the  birefringence,  or  the  difference  between  the 
refractive  indices,  for  the  ordinary  and  extraordinary  ray,  and  also  upon  the 
thickness  of  the  plate.  The  stronger  the  double  refraction  and  the  thicker 
the  plate,  the  smaller  the  angle  of  the  light-cone  which  will  give  a  certain 
amount  of  retardation,  or,  in  other  words,  the  nearer  the  circles  will  be  to  the 
center.  Further,  for  the  same  section  the  circles  will  be  nearer  for  blue  light 
than  for  red,  because  of  their  shorter  wave-length.  When  the  plate  is  either 
quite  thin  or  quite  thick  only  the  black  brushes  will  be  distinctly  seen. 

390.  Determination  of  the  Positive  or  Negative  Character  of  the  Bire- 
fringence of  a  Uniaxial  Mineral  from  Its  Interference  Figure. 

Use  of  the  Mica  Plate.  —  For  the  identification  of  a  uniaxial  mineral  it 
is  naturally  important  to  determine  whether  the  character  of  its  birefringence 
is  positive  or  negative.  This  can  usually  be  best  accomplished  by  tests  made 
upon  its  interference  figure.  One  of  the  common  ways  of  making  this  'test  is 
by  the  use  of  a  sheet  of  muscovite  mica,  cleaved  so  thin  that,  of  the  two  rays 
of  light  passing  through  it,  one  has  gained  one  quarter  of  a  wave-length  in 
phase  over  the  other.  The  mica  is  usually  mounted  between  long  and  narrow 
glass  plates  and  is  known  as  the  one  quarter  wave-length  mica  plate.  It  is 

commonly  marked  1  /4M  with 
an  arrow  indicating  the  Z 
optical  direction.  In  testing 
an  interference  figure  by 
means  of  the  mica  plate  the 
latter  is  inserted  somewhere 
between  the  polarizer  and 
analyzer  (in  the  microscope 
commonly  through  the  slot 
just  above  the  objective)  and 
is  so  orientated  that  the  Z 
direction  makes  an  angle  of 
45°  with  the  planes  of  vibra- 
tion of  the  nicols. 

In  Fig.  566  let  P-P  rep- 
resent the  plane  of  vibra- 
tion of  the  polarizer  and 
A-A  the  plane  of  vibration  of 
the  analyzer  of  a  conoscope. 
Let  0  be  the  point  of  emer- 
gence of  the  optic  axis  of  a 
positive  uniaxial  mineral. 
Suppose  a  single  conical  ray  of  light  enters  the  section.  It  is  broken  up  in  the 
mineral  into  two  rays,  o  and  e,  which  emerge  from  the  section  along  the  arcs  of 
the  circles  shown  in  Fig.  566.  The  trace  of  the  ordinary  ray,  o,  will  be  within 
that  of  the  extraordinary  ray,  e,  because  in  a  positive  mineral  the  o  ray  travels 
the  faster  and  is  less  refracted.  The  directions  of  vibration  of  these  two  rays  at 
the  45°  points  R  and  R'  are  represented  by  the  double-headed  arrows.  When 
these  rays  reach  the  analyzer  they  will  be  resolved  into  components  vibrating 
parallel  to  A-A .  There  are  an  infinite  number  of  such  rays  entering  and  pass- 
ing through  the  mineral  section  with  varying  angles  of  inclination  and  there- 
fore varying  lengths  of  path.  At  some  certain  distance  out  from  the  center 
0  two  rays  will  emerge  on  the  same  circle  with  a  difference  of  phase  of  one 


CHARACTERS   DEPENDING   UPON   LIGHT  265 

whole  wave-length  and  when  resolved  in  the  upper  nicol  into  rays  vibrating 
in  the  same  plane  will  interfere  with  each  other  and  produce  the  first  dark 
ring  of  the  interference  figure  as  it  is  viewed  in  monochromatic  light. 

If  the  mica  plate  is  introduced  above  the  section  a  change  in  the  inter- 
ference figure  is  noted.  The  optical  character  of  the  mica  cannot  be  fully 
explained  at  this  point.  It  is  sufficient  for  present  purposes  to  know  that 
it  is  a  doubly  refracting  mineral  which  breaks  light  up  into  two  rays  which 
are  polarized  in  planes  at  right  angles  to  each  other  and  which,  traveling  with 
different  velocities  through  the  mica,  will  emerge  from  it  with  different  phases. 
As  stated  above,  the  mica  plate  is  cleaved  to  the  requisite  thickness  so  that  the 
two  rays  emerge  from  it  with  a  difference  of  phase  of  one  quarter  of  a  wave- 
length. Consider  what  takes  place  when  such  a  plate  is  introduced  above  the 
section  represented  in  Fig.  566  in  such  a  position  that  its  vibration  direction 
Z  is  parallel  to  the  direction  R-O-R  of  the  figure.  Consider  what  takes  place 
at  the  points  R.  There  the  vibration  direction  of  the  e  ray  coincides  with 
the  vibration  direction  Z  of  the  mica  plate.  These  vibration  directions  in 
each  case  are  those  of  the  rays  traveling  with  the  smaller  velocity.  On  the 
other  hand,  at  the  same  point  the  vibration  direction  of  the  o  ray  in  the  mineral 
coincides  with  the  vibration  direction  X  in  the  plate,  both  of  these  being  of 
the  rays  with  the  greater  velocity.  So  at  this  point  the  effect  of  the  mica 
plate  is  to  increase  the  difference  of  phase  between  o  and  e  and  to  produce  the 
same  result  as  if  the  mineral  section  had  been  thickened.  Consequently  the 
interference  rings  along  the  line  R-O-R  are  increased  in  number  and  drawn 
toward  the  center  of  the  figure.  At  the  points  R'  the  opposite  is  true.  The 
vibration  direction  of  e  coincides  now  with  that  of  X  in  the  mica  plate;  the 
direction  of  least  velocity  in  the  mineral  with  that  of  the  greatest  in  the  mica. 
Also  the  vibration  direction  of  o  coincides  with  that  of  Z\  that  of  the  greater 
velocity  in  the  mineral  with  the  less  velocity  in  the  mica.  So  at  this  point 
the  mica  will  decrease  the  difference  in  phase  between  o  and  e  and  produce  the 
effect  of  thinning  the  section  and  so  spreading  the  interference  rings  farther 
apart  along  the  line  R'-O-R'.  In  quadrants  2  and  4,  therefore,  the  rings  will 
be  drawn  nearer  the  center,  while  in  quadrants  1  and  3  they  will  be  spread 
farther  apart.  Another  effect  caused  by  the  introduction  of  the  mica  plate  is 
even  more  pronounced.  In  quadrants  1  and  3,  in  the  case  illustrated  in  Fig. 
566,  black  dots  will  appear  near  the  center  of  the  figure.  In  the  interference 
figure,  before  the  introduction  of  the  mica  plate,  there  were  points  in  quadrants 
1  and  3  at  short  distances  from  the  center,  0,  where  the  two  rays,  o  and  e, 
emerged  from  the  section  with  a  difference  of  phase  of  one  quarter  wave-length. 
Under  these  conditions  no  interference  could  take  place  and  these  spots  were 
light.  The  effect  of  the  mica  plate  in  these  two  quadrants  is  to  everywhere 
reduce  the  birefringence  due  to  the  mineral  by  one  quarter  of  a  wave-length. 
Therefore  at  these  two  points  the  difference  of  phase  caused  by  the  birefring- 
ence of  the  mineral  is  annulled  by  the  mica  plate  and  consequently  at  these 
points  interference  will  result  and  black  dots  appear.  The  mica  plate  produces 
still  other  effects.  The  brushes  which  were  dark  in  the  interference  figure  be- 
come light.  Light  coming  from  the  crystal  section  along  the  lines  of  the  brushes 
is  vibrating  only  in  the  vibration  direction  of  the  polarizer  and  ordinarily  is 
wholly  cut  out  by  the  analyzer  above.  But  with  the  mica  plate  intervening  this 
light  is  broken  up  in  the  mica  into  two  rays  which  vibrate  in  the  vibration 
planes  of  the  mica  and  as  these  are  inclined  to  the  plane  of  the  analyzer  a 
portion  of  the  light  will  come  through  to  the  eye.  As  the  light  coming  from 


266 


PHYSICAL   MINERALOGY 


the  section  along  the  lines  of  the  brushes  had  only  a  single  velocity  (was 
entirely  either  the  ordinary  or  extraordinary  ray)  there  are  only  two  rays 
emerging  from  the  mica  plate  along  these  directions  and  their  difference  of 
phase  is  one  quarter  of  a  wave-length.  Under  these  conditions  there  can  be  no 
interference  and  white  brushes  result.  In  the  same  way  the  dark  center  of 
the  interference  figure  becomes  light. 

667 


Determination  of  Optical  Character  with  Mica  Plate 

Fig.  567,  A,  is  a  diagrammatic  representation  of  the  interference  figure  of 
a  positive  mineral  as  affected  by  the  insertion  of  the  mica  plate,  the  direction 
of  the  arrow  indicating  the  direction  Z  of  the  mica,  i.e.,  the  direction  of  vibra- 
tion of  the  ray  having  the  smaller  velocity.  In  the  case  of  a  negative  mineral 
the  conditions  as  described  above  will  be  completely  reversed.  Fig.  567,  B, 
represents  the  appearance  of  an  interference  figure  of  a  negative  mineral  when 
the  mica  plate  is  used. 

Therefore,  to  determine  the  optical  character  of  a  uniaxial  mineral  from 
its  interference  figure  insert  a  mica  plate  above  the  section  with  its  Z  direction 
making  45°  with  the  vibration  planes  of  the  nicols.  Then,  if  this  direction  Z 
is  at  right  angles  to  a  line  joining  the  two  black  dots  that  appear  near  the  cen- 
ter of  the  figure  (i.e.,  the  two  lines  form  a  plus  sign),  the  mineral  is  positive; 
if,  on  the  other  hand,  these  two  directions  coincide  (form  together  a  minus 
sign)  the  mineral  is  negative. 

Use  of  the  Sensitive  Tint.  —  The  sensitive  tint,  see  Art.  344,  is  used  to  deter- 
mine the  positive  or  negative  character  of  a  uniaxial  mineral  from  its  inter- 
ference figure  when  the  mineral  section  is  so  thin,  or  the  mineral  possesses 
such  a  low  birefringence,  as  to  show  in  the  figure  only  a  black  cross  without 
any  rings.  Under  such  conditions  the  mica  plate  would  not  give  a  decisive 
test.  The  sensitive  tint  is  usually  so  mounted  that  its  longer  direction  coin- 
cides with  the  direction  of  the  vibration  of  the  faster  ray,  i.e.,  the  direction  X. 
The  sensitive  tint  is  introduced  somewhere  between  the  polarizer  and  ana- 
lyzer in  such  a  position  that  its  vibration  directions  are  at  45°  with  the  planes 
of  vibration  of  the  nicols.  Let  it  be  assumed  that  we  have  the  interference 
figure  from  a  positive  mineral,  such  as  is  represented  in  Fig.  566.  If  the 
sensitive  tint  is  introduced  in  such  a  position  that  its  X  direction  is  parallel 
to  the  line  R-O-R  the  X  direction  of  the  sensitive  tint  will  be  parallel  to  the 
direction  of  vibration  of  the  e  ray  in  the  mineral.  Since  the  mineral  is  positive 
the  e  ray  will  have  the  smaller  velocity  and  therefore  in  quadrants  2  and  4  the 


CHARACTERS   DEPENDING   UPON    LIGHT 


267 


optical  orientation  of  the  mineral  and  the  sensitive  tint  will  be  opposed  to 
each  other.  The  sensitive  tint  alone  would  produce  an  interference  color  of 
red  of  the  first  order.  But  if  the  effect  of  the  birefringence  of  the  mineral  is 
such  as  to  subtract  from  the  birefringence  of  the  sensitive  tint  the  color  will 
change  to  yellow.  Consequently  in  these  quadrants  yellow  spots  will  appear 
near  the  center  of  the  field  at  the  points  where  the  effect  of  the  mineral  has 
been  sufficient  to  lower  the  interference  color  to  that  extent.  In  the  other 
quadrants,  1  and  3,  the  faster  and  slower  rays  of  the  mineral  and  sensitive 
tint  coincide  in  their  directions  and  the  effect  of  the  two  substances  is  an  addi- 
tive  one.  Con- 
sequently in  these  two  568 
quadrants  the  color 
will  rise  to  blue. 

In  making  the  above 
test  with  the  sensitive 
tint  it  is  convenient 
to  follow  the  rule  that 
if  the  direction  X  of 
the  sensitive  tint 
crosses  a  line  uniting 
the  two  blue  dots 
(makes  a  plus  sign) 
the  mineral  is  positive ; 
if,  on  the  other  hand, 
these  two  directions 
coincide  ( make  to- 
gether a  minus  sign)  the  mineral  is  negative 

391.   Interference  Figures  from  Inclined  Sections  of  Uniaxial  Minerals. 

569 


Determination  of  Optical  Character  with  Sensitive  Tint 

These  conditions  are  illustrated 


Eccentric  Uniaxial  Interference  Figures 


268 


PHYSICAL   MINERALOGY 


570 


An  interference  figure  obtained  from  such  an  inclined  section  will  of  course  be 
eccentric  to  the  microscope  field.  If  the  section  is  inclined  only  a  little  to  the 
basal  plane,  the  center  of  the  figure  (i.e.,  the  point  of  emergence  of  the  optic 
axis)  will  still  be  within  the  field  of  vision  and  will  move  in  a  circle  about  the 
center  of  the  field  wtien  the  section  is  revolved  upon  the  microscope  stage. 
Fig.  569,  A,  shows  the  successive  positions  of  such  an  interference  figure  during 
revolution.  If  the  section  is  more  sharply  inclined  the  center  of  the  inter- 
ference figure  may  be  quite  outside  the  field.  As  the  section  is  turned  on  the 
stage  the  four  arms  of  the  interference  cross  will  traverse  the  field  in  succession. 
They  will  move  across  the  field  as  straight  bars  and,  provided  the  section  has 
been  cut  not  too  highly  inclined  to  the  optic  axis,  will  move  across  the  field 
parallel  to  the  cross-hairs  of  the  microscope.  This  fact  is  of  importance  in 
order  to  distinguish  such  a  uniaxial  interference  figure  from  certain  biaxial 
figures.  The  latter  will  often  show  similar  bars  which,  however,  will  always 
curve  as  they  cross-  the  field  of  the  microscope.  If  the  first  of  these  bars  in 
the  uniaxial  figure  moves  from  left  to  right  across  the  field,  the  second  will 
move  from  the  top  to  the  bottom,  the  third  from  right  to  left  and  the  last 
from  the  bottom  to  the  top,  etc.  Fig.  569,  B,  shows  the  different  position  of 
such  a  figure  during  one  quarter  of  a  revolution. 

The  positive  or  negative  character  of  the  mineral  can  usually  be  deter- 
mined from  an  eccentric  figure  if  care  is  taken 
to  make  certain  .  which  quadrant  is  visible 
when  the  test  is  made.  For  instance,  in  Fig. 
570  is  shown  how  the  test  is  made  with  the 
sensitive  tint  upon  the  eccentric  interference 
figure  of  a  positive  mineral. 

In  examining  unorientated  sections  of  a 
mineral,  such  as  the  random  section  found  in 
a  rock  section  or  the  small  fragments  of  a 
mineral  placed  upon  a  glass  slide,  it  is  advis- 
able always  to  hunt  for  that  section  that  gives 
the  lowest  interference  color.  The  amount 
of  birefringence  shown  in  various  sections 
of  a  uniaxial  mineral  decreases  as  the  section 
approaches  the  orientation  of  the  basal  plane. 
Consequently  that  section  showing  the 
lowest  interference  color  will  yield  the  most 
nearly  symmetrical  interference  figure. 
392.  Interference  Figure  from  a  Prismatic  Section  of  a  Uniaxial 
Mineral.  —  When  a  prismatic  section  of  a  uniaxial  mineral  is  examined 
for  an  interference  figure  an  indefinite  result  is  obtained.  The  figure  is  analo- 
gous to  one  obtained  in  the  case  of  biaxial  crystals.  The  reasons  for  this 
resemblance  will  be  pointed  out  in  a  later  article.  The  two  types  of  figures 
cannot  be  in  this  case  easily  differentiated.  Two  dark  and  usually  indefinite 
hyperbolas  approach  each  other  as  the  section  is  turned  on  the  microscope 
stage,  form  an  indistinct  cross,  and  rapidly  separate.  These  bars  differ  from 
those  obtained  in  a  biaxial  interference  figure  in  that  they  rapidly  fade  out  as 
they  move  away  from  the  crossed  position.  This  type  of  interference  figure 
can  be  obtained  easily  from  the  quartz  wedge. 

wu393:  AbsorPtion  Phenomena  of  Uniaxial  Crystals.  Dichroism.  — 
When  light  enters  colored  minerals  as  rays  of  white  light,  i.e.,  containing  vibra- 


Sensitive  Tint  with 
Eccentric  Interference  Figure 


CHARACTERS   DEPENDING   UPON    LIGHT 


269 


P 1 


Vertical  Axis     ^ 


tions  of  all  wave-lengths  from  that  of  violet  light  at  one  end  of  the  spectrum 
to  that  of  red  light  at  the  other,  certain  wave-lengths  will  be  absorbed  during 
the  passage  of  the  light  through  the  mineral,  so  that  the  light,  as  it  emerges, 
has  a  definite  color.  It  happens  in  certain  deeply  colored  minerals  that  the 
amount  and  character  of  this  absorption  depends  upon  the  direction  of  the 
light  vibration.  For  instance  in  the  case  of  uniaxial  minerals,  the  ordinary 
and  extraordinary  rays  may  emerge  from  the  section  with  distinctly  different 
colors.  Take,  for  instance,  a  prismatic  section  of  a  brown  colored  tourmaline 
and  observe  it  in  plane  polarized  light  without  the  use  of  the  upper  nicol.  As 
the  section  is  revolved  upon  the  stage  of  the  polariscope  the  color  may  change 
from  a  dark  brown  to  a  light  yellow-brown.  The  greatest  difference  in  the 
color  occurs  at  positions  90°  apart  and  when  the  crystallographic  directions  of 
the  section,  i.e.,  the  vertical  crystallographic 
axis  and  the  trace  of  the  plane  of  the  horizontal 
axes,  are  either  parallel  or  perpendicular  to  the 
vibration  plane  of  the  polarizer.  In  other 
words,  these  extremes  of  color  occur  when  the 
directions  of  the  vibration  of  the  ordinary  and 
extraordinary  rays  in  the  section  are  parallel  or 
perpendicular  to  the  vibration  plane  of  the 
light  entering  the  section.  In  Fig.  571,  A,  let 
P-P  represent  the  vibration  direction  of  the 
light  entering  the  section.  The  mineral  section 
is  so  placed  that  the  direction  of  the  vertical 
crystal  axis  is  perpendicular  to  P-P.  The 
light  on  entering  the  section  will  therefore 
vibrate  in  the  plane  of  the  horizontal  axes  or 
as  the  ordinary  ray,  o.  In  this  position  the 
tourmaline  section  is  dark  colored  and  con- 
sequently it  is  seen  that  light  vibrating  in  the 
mineral  as  the  ordinary  ray  is  largely  absorbed. 
Now  turn  the  section  through  a  90°  angle  to 
the  position  shown  in  Fig.  571,  B.  In 
this  position  the  light  must  vibrate  in  the  section  wholly  as  the 
extraordinary  ray,  e,  and  the  color  is  a  light  yellow-brown.  There- 
fore the  extraordinary  ray  is  only  slightly  absorbed.  This  difference  in 
the  absorption  or  the  color  of  the  two  rays  is  known  as  dichroism.  Either 
the  ordinary  or  the  extraordinary  ray  may  be  the  most  absorbed  and  the  two 
cases  are  expressed  as  either  o  >  e  (o>  >  e)  or  e  >  o  (e  >  co).  In  uniaxial 
minerals  dichroism  is  to  be  best  observed  in  prismatic  sections  where  it  attains 
its  full  intensity.  Basal  sections  show  no  dichroism,  since  light  passing  through 
the  section  parallel  to  the  optic  axis  must  all  vibrate  in  the  horizontal  axial 
plane  and  belong  wholly  to  the  ordinary  ray. 

An  instrument  called  a  dichroscope,  contrived  by  Haidinger,  is  sometimes  used  for 
examining  this  property  of  crystals.  An  oblong  rhombohedron  of  Iceland  spar  is  placed 
in  a  metallic  cylindrical  case,  having  a  convex  lens  at  one  end,  and  a  square  hole  at  the 
other.  On  looking  through  it,  the  square  hole  appears  double;  one  image  belongs  to  the 
ordinary  and  the  other  to  the  extraordinary  ray.  When  a  pleochroic  crystal  is  examined 
with  it  by  transmitted  light,  on  revolving  it  the  two  squares,  at  intervals  of  90°  in  the  revo- 
lution, have  different  colors,  corresponding  to  the  vibration-planes  of  the  ordinary  and 
extraordinary  ray  in  calcite.  Since  the  two  images  are  situated  side  by  side,  a  very  slight 
difference  of  color  is  perceptible.  A  similar  device  is  sometimes  used  as  an  ocular  in  the 
microscope. 


1 

i 
>e 

\ 
Light 

fellow 

270  PHYSICAL   MINERALOGY 

394.  Circular  Polarization.  —  The  subject  9f  elliptically  polarized  light  and  circular 
polarization  has  already  been  briefly  alluded  to  in  Art.  350.  This  phenomenon  is  most  dis- 
tinctly observed  among  minerals  in  the  case  of  crystals  belonging  to  the  rhombohedral- 
trapezohedral  class,  that  is,  quartz  and  cinnabar. 

It  has  been  explained  that  a  section  of  an  ordinary  uniaxial  crystal  cut  normal  to  the 
vertical  (optic)  axis  appears  dark  in  parallel  polarized  light  for  every  position  between 
crossed  nicols.  If,  however,  a  similar  section  of  quartz,  say  1  mm.  in  thickness,  be  examined 
under  these  conditions,  it  appears  dark  in  monochromatic  light  only,  and  that  not  until 
the  analyzer  has  been  rotated  so  that  its  vibration-plane  makes  for  sodium  light  an  angle 
of  24°  with  that  of  the  polarizer.  In  other  words,  this  quartz  section  has  rotated  the  plane 
of  vibration  some  24°,  and  here  either  to  the  right  or  to  the  left,  looking  in  the  direction  of 
the  light.  The  amount  of  this  rotation  increases  with  the  thickness  of  the  section,  and,  as 
the  wave-length  of  the  light  diminishes  (for  red  this  angle  of  rotation  for  a  section  of  1  mm. 
is  about  19°,  for  blue  32°).  The  direction  of  the  rotation  is  to  the  right  or  left,  as  denned 
above  —  according  as  the  crystal  is  crystallographically  right-handed  or  left-handed  (p.  113). 

If  the  same  section  of  quartz  (cut  perpendicular  to  the  axis)  be  viewed  between  crossed 
nicols  in  converging  polarized  light,  it  is  found  that  the  interference-figure  differs  from  that 
of  an  ordinary  uniaxial  crystal.  The  central  portion  of  the  black  cross  has  disappeared, 
and  instead  the  space  within  the  inner  ring  is  brilliantly  colored.*  Furthermore,  when  the 
analyzing  nicol  is  revolved,  this  color  changes  from  blue  to  yellow  to  red,  and  it  is  found 
that  in  some  cases  this  change  is  produced  by  revolving  the  nicol  to  the  right,  and  in  other 
cases  to  the  left;  the  first  is  true  with  right-handed  crystals,  and  the  second  with  left-handed. 
If  sections  of  a  right-handed  and  left-handed  crystal  are  placed  together  in  the  polariscope, 
the  center  of  the  interference-figure  is  occupied  with  a  four-rayed  spiral  curve,  called,  from 
the  discoverer,  Airy's  spiral.  Twins  of  quartz  crystals  are  not  uncommon,  consisting  of 
the  combination  of  right-  and  left-handed  individuals  (according  to  the  Brazil  law)  which 
show  these  spirals  of  Airy.  With  cinnabar  similar  phenomena  are  observed.  Twins  of 
this  species  also  not  infrequently  show  Airy's  spirals  in  the  polariscope. 

395.  Summary  of  the  Optical  Characters  of  Uniaxial  Crystals.  —  All 

sections  of  uniaxial  crystals  show  double  refraction  except  those  that  are  cut 
parallel  to  the  basal  plane.  All  doubly  refracting  sections  show  parallel  ex- 
tinction. When  viewed  in  convergent  polarized  light  with  crossed  nicols  all 
sections  show  a  characteristic  uniaxial  interference  figure  except  those  that 
lie  in  the  prism  zone  of  the  crystal  or  that  are  only  slightly  inclined  to  that 
zone.  All  doubly  refracting  sections  have  two  refractive  indices  correspond- 
ing to  the  two  extinction  directions :  one  of  these  is  always  co  and  the  other  has 
a  value  (c')  ranging  from  co  to  e,  dependent  on  the  inclination  of  the  section  to 
the  optic  axis.  Dark  colored  minerals  may  show  dichroism.  Tetragonal 
and  hexagonal  substances  cannot  be  distinguished  from  each  other  by  optical 
tests.  They  may  be  at  times  told  apart  by  characteristic  cross  sections  of 
their  crystals. 

C.   BIAXIAL  CRYSTALS 

General  Optical  Relations 

The  crystals  of  the  remaining  systems,  i.e.,  the  orthorhombic,  monoclinic, 
and  triclinic  belong  optically  to  what  is  known  as  the  Biaxial  Group. 

396.  The  Behavior  of  Light  in  Biaxial  Crystals.  —  In  biaxial  crystals 
there  are  three  especially  important  directions  at  right  angles  to  each  other 
which  are  designated  as  X,  Y,  and  Z  (also  a,  fo,  and  c).     These  three  direc- 
tions are  sometimes  spoken  of  as  axes  of  elasticity  in  reference  to  certain 
assumed  differences  in  the  ether  along  them.     The  nature  of  these  three  direc- 
tions is  as  follows.     Light  which  results  from  vibrations  parallel  to  X  (axis  of 
greatest  elasticity)  is  propagated  with  the  maximum  velocity;  that  from  vibra- 

*  Very  thin  sections  of  quartz,  however,  show  (e.g.,  with  the  microscope)  the  dark  cross 
of  an  ordinary  uniaxial  crystal. 


CHARACTERS   DEPENDING   UPON   LIGHT 


271 


572 


tions  parallel  to  Z  (axis  of  least  elasticity)  with  minimum  velocity;  and  that 
from-  vibrations  parallel  to  Y  with  an  intermediate  velocity.  It  is  to  be 
emphasized  that  these  directions,  X,  Y,  and  Z  refer  to  directions  of  vibration 
and  not  to  directions  of  propagation.  Corresponding  to  the  maximum  inter- 
mediate and  minimum  light  velocities  are  three  principle  indices  of  refraction 
designated  respectively  as  a,  ft  and  y.  Of  these  a,  belonging  to  light  with  the 
maximum  velocity,  will  have  the  least  value  and  7  belonging  to  light  with  the 
minimum  velocity,  will  have  the  greatest  value.  The  value  of  B  will  be  inter- 
mediate between  the  other 
two,  sometimes  being 
nearer  to  a  and  at  other 
times  being  nearer  to  7;  it 
is  not  the  arithmetical 
mean  between  them.  The 
various  methods  of  deter- 
mining the  values  of  these 
three  principal  indices  of 
refraction  will  be  consid- 
ered in  a  later  article. 

In  studying  the  prop- 
agation of  light  within  a 
biaxial  crystal  let  it  be 
assumed  that  Fig.  572 
represents  a  rectangular 
parallelopiped  in  which 
the  front  to  back  axis  is 
the  direction  X,  the  left  to 
right  axis  is  Y,  and  the 
vertical  axis  is  Z.  In 
connection  with  the  figure  and  those  which  follow  it  is  helpful  to 
make  use  of  a  model  (a  pasteboard  box  would  answer)  orientated  so  that  its 
longer  edge  runs  from  front  to  back,  its  mean  edge  from  left  to  right  and  its 
shortest  edge  vertical,  corresponding  to  the  X,  Y,  and  Z  directions  of  the  figure. 
In  the  development  of  the  figures  that  follow  it  has  been  assumed  that  the 
three  principle  indices  of  refraction  are  a  =  1.5,  (3  =  1.6,  7  =  2.5,  a  difference 
between  a  and  7  far  exceeding  anything  observed  in  actual  crystals.  In 
general,  this  difference  does  not  exceed  0.1;  hence  it  is  necessary  to  greatly 
exaggerate  the  actual  values  in  order  that  the  phenomena  may  be  distinctly 
shown  by  diagrams  drawn  on  a  small  scale. 

In  the  discussion  that  follows  it  will  be  assumed  that  light  originates  at  the 
center  of  a  crystal,  0,  Fig.  572,  and  the  endeavor  will  be  made  to  determine 
the  character  of  the  rays  which  radiate  from  0  in  all  directions.  The  simplest 
directions,  and  the  ones  which  in  reality  are  the  most  important,  are  those 
that  lie  in  the  axial  planes  of  the  figure,  XOY,  YOZ,  and  XOZ.  These  will 
be  considered  first. 

Consider  the  plane  of  the  X  and  Y  directions,  Fig.  572.  Light  will  radiate 
from  0  toward  X  and  Y  and  in  all  intermediate  directions  with  vibrations 
parallel  to  Z  and  hence  traveling  with  a  uniform  and  at  the  same  time  mini- 
mum velocity,  1/7.  The  distance  such  light  will  travel  in  a  given  moment  of 
time  may  be  plotted  by  drawing  a  circle  about  0  with  the  radius,  1/7,  Fig. 
573.  In  the  direction  OX  there  must  also  travel  a  second  polarized  ray  result- 


272 


PHYSICAL   MINERALOGY 


573 


ing  from  vibrations  parallel  to  OF,  hence  traveling  with  mean  velocity  1/0. 

Likewise  in  the  direction  OF  there  will  be  a  ray  resulting  from  vibrations 

parallel  to  OX,  hence  travel- 
ing with  the  maximum 
velocity,  I/a.  In  all  direc- 
tions intermediate  between 
X  and  F  the  light  velocities 
will  be  proportional  to  the 
radii  of  an  ellipse  having 
1/0  and  I/ a  respectively  as 
its  semi-minor  and  semi-major 
diameters,  Fig.  573.  In  the 
plane  of  the  X  and  F 
directions,  therefore,  in  a 
given  moment  of  time  light 
will  radiate  from  the  center 
as  ordinary  and  extraordinary 
rays,  the  wave  fronts  being 
represented  by  a  circle  within 
an  ellipse. 

Consider  next  the  plane  of 
the  F  and  Z  directions,  Fig. 
572.  Light  will  radiate 

from   0  toward    F   and  Z    and   in    all    intermediate    directions    resulting 

from  vibrations  parallel  to  OX.     It  will  therefore  travel  with  uniform  and  the 

maximum  velocity,  I/a.    The 

distance  traveled  in  a  given 

moment    of    time    may    be 

plotted  by  drawing  a  circle 

about    0   with    the     radius 

I/a,     Fig.     574.       Likewise 

there    will    travel     in     the 

direction   OF  a  second  ray 

resulting     from     vibrations 

parallel    to  OZ,  hence   mov- 
ing    with      the      minimum 

velocity,    l/y.      Also  in  the 

direction  OZ  there  will  be  a 

ray  resulting  from  vibrations 

parallel    to     OF    with     the 

velocity    1/0.     In  directions 

intermediate  between  F  and 

Z  the  light  velocities  will  be 

proportional  to  the  radii  of 

an   ellipse    having    l/y    and 

1/0  respectively  as  its  semi- 
minor  and    semi-major 

diameters,     Fig.     574.       In 

the  plane  of  the  F  and  Z  directions,  therefore,  in  a  given  moment  of  time,  light 

will  radiate  from  the  center  as  ordinary  and  extraordinary  rays,  the  wave 

fronts  being  represented  by  an  ellipse  within  a  circle. 


CHARACTERS    DEPENDING   UPON   LIGHT 


273 


The  last  and  most  important  plane  to  be  considered  is  that  of  the  X  and  Z 
directions,  Fig.  572.  Light  will  radiate  from  0  toward  X  and  Z  and  all  in- 
termediate directions  with  vibrations  parallel  to  OF,  hence  traveling  with  a 
uniform  and  intermediate  veloc- 
ity, 1/jS.  The  distance  traveled 
in  a  given  moment  of  time  is 
represented  in  Fig.  575  by  the 
circle  with  the  radius  1/0. 
There  will  likewise  travel  in  the 
direction  OZ  a  ray  resulting 
from  vibrations  parallel  to  OX, 
hence  moving  with  the  max- 
imum velocity,  I/a.  Also  a 
ray  will  travel  in  the  direction 
OX  with  vibrations  parallel  to 
OZ,  hence  having  the  minimum 
velocity,  l/y.  In  intermediate 
positions  the  light  velocity  will 
be  proportional  to  the  radii  of 
an  ellipse  with  I/a  and  l/y 
respectively  as  its  semi-major 
and  semi-minor  diameters,  Fig. 
575.  In  the  plane  of  the  X  and 
Z  directions,  therefore,  in  a  given 
moment  of  time,  light  will 
radiate  from  the  center  as  or- 
dinary and  extraordinary  rays, 
the  wave  fronts  represented,  by  a  circle  intersecting  an  ellipse.  It  is  to  be 
noted  that  in  this  last  plane  there  are  four  points  where  the  two  wave 

fronts  coincide.  In  other 
words,  light  traveling  along 
the  radial  lines  connecting 
these  points  will  be  moving 
with  uniform  velocity  and 
consequently  along  these 
directions  there  will  be  no 
double  refraction.  These 
directions  are  known  as  the 
optic  axes  of  the  crystal 
and  since  there  are  two  of 
them  the  optical  group  is 
spoken  of  as  biaxial.  The 
character  of  these  optic 
axes  will  be  more  fully 
developed  in  a  later  article. 
In  the  above  paragraphs 
the  wave  fronts  for  light 
moving  in  the  three  prin- 
cipal optical  planes  of  the 
crystal  have  been  discussed.  Fig.  576  represents  the  wave  fronts  in  these 
three  planes  as  they  appear  when  bounding  one  octant.  The  complete  wave 


Ellipse 


274 


PHYSICAL   MINERALOGY 


surfaces  for  light  propagated  in  all   directions   consist  of   warped  figures 

which  conform  to  the  circular  or  elliptical  wave  fronts  already  described  in 

the  three  principal  planes  and  have  intermediate  positions  elsewhere.     The 

only  satisfactory  way  to  represent  these  complete  surfaces  is  by  means  of 

a  model. 

397.   Biaxial  Indicatrix.  —  It  is  found  further  that  the  optical  structure 

of  a  biaxial  crystal  can  be  represented  by  an  ellipsoid,  .known  as  the  indicatrix, 
having  as  its  axes  three  lines  which  are  at  right 
angles  to  each  other  and  proportional  in  length  to 
the  indices  a,  /3,  7.  This  is  analogous  to  the  similar 
figure  for  uniaxial  crystals  described  in  Art.  382. 

This  ellipsoid,  whose  axes  represent  in  magnitude 
the  three  principal  refractive  indices,  a  /3,  7  (where 
a  <  |8  <  7),  (see  Fig.  577),  not  only  exhibits 
the  character  of  the  optical  symmetry,  but  from  it 
may  be  derived  the  direction,  velocity  and  plane  of 
vibration  of  any  light  ray  traversing  the  crystal. 

In  general  it  may  be  stated  that  the  character  of 
the  two  light  rays  which  result  from  a  single  incident, 
ray  may  be  derived  from  a  study  of  that  elliptical 
section  of  the  indicatrix  which  is  normal  to  the 
incident  ray.  If  this  section  happens  to  be  one  of 
the  three  principal  sections  of  the  indicatrix,  A  BAB, 
ACAC,  or  BCBC,  Fig.  577,  its  major,  and 
minor  diameters  give  the  directions  of  vibration 
and  their  semi-lengths  the  indices  of  refrac- 
tion of  the  two  rays.  If  the  incident  ray  has  some 
direction  different  from  the  directions  of  the 

three  axes  of  the  indicatrix  ellipsoid  the  derivation  of  the  character  of  the 

two  refracted  rays  is  not  as  simple.     Let  Fig.  578  represent  such  an  elliptical 

section  normal  to  the  inclined  ray  L-L.     In  this  case  the  major  and  minor 

diameters  R-O-R  and  r-0-r  of  the 

elliptical  section  lie  in  the  vibration  „    L 

planes  of  the  two   rays  but   the 

directions     of    vibration    of    the 

latter  will  be  somewhat  inclined 

to  the  elliptical  section.      These 

directions    of    vibration   may   be 

obtained  by  erecting  normals  to 

the   surface  of   the  indicatrix  at 

the   points    R    and  r  where  the 

major  and  minor  diameters  of  the 

elliptical  section  meet  that  surf  ace. 

These  normals  RN  and  rn,  when 

extended  to  the  line  of  the  incident 

ray  L-L,  yield  the  directions  of 

vibration  and  the  refractive  indices  of  the  two  refracted  rays.      Their  direc- 
tions of  transmission  (the  lines  OS  and  OT)  will  be  perpendicular  to  these 

normals  and  since  neither  of  the  latter  lie  in  the  elliptical  section  both  rays 

will  be  refracted  and  behave  as  extraordinary  rays. 

There  are  two  special  sections  of  the  indicatrix  that  require  notice.     The 


Biaxial  Indicatrix 


CHARACTERS   DEPENDING   UPON   LIGHT 


275 


line  B-O-B  (Fig.  577)  is  longer  than  the  line  A-O-A  but  shorter  than  the  line 
C-O-C.  Obviously,  in  some  position  intermediate  between  A-O-A  and 
C-O-C  there  will  be  a  diameter  of  the  ellipse  AC  AC  which  will  be  equal  in 
length  to  B-O-B.  There  are  two  such  lines,  as  S-O-S  and  S'-O-S'  in  Fig. 
577.  The  major  and  minor  diameters  of  these  sections  of  the  indicatrix, 
BSBS  and  BS'BS',  are  equal  and  the  sections  therefore  become  circles.  Con- 
sequently light  passing  through  a  section  of  a  crystal  cut  parallel  to  either  of 
these  circular  sections  of  its  indicatrix  will  have  a  uniform  velocity  and  may 
vibrate  in  any  transverse  direction.  In  other  words,  there  will  be  no  double 
refraction  along  the  lines  normal  to  these  two  sections.  These  lines  consti- 
tute what  are  known  as  the  primary  optic  axes  of  the  crystal;  see  further  in 
Art.  398. 

The  major  and  minor  diameters  of  any  section  of  the  indicatrix  yield  the 
traces  upon  that  section  of  the  planes  of  vibrations  of  the  two  rays  into  which 
the  ray  normal  to  the  section  is  refracted.  In  other  words,  the  major  and  minor 
diameters  of  the  elliptical  section  of  the  indicatrix  give  the  directions  of  extinc- 
tion of  a  crystal  section  having  this  optical  orientation.  Further,  these 
extinction  directions  bisect  the  angles  made  by  the  traces  upon  the  section  of 
two  planes,  each  of  which  includes  the  pole  of  the  section  and  one  of  the  two 
optic  axes.  This  may  be  demonstrated  by  aid  of  Fig.  579  which  represents 
a  general  elliptical  section  of  an  indicatrix.  A- A  and  B-B  are  the  major  and 
minor  diameters  of  the  ellipse  and  so  represent  the  extinction  directions  of  the 
mineral  section.  C-C  and  C'-C'  represent  the  intersections  of  the  two  circu- 
lar sections  of  the  indicatrix  with  this  elliptical  section.  As  these  lines  are 
diameters  of  equal  circles  they  must  be  equal  in  length  and  it  therefore  follows 
from  the  geometrical  nature  of  an  ellipse  that  the  angles  AOC  and  AOC'  are 
equal.  Let  the  line  P-P  represent  the  intersection  with  this  elliptical  section 
of  a  plane  in  which  lie  the  normal  to  the  section  and  one  of  the  optic  axes. 
Since  this  plane  includes  an  optic  axis  it  must 
be  perpendicular  to  the  circular  section  of 
the  indicatrix  of  which  the  line  C'-C'  is  a 
diameter.  Also  since  this  plane  includes  the 
normal  to  the  elliptical  section  under  consid- 
eration it  must  be  at  right  angles  to  the 
latter  plane.  Under  these  conditions  it  is 
obvious  that  the  lines  P-P  and  C'-C'  in  Fig. 
579  must  be  at  right  angles  to  each  other. 
In  the  same  way  it  can  be  proved  that  the 
lines  P'-P'  and  C-C  are  also  at  right  angles 
to  each  other.  Since  the  angles  AOC  and 
AOC'  are  equal  and  the  angles  POC'  and 
P'OC  are  also  equal  it  follows  that  the  angles 
A  OP*  and  A  OP'  are  likewise  equal.  In  other 
words  the  lines  A-A  and  B-B  representing 
the  directions  of  extinction  of  the  section 
bisect  the  angles  made  by  the  traces  upon 
the  section  of  the  two  planes  which 
respectively  pass  through  each  optic  axis  and 
the  normal  to  the  section.  This  fact  will  be 
made  use  of  later,  see  Art.  407,  in  explaining  the  characters  of  the  biaxial 
interference  figure. 


579 


276 


PHYSICAL  MINERALOGY 


580 


Primary  and  Secondary  Optic  Axes.  —  It  has  already  been  stated 
(Art.  397)  that  there  are  two  directions,  namely,  those  normal  to  the  circular 

cross  sections  of  the  indicatrix  (SS,  S'S', 
Fig.  577)  in  which  all  light  is  propagated 
with  uniform  velocity.  Hence  in  these 
directions  there  can  be  no  double  refraction 
within  a  crystal;  nor  is  there  when  the  ray 
emerges.  These  two  directions  bear  so  close 
an  analogy  to  the  optic  axes  of  a  uniaxial 
crystal  that  they  are  also  called  optic  axes, 
and  the  crystals  here  considered  are  hence 
named  biaxial.  In  Fig.  575,  which  represents 
a  cross  section  of  the  wave-surfaces  in  the 
plane  of  the  X  and  Z  directions,  these  optic 
axes  have  the  direction  SS,  S'S'  normal  to 
the  tangent  planes  tt,  t't',  and  the  direction 
of  the  external  wave  is  given  by  the  normal 
Str  (Fig.  580). 

Properly  speaking  the  directions  mentioned 
are  those  of  the  primary  optic  axes,  for  there 
are  also  two  other  somewhat  analogous  directions,  PP,  P'P',  of  Fig.  575, 
called  for  sake  of  distinction  the  secondary  optic  axes.  The  properties  of  the 
latter  directions  are  obvious  from  the  following  considerations. 

In  the  section  of  the  wave-surface  shown  in  Fig.  575  (also  enlarged,  in  Fig. 
580),  corresponding  to  the  axial  plane  XZ,  it  is  seen  that  the  circle  with  radius 

-  intersects  the  ellipse  whose  major  and  minor  axes  are  -  and  -  in  the  four 

points  P,  P,  Pf,  P'.  Corresponding  to  these  directions  the  velocity  of  propa- 
gation is  obviously  the  same*  for  both  rays.  Hence  within  the  crystal  these 
rays  travel  together  without  double  refraction.  Since,  however,  there  is 
no  common  wave-front  for  these  two  rays  (for  the  tangent  for  one  ray  is  repre- 
sented by  mm  and  for  the  other  by  nn,  Fig.  580)  they  do  suffer  double  refrac- 
tion on  emerging;  in  fact,  two  external  light-waves  are  formed  whose  directions 
are  given  by  the  normals  Pju  and  Pv.  These  directions,  PP,  P'P',  therefore, 
have  a  relatively  minor  interest,  and  whenever,  in  the  pages  following,  optic 
axes  are  spoken  of,  they  are  always  the  primary  optic  axes,  that  is,  those  having 
the  directions  SS,  S'S'  (Fig.  575),  or  OS,  Fig.  580.  In  practice,  however,  as 
remarked  in  the  next  article,  the  angular  variation  between  the  two  sets  of 
axes  is  usually  very  small,  perhaps  1°  or  less. 

399.  Interior  and  Exterior  Conical  Refraction.  —  The  tangent  plane  to  the  wave-surface 
drawn  normal  to  the  line  OS  through  the  point  S  (Fig.  580)  may  be  shown  to  meet  it  in  a 
small  circle  on  whose  circumference  lie  the  points  S  and  T.  This  circle  is  the  base  .of  the 
interior  cone  of  rays  SOT,  whose  remarkable  properties  will  be  briefly  hinted  at.  If  a 
section  of  a  biaxial  crystal  be  cut  with  its  faces  normal  to  OS,  those  parallel  rays  belonging 
to  a  cylinder  having  this  circle  as  its  base,  incident  upon  it  from  without,  will  be  propagated 
within  as  the  cone  SOT.  Conversely,  rays  from  within  corresponding  in  position  to  the 
surface  of  this  cone  will  emerge  parallel  and  form  a  circular  cylinder.  This  phenomenon 
is  called  interior  conical  refraction. 

On  the  other  hand,  if  a  section  be  cut  with  its  faces  normal  to  OP,  those  rays  having 
the  direction  of  the  surface  of  a  cone  formed  by  perpendiculars  to  mm  and  nn  will  be  propa- 
gated within  parallel  to  OP,  and  emerging  on  the  other  surface  form  without  a  similar  cone 
on  the  other  side.  This  phenomenon  is  called  exterior  conical  refraction. 

In  the  various  figures  given  (573-580)  the  relations  are  much  exaggerated  for  the  sake 


CHARACTERS   DEPENDING   UPON   LIGHT  277 

of  clearness;    in  practice  the  relatively  small  difference  between  the  indices  of  refraction 
a  and  7  makes  this  cone  of  small  angular  size,  rarely  over  2°. 

400.  Optic  Axial  Angle.  Bisectrices.  Positive  and  Negative  Biaxial 
Crystals.  —  The  optic  axes  always  lie  in  the  plane  of  the  X  and  Z  optical 
directions;  this  plane  is  called  the  optic  axial  plane  (or,  briefly,  ax.  pi.).  It  is 
obvious  from  a  consideration  of  the  indicatrix  ellipsoid  that  the  position  of 
its  circular  sections  and  consequently  of  the  optic  axes  normal  to  them,  will 
vary  with  a  variation  in  the  relative  values  of  the  indices  of  refraction.  As 
already  stated  the  index  0  is  not  an  arithmetical  mean  between  a  and  7  but 
may  at  times  be  nearer  to  a  than  to  7  or  the  reverse.  As  these  relations 
change,  the  shape  of  the  indicatrix  and  the  position  of  its  circular  sections  and 
the  angle  between  the  optic  axes  will  also  change.  The  mathematical  relations 
between  the  optic  axial  angle  and  the  principle  refractive  indices  are  given  in 
the  next  article.  From  the  above  it  is  obvious  that  for  certain  relative  values 
of  the  refractive  indices,  the  optic  angle  must  be  90°.*  Such  a  case,  however, 
is  rarely  observed  and  when  it  occurs  it  is  true  for  light  of  a  certain  color  f 
(wave-length)  only  and  not  for  others. 

The  X  and  Z  optical  directions  bisect  the  angles  between  the  optic  axes 
and  are  therefore  known  as  bisectrices.  The  one  that  bisects  the  acute  axial 
angle  is  called  the  acute  bisectrix  (or  Bxa)  while  the  one  bisecting  the  obtuse 
angle  is  the  obtuse  bisectrix  (or  Bx0) .  If  the  word  bisectrix  is  used  alone  with- 
out special  qualification  it  is  always  to  be  understood  as  referring  to  the  acute 
bisectrix. 

Either  X  or  Z  may  be  the  acute  bisectrix.  If  X  is  the  acute  bisectrix  the 
substance  is  said  to  be  optically  negative,  while  if  Z  is  the  acute  bisectrix  it  is 
optically  positive. 

Roughly  expressed,  the  optic  axes  will  lie  nearer  to  Z  than  to  X  —  that  is, 
Z  will  be  the  bisectrix  —  when  the  value  of  the  intermediate  index,  /3,  is  nearer 
to  that  of  a  than  to  that  of  7.  It  is  obvious  (cf .  Fig.  575)  that  in  this  case,  as 
the  angle  diminishes  and  becomes  nearly  equal  to  zero,  the  form  of  the  ellip- 
soid then  approaches  that  of  the  prolate  spheroid  of  the  positive  uniaxial 
crystal  as  its  limit  (Fig.  557,  p.  256) ;  this  shows  the  appropriateness  of  the 
+  sign  here  used. 

On  the  other  hand,  the  optic  axes  will  lie  nearer  to  X  than  to  Z  —  that  is, 
X  will  be  the  bisectrix  —  if  the  value  of  the  mean  index  0  is  nearer  to  that  of 
7  than  to  that  of  a.  Such  a  crystal,  for  which  Bxa  =  X,  is  called  optically 
negative.  In  this  case  the  smaller  the  angle  the  more  the  ellipsoid  approaches 
the  oblate  spheroid  of  the  negative  uniaxial  crystal  (Fig.  556,  p.  256). 

The  following  are  a  few  examples  of  positive  and  negative  biaxial  crystals: 

Positive  (+).  Negative  (-). 

Sulphur.  Aragonite. 

Enstatite.  Hypersthene. 

Topaz.  Muscovite. 

Barite.  Orthoclase. 

Chrysolite.  Epidpte. 

Albite.  Axinite. 

*  The  axial  angle  will  equal  90°  when  the  indices  satisfy  the  following  equation: 

1 _! -  I     1 

a2       j82        ft2       72' 
t  For  danburite  axial  angle  =  89°  14'  for  green  (thallium)  and  90°  14'  for  blue  (CuSO4). 


278 


PHYSICAL  MINERALOGY 


401.  Relation  of  the  Axial  Angle  to  the  Refractive  Indices.  —  If  in  a 
given  case  the  values  of  a,  0,  and  7  are  known,  the  value  of  the  interior  optic 
axial  angle  known  as  2V;  see  also  Art.  408,  can  be  calculated  from  them  by 
the  following  formulas: 

11  11 


cos2F 


P        72 


a2       72 


or    tan2  V  = 


681 


Examination  of  Biaxial  Crystals  in  Polarized  Light 

402.  Sections  in  Parallel  Polarized  Light  with  Crossed  Nicols. 

Interference  Colors.  Thin  sections  of  biaxial  crystals  when  examined  between 
crossed  nicols  in  general  show  some  interference  color.  This  color  will  depend 
upon  the  following  factors :  the  thickness  of  the  section,  —  the  thicker  the  sec- 
tion the  higher  the  order  of  color;  the  birefringence  of  the  substance,  —  the  higher 
the  birefringence  (i.e.,  the  greater  the  difference  between  the  values  of  a  and 
7)  the  higher  the  order  of  color;  the  optical  orientation  of  the  section,  —  in  gen- 
eral, the  nearer  the  section  comes  to  being  parallel  to  the  optic  axial  plane, 
in  which  he  the  vibration  directions  of  the  fastest  and  slowest  rays,  the  higher 
will  be  its  birefringence  and  the  order  of  its  interference  color. 

Extinction  Directions.  A  section  which,  in  general,  is  colored  will  show  dur- 
ing a  complete  revolution  on  the  microscope  stage  four  positions  at  90°  inter- 
vals in  which  it  appears  dark.  These  are  the  positions  of  extinction,  or  are 
those  positions  in  which  the  vibration  planes  of  the  section  coincide  with  those 
of  the  nicols.  When  the  directions  of  extinction  of  a  section  are  parallel  or 
at  right  angles  to  a  crystallographic  axis  or  to  the  trace,  upon  the  section,  of 
a  crystallographic  axial  plane  it  is  said  to  show  parallel  extinction.  If  the 

extinction  directions  are  not  parallel  to  these 
crystallographic  directions  the  extinction  is 
said  to  be  inclined. 

For  example,  in  Fig.  581,  let  the  two  larger 
rectangular  arrows  represent  the  vibration 
.,6'  directions  for  the  two  nicols,  and  between 
which  suppose  a  section  of  a  biaxial  crystal, 
— ^-P  abed,  to  be  placed  so  that  one  edge  of  a  known 
crystallographic  plane  coincides  with  the  direc- 
tion of  one  of  these  lines.  The  vibration 
directions  of  the  section  are  indicated  by  the 
dotted  arrows  and  as  in  this  position  of  the 
section  these  directions  do  not  coincide  with  the 
vibration  directions  of  the  nicols  the  section  will 
appear  light.  The  section  will  have  to  be  turned  to  the  position  a'b'c'd' 
in  order  to  achieve  this  coincidence  and  so  bring  about  extinction.  The 
angle  (indicated  in  the  figure)  which  it  has  been  necessary  to  revolve  the 
plate  to  obtain  the  effect  described,  is  the  angle  which  one  of  the  vibration 
directions  in  the  given  plate  makes  with  the  given  crystallographic  edge  ad', 
it  is  called  the  extinction  angle. 

403.  Measurement  of  the  Extinction  Angle.  —  It  frequently  becomes 
important  to  measure  as  accurately  as  possible  the  extinction  angle  of  a  sec- 


CHARACTERS   DEPENDING   UPON   LIGHT  270 

tion.  This  is  most  commonly  done  with  a  microscope  which  is  provided  with 
a  revolving  stage  having  a  graduated  circle  for  measuring  angles  of  rotation. 
In  order  to  measure  an  extinction  angle  it  is  of  course  necessary  to  be  able  to 
locate  in  the  section  some  definite  crystallographic  direction.  This  is  usually 
provided  by  some  crystal  outline  or  cleavage  crack.  This  crystallography 
direction  is  brought  parallel  to  one  of  the  cross-hairs  of  the  microscope  and 
the  angular  position  of  the  microscope  stage  noted.  Then  the  stage  is  rotated 
until  the  section  shows  its  maximum  darkness.  The  angle  between  these  two 
positions  is  the  angle  of  extinction  desired.  The  difficulty  in  the  measure- 
ment lies  in  the  accurate  determination  of  the  position  of  maximum  extinction. 
Frequently  it  is  possible  to  rotate  the  microscope  stage  through  an  arc  of  one 
to  two  degrees  without  any  appreciable  brightening  of  the  field.  It  will  help 
in  determining  the  point  of  maximum  extinction  if  the  plate  is  turned  beyond 
the  point  of  extinction  until  the  first  faint  illumination  is  observed  and  then 
back  in  the  other  direction  until  the  same  strength  of  illumination  occurs. 
The  point  half  way  between  these  two  positions  should  be  very  close  to  the 
point  desired.  The  measurements  should  be  repeated  a  number  of  times  and 
the  average  taken.  It  is  also  advisable  to  make  the  measurements  on  both 
sides  of  the  position  of  the  crystallographic  direction.  The  illumination  in 
most  cases  had  better  be  in  the  monochromatic  sodium-light. 

Various  devices  are  used  at  times  in  order  to  increase  the  accuracy  with 
which  the  position  of  maximum  extinction  can  be  determined.*  The  sensi- 
tive tint  is  sometimes  used  for  this  purpose.  If  this  is  inserted  in  the  diagonal 
slot  of  the  microscope  tube  below  the  analyzer  the  field  will  be  uniformly 
colored  red  of  the  first  order  when  the  section  on  the  microscope  stage  is  at 
the  position  of  extinction.  But  if  the  section  is  turned,  even  very  slightly, 
from  this  position  it  will  also  affect  the  light  and  change  the  interference 
color  observed.  The  sensitive  tint  in  specially  favorable  cases  can  be  used 
in  this  way  to  advantage  but  it  has  been  shown  that  in  the  majority  of  cases 
its  use  does  not  materially  increase  the  accuracy  of  the  measurements. 

The  power  of  quartz  plates  cut  normal  to  the  vertical  crystallographic 
axis  to  rotate  the  plane  of  polarization  of  light  (see  Art.  394)  is  used  in  other 
devices  to  increase  the  accuracy  of  the  measurement  of  the  angle  of  extinction. 
The  Bertrand  ocular  contains  four  such  sectors  of  quartz;  two  of  these  placed 
diagonally  opposite  to  each  other  are  from  a  right-handed  quartz  crystal  while 
the  other  two  are  from  a  left-handed  crystal.     This  ocular  is  inserted  in  the 
microscope  tube  in  place  of  the  regular  ocular;  the  analyzer  is  pushed  out  of 
the  microscope  tube  and  a  nicol  prism  mounted  in  an  appropriate  holder  is 
placed  over  the  ocular.     If  this  upper  nicol  is  turned 
about  in  various  positions  it  will  be  noted  that,  in  general, 
opposite  quadrants  of  the  field  are  colored  alike  but  differ 
in  color  from  the  adjacent  quadrants,  see  Fig.  582.      But 
when  the  plane  of  the  cap  nicol  is  exactly  at  right  angles 
to  the  plane  of  the  polarizer  below  all  four  quadrants 
show  the  same  color.       If  a  double  refracting  mineral 
be  placed  on  the  stage  of  the  microscope  with  its  vibration 
Bertrand~Ocular      directions   parallel  to   those  of   the  nicols,  since  in  this 
position  it  has  no  birefringent  effect  upon  the  light,  the 
field  will  still  remain  uniformly  colored.     But  if  the  section  is  turned  from  its 

*  Detailed  descriptions  of  these  various  devices  with  comment  on  their  accuracy  are 
given  by  F.  E.  Wright  in  The  Methods  of  Petrographic-Microscopic  Research. 


280  PHYSICAL  MINERALOGY 

position  of  extinction  its  birefringent  effect  is  added  to  that  of  the  two 
opposite  quadrants  of  the  ocular  and  subtracted  from  that  of  the  remaining 
two.  Consequently  adjacent  quadrants  become  differently  colored.  A  very 
slight  rotation  of  the  section  is  sufficient  to  produce  an  appreciable  effect. 

Another  microscope  accessory  using  the  same  principle  as  the  Bertrand 
ocular  is  the  so-called  bi-quartz  wedge  plate  described  by  Wright.  This  con- 
sists of  two  adjacent  plates  of  quartz  cut  normal  to  the  c  crystal  axis,  one  from 
a  left-handed  and  the  other  from  a  right-handed  crystal.  Above  these  are 
placed  two  wedges  of  quartz,  a  right-handed  wedge  above  the  left-handed 
plate,  etc.  At  the  point  where  the  wedge  is  equal  in  thickness  to  the  plate 
beneath  there  will  be  zero  rotation  of  the  light  and  between  crossed  nicols  this 
will  produce  a  dark  line  across  the  field.  As  the  distance  increases  from  this 
point  the  amount  of  rotation  of  the  light  increases  equally  but  in  opposite 
directions  on  either  side  of  the  central  dividing  line  of  the  plate.  Both  halves 
of  the  plate  will  be  equally  illuminated  if  the  mineral  section  is  in  the  position 
of  extinction,  but  if  the  latter  is  turned  so  that  it  adds  or  subtracts  its  bire- 
fringent effect  to  that  of  the  quartz  plate  the  two  halves  become  differently 
illuminated.  By  moving  the  plate  in  or  out  a  position  can  be  found  where 
this  change  in  illumination  is  most  marked.  This  quartz  plate  is  used  with 
a  special  ocular  provided  with  a  slot  in  such  a  position  that  the  quartz  plate 
may  be  introduced  into  the  microscope  tube  at  the  focal  plane  of  the  ocular 
and  with  the  medial  line  of  the  plate  parallel  to  the  plane  of  vibration  of  the 
polarizer.  A  cap  nicol  is  used  above  the  ocular. 

404.  Determination  of  the  Birefringence  with  the  Microscope.  —  The 
value  of  the  maximum  birefringence  (7  —  a)  is  obviously  given  at  once  when 
the  refractive  indices  are  known.     It  can  be  approximately  estimated  for  a 
section  of  proper  orientation  and  of  measured  thickness  by  noting  the  inter- 
ference-color as  described  in  Art.  347. 

405.  Determination  of  the  Relative  Refractive  Power.  —  The  relative 
refractive  power  of  the  two  vibration-directions  in  a  thin  section  is  readily 
determined  with  the  microscope  (in  parallel  polarized  light)  by  the  method  of 
compensation.     This  Is  applicable  to  any  section,  whatever  its  orientation  and 
whether  uniaxial  or  biaxial.     The  methods  employed  have  already  been 
described  in  Art  348. 

A  crystal-section  is  said  to  have  positive  elongation  if  its  direction  of  exten- 
sion approximately  coincides  with  the  ether-axis  Z;  if  with  X  the  elongation 
is  negative.  The  same  terms  are  also  used,  in  general,  according  to  the  relative 
refractive  power  of  the  two  directions. 

406.  Determination  of  the  Indices  of  Refraction  of  a  Biaxial  Mineral. 
—  The  indices  of  refraction  of  a  biaxial  mineral  are  determined  by  the  same 
methods  as  outlined  previously,  see  Art.  327,  the  only  modification  introduced 
being  necessitated  by  the  fact  that  three  principal  indices,  a,  ft  and  7,  are  to 
be  determined. 

Measurement  of  the  Angles  of  Refraction  by  Means  of  Prisms.  Two  or 
three  prisms  must  be  used  to  determine  the  three  indices.  If  three  prisms 
are  used  they  are  cut  so  that  their  edges  are  parallel  respectively  to  the  X,  F, 
and  Z  directions  of  the  mineral.  In  the  case  of  an  orthorhombic  mineral,  in 
which  these  directions  are  parallel  to  the  directions  of  the  three  crystallo- 
graphic  axes,  the  prism  edges  would  have  to  be  respectively  parallel  to  the 
a,  b,  and  c  crystal  axes.  In  crystals  of  the  monoclinic  and  triclinic  systems 
the  proper  orientation  of  the  three  prisms  is  a  matter  of  considerable  difficulty. 


CHARACTERS   DEPENDING    UPON    LIGHT  281 

Each  such  prism  will  yield  two  refracted  and  polarized  rays  but  only  the  one 
whose  light  has  its  vibrations  parallel  to  the  edge  of  the  prism  (to  be  deter- 
mined by  the  use  of  a  nicol)  is  considered.  In  certain  cases  all  three  indices 
may  be  obtained  from  two  prisms.  If  one  prism  is  cut  so  that  not  only  is  its 
edge  parallel  to  one  of  the  directions  X,  Y,  and  Z  but  so  that  its  medial  plane 
contains  not  only  this  direction  but  one  other,  then  by  the  use  of  the  method 
of  minimum  deviation  an  index  may  be  determined  from  each  of  the  two 
refracted  rays.  Or  with  a  small  angle  prism  cut  so  that  one  of  its  faces  con- 
tains two  of  these  directions  the  corresponding  two  indices  may  be  determined 
when  the  method  of  perpendicular  incidence  is  used  upon  this  face.  In  mak- 
ing these  measurements  it  is  important  to  note  the  crystallographic  directions 
parallel  to  which  the  different  rays  vibrate.  In  this  way  the  optical  orienta- 
tion in  respect  to  the  crystallographic  directions  can  be  determined. 

Method  of  Total  Reflection.  The  method  of  total  reflection  for  determining 
the  indices  of  refraction  of  a  biaxial  mineral  has  the  obvious  advantage  that 
only  polished  plates  of  the  mineral  are  required  instead  of  carefully  orientated 
prisms.  In  general,  the  plane  surface  of  a  plate  will  give  with  the  total 
refractometer  two  boundaries  of  total  reflection.  Both  of  these  shadows  move 
when  the  section  is  rotated.  Four  readings  should  be  taken  corresponding 
to  the  maximum  and  minimum  positions  of  each  boundary.  The  largest  and 
smallest  angles  read  will  give  on  calculation  the  values  for  the  greatest  and 
least  indices  of  refraction,  i.e.,  j  and  a.  The  mean  index  of  refraction,  0,  can 
be  derived  from  one  of  the  other  measurements.  There  are  certain  more  or 
less  complicated  methods  by  which  these  two  intermediate  readings  can  be 
tested  in  order  to  prove  which  is  the  correct  one  for  the  index  |8.  It  is  com- 
monly simpler  to  make  use  of  another  plate  having  a  different  crystallographic 
orientation.  It  will  be  found  that  in  the  second  plate  one  of  the  intermediate 
angles  corresponds  with  one  already  observed  on  the  first  plate  while  the 
second  angle  shows  no  such  correspondence.  The  angle  that  is  common  to 
the  two  plates  is  the  one  desired.  If  the  plate  is  orientated  so  that  its  plane 
contains  two  of  the  three  optical  directions,  X,  Y  and  Z,  all  three  indices  can 
be  obtained  easily  from  the  single  plate.  In  this  case  one  of  the  boundaries 
of  total  reflection  is  stationary  for  different  positions  of  the  plate.  This 
corresponds  to  the  ray  whose  vibrations  are  normal  to  the  surface  of  the  plate. 
The  other  boundary  will  vary  its  position  as  the  plate  is  rotated  and  yield  at 
its  maximum  and  minimum  positions  the  angles  corresponding  to  the  other 
two  indices  of  refraction. 

407.  Sections  of  Biaxial  Crystals  in  Convergent  Polarized  Light.  — -  In 
general,  sections  of  biaxial  crystals  when  examined  in  convergent  polarized 
light  show  interference  figures.  The  best  and  most  symmetrical  figures  are 
to  be  observed  when  the  section  has  been  cut  perpendicular  to  a  bisectrix, 
and  preferably  to  the  acute  bisectrix.  If  such  a  section  is  examined  under 
the  conditions  described  in  the  case  of  uniaxial  crystals,  see  Art.  389,  figures 
similar  to  those  shown  in  Fig.  583  will  be  observed.  When  the  axial  plane, 
i.e.,  the  plane  including  the  two  optic  axes,  lies  parallel  to  the  direction  of 
vibration  of  the  polarizer  the  figure  is  similar  to  that  of  Fig.  583,  A.  When 
these  two  directions  are  inclined  at  a  45°  angle  the  figure  is  like  that  shown  in 
Fig.  583,  B. 

First  consider  the  interference  figure  in  the  parallel  position,  Fig.  583,  A 
and  when  viewed  in  monochromatic  light.  It  consists  of  two  black  bars  that 
form  a  cross  somewhat  similar  to  the  cross  of  a  uniaxial  figure.  The  horizon- 


282  PHYSICAL  MINERALOGY 

tal  bar  is  thinner  and  better  denned  than  the  vertical  one.  About  two  points 
on  the  horizontal  bar,  there  will  be  observed  a  concentric  series  of  dark  ellip- 
tical curves  which,  as  they  enlarge,  coalesce,  forming  first  a  figure  eight  and 

583 


Biaxial  Interference  Figures 

then  a  double  curve.  As  the  section  is  rotated  on  the  microscope  or  polar- 
iscope  stage,  the  black  bars  forming  the  cross  separate  at  the  center  and  curve 
across  the  field  pivoting  on  these  points  until  at  the  45°  position,  Fig.  583,  B, 
they  form  the  two  arms  of  a  hyperbola. 

A  biaxial  mineral  has  two  directions,  the  directions  of  the  optic  axes,  along 
which  light  travels  with  no  double  refraction.  At  these  points  there  would 
be  no  birefringence  and  consequently  dark  spots  would  result.  As  the  paths 
of  the  light  rays  become  inclined  to  the  directions  of  the  optic  axes  the  light 
suffers  double  refraction  and  in  increasing  degree  as  the  amount  of  inclination 
becomes  greater.  Consequently  at  short  distances  away  from  these  points 
the  light  must  be  refracted  into  two  rays  which  have  a  difference  of  phase  of 
one  wave-length  for  a  certain  colored  light,  the  yellow  of  the  sodium  flame  in 
this  case.  The  result  will  be  extinguishment  at  such  points.  The  assem- 
blage of  all  points  where  the  difference  of  phase  equals  one  wave-length  yields 
the  first  dark  elliptical-like  curve,  called  a  lemniscate,  shown  in  the  figure. 
Further  out  will  be  found  curves  embracing  the  points  where  the  difference  o" 
phase  is  two  wave-lengths,  three  wave-lengths,  etc. 

If  the  interference  figure  is  viewed  in  daylight  instead  of  the  monochr 
niatic  light  the  black  curves  will  be  replaced  by  colored  ones.  Each  colored 
curve  is  produced  by  the  elimination  from  the  white  light  of  some  particular 
wave-length  of  light  on  account  of  the  interference  explained  above. 

The  convergent  bundle  of  light  rays  that  pass  through  the  section  will  each 
have  its  own  particular  plane  of  vibration.  The  directions  of  the  planes  of 
vibration  for  light  emerging  from  the  section  at  any  given  point  can  be  found, 
as  explained  in  Art.  397,  by  bisecting  the  angles  made  by  two  lines  connecting 
this  point  with  the  two  points  of  emergence  of  the  optic  axes.  Fig.  584  shows 
how  the  direction  of  vibration  of  the  two  rays  emerging  from  given  points 
can  be  obtained  in  this  way.  These  directions  of  vibration  vary  over  the 
field  and  consequently  some  of  them  must  always  be  parallel  or  very  nearly 
so  to  the  planes  of  vibration  of  the  nicol  prisms.  When  this  happens  the  light 
is  extinguished  and  darkness  results.  This  explains  the  formation  of  the  black 
bars  of  the  interference  figure.  Fig.  585  shows  the  bars  in  the  crossed  position 


ire. 

i 

TOV 


CHARACTERS   DEPENDING   UPON   LIGHT 


283 


and  Fig.  586  when  separated  into  the  hyperbola  arms.     As  the  section  is 

turned  the  vibration  directions  of  new  points  successively  become  parallel 

to  the  planes  of  the  nicols  and  so  the  dark  bars  sweep  and  curve  across  the  field. 

584  585  586 


With  a  thick  section  or  one  of  a  mineral  of  high  birefringence,  the  number 
of  colored  curves  (when  the  figure  is  viewed  in  daylight)  is  greater  than  with 
a  thinner  section  or  one  with  low  birefringence.  An  instructive  experiment 
can  be  made  by  noting  the  changes  in  the  interference  figure  obtained  from  a 
section  of  muscovite  as  the  mineral  is  cleaved  into  thinner  and  thinner  sheets. 
In  most  rock  sections  the  minerals  are  ground  so  thin  that  their  interference 
figures  do  not  show  any  colored  curves  but  rather  only  the  dark  hyperbola 
bars. 

The  biaxial  interference  figure  varies  in  appearance  with  the  change  in 
the  angle  between  the  optic  axes.  Where  this  angle  is  very  small  the  figure 
becomes  practically  the  same  as  that  of  a  uniaxial  crystal.  Where  this 
angle  becomes  greater  than  60°  the  points  of  the  emergence  of  the  optic  axes 
will  commonly  lie  outside  the  microscope  field.  In  the  latter  case  the  hyper- 
bola arms  will  appear  as  the  section  is  brought  into  the  parallel  position,  form 
a  cross,  and  then  as  the  section  is  further  revolved  will  curve  out  of  the  field 
again.  The  larger  the  axial  angle  the  more  rapidly  will  the  bars  disappear 
from  the  field.  A  comparative  measurement  of  the  axial  angles  of  two 
minerals  can  be  made  by  noting  the  angle  through  which  the  microscope  stage 
has  to  be  turned  in  order  to  cause  the  bars  to  leave  the  field.  The  system  of 
lenses  must  be  kept  the  same  for  the  two  experiments.  Or  by  experimenting 
with  various  minerals  with  known  axial  angles  a  scale  could  be  derived  for  a 
certain  microscope  and  system  of  lenses  so  that  the  axial  angle  of  any  other 
mineral  could  be  approximately  measured  in  this  way. 

A  symmetrical  interference  figure  may  also  be  obtained  from  a  section  cut 
perpendicular  to  the  obtuse  bisectrix.  In  general,  the  obtuse  axial  angle  is 
considerably  larger  than  the  acute  angle  and  the  interference  figure  will  differ 
therefore  in  this  respect  from  that  obtained  from  the  section  cut  perpendicular 
to  the  acute  bisectrix. 

It  is  important  to  be  able  to  recognize  the  biaxial  interference  figures 
which  are  obtained  from  inclined  sections.  They  are  chiefly  characterized 
by  the  fact  that  the  hyperbola  bars  curve  as  they  cross  the  field.  This  charac- 
teristic distinguishes  the  figure  from  an  eccentric  uniaxial  figure  in  which  the 
bars  of  the  cross  move  in  straight  lines  as  the  section  is  turned.  Fig.  587 
shows  in  the  row  A  a  series  illustrating  the  appearance  in  different  positions 


284 


PHYSICAL  MINERALOGY 


of  the  figure  when  the  section  is  slightly  inclined  to  the  bisectrix.  In  row  B, 
a  series  where  the  section  is  cut  perpendicular  to  an  optic  axis  and  the  hyper- 
bola bar  revolves  in  the  field  as  upon  a  pivot.  In  this  case  the  bar  curves 


687 


Eccentric  Biaxial  Interference  Figures 

with  its  convex  side  toward  the  acute  bisectrix.  If  the  axial  angle  was  90° 
there  would  be  no  distinction  between  acute  and  obtuse  bisectrices  and  the 
bar  would  then  revolve  as  a  straight  line.  Therefore  such  a  figure  indicates 
by  the  amount  of  the  curvature  of  the  bar  the  size  of  the  axial  angle.  The 
figures  given  by  planes  cut  nearly  normal  to  an  optic  axis  are  often  of  great 
use  in  the  optical  examination  of  a  mineral.  Sections  which  will  furnish  them 
are  easily  found  by  noting  those  sections  of  the  mineral  that  remain  dark  or 
nearly  so  during  their  rotation  between  crossed  nicols.  If  the  single  bar 
shown  in  such  a  figure  exhibits  a  decided  curvature  it  indicates  that  the 
direction  of  the  acute  bisectrix  is  not  very  much  inclined  to  the  plane  of  the 
section  and  consequently  its  character,  whether  X  or  Z,  can  be  determined  by 
noting  the  character  of  that  extinction  direction  which  symmetrically  bisects 
the  curve.  From  this  observation  the  positive  or  negative  character  of  the 
mineral  can  be  determined.  In  row  C,  Fig.  587,  is  shown  a  series  of  figures 
where  the  section  has  a  still  greater  inclination.  A  section  cut  parallel  to  the 
axial  plane  does  not  give  a  decisive  interference  figure.  Often  it  is  difficult  to 
distinguish  it  from  the  figure  obtained  from  a  section  cut  parallel  to  the  optic 
axis  of  a  uniaxial  mineral,  see  Art.  392.  It  should  be  pointed  out  that,  while 
in  general  the  interference  figures  of  these  two  optical  classes  are  to  be  clearly 
distinguished  from  each  other,  cases  may  arise  in  which  such  differentiation 
is  difficult  if  not  impossible. 

408.  Measurement  of  the  Axial  Angle.  —  The  determination  of  the  angle 
made  by  the  optic  axes  is  most  accurately  accomplished  by  use  of  the  instru- 
ment shown  in  Fig.  588.  The  section  of  the  crystal,  cut  at  right  angles  to  the 
bisectrix,  is  held  in  the  pincers  at  p,  with  the  plane  of  the  axes  horizontal,  and 
making  an  angle  of  45°  with  the  vibration-plane  of  the  nicols.  There  is  a 
cross-wire  in  the  focus  of  the  eyepiece,  and  as  the  pincers  holding  the  section 
are  turned  by  the  screw  at  the  top  (here  omitted)  one  of  the  axes,  that  is,  one 
black  hyperbola,  is  brought  in  coincidence  with  the  vertical  cross-wire,  and 


CHARACTERS   DEPENDING   UPON   LIGHT 


285 


then,  by  a  further  revolution,  the  second.  The  angle  which  the  section  has 
been  turned  from  one  axis  to  the  second,  as  read  off  at  the  vernier  on  the 
graduated  circle  above,  is  the  apparent  angle  for  the  axes  of  the  given  crystal 

688 


Axial  Angle  Apparatus 

as  seen  in  the  air  (aca  =  2E,  Fig.  589).  It  is  only  the  apparent  angle,  for,  on 
passing  from  the  section  of  the  crystal  to  the  air,  the  true  axial  angle  is  more  or 
less  increased,  according  to  the  refractive  power  of  the  given  crystal.  The 
relation  between  the  real  interior  angle  and 
the  measured  angle  is  given  below. 

If  the  axial  angle  is  large,  the  axes  may 
suffer  total  reflection.  In  this  case  some 
oil  or  liquid  with  a  high  refractive  power 
is  interposed  so  that  the  axes  will  no 
longer  be  totally  reflected  but  emerge  into 
the  liquid  and  thence  into  the  air.  In  the 
instrument  described  a  small  receptacle 
holding  the  oil  is  brought  between  the 
tubes,  as  seen  in  the  figure,  and  the  pincers 
holding  the  section  are  immersed  in  this 
and  the  angle  measured  as  before. 

In  the  majority  of  cases  it  is  only  the 
acute  axial  angle  that  it  is  practicable  to 
measure;  but  sometimes,  especially  when 


Measurement  of  Axial  Angle 


oil  (or  other  liquid)  is  made  use  of,  the  obtuse  angle  can  also  be  determined 
from  a  second  section  normal  to  the  obtuse  bisectrix. 

If  E    =  the  apparent  semi-acute  axial  angle  in  air  (Fig.  589), 

Ha  =    "  "  u  "     in  oil, 

Ho  =    "  "        semi-obtuse  angle  in  oil, 

Va  =  the  (real  or  interior)  semi-acute  angle, 


286  PHYSICAL  MINERALOGY 

V0  =  the  (real  or  interior)  semi-obtuse  angle, 
n  =  refractive  index  for  the  oil  or  other  medium, 
|8  =  the  mean  refractive  index  for  the  given  crystallized  substance, 
the  following  simple  relations  connect  the  various  quantities  mentioned: 

Bin  E  =  0  sin  7«;  sin  E  =  n  sin  Ha;  sin  Va  =  ^  sin  Ha;  sin  V0  =  ^  sin  H0. 

These  formulas  give  the  true  interior  angle  (2F)  from  the  measured 
apparent  angle  in  air  (2E)  or  in  oil  (2H)  when  the  mean  refractive  index  (0) 
is  known. 

409.  Axial  Angle  Measured  with  the  Microscope.  —  Approximate  measurements  of 
the  axial  angle  may  be  made  by  various  methods  with  the  microscope.  In  most  cases  some 
sort  of  a  micrometer  ocular  is  used  which  contains  an  engraved  scale.  By  means  of  this 
scale  the  distance  between  the  points  of  emergence  of  the  optic  axes  can  be  determined. 
Mallard  *  showed  that  the  distance  of  any  point  from  the  center  of  the  interference  figure 
as  observed  in  the  microscope  is  very  closely  the  same  as  the  sine  of  the  angle  which  the 
ray  emerging  at  this  point  makes  with  the  axis  of  the  microscope.  The  Mallard  equation 
for  the  derivation  of  the  axial  angle  is  D  =  K  sin  E,  in  which  D  equals  one  half  the  meas- 
ured distance  between  the  optic  axes  and  K  a  constant  which  varies  with  the  microscope 
and  the  system  of  lenses  used.  K  for  a  given  set  of  lenses  may  be  determined  by  observing 
the  interference  figures  derived  from  plates  of  minerals  with  known  axial  angles  and  then 
substituting  the  values  for  D  and  E  in  the  above  equation.  The  angular  values  of  the 
divisions  on  the  micrometer  scale  of  the  ocular  may  also  be  determined  directly  by  the  use 
of  an  instrument  known  as  the  apertometer.  The  measurement  of  an  axial  angle  by  means 
of  the  microscope  is  naturally  most  easily  accomplished  when  the  points  of  emergence  of 
both  optic  axes  are  visible  in  the  field.  It  is  possible,  however,  by  various  ingenious  methods 
to  determine  its  value  when  only  one  optic  axis  is  in  view.  These  methods  are  too  com- 
plicated and  too  seldom  used  to  be  explained  here  and  the  reader  is  referred  to  the  text 
books  on  the  methods  of  petrographic  investigation-  for  their  details,  f 

410.  Determination  of  the  Optical  Character  of  a  Biaxial  Mineral 
from  Its  Interference  Figure.  Use  of  the  Quartz  Wedge.  —  If  the  section 
is  turned  until  its  interference  figure  is  in  the  45°  position  and  then  the  quartz 
wedge  inserted  above  the  section  through  the  45°  slot  in  the  microscope  tube 
the  vibration  directions  of  the  section  along  a  line  that  joins  the  optical  axes 
and  a  line  at  right  angles  to  this  through  the  center  of  the  figure  will  be  paral- 
lel to  the  vibration  directions  of  the  quartz-wedge.  Under  these  circum- 
stances the  effect  of  the  introduction  of  the  quartz  wedge  will  be  to  gradually 
increase  or  diminish  along  these  lines  the  birefringence  due  to  the  section  alone. 
If  the  directions  of  vibration  of  the  faster  and  slower  rays  in  the  quartz  coin- 
cide with  the  vibration  directions  of  the  similar  rays  in  the  section,  the  total 
birefringence  will  be  increased  and  the  effect  upon  the  interference  figure  will 
be  as  if  the  section  had  been  thickened.  Complete  interference  will  take  place 
with  rays  of  less  obliquity  and  the  colored  curves  will  be  drawn  closer  together. 
They  will  move,  as  the  quartz  wedge  is  pushed  in  over  the  section,  as  indicated 
by  the  arrows  shown  in  Fig.  590.  On  the  other  hand,  if  the  quartz  wedge  is  so 
placed  that  its  optical  orientation  is  opposed  to  that  of  the  section,  the  effect 
will  be  the  same  as  if  the  section  was  being  gradually  thinned.  The  colored 
rings  about  the  points  of  the  optic  axes  will  expand  until  they  meet  in  the  cen- 
ter as  a  figure  eight  and  then  grow  outwards  as  a  continuous  curve.  The 
directions  of  their  movements  are  shown  by  the  arrows  in  Fig.  591.  There- 
fore, by  knowing  the  optical  orientation  of  the  quartz-wedge  and  noting  the 

*  Bull.  Soc.  Min.,  6,  7787,  1882. 

t  See  especially  Wright,  The  Methods  of  Petrographic  Microscopic  Research,  and 
Johannsen,  Manual  of  Petrographic  Methods. 


CHARACTERS   DEPENDING   UPON    LIGHT 


287 


effect  of  its  introduction  over  a  section  upon  the  interference  figure,  it  is  pos- 
sible to  determine  the  relative  character  of  the  two  important  extinction 
directions  of  the  sections;  that  is,  to  determine  whether  the  ray  vibrating  in 
the  plane  which  includes  the  optic  axes  is  faster  or  slower  than  the  one  which 
vibrates  in  the  plane  at  right  angles  to  this  direction. 

In  the  case  of  a  positive  mineral  the  acute  bisectrix,  which  in  a  sym- 
metrical interference  figure  is  the  direction  normal  to  the  section,  is  the 
direction  Z.  Consequently  the  direction  of  the  line  in  the  section  which 
passes  through  the  points  of  emergence  of  the  two  optic  axes  is  the  direction 
of  the  obtuse  bisectrix,  or  in  this  case  the  direction  X.  The  direction  Y  then 
will  lie  in  the  plane  of  the  section  and  at  right  angles  to  the  line  joining  the 
points  of  emergence  of  the  optic  axes.  In  the  case,  therefore,  of  a  positive 


Determination  of  Optical  Character  of  Biaxial  Mineral  with  Quartz  Wedge 

mineral,  the  faster  ray  has  its  vibrations  lying  in  the  optical  axial  plane 
With  a  negative  mineral  the  direction  X  becomes  the  acute  bisectrix  and 
will  be  normal  to  the  section,  while  the  direction  Z  will  lie  in  the  section 
along  the  line  connecting  the  points  of  emergence  of  the  optic  axes.  With 
a  negative  mineral,  therefore,  the  vibration  direction  which  lies  in  the 
optical  axial  plane  is  of  the  slower  ray.  By  finding,  therefore,  the 
relative  character  of  these  two  vibration  directions  the  optical  char- 
acter of  the  mineral  is  determined.  The  effects  produced  by  an 
interference  figure  which  is  perpendicular  to  an  obtuse  bisectrix  would  be 
exactly  opposite  to  those  described  above.  It  is  imperative,  therefore,  that 
the  positions  of  the  two  bisectrices  be  definitely  known.  With  sections  that 
are  very  thin  or  with  minerals  of  low  birefringence  the  interference  figure  may 
show  only  the  black  hyperbolas  without  any  colored  rings.  In  such  cases, 
frequently  the  introduction  of  the  quartz  wedge  in  such  a  position  that  its 
optical  orientation  is  parallel  to  that  of  the  section  will  suffice  to  so  thicken 
the  section  in  effect  as  to  cause  the  appearance  of  colored  rings.  Further,  with 
such  sections  it  is  possible  to  establish  the  directions  in  the  section  that  are 
parallel  and  at  right  angles  to  the  trace  upon  the  section  of  the  optical  axial 
plane.  Then,  by  use  of  the  sensitive  tint,  when  the  convergent  lens  has  been 
removed  the  character  of  the  vibrations  parallel  to  these  two  directions  is 
easily  determined. 


288  PHYSICAL   MINERALOGY 

411.  Absorption    Phenomena    of    Biaxial    Crystals.     Pleochroism.  — 

Colored  biaxial  crystals  like  similar  uniaxial  crystals  may  show  different  de- 
grees or  kinds  of  absorption  of  the  light  passing  through  them  depending  upon 
the  direction  of  vibration  of  the  light.  In  biaxial  crystals  there  may  be  three 
different  degrees  of  absorption  corresponding  to  three  different  directions  of 
vibration  lying  at  right  angles  to  each  other.  In  general,  these  directions  co- 
incide with  the  optical  directions  X,  F,  and  Z.  Variations  from  this  parallel- 
ism may  be  observed,  however,  in  crystals  of  the  monoclinic  and  triclinic 
systems.  It  is  customary,  however,  to  describe  the  absorption  as  it  is  ob- 
served parallel  to  the  directions  X,  Y,  and  Z.  If  light  vibrating  parallel  to 
X  is  the  most  absorbed  and  light  vibrating  parallel  to  Z  is  the  least  absorbed 
these  facts  are  expressed  asX  >  Y  >  Z.  There  are  various  other  possibili- 
ties, such  as  X  >  Y  =  Z,  Z  >  X  >  F,  etc.  Further,  according  to  the  kind 
of  selective  absorption,  the  crystal  may  show  distinctly  different  colors  for 
'  light  vibrating  in  the  different  directions,  or  in  general  show  pleochr9ism. 
The  character  of  the  pleochroism  is  stated  by  giving  the  colors  correspond- 
ing to  the  vibrations  parallel  to  X,  F,  and  Z.  For  instance,  in  the  case  of 
riebeckite,  X  =  deep  blue,  F  =  light  blue,  Z  =  yellow-green.  In  order  to 
investigate  the  absorption  properties  of  a  biaxial  crystal  at  (least  two  sections 
must  be  obtained  in  which  will  lie  the  directions  X,  F,  and  Z.  These  sec- 
tions are  examined  on  the  stage  of  the  polariscope  or  microscope  without  the 
upper  nicol.  They  will  show  as  they  are  rotated  upon  the  stage,  variations 
in  absorption  and  in  color  as  the  light  passing  through  them  vibrates  parallel  to 
first  one  and  then  the  other  of  their  vibration  directions.  See  the  discussion 
of  dichroism  in  uniaxial  minerals,  Art.  393. 

When  a  section  cut  normal  to  an  optic  axis  of  a  crystal  characterized  by  a  high  degree 
of  color-absorption  is  examined  by  the  eye  alone  (or  with  the  microscope)  in  strongly  con- 
verging light,  it  often  shows  the  so-called  epoptic  figures,  polarization-brushes,  or  houppes 
somewhat  resembling  the  ordinary  axial  interference-figures.  This  is  true  of  andalusite, 
epidote,  iolite,  also  tourmaline,  etc.  A  cleavage  section  of  epidote  ||c(001)  held  close  to  the 
eye  and  looked  through  to  a  bright  sky  shows  the  polarization-brushes,  here  brown  on  a 
green  ground.  These  figures  are  caused  by  the  light  being  differently  absorbed  as  it  passes 
through  the  section  with  different  degrees  of  inclination. 

In  certain  minerals  small  circular  or  elliptical  spots  may  be  observed  in  which  the  pleo- 
chroism is  stronger  than  in  the  surrounding  mineral.  These  are  commonly  spoken  of  as 
pleochroic  halos.  They  are  found  to  surround  minute  inclusions  of  some  other  mineral. 
There  have  been  many  diverse  theories  to  account  for  these  ''halos"  but  recently  it  has 
been  shown  that  they  are  probably  due  to  some  radioactive  property  of  the  inclosed  crystal. 
Pleochroic  halos  have  been  observed  in  biotite,  iolite,  andalusite,  pyroxene,  hornblende, 
tourmaline,  etc.,  while  the  included  crystals  belong  to  allanite,  rutile,  titanite,  zircon,  apa- 
tite, etc. 

Special  Optical  Characters  of  Orthorhombic  Crystals 

412.  Position  of  the  Ether-axis.  —  In  the  ORTHORHOMBIC  SYSTEM,  in 
accordance  with  the  symmetry  of  the  crystallization,  the  three  axes  of  the 
indicatrix,  that  is,  the  directions  X,  F,  and  Z,  coincide  with  the  three  crystal- 
lographic axes,  and  the  three  crystallographic  axial  planes  of  symmetry  cor- 
respond to  the  planes  of  symmetry  of  the  ellipsoid.     Further  than  this,  there 
is  no  immediate  relation  between  the  two  sets  of  axes  in  respect  to  magnitude, 
for  the  reason  that,  as  has  been  stated,  the  choice  of  the  crystallographic 
axes  is  arbitrary  so  far  as  relative  length  and  position  are  concerned,  and  hence 
made,  in  most  cases,  without  reference  to  the  optical  character. 

Sections  of  an  orthorhombic  crystal  parallel  to  a  pinacoid  plane  (a  (100), 
6(010),  or  c(001))  appear  dark  between  crossed  nicols,  when  the  axial  directions 


CHARACTERS    DEPENDING    UPON    LIGHT 


289 


coincide  with  the  vibration-planes  of  the  nicols;  in  other  words,  such  sections 
show  parallel  extinction. 

The  same  is  true  of  all  sections  that  are  parallel  to  one  of  the  three  crys- 
tallographic  axes,  i.e.,  sections  lying  in  the  prism,  macrodome  and  brachydome 
zones.  Sections,  however,  that  are  inclined  to  all  three  crystallographic 
axes,  i.e.,  pyramidal  sections,  will  show  inclined  extinction. 

413.  Determination  of  the  Plane  of  the  Optic  Axes.  —  The  plane  of 
the  optic  axes,  that  is,  the  plane  including  the  directions  X  and  Z,  must  be 
parallel  to  one  of  the  three  pinacoids.  Further,  the  acute  bisectrix  must  be 
normal  to  one  of  the  two  pinacoids  that  are  at  right  angles  to  the  optic  axial 
plane  while  the  obtuse  bisectrix  is  normal  to  the  other  such  pinacoid.  The 
optical  orientation,  i.e.,  the  relation  between  the  principal  optical  and  crystal- 
lographic directions,  can  be  easily  determined  by  the  examination  of  sections 
of  a  crystal  which  are  cut  parallel  to  the  three  pinacoids.  To  illustrate  by 
an  example,  let  it  be  assumed  that  such  sections  of  the  mineral  aragonite  are 
available.  These  are  represented  in  Fig.  592,  A,  B,  and  C.  If  the  relative 


100 

C 

_    Slower 

ray       _, 

^                t« 

] 

1 

X 

592 

a  axis 

010 

^ 

J 
& 

f 

Y  , 

Slower 

ray     yy 

I 

£ 

X 

6  axis 


Optical  Orientation  of  Aragonite 


characters  of  the  vibration  directions  of  each  section  are  determined  it  will  be 
found  that  light  vibrating  parallel  to  the  c  axis  in  sections  parallel  to  (100) 
and  (010)  is  in  both  cases  moving  with  the  greater  velocity,  that  light  vibrat- 
ing parallel  to  the  6  axis  in  (100)  and  (001)  is  in  both  cases  the  slower  ray,  and 
that  light  vibrating  parallel  to  the  a  axis  is  the  faster  ray  in  (001)  but  the  slower 
ray  in  (010).  From  this  it  is  seen  that  the  a  axis  must  coincide  with  the  direc- 
tion of  vibration  of  the  ray  having  the  intermediate  velocity,  or  be  the  same 
as  the  optical  direction  Y.  Also  it  follows  that  c  axis  =  X  and  b  axis  =  Z. 
The  optic  axial  plane,  therefore,  since  it  must  include  X  and  Z,  lies  parallel  to 
(100).  If  the  sections  parallel  to  (001)  and  (010)  are  examined  in  convergent 
light  both  will  show  biaxial  interference  figures  with  the  points  of  emergence 
of  the  optic  axes  lying  as  illustrated  in  B  and  C,  Fig.  592.  The  axial  angle 
observed  with  the  section  parallel  to  (001)  is  much  smaller  than  that  obtained 
from  (010).  Consequently  the  acute  bisectrix  is  normal  to  the  base  (001) 
and  since  it  is  the  direction  X  the  mineral  is  optically  negative.  These  facts 
of  optical  orientation  may  be  summarized  in  the  statements:  optically  —  , 
Ax.pl.  ||a(100),  Bxa.1  c(001). 


290 


PHYSICAL  MINERALOGY 


414.   Dispersion  of  the  Optic  Axes  in  Orthorhombic  Crystals.  —  In 

determining  the  indices  of  refraction  of  a  crystal  by  means  of  the  prism  method 
it  is  to  be  noted  that  when  the  incident  ray  is  of  white  light  the  refracted  ray 
will  in  general  show  this  white  light  dispersed  into  its  primary  colors.  The 
amount  of  this  dispersion  is  usually  small  but  in  certain  substances  becomes 
considerable.  Obviously  since  the  angle  of  refraction  varies  in  this  way 
with  the  different  wave-lengths  of  light  the  indices  of  refraction  will  also  vary. 
In  biaxial  minerals,  as  already  stated,  the  optic  axial  angle  is  directly  depend- 
ent upon  the  relative  values  of  the  three  indices  of  refraction,  a,  0,  and  y. 
As  these  indices  may  show  considerable  differences,  depending  upon  the 

wave-length  of  the  refracted  ray,  it  follows 
that  the  optic  axial  angle  will  also  vary  with 
the  color  of  the  light  used.  In  other  words, 
the  optic  axes  may  be  dispersed.  Fig.  593 
represents  such  a  case  in  which  the  angle 
between  the  optic  axes  for  red  light  is 
greater  than  that  for  blue.  The  opposite 
condition  may  hold,  in  which  the  angle  for 
blue  is  greater  than  for  red.  From  this  it 
follows  that  the  interference  figure  when 
observed  in  blue  light  will  not  exactly  co- 
incide with  that  produced  by  rod  light. 
The  bisectrices  of  both  figures  will  be  the 
same  but  the  position  of  the  points  where 
the  optic  axes  emerge  will  be  different  and 
consequently  the  positions  of  the  hyper- 
bolas and  lemniscate  curves  will  also  be 
orthorhombic  Ditpemoo  different.  In  the  case  of  orthorhombic 

crystals  the  dispersion  will  always  be  symmetrical  to  the  two  symmetry 
planes  of  the  indicatrix  that  pass  through  the  acute  bisectrix,  i.e.,  the  direc- 
tions M-M  and  N-N  594  595 
in  Figs.  594  and  595.                     A  A 
This  particular  type  of 
dispersion  is  said  to  be 
Orthorhombic  Disper- 
sion, in  order  to  distin- 
guish it  from  that  ob- 
served in  biaxial  crys- 
tals of   other   systems. 
The  two  possible  cases 
of  orthorhombic  disper- 
sion are  shown  in  Figs. 
594  and  595.  In  expres- 
sing these  two  cases  the                             Orthorhombic  Dispersion 

Greek  letters  p  (for  red)  and  v  (for  violet)  are  used.  When  the  axes  for  red 
light  are  more  dispersed  than  those  for  blue  that  fact  is  expressed  as  p  >  v 
or  in  the  reverse  case  it  is  p  <  v. 

In  the  majority  of  cases  the  effect  produced  upon  the  interference  figure 
by  the  dispersion  of  the  optic  axes  is  too  slight  to  be  noted.  In  exceptional 
cases  where  the  amount  of  dispersion  is  large  the  effects  are  clearly  seen.  The 
hyperbola  bars,  which  are  ordinarily  black  throughout,  will,  when  the  figure 


N 


CHARACTERS    DEPENDING    UPON    LIGHT 


291 


is  observed  in  white  light,  be  seen,  near  the  center,  to  be  bordered  on  one  side 
by  a  red  fringe  and  on  the  other  by  a  blue  one.  The  first  one  or  two  of  the 
colored  lemniscates  will  also  be  broadened  out  along  the  line  joining  the  two 
optic  axes.  As  already  stated  these  changes  in  the  appearance  of  the  figure 
will  always  be  symmetrical  in  respect  to  the  traces  of  the  two  symmetry  planes 
596  597 


'Blue 


-Red 


Orthorhombic  Dispersion 

lying  at  right  angles  to  each  other.  In  the  case,  Fig.  594,  where  the  axes  for 
red  light  are  farther  apart  than  those  for  blue  (p  >  v),  the  hyperbolas  in  the 
interference  figure  for  the  two  different  wave-lengths  of  light  will  not  coincide 
and  the  ones  where  the  red  light  is  extinguished  will  be  farther  out  than  those 
for  blue  light.  When  red  light  is  taken  out  of  the  white  light,  blue  remains, 
and  conversely  when  blue  is  subtracted  the  resultant  color  is  red.  Conse- 
quently in  this  case  the  hyperbola  bars  will  be  bordered  on  their  concave  sides 
by  blue  and  on  their  convex  sides  by  red,  Fig.  596.  In  the  other  case,  where 
p  <  v,  the  hyperbolas  will  be  bordered  on  their  concave  sides  by  red  and  on 
their  convex  sides  by  blue,  Fig.  597.  In  other  words,  if  blue  light  shows  at  the 
larger  angle  it  means  that  red  light  has  been  eliminated  from  these  positions 
and  the  optic  axes  for  red  are  more  dispersed  than  those  for  blue,  etc. 

Special  Optical  Characters  of  Monoclinic  Crystals 

415.  Optical  Orientation  of  Monoclinic  Crystals.  —  In  monoclinic  crys- 
stals  there  is  one  axis  of  symmetry,  the  b  crystallographic  axis,  and  one  plane 
of  symmetry,  the  plane  of  the  a  and  c  crystallographic  axes.  These  are  the 
only  crystallographic  elements  that  are  definitely  fixed  in  position.  One  of 
the  three  chief  optical  directions,  X,  Y,  or  Z,  is  coincident  with  the  6  crystal- 
lographic axis,  while  the  other  two  lie  in  the  symmetry  plane,  (010),  but  not 
parallel  to  any  crystal  direction.  There  are  obviously  three  possible  cases. 
If  Y  coincides  with  the  axis  b  (and  this  is  apparently  the  most  common  case) 
the  directions  X  and  Z  will  lie  in  the  crystal  symmetry  plane,  which  therefore 
becomes  the  optic  axial  plane.  If  X  or  Z  coincides  with  the"  6  axis  the  optic 
axial  plane  will  be  at  right  angles  to  (010)  and  either  the  acute  or  obtuse  bisec- 
trix -will  be  normal  to  that  plane.  This  clino-pinacoid  of  a  monoclinic  crystal 
is  usually  the  best  plane  upon  which  to  study  its  optical  orientation.  Fig. 
598  represents  such  a  section  cleaved  from  an  ordinary  crystal  of  gypsum. 
The  cleavages  parallel  to  (100)  and  (111)  will  serve  to  give  its  crystallo- 
graphic orientation.  Examination  of  the  section  in  convergent  light  fails  to 
show  a  distinct  interference  figure,  consequently  it  is  to  be  assumed  that  the 
section  itself  is  parallel  to  the  optic  axial  plane  and  that  the  direction  Y  is 


292 


PHYSICAL   MINERALOGY 


598 


(100) 


to  (111) 


Optical  Orientation  of  Gypsum 


normal  to  the  section.  When  the  section  is  rotated  on  the  microscope  stage 
between  crossed  nicols  its  extinction  directions  are  seen  to  be  inclined  to  the 
direction  of  the  c  crystallographic  axis,  the  angle  of  inclination  being  measured 
as  52J°.  The  relative  character  of  the  two  extinction  directions  can  be 

easily  determined  by  the  use  of  the  quartz  wedge 
and  so  the  position  of  X  and  Z  established.  In 
this  way  the  orientation  of  the  X,  Y  and  Z 
directions  can  be  determined.  It  is  also  pos- 
sible from  this  section  to  determine  whether 
the  mineral  is  optically  positive  or  negative.  If 
the  section  is  viewed  in  convergent  light  a  some- 
what vague  interference  figure  is  observed. 
When  the  section  is  turned  from  its  position  of 
extinction  it  will  be  noted  that  faint  dark 
hyperbolas  rapidly  move  out  of  the  field. 
Careful  observation  will  show  that  they  disappear 
more  slowly  into  one  set  of -quadrants  than  into 
the  other.  The  line  bisecting  the  opposite 
quadrants  into  which  the  hyperbola  bars 
disappear  more  slowly  is  the  direction  of  the 
acute  bisectrix.  The  X  or  Z  character  of  this 
direction  can  be  determined  and  from  this  the 
positive  or  negative  character  of  the  mineral.  In 
a  similar  way  the  clino-pinacoid  section  of  crystals 
belonging  to  the  two  other  possible  classes  would 
yield  data  concerning  their  optical  orientations. 

416.  Extinction  in  Monoclinic  Crystals.  —  Since  only  one  of  the  three 
principal  optical  directions,  X,  F,  or  Z,  of  a  monoclinic  crystal  coincides  with 
a  crystallographic  axis,  namely  the  symmetry  axis  6,  it  follows  that  only  sec- 
tions that  are  parallel  to  this  axis,  i.e.,  sections 

in  the  orthodome  zone,  will  show  parallel 
extinction.  All  other  sections  will  exhibit 
inclined  extinction. 

417.  Dispersion  in  Monoclinic  Crystals.  - 
As  previously  stated  there   are  three  possible 
optical  orientations  of  a  monoclinic  crystal.     In 
the  first  case  the  vibration  direction  Y  coincides 
with  that  of  the  symmetry  axis  6  and  the  optic 
axial  plane  coincides  with  the  symmetry  plane 
(010).     In  the  other  cases  either  the  vibration 
direction  X  or  Z  coincides  with  the  crystal- 
lographic axis  b  and  the  optic  axial  plane  is  at 
right  angles  to  "the  crystallographic  symmetry 
plane.     Under  these  conditions  either  the  acute 
or  obtuse  bisectrix  may  coincide  with  the  axis  b. 
Each  of  these  three  possibilities  may  produce  a 
different  kind  of  dispersion.     It  should  be  em- 
phasized that  the  phenomenon  of  dispersion  is 
seldom  to  be  clearly  observed  and  then  com- 
monly only  in  unusually  thick  mineral  sections.  Inclined  Dispersion 

Case  1.   Inclined  Dispersion.     Inclined  dispersion  is  observed  in  the  case 


599 


CHARACTERS  DEPENDING  UPON  LIGHT 


293 


where  the  direction  Y  coincides  with  the  axis  6.    This  is  illustrated  in  Fig.  599. 
In  this   case   not   only  may   the   axial  angles  vary  for  light  of  different 
wave-lengths  but  -the  bisectrices  of  these  angles  may  lie  along  different  lines. 
600  601 

f 


602 


r  all  Colon 


Red 


Inclined  Dispersion, p=*v 

So,  here,  both  the  optical  axes  and  the  bisectrices  may  be  dispersed.  In  Fig. 
599  with  p  >  v  the  angle  between  the  optic  axes  for  red  light  is  greater  than 
that  for  blue.  But  because  of  the 
dispersion  of  the  bisectrices  it  follows 
that  on  one  side  the  point  of  emergence 
of  the  optic  axis  for  red  light  lies  beyond 
that  for  blue,  while  on  the  other  side 
the  conditions  are  reversed.  Also  the 
optic  axes  for  red  and  blue  will  be 
farther  apart  on  one  side  of  the  interfer- 
ence figure  than  on  the  other  side. 
With  this  sort  of  dispersion  the  interfer- 
ence figure  will  be  symmetrical  only  in 
respect  to  the  line  which  is  the  trace 
upon  the  section  of  the  optic  axial  plane, 
N-N,  Fig.  600,  but  is  unsymmetrical  to  J 
the  line  at  right  angles  to  it,  M-M. 

Inclined  dispersion  is  shown  in  the 
interference  figure  by  the  fact  that  the 
colored  borders  to  the  hyperbola  bars 
are  reversed  in  the  two  cases,  i.e.,  if  blue 
is  on  the  concave  side  of  one,  red  will 
be  on  the  concave  side  of  the  other. 
Further,  tho  amount  of  dispersion  shown 
is  much  greater  with  one  bar  than  with  the  other.  Fig.  601  represents  a 
case  of  inclined  dispersion. 

Case  2.  Horizontal  Dispersion.  In  this  case  the  crystallographic  axis  b 
coincides  with  the  obtuse  bisectrix  which  may  be  either  the  X  or  Z  direction, 
depending  upon  whether  the  crystal  is  optically  positive  or  negative  in  charac- 
ter. In  this  case  the  direction  of  the  obtuse  bisectrix  is  fixed  for  light  of  all 
wave-lengths.  The  angle  between  the  optic  axes  may  vary  and  further  the 
position  of  the  acute  bisectrix  may  vary  as  long  as  it  lies  in  the  crystallographic 
symmetry  plane.  In  other  words,  the  axial  planes  may  be  dispersed,  see 
Fig.  602.  The  points  of  emergence  of  the  optic  axes,  when  p  >  v,  for  blue  and 
red  light,  might  therefore  be  like  that  shown  in  Fig.  603.  It  will  be  noted  that 
in  this  case  the  interference  figure  (obtained  of  course  from  a  section  approx- 


Horizontal  Dispersion 


294 


PHYSICAL   MINERALOGY 


imately  perpendicular  to  the  acute  bisectrix)  is  symmetrical  to  the  line  M-M 
but  unsymmetrical  in  respect  to  the  line  N-N.  Fig.  604  shows  the  effect  of 
horizontal  dispersion  upon  the  interference  figure. 

603  604 


Axis  for  Red 
£p  Axis  for  Blue 
•P 


Horizontal  Dispersion.  p>v 


Case  3. 


Crossed 
605, 


ion. 


In 


Blue 


Red 


r  all  Colors 


this  case  the  crystallographic  axis  b 
coincides  with  the  acute  bisectrix, 
which  may  be  either  the  X  or  Z  direc- 
tion depending  upon  the  optical  char- 
acter of  the  crystal.  In  this  case  the 
direction  of  the  acute  bisectrix  is  fixed 
for  light  of  all  wave-lengths.  The 
angle  between  the  optic  axes  may  vary 
and  further  the  position  of  the  axial 
planes  for  different  wave-lengths  may 
vary  as  long  as  they  remain  perpendic- 
ular to  the  crystallographic  symmetry 
plane.  A  case  of  this  sort  is  shown 
in  Fig.  605.  The  points  of  emer- 
gence of  the  optic  axes  when  p  >  v  f or 
blue  and  red  light  might  therefore  be 
like  that  shown  in  Fig.  606.  It  will  be 
seen  that  in  this  case  the  figure  is  sym- 
metrical to  neither  the  line  M-M  nor 
N-N  but  only  to  the  central  point  of 
the  figure,  i.e.,  the  point  of  emergence 
of  the  acute  bisectrix.  Fig.  607  shows 


Crossed  Dispersion 

the  effect  of  crossed  dispersion  upon  the  interference  figure. 
606  607 


Crossed  Dispersion  p>v 


CHARACTERS   DEPENDING   UPON    LIGHT  295 

Special  Optical  Characters  of  Triclinic  Crystals 

418.  Optical   Orientation  of  Triclinic  Crystals.  —  The  center  of  the 
optical  ellipsoidal  figure  coincides  with  the  center  of  the  system  of  crystallo- 
graphic  axes  but  there  is  no  further  correspondence  between  optical  and  crys- 
tallographic  directions. 

419.  Extinction  in  Triclinic  Crystals.  —  Since  there  is  no  parallel  rela- 
tion existing  between  optical  and  crystallographic  directions  in  triclinic  crys- 
tals all  sections  will  show  inclined  extinction. 

420.  Dispersion  in  Triclinic  Crystals.  —  Because  of  the  lack  of  coinci- 
dence between  any  optical  and  crystallographic  direction  in  triclinic  crystals  it 
follows  that  the  optic  axes  and  bisectrices  for  different  wave-lengths  of  light 
may  be  dispersed  in  any  direction.     Consequently  the  dispersion  shown  in 
an  interference  figure  obtained  from  a  triclinic  crystal  is  irregular  and  without 
symmetry. 

421.  Suggestions  as  to  Methods  and  Order  of  Optical  Tests  upon  an 
Unknown  Mineral.  —  Preparation  of  Material.     The  size  and  character  of 
the  fragments  or  section  of  a  mineral  to  be  studied  will  depend  upon  various 
circumstances.     In  the  majority  of  cases  it  will  probably  be  most  convenient 
to  crush  the  mineral  into  small  uniform  sized  fragments.     In  other  cases  a 
cleavage  flake  of  the  mineral  will  serve,  and  under  still  other  conditions  it  may 
be  preferable  to  cut  an  unorientated  or,  better,  an  orientated  section.     For  at 
least  the  preliminary  examination  small  irregular  fragments  of  varying  orienta- 
tion will  most  often  be  used.     Take  a  few  of  these  mineral  grains  and  place 
them  upon  an  object  glass  and  immerse  ^them  either  in  Canada  balsam  or  in 
some  oil  with  known  refractive  index  and  cover  with  a  piece  of  thin  cover 
glass.     In  the  majority  of  cases  it  will  prove  more  expeditious  and  conven- 
ient to  place  the  fragments  in  an  oil. 

Order  of  Optical  Tests.     Below  is  given  a  brief  outline  of  the  natural  order 
of  observations  and  tests  to  be  made  upon  the  mineral. 

1.  Observations  in  plane  polarized  light  without  the  upper  nicol. 

a.  Note  color  of  mineral,  whether  uniform  or  not. 

b.  By  rotating  slide  on  microscope  stage  test  for  possible  pleochroism. 

If  the  mineral  exhibits  pleochroism  it  cannot  be  isotropic.  Con- 
nect as  far  as  possible  the  directions  of  absorption  with  crystal- 
lographic directions. 

c.  Note  crystal  outline,  if  any;  cleavage  cracks,  etc. 

d.  Note  any  inclusions,  their  shape  and  arrangement. 

e.  Index  of  refraction.     Determine  approximately  the  refractive  index. 

Note  character  of  relief  and  determine  whether  mineral  has  a 
higher  or  lower  index  than  the  medium  in  which  it  is  immersed 
(see  Art.  325). 

2.  Observations  in  plane  polarized  light  with  crossed  nicols. 

a.  If  the  section  is  dark  between  crossed  nicols  and  remains  so  during 

the  rotation  of  the  stage  the  mineral  is  either  isotropic  or 
orientated  perpendicular  to  an  optic  axis.  In  the  latter  case  test 
as  indicated  below  under  3a. 

b.  If  the  section  is  alternately  light  and  dark  during  the  rotation  of  the 

stage  the  mineral  is  anisotropic. 

c.  Note  position  of  extinction  directions.     If  they  are  inclined  to  some 

known  crystallographic  direction  measure  the  angle  of  inclina- 
tion. 


296  PHYSICAL  MINERALOGY 

d.  Determine  the  relative  character  of  the  two  vibration  directions  of 

the  section  (i.e.,  the  two  extinction  directions),  as  to  which  cor- 
responds to  the  faster  and  which  to  the  slower  ray.  Test  to  be 
made  with  quartz  wedge  or  sensitive  tint,  see  Art.  348. 

e.  Find  the  grain  showing  the  highest  order  of  interference  color  and 

so  approximately  determine  the  strength  of  the  mineral's  bire- 
fringence. 

/.    By  immersion  in  oils  of  known  refractive  indices  determine  as 
accurately  as  possible  the  range  of  the  refractive  indices  shown 
by  the  mineral.     It  may  be   possible  in  connection  with  tests 
made  under  3  to  determine  the  values  for  certain  of  the  prin- 
.    cipal  refractive  indices. 
3.   Observations  in  convergent  polarized  light  with  crossed  nicols. 

a.   Note  whether  the  mineral  shows  an  interference  figure,  and  if  so 

whether  it  is  uniaxial  or  biaxial. 

6.  If  mineral  is  uniaxial  determine  the  position  of  the  optic  axis  in 
respect  to  the  plane  of  the  given  section  and  if  possible  determine 
the  positive  or  negative  character  of  the  mineral. 
c.  If  the  mineral  is  biaxial  determine  the  position  of  the  axial  plane  in 
respect  to  the  section.  Determine,  if  possible,  the  positive  or 
negative  character  of  the  mineral.  Obtain,  if  possible,  an  approx- 
imate idea  as  to  the  size  of  the  axial  angle.  Note  any  evidences 
of  dispersion. 

Note.  —  In  making  the  above  tests  it  is  helpful  to  keep,  as  far  as  possible, 
a  graphic  record  of  the  results,  something  like  that  illustrated  in  Fig.  592. 

422.  Effect  of  Heat  upon  Optical  Characters.  —  The  general  effects  of 
heat  upon  crystals  as  regards  expansion,  etc.,  are  spoken  of  later.  It  is  con- 
venient, however,  to  consider  here,  briefly,  the  changes  produced  by  this 
means  in  the  special  optical  characters.  It  is  assumed  that  no  alteration  of 
the  chemical  composition  takes  place  and  no  abnormal  change  in  molecular 
structure.  In  general,  the  effect  of  a  temperature  change  causes  a  change  in 
the  refractive  indices.  In  the  majority  of  cases  the  indices  decrease  in 
value  with  rise  of  temperature  but  in  certain  cases  the  reverse  is  true.  It 
is  consequently  important  in  any  exact  statement  of  a  refractive  index  to 
give  the  temperature  at  which  it  was  determined.  The  particular  facts  for 
the  different  optical  classes  are  as  follows : 

(1)  Isotropic  crystals  remain  isotropic  at  all  temperatures.     Crystals,  how- 
ever, which,  like  sodium  chlorate  (NaClO3  of  Class  5,  p.  72),  show  circular 
polarization  may  have  their  rotatory  power  altered;  in  this  substance  it  is  in- 
creased by  rise  of  temperature. 

(2)  Uniaxial  crystals  similarly  remain  uniaxial  with  rise  or  fall  of  tempera- 
ture; the  only  change  noted  is  a  variation  in  the  relative  values  of  co  and  e,  that 
is,  in  the  strength  of  the  double  refraction.     This  increases,  for  example,  with 
calcite  and  grows  weaker  with  beryl  and  quartz.     It  is,  further,  interesting  to 
note  that  the  rotatory  power  of  quartz  increases  with  rise  of  temperature,  but 
the  relation  for  all  parts  of  the  spectrum  remains  sensibly  the  same. 

(3)  With  Biaxial  crystals,  the  effect  of  change  of  temperature  varies  with 
the  system  to  which  they  belong. 

The  axial  angle  of  biaxial  crystals  may  be  measured  at  any  required  temperature  by  the 
use  of  a  metal  air-bath.  This  is  placed  at  P  (Fig.  588)  and  extends  beyond  the  instrument 
on  either  side,  so  as  to  allow  of  its  being  heated  with  gas-burners;  a  thermometer  inserted 


CHARACTERS   DEPENDING   UPON   LIGHT  297 

in  the  bath  makes  it  possible  to  regulate  the  temperature  as  may  be  desired.  This  bath  has 
two  openings,  closed  with  glass  plates,  corresponding  to  the  two  tubes  carrying  the  lenses, 
and  the  crystal-section,  held  as  usual  in  the  pincers,  is  seen  through  these  glass  windows. 
Suitable  accessories  to  the  refractometer  also  allow  of  the  measurement  of  the  refractive 
indices  at  different  temperatures. 

In  the  case  of  orthorhombic  crystals,  the  position  of  the  three  rectangular 
ether-axes  cannot  alter,  since  they  must  always  coincide  with  the  crystallo- 
graphic  axes.  The  values  of  the  refractive  indices,  however,  may  change,  and 
hence  with  them  also  the  optic  axial  angle;  indeed  a  change  of  axial  plane  or 
of  the  optical  character  is  thus  possible. 

With  monodinic  crystals,  one  ether-axis  must  coincide  at  all  temperatures 
with  the  axis  of  symmetry,  but  the  position  of  the  other  two  in  the  plane  of 
symmetry  may  alter,  and  this,  with  the  possible  change  in  the  value  of  the 
•refractive  indices,  may  cause  a  variation  in  the  degree  (or  kind)  of  dispersion  as 
well  as  in  the  axial  angle. 

With  triclinic  crystals,  both  the  positions  of  the  ether-axes  and  the  values 
of  the  refractive  indices  may  change.  The  observed  optical  characters  may 
therefore  vary  widely. 

A  striking  example  of  the  change  of  optical  characters  with  change  of  temperature  is 
furnished  by  gypsum,  as  investigated  by  Des  Cloizeaux.  At  ordinary  temperatures,  the 
dispersion  is  inclined,  the  optic  axial  plane  is  ||  6(010)  and  2Er  =  95°.  As  the  temperature 
rises  this  angle  diminishes;  thus,  at  47°,  2Er  =  76°;  at  95°,  2Er  =  39°;  and  at  116°,  2Er  =  0. 
At  this  last  temperature  the  axes  for  blue  rays  have  already  separated  in  a  plane  _1_  6(010); 
at  120°  the  axes  for  red  rays  also  separate  in  this  plane  (_L  6)  and  the  dispersion  becomes 
horizontal.  The  motion  toward  the  center  of  one  red  axis  is  more  rapid  than  that  of  the 
other,  namely,  between  20°  and  95°,  one  axis  moves  33°  55'  while  the  other  moves  only 
22°  38';  thus  Bxr  moves  5°  38'. 

Another  interesting  case  is  that  of  glauberite.  Its  optical  characters  under  normal  con- 
ditions are  described  as  follows:  Optically  — .  Ax.  pi.  J_  6(010),  Bxa.r  A  c  axis  =  —31°  3', 
Bxa.y  A  c  axis  =  -30°  46',  Bxa.bi  A  c  axis  =  -30°  10'.  The  optical  character  (-)  and 
the  position  of  the  axes  of  elasticity  remain  sensibly  constant  between  0°  and  100°.  The 
ax.  pi.,  however,  at  first  _l_  6(010)  with  horizontal  dispersion  and  v  <  p  becomes  on  rise  of 
temperature  1 1  6  with  inclined  dispersion  and  v  >  p.  The  axial  angle  accordingly  diminishes 
to  0°  at  a  temperature  depending  upon  the  wave-length  and  then  increases  in  the  new 
plane.  In  white  light,  therefore,  the  interference-figures  are  abnormal  and  change  with 
rise  in  temperature. 

Des  Cloizeaux  found  that  the  feldspars,  when  heated  up  to  a  certain  point,  suffer  a 
change  in  the  position  of  the  axes,  and  if  the  heat  becomes  greater  and  is  long  continued 
they  do  not  return  again  to  their  original  position,  but  remain  altered. 

In  addition  to  the  typical  cases  referred  to,  it  is  to  be  noted  that  when  eleva- 
tion of  temperature  is  connected  with  change  of  chemical  composition  wide 
changes  in  optical  characters  are  possible.  This  is  illustrated  by  the  zeolites 
and  related  species,  where  the  effect  of  loss  of  water  has  been  particularly 
investigated. 

Further,  with  some  crystals,  heat  serves  to  bring  about  a  change  of  molec- 
ular structure  and  with  that  a  total  change  of  optical  characters.  For  exam- 
ple, the  greenish-yellow  (artificial)  orthorhombic  crystals  of  antimony  iodide 
(SbI3)  on  heating  (to  about  114°)  change  to  red  uniaxial  hexagonal  crystals. 
Note  also  the  remarks  made  later  in  regard  to  the  effect  of  heat  upon  leucite 
and  boracite  (Art.  429). 

423.  Some  Peculiarities  in  Axial  Interference-figures.*  —  In  the  case  of  uniaxial  crys- 
tals, the  characteristic  interference-figure  varies  but  little  from  one  species  to  another,  such 

*  Variations  in  the  axial  figures  embraced  under  the  head  .of  optical  anomalies  are  spoken 
of  later  (Art.  429). 


298  PHYSICAL   MINERALOGY 

variation  as  is  observed  being  usually  due  19  the  thickness  of  the  section  and  the  bire- 
fringence. In  some  cases,  however,  peculiarities  are  noted.  For  example,  the  interference- 
figure  of  apophyllite  is  somewhat  peculiar,  since  its  birefringence  is  very  weak,  and  it  may 
be  optically  positive  for  one  part  of  the  spectrum  and  negative  for  the  other. 

In  the  case  of  biaxial  crystals,  peculiarities  are  more  common.  The  following  are  some 
typical  examples: 

Brookite  is  optically  +  and  the  acute  bisectrix  is  always  normal  to  a (100).  While,  how- 
ever, the  axial  plane  is  ||  c(001)  for  red  and  yellow,  with  2ET  =  55°,  2EV  =  30°,  it  is  com- 
monly ||  6(010)  for  green  and  blue,  with  2Egr  =  34°.  Hence  a  section  1 1  a(100)  in  the  cono- 
scope  shows  a  figure  somewhat  resembling  that  of  a  uniaxial  crystal  but  with  four  sets  of 
hyperbolic  bands. 

Titanite  also  gives  a  peculiar  interference-figure  with  colored  hyperbolas  because  of 
the  high  color-dispersion,  p  >  v,  the  variation  between  2E  for  red  and  green  light  being 
approximately  10°;  the  dispersion  of  the  bisectrices  is,  however,  very  small. 

The  most  striking  cases  of  peculiar  axial  figures  are  afforded  by  twin  crystals  (Art.  425). 

424.  Relation  of  Optical  Properties  to  Chemical  Composition.  —  The 

effect  of  varying  chemical  composition  upon  the  optical  characters  has  been 
minutely  studied  in  the  case  of  many  series  of  isomorphous  salts,  and  with 
important  results.  It  is,  indeed,  only  a  part  of  the  general  subject  of  the  rela- 
tion between  crystalline  form  and  molecular  structure  on  the  one  hand  and 
chemical  composition  on  the  other,  one  part  of  which  has  been  discussed  in 
Art.  322.  It  was  shown  there  that  the  refractive  index  can  often  be  approx- 
imately calculated  from  the  chemical  composition. 

Among  minerals,  the  most  important  examples  of  the  relation  between  composition  and 
optical  characters  are  afforded  by  the  triclinic  feldspars  of  the  albite-anorthite  series. 
Here,  as  explained  in  detail  in  the  descriptive  part  of  this  work,  the  relation  is  so  close 
that  the  composition  of  any  intermediate  member  of  this  isomorphous  group  can  be  pre- 
dicted from  the  position  of  its  ether-axes,  or  more  simply  from  the  vibration  directions  on 
the  fundamental  cleavage-directions,  ||  c(001)  and  ||  6(010). 

The  effect  of  varying  amounts  of  iron  protoxide  (FeO)  is  illustrated  in  the  case  of  the 
monoclinic  pyroxenes,  where,  for  example,  the  angle  Bxa  A  c  axis  is  38°  in  diopside  (2'9 
p.  c.  FeO)  and  47°  in  hedenbergite  (26  p.  c.  FeO).  This  is  also  shown  in  the  closely  related 
orthorhombic  species  of  the  same  group,  enstatite,  MgSiOs  with  little  iron,  and  hypersthene, 
(Mg,Fe)SiO3  with  iron  to  nearly  30  p.  c.  With  both  of  these  species  the  axial  plane  is 
parallel  to  6(010),  but  the  former  is  optically  +  (Bxa  =  Z)  and  the  dispersion  p  <  v,  the 
latter  is  optically  —  (Bxa  =  A^)  and  dispersion  p  >  v.  In  other  words,the  optic  axial  angle 
changes  rapidly  with  the  FeO  percentage,  being  about  90°  for  FeO  =  10  p.  c.  In  the  case 
of  the  chrysolites,  the  epidotes,  the  species  triphylite  and  lithiophilite,  and  others,  analogous 
relations  have  been  made  out.- 

425.  Optical  Properties  of  Twin  Crystals.  —  The  examination  of  sec- 
tions of  twin  crystals  of  any  other  than  the  isometric  system  in  polarized  light 
serves  to  establish  the  compound  character  at  once  a'nd  also  to  show  the 
relative  orientation  of  the  several  parts.     This  is  most  distinct  in  the  case  of 
contact-twins,  but  is  also  well  shown  with  penetration-twins,  though  here  the 
parts  are  usually  not  separated  by  a  sharp  line. 

Thus  the  examination  of  a  section  parallel  to  6(010)  of  a  twin  crystal  of 
gypsum,  of  the  type  of  Fig.  608,  makes  it  easy  not  only  to  establish  the  fact 
of  the  twinning  but  also  to  fix  the  relative  positions  of  the  ether-axes  in  the 
two  parts.  The  measurement  can  in  such  cases  be  made  between  the  extinc- 
tion-directions in  the  two  halves,  instead  of  between  one  of  these  and  some 
definite  crystallographic  line,  as  the  vertical  axis. 

The  polysynthetic  twinning  of  certain  species,  as  the  triclinic  feldspars,  appears  with 
great  distinctness  in  polarized  light.  For  example,  in  the  case  of  a  section  of  albite,  parallel 
to  the  basal  cleavage,  the  alternate  bands  extinguish  together  and  assume  the  same  tint 
when  the  quartz  section  is  inserted.  Hence  the  angle  between  these  directions  is  easily 
measured,  and  this  is  obviously  double  the  extinction-angle  made  with  the  edge  6(010) 
A  c(001).  A  basal  section  of  microcline  in  the  same  way  shows  its  compound  twinning 


CHAEACTERS   DEPENDING.  UPON   LIGHT 


299 


according  to  both  the  albite  and  pericline  laws,  the  characteristic  grating  structure  being 
clearly  revealed  in  polarized  light.  Fig.  609  of  a  section  of  chondrodite  (from  Des  Cloizeaux) 
shows  how  the  compound  structure  is  shown  by  optical  examination;  the  position  of  the 

609 


001 


axial  plane  is  indicated  in  the  case  of  the  successive  polysynthetic  lamellae.  The  complex 
penetration-twins  of  right-  and  left-handed  crystals  of  quartz  (see  the  description  of  that 
species)  also  have  their  character  strikingly  revealed  in  polarized  light. 


610 


612 


Witherite  Bromlite  (Des  Cloizeaux) 

Still  again,  the  true  structure  of  complex  multiple  twins,  exhibiting  pseudo-symmetry 
in  their  external  form,  can  only  be  fully  made  out  in  this  way.  This  is  illustrated  by  Fig. 
610,  a  basal  section  of  an  apparent  hexagonal  pyramid  of  witherite.  The  analogous  six- 

613  614  615 


Stilbite  (Lasaulx) 

sided  pyramid  of  bromlite  (Fig.  611)  has  a  still  more  complex  structure,  as  shown  in  Fig. 
612.  Fig.  613  shows  a  simple  crystal  of  stilbite;  Fig.  614  is  the  common  type  of  twin- 
crystal,  and  Fig.  615  illustrates  how  the  complex  structure  (||6010)  is  revealed  in  polarized 


300  PHYSICAL   MINERALOGY 

light.  Other  illustrations  are  given  in  Art.  429.  It  will  be  understood  that  the  axial 
interference-figures  of  twin  crystals,  where  the  parts  are  superposed,  often  show  many 
peculiarities;  the  Airy  spirals  of  quartz  (p.  270)  will  serve  as  an  illustration. 

426.  A  particularly  interesting  case,  related  to  the  subject  discussed  in  the 
preceding  article,  is  that  of  the  special  properties  of  superposed  cleavage- 
sections  of  mica.     If  three  or  more  of  these,  say  of  rectangular  form,  be  super- 
posed and  so  placed  that  the  lines  of  the  axial  planes  make  equal  angles  of 
60°  (45°,  etc.)  with  each  other  the  effect  is  that  polarized  light  which  has  passed 
through  the  center  suffers  circular  polarization,  with  a  rotation  to  right  or 
left  according  to  the  way  in  which  the  sections  are  built  up.     The  inter- 
ference-figure resembles  that  of  a  section  of  quartz  cut  normal  to  the  axis. 

If  the  sections  are  numerous  and  very  thin  the  imitation  of  the  phenomena 
of  quartz  is  closer.  These  facts  throw  much  light  upon  the  ultimate  molec- 
ular structure  of  a  crystallized  medium  showing  circular  polarization.  Fur- 
ther, it  is  easy  from  this  to  understand  how  it  is  possible  to  have  in  sections 
of  certain  crystals  (e.g.,  of  clinochlore)  portions  which  are  biaxial  and  others 
that  are  uniaxial,  the  latter  being  due  to  an  intimate  twinning  after  this 
method  of  biaxial  portions. 

427.  Optical  Properties  of  Crystalline  Aggregates.  —  The  special  optical  phenomena  of 
the  different  kinds  of  crystalline  aggregates  described  on  pp.  182,  183,  and  the  extent  to 
which  their  optical  characters  can  be  determined,  depend  upon  the  distinctness  in  the 
development  of  the  individuals  and  their  relative  orientation.     The  case  of  ordinary  granu- 
lar, fibrous,  or  columnar  aggregates  needs  no  special  discussion.     Where,  however,  the 
doubly  refracting  grains  are  extremely  small,  the  microscope  may  hardly  serve  to  do  more 
than  to  show  the  aggregate  polarization  present. 

A  case  of  special  interest  is  that  of  spherulites,  that  is,  aggregates  spherical  in  form  and 
radiated  or  concentric  in  structure;  such  aggregates  occur  with  calcite,  various  chlorites, 
feldspars,  etc.  If  they  are  formed  of  a  doubly  refracting  crystalline  mineral,  or  of  an 
amorphous  substance  which  has  birefringent  characters  due  to  internal  tension,  they  com- 
monly exhibit  a  dark  cross  in  the  microscope  between  crossed  nicols;  further,  this  cross,  as 
the  section  is  revolved  on  the  stage,  though  actually  stationary,  seems  to  rotate  backward. 

A  distinct  and  more  special  case  is  that  of  spherical  aggregates  of  a  mineral  optically 
uniaxial  (or  biaxial  with  a  small  angle) .  Sections  of  these  (not  central)  in  parallel  polarized 
light  show  more  or  less  distinctly  the  interference-figure  of  a  uniaxial  crystal.  The  objec- 
tive must  be  focussed  on  a  point  a  little  removed  from  the  section  itself,  say  on  the  surface 
of  the  sphere  of  which  it  is  a  part.  In  such  cases  the  +  or  —  character  of  the  double 
refraction  can  be  determined  as  usual. 

428.  Change  of  Optical  Character  Induced  by  Pressure.  —  As  the  difference  between 
the  optical  phenomena  exhibited  by  an  isometric  crystal  on  the  one  hand  and  a  uniaxial  or 
biaxial  crystal  on  the  other  is  referred  to  a  difference  in  molecular  structure  modifying  the 
properties  of  the  ether,  it  would  be  inferred  that  if  an  amorphous  substance  were  subjected 
to  conditions  tending  to  develop  an  analogous  difference  in  its  molecular  structure  it  would 
also  show  doubly  refracting  properties. 

This  is  found  to  be  the  case.  Glass  which  has  been  suddenly  cooled  from  a  state  of 
fusion,  and  which  is  therefore  characterized  by  strong  internal  tension,  usually  shows 
marked  double  refraction.  Further,  glass  plates  subjected  to  great  mechanical  pressure  in 
one  direction  show  in  polarized  light  more  or  less  distinct  interference-curves.  Gelatine 
sections,  also,  under  pressure  exhibit  like  phenomena.  Even  the  strain  in  a  glass  block 
developed  under  the  influence  of  unlike  charges  of  electricity  of  great  difference  of  potential 
on  its  opposite  sides  is  sufficient  to  make  it  doubly  refracting. 

In  an  analogous  manner  the  double  refraction  of  a  crystal  may  be  changed  by  the  appli- 
cation of  mechanical  force.  Pressure  exerted  normal  to  the  vertical  axis  of  a  section  of  a 
tetragonal  or  hexagonal  crystal  which  has  been  cut  _L  c  axis,  changes  the  uniaxial  inter- 
ference-figure into  a  biaxial,  and  with  substances  optically  positive,  the  plane  of  the  optic 
axes  is  parallel,  and  with  negative  substances  normal,  to  the  direction  of  pressure. 

The  o.uartz  crystals  in  rocks,  which  have  been  subjected  to  great  pressure,  are  often 
found  to  be  in  an  abnormal  state  of  tension,  showing  an  undulatory  extinction  in  polarized 
light. 


CHARACTERS    DEPENDING   UPON    LIGHT  301 

429.  Optical  An6malies.  —  Since  the  early  investigations  of  Brewster, 
Herschel,  and  others  (1815  et  seq.)  it  has  been  recognized  that  many  crystals 
exhibit  optical  phenomena  which  are  not  in  harmony  with  the  apparent 
symmetry  of  their  external  form.  Crystals  of  many  isometric  species,  as 
analcite,  alum,  boracite,  garnet,  etc.,  often  show  more  or  less  pronounced 
double  refraction,  and  sometimes  they  are  distinctly  uniaxial  or  biaxial.  A 
section  examined  in  parallel  polarized  light  may  show  more  or  less  sharply 
denned  doubly  refracting  areas,  or  parallel  bands  or  lamellae  with  varying 
extinction.  Occasionally,  as  noted  by  Klein  in  the  case  of  garnet,  while  most 
crystals  are  normally  isotropic,  others  show  optical  characters  which  seem  to 
be  determined  by  the  external  bounding  faces  and  edges;  thus,  a  dodecahedron 
may  appear  to  be  made  up  of  twelve  rhombic  pyramids  (biaxial)  whose  apices 
are  at  the  center;  a  hexoctahedron  similarly  may  seem  to  be  made  up  of  forty- 
eight  triangular  pyramids,  etc. 

Similarly,  crystals  of  many  common  tetragonal  or  hexagonal  species,  as 
vesuvianite,  zircon,  beryl,  apatite,  corundum,  chabazite,  etc.,  give  interfer- 
ence-figures resembling  those  of  biaxial  crystals.  Also,  analogous  contra- 
dictions between  form  and  optical  characters  are  noted  with  crystals  of 
orthorhombic  and  monoclinic  species,  e.g.,  topaz,  natrolite,  orthoclase,  etc. 
All  cases  such  as  those  mentioned  are  embraced  under  the  common  term  of 
optical  anomalies. 

This  subject  has  been  minutely  studied  by  many  investigators  in  recent 
years  and  important  additions  have  been  made  to  it  both  on  the  practical  and 
the  theoretical  side.  The  result  is  that,  though  doubtful  cases  still  remain, 
many  of  the  typical  ones  have  found  a  satisfactory  explanation.  No  single 
theory,  however,  can  be  universally  applied. 

The  chief  question  involved  has  been  whether  the  anomalies  are  to  be 
considered  as  secondary  and  non-essential,  or  whether  they  belong  to  the 
inherent  molecular  structure  of  the  crystals  in  question.  On  the  one  hand, 
it  has  been  urged  that  internal  tension  suffices  (Art.  428)  to  call  out  double 
refraction  in  an  isotropic  substance  or  to  give  a  uniaxial  crystal  the  typical 
optical  structure  of  a  biaxial  crystal.  On  the  other  hand,  it  is  equally  clear 
that  twinning  often  produces  pseudo-symmetry  in  external  form,  and  at  the 
same  time  conceals  or  changes  the  optical  characters.  From  the  simplest  case, 
as  that  of  aragonite,  we  pass  to  more  complex  cases,  as  witherite  (Fig.  610), 
bromlite  (Figs.  611,  612),  phillipsite  (Figs.  400,  452-454),  which  last  is  some- 
times pseudo-isometric  in  form  though  optical  study  shows  the  monoclinic 
character  of  the  individuals.*  Reasoning  from  the  analogy  of  these  last  cases, 
Mallard  was  led  (1876)  to  the  theory  that  the  optical  anomalies  could  in  most 
cases  be  explained  by  the  assumption  of  a  similar  but  still  more  intimate 
grouping  of  molecules  which  themselves  without  this  would  unite  to  form  crys- 
tals of  a  lower  grade  of  symmetry  than  that  which  their  complex  twinned 
crystals  actually  simulate. 

In  regard  to  the  two  points  of  view  mentioned,  it  seems  probable  that 
internal  tension  (due  to  pressure,  sudden  cooling,  or  rapidity  of  growth,  etc.) 
can  be  safely  appealed  to  to  explain  the  anomalous  optical  character  of  many 
species,  as  diamond,  halite,  beryl,  quartz,  etc.  Again,  it  has  been  fully  proved 
that  the  later  growth  of  isomorphous  layers  of  varying  composition  may 

*  Crystals  showing  pseudo-symmetry  of  highly  complex  type  are  called  mimetic  crystals 
by  Tschermak. 


302 


PHYSICAL   MINERALOGY 


produce  optical  anomalies,  probably  here  also  to  be  referred  to  tension.  Alum 
is  a  striking  example.  The  peculiarities  of  this  species  were  early  investigated 
by  Biot  and  made  by  him  the  basis  of  his  theory  of  "  lamellar  polarization," 
but  the  present  explanation  is  doubtless  the  true  one.  Fig.  616  (from  Brauns) 
shows  the  appearance  in  polarized  light  of  a  section  ||  0(111)  from  a  crystal  in 
which  the  successive  layers  have  different  composition.  Further,  according  to 
Brauns,  the  optical  peculiarities  of  many  other  species  may  be  referred  to  this 
same  cause.  He  includes  here,  particularly,  those  cases  (as  with  some  garnets) 
in  which  the  optical  characters  seem  to  depend  upon  the  external  form,  as 
noted  above.  Here  belongs  also  apophyllite,  a  section  of  which  (from  Golden, 
Col.,  by  Klein)  is  shown  in  Fig.  617.  The  section  has  been  cut  ||  c(001) 

616  617  618 


Alum,  ||  111 


Apophyllite,  ||  001 


Leucite,  ||  100 


through  the  center  of  the  crystal  and  is  represented  as  it  appears  in  parallel 
polarized  light. 

Another  quite  distinct  but  most  important  class  is  that  including  species 
such  as  boracite  and  leucite,  which  are  dimorphous;  that  is,  those  species 
which  at  a  certain  elevation  of  temperature  (300°  for  boracite  and  500°  to  600° 
for  leucite)  become  strictly  isotropic.  Under  ordinary  conditions,  these  species 
are  anisotropic,  but  the  fact  stated  makes  it  probable  that  originally  their 
crystalline  form  and  optical  characters  were  in  harmony.  The  relations  for 
leucite  deserve  to  be  more  minutely  stated. 

Leucite  usually  shows  very  feeble  double  refraction:  to  =  1'508,  e  =  1'509.  This 
anomalous  double  refraction,  early  noted  (Brewster,  Biot),  was  variously  explained.  In 
1873,  Rath,  on  the  basis  of  careful  measurements,  referred  the  seemingly  isometric  crystals 
to  the  tetragonal  system,  the  trapezohedral  face  112  being  taken  as  111  and  211,  121  as 
421,  241;  respectively;  also  101,  Oil  as  201,  021.  Later  Weisbach  (1880),  on  the 
same  ground,  made  them  orthorhombic;  Mallard,  however,  referred  them  (1876),  chiefly  on 
optical  grounds,  to  the  monoclinic  system,  and  Fouque  and  Levy  (1879)  to  the  triclinic. 
The  true  symmetry,  corresponding  to  the  molecular  structure  which  they  possess  or  tend 
to  possess  at  ordinary  temperatures,  is  in  doubt,  but  it  has  been  shown  (Klein,  Penfield) 
that  at  500°  to  600°  sections  become  isotropic;  and  further  (Rosenbusch)  that  the  twinning 
striations  disappear  on  heating,  to  reappear  again  in  new  position  on  cooling.  Sections 
ordinarily  show  twinning-lamellae  |j  d(110);  in  some  cases  a  bisectrix  (+)  is  normal  to  what 
corresponds  to  a  cubic  face,  the  axial  angle  being  very  small.  The  structure  corresponds  in 
general  (Klein)  to  the  interpenetration  of  three  crystals,  in  twinning  position  ||  d,  which 
may  be  equally  or  unequally  developed;  or  there  may  be  one  fundamental  individual  with 
inclosed  twinning-lamellse.  Fig.  618  shows  a  section  of  a  crystal  (||  a,  100)  which  is  ap- 
parently made  up  by  the  twinning  of  three  individuals. 

Still  again,  in  a  limited  number  of  cases,  it  can  be  shown  that  -the  inter- 
growth  of  lamellae  having  slightly  different  crystallographic  orientation  is  the 
cause  of  the  optical  peculiarities.  Prehnite  is  a  conspicuous  example  of 
this  class. 


CHARACTERS  DEPENDING  UPON  HEAT  303 

After  all  the  various  possible  explanations  have  been  applied  there  still 
remain,  however,  many  species  about  which  no  certain  conclusion  can  be 
reached.  To  many  of  these  species  the  theory  of  Mallard  may  probably  be 
applicable.  Indeed  it  may  be  added  that  much  difference  of  opinion  still  exists 
as  to  the  cause  of  the  "  optical  anomalies  "  in  a  considerable  number  of  minerals. 

LITERATURE 
.    Optical  Anomalies  * 

Brewster.  Many  papers  in  Phil.  Trans.,  1814,  1815,  and  later;  also  in  Ed.  Trans., 
Ed.  Phil.  J.,  etc. 

Biot  Recherches  sur  la  polarisation  lamellaire,  etc.  C.  R.,  12,  967,  1841:  13.  155, 
391,  839,  1841;  in  full  in  Mem.  de  I'Institut,  18,  539. 

Volger.     Monographic  des  Boracits.     Hannover,  1857. 

Marbach.  Ueber  die  optischen  Eigenschaf  ten  einiger  Krystalle  des  tesseralen  Systems. 
Pogg.  Ann.,  94,  412,  1855. 

Pfaff.  Versuche  iiber  den  Einfluss  des  Drucks  auf  die  optischen  Eigenschaften  der 
Krystalle.  Pogg.  Ann.,  107,  333,  1859;  108,  598,  1859. 

Des  Cloizeaux.  Ann.  Mines  11,  261,  1857;  14,  339,  1858,  6,  557,  1864.  Also  Nou- 
velles  Recherches,  etc.,  1867. 

Reusch.  Ueber  die  sogennante  Lamellarpolarisation  des  Alauns.  Pogg.  Ann.,  132, 
618,  1867. 

Rumpf.     Apophyllite.     Min.  petr.  Mitth.,  2,  369,  1870. 

Hirschwald.     Leucite.     Min.  Mitth.,  227,  1875. 

Lasaulx.     Tridymite.     Zs.  Kr.,  2,  253,  1878. 

Mallard.  Application  des  phenomenes  optiques  anomaux  que  presentent  un  grand 
nombre  de  substances  cristallisees.  Annales  des  Mines  (Ann.  Min.)  10,  pp.  60-196,  1876 
(Abstract  in  Zs.  Kr.,  1,  309-320).  See  also  Bull.  Soc.  Min.,  1,  107,  1878.  Sur  les  pro- 
prietes  optiques  des  melanges  de  substances  isomorphes  et  sur  les  anomalies  optiques  des 
cristaux.  Bull.  Soc.  Min.,  3,  3,  1880,  Also  ibid.,  4,  71,  1881;  5,  144,  1882. 

Bertrand.     Numerous  papers  in  Bull.  Soc.  Min.,  1878-1882. 

Becke.     Chabazite.     Min.  petr.  Mitth.,  2,  391,  1879. 

Baumhauer.     Perovskite.     Zs.  Kr.,  4,  187,  1879. 

Tschermak.     "  Mimetische  Formen."     Zs.  G.  Ges.,  31,  637,  1879. 

Jannettaz.     Diamond.     Bull.  Soc.  Min.,  2,  124,  1879;  alum,  ibid.,  2,  191;  3,  20. 

Bucking.  Ueber  durch  Druck  hervorgerufene  optische  Anomalien.  Zs.  G.  Ges.,  32, 
199,  1880.  Also,  Zs.  Kr.,  7,  555,  1883. 

Arzruni  and  S.  Kock.     Analcite.     Zs.  Kr.,  5,  483,  1881. 

Klocke.  Ueber  Doppelbrechung  regularer  Krystalle.  Jb.  Min.,  1,  53,  1880  (also 
2,  97,  13  ref.;  1,  204,  1881,  and  Verh.  nat.  Ges.  Freiburg,  8,  31).  Ueber  einige  optische 
Eigenschaften  optisch  anomaler  Krystalle  und  deren  Nachahmung  durch  gespannte  und 
gepresste  Colloide.  Jb.  Min.,  2,  249,  1881. 

C.  Klein.  Boracite.  Jb.  Min.,  2,  209,  1880;  1,  239,  1881;  1,  235,  1884.  Garnet. 
Nachr.  Ges.  Gottingen,  1882;  Jb.  Min.,  1,  87,  1883.  Apophyllite  (influence  of  heat). 
Jb.  Min.,  2,  165,  1892.  Garnet,  vesuvianite,  etc.  Ibid.,  2,  68,  1895. 

W.  Klein.  Beitrage  zur  Kenntniss  der  optischen  Aenderungen  in  Krystallen  unter 
dem  Einflusse  der  Erwarmung.  Zs.  Kr.,  9,  38,  1884. 

Brauns.  Die  optischen  Anomalien  der  Krystalle.  (Preisschrift),  Leipzig,  1891.  Also 
earlier  papers:  Jb.  Min.,  2,  102,  1883;  1,  96,  1885;  1,  47,  1887. 

Ben  Saude.  Beitrag  zu  einer  Theorie  der  Optischen  Anomalien  der  regularen  Krys- 
talle. Lisbon,  1894.  Also  earlier:  Analcite,  Jb.  Min.,  1,  41,  1882.  Perovskite  (Preiss- 
chrift), Gottingen,  1882. 

Wallerant.  Theorie  des  anomales  optiques,  de  1'isomorphisme  et  du  polymorphisme. 
Bull.  Soc.  Min.,  21,  188,  1898. 


IV.  CHARACTERS  DEPENDING  UPON  HEAT 

430.   The  more  important  of  the  special  properties  of  a  mineral  species  with 
respect  to  heat  include  the  following:  Fusibility;  conductivity  and  expansion, 

*  A  complete  bibliography  is  given  in  the  memoir  by  Brauns  (1891),  see  above. 


304  PHYSICAL   MINERALOGY 

especially  in  their  relation  to  crystalline  structure;  change  in  optical  charac- 
ters with  change  of  temperature;  specific  heat;  also  diathermancy,  or  the  power 
of  transmitting  heat  radiation.  The  full  discussion  of  these  and  other  related 
subjects  lies  outside  of  the  range  of  the  present  text-book.  A  few  brief 
remarks  are  made  upon  them,  and  beyond  these  reference  must  be  made  to 
text-books  on  Physics  and  to  special  memoirs,  some  of  which  are  mentioned 
in  the  literature  (p.  305). 

431.  Fusibility.  —  The  approximate  relative  fusibility  of  different  min- 
erals is  an  important  character  in  distinguishing  different  species  from  one 
another  by  means  of  the  blowpipe.     For  this  purpose  a  scale  is  conveniently 
used  for  comparison,  as  explained  in  the  articles  later  devoted  to  the  blowpipe. 
Accurate  determinations  of  the  fusibility  are  difficult,  and  though  of  little 
importance  for  the  above  object,  they  are  interesting  from  a  theoretical  stand- 
point.    They  have  been  attempted  by  various  authors  by  the  use  of  a  number 
of  different    methods.     The  following   are   the    approximate   melting-point 
values  for  the  minerals  used  in  von  KobelPs  scale  (Art.  491) :  Stibnite,  525° : 
natrolite,    965°;     almandite,    1200°;     actinolite,    1296°;     orthoclase,    1200°; 
bronzite,  1380°;  also  for  quartz,  about  1600°. 

432.  Conductivity.  —  The  conducting  power  of  different  crystallized 
media  was  early  investigated  by  Senarmont.     He  covered  the  faces  of  the  sub- 
stance under  investigation  with  wax  and  observed  the  form  of  the  figure 
melted  by  a  hot  wire  placed  in  contact  with  the  surface  at  its  middle  point. 
Later  investigations  have  been  made  by  Rontgen  (who  modified  the  method  of 
Senarmont),  by  Jannettaz,  and  others.     In  general  it  Is  found  that,  as  regards 
their  thermal  conductivity,  crystals  are  to  be  divided  into  the  three  classes 
noted  on  p.  252.     In  other  words,  the  conductivity  for  heat  seems  to  follow 
the  same  general  laws  as  the  propagation  of  light.     It  is  to  be  stated,  however, 
that  experiments  by  S.  P.  Thompson  and  0.  J.  Lodge  have  shown  a  different 
rate  of  conductivity  in  tourmaline  in  the  opposite  directions  of  the  vertical 
axis. 

433.  Expansion.  —  Expansion,  that  is,  increase  in  volume  upon  rise  of 
temperature,  is  a  nearly  universal  property  for  all  solids.     The  increment  of 
volume  for  the  unit  volume  in  passing  from  0°  to  1°  C.  is  called  the  coefficient 
of  expansion.     This  quantity  has  been  determined  for  a  number  of  species. 
Further,  the  relative  expansion  in  different  directions  is  found  to  obey  the 
same  laws  as  the  light-propagation.     Crystals,  as  regards  heat-expansion,  are 
thus  divided  into  the  same  three  classes  mentioned  on  p.  252  and  referred  to 
in  the  preceding  article. 

The  amount  of  expansion  varies  widely,  and,  as  shown  by  Jannettaz,  is 
influenced  particularly  by  the  cleavage.  Mitscherlich  found  that  in  calcite 
there  was  a  diminution  of  8'  37"  in  the  angle  of  the  rhombohedron  on  passing 
from  0°  to  100°  C.,  the  form  thus  approaching  that  of  a  cube  as  the  tempera- 
ture increased.  The  rhombohedron  of  dolomite,  for  the  same  range  of  tem- 
perature, diminishes  4'  46";  and  in  aragonite,  for  a  rise  in  temperature  from 
21°  to  100°,  the  angle  of  the  prism  diminishes  2'  46".  In  some  rhombohedrons, 
as  of  calcite,  the  vertical  axis  is  lengthened  (and  the  horizontal  shortened), 
while  in  others,  like  quartz,  the  reverse  is  true.  The  variation  is  such  in  both 
cases  that  the  birefringence  is  diminished  with  the  increase  of  temperature, 
for  calcite  possesses  negative  double  refraction,  and  quartz,  positive. 

It  is  to  be  noted  that  in  general  the  expansion  by  heat,  while  it  may  serve 
to  alter  the  angles  of  crystals,  other  than  those  of  the  isometric  system,  does 


CHARACTERS  DEPENDING  UPON  HEAT 


305 


Oeberg 
01291 

01645 
01758 
0-1861 

Orthoclase 
Albite 
Amphibole,  black 
Beryl 
Calcite         0'2034 
Aragonite 

Joly                     Oeberg 
01869              0-1877 
01983              0-1976 
0-1963  Augite  01830 
0-2066              0-1979 
-  0-2044              0*2042 
0-2036 

not  alter  the  zone-relations  and  the  crystalline  symmetry.  In  certain  cases, 
however,  the  effect  of  heat  may  be  to  give  rise  to  twinning-lamellse  (as  in 
anhydrite)  or  to  cause  their  disappearance  (as  in  calcite).  Rarely  heat  serves 
to  develop  a  new  molecular  structure;  thus,  as  explained  in  Art.  429,  boracite 
and  leucite,  which  are  anisotropic  at  ordinary  temperatures,  become  isotropic 
when  heated,  the  former  to  300°  the  latter  to  500°  or  600°.  The  change  in 
the  optical  properties  of  crystals  produced  by  heat  has  already  been  noticed 
(Art.  422). 

434.  Specific  Heat.  —  Determinations  of  the  specific  heat  of  many 
minerals  have  been  made  by  Joly,  by  Oeberg,  and  others.     Some  of  the  results 
reached  are  as  follows: 

Joly 

Galena,  cryst.  0'0541 

Chalcopyrite  01271 

Pyrite  01306 

Hematite  01683 

Garnet,  red  cryst.  01780  —  01793 
Epidote  G'1877 

435.  Diathermancy.  —  Besides  the  slow  molecular  propagation  of  heat 
in  a  body,  measured  by  its  thermal  conductivity,  there  is  also  to  be  considered 
the  rapid  propagation  of  what  is  called  radiant  heat  through  it  by  the  wave- 
motion  of  the  ether  which  surrounds  its  molecules.     This  is  merely  a  part  of 
the  general  subject  of  light-propagation  already  fully  discussed,  since  heat- 
waves, in  the  restricted  sense,  differ  from  light-waves  only  in  their  relatively 
greater  length  *     The  degree  of  absorption  exerted  by  the  body  is  measured  by 
its  diathermancy,  which  corresponds  to  transparency  in  light.     In  this  sense 
halite,  sylvite,  and  fluorite  are  highly  diathermanous,  since  they  absorb  but 
little  of  the  heat-waves  passing  through  them;   on  the  other  hand,  gypsum 
and,  still  more,  alum  are  comparatively  athermanous,  since  while  transparent 
to  the  short  light-waves  they  absorb  the  long  heat-waves,  transforming  the 
energy  into  that  of  sensible  heat.     Measurements  of  the  diathermancy  were 
early  made  by  Melloni,  later  by  Tyndall,  Langley,  and  others. 

LITERATURE 
Heat 


Mitscherlich.     Pogg.  Ann.,  1,  125,  1824;  10,  137,  1827. 
F.  E.  Neumann.     Gypsum.     Pogg.  Ann.,  27,  240,  1833. 

Senarmont.  Ann.  Ch.  Phys.,  21,  457,  1847;  22,  179,  1848;  also  in  Pogg.  Ann.,  73, 
191;  74,  190;  75.  50,  482. 

Angstrom.     Pogg.  Ann.,  86,  206,  1852. 

Grailich  and  von  Lang.     Ber.  Ak.  Wien,  33,  369,  1858. 

Fizeau.  Thermal  expansion.  C.  R.,  58,  923,  1864.  Ann.  Ch.  Phys.,  2,  143,  1864;  8, 
335,  1866;  also  C.  R.,  1864-1867. 

C.  Neumann.     Pogg.  Ann.,  114,  492,  1868. 

Pape.     Thermic  axes  of  blue  vitriol.     Wied.  Ann.,  1,  126,  1877. 

Rontgen.     Pogg.  Ann.,  151,  603,  1874;  Zs.  Kr.,  3,  17,  1878. 

Jannettaz.  Conductivity  of  crystals.  Bull.  Soc.  Geol.,  (3)  1,  117,  252;  2,  264;  3, 
499;  4,  116,  554;  9,  196.  Bull.  Soc.  Min.,  1,  19,  1879.  C.  R.,  1848,  114,  1352,  1892. 

O.  J.  Lodge.     Thermal  conductivity.     Phil.  Mag.,  5,  110,  1878. 

S.  P.  Thompson  and  O.  J.  Lodge.  Conductivity  of  tourmaline.  Phil.  Mag.,  8,  18, 
1879. 

Arzruni.     Effect  of  heat  on  refractive  indices  of  barite,  etc.     Zs.  Kr.,  1,  165,  1877. 

Beckenkamp.     Expansion'of  monoclinic  and  triclinic  crystals.     Zs.  Kr.,  5,  436,  1881. 

H.  Dufet.  Effect  of  heat  on  refractive  indices  of  gypsum.  Bull.  Soc.  Min.,  4,  113, 
191,  1881. 


306  PHYSICAL   MINERALOGY 

A.  Schrauf.     Sulphur.     Zs.  Kr.,  12,  321,  1887;  TiO2,  ibid.,  9,  433,  1884. 
L.  Fletcher.     Expansion  of  crystals.     Zs.  Kr.,  4,  337,  1880. 


Joly.     Meldometer.     Ch.  News,  65,  1,  16,  1892,  and  Proc.  Roy.  Irish  Acad.,  2,  38, 
1891.     Specific  heat.     Proc.  Roy.  Soc.,  41,  250,  352,  1887. 

f^.      1  Ct  •  C.         •"  •  f^      e  A  1          Ctj._-l_t_          TVT_       O       /IO       1OOC 

Oeberg.     Specifn 

Doelter.     For  m 

chemie,  1,  628  et  seq. 


X.  kJfJV/V-'ll.lV-'     AXV/C*V»  -1.    J.W.      -*.vv^    .      F 

Oeberg.     Specific  heat.     Oefv.  Ak.  Stockh.,  No.  8,  43,  1885. 

Doelter.     For  methods  and  results  in  fusing  silicates,  see  Handbuch  der  Mineral- 


V.   CHARACTERS  DEPENDING  UPON  ELECTRICITY 
AND  MAGNETISM 

1.     ELECTRICITY 

436.  Electrical  Conductivity.  —  The  subject  of  the  relative  conducting 
power  of  different  minerals  is  one  of  minor  interest.*     In  general  most  min- 
erals, except  those  having  a  metallic  luster  among  the  sulphides  and  oxides,  are 
non-conductors.     Only  the  non-conductors  can  show  pyro-electrical  phenom- 
ena, and  only  the  conductors  can  give  a  thermo-electric  current. 

437.  Frictional  Electricity.  —  The  development  of  an  electrical  charge 
on  many  bodies  by  friction  is  a  familiar  subject.     All  minerals  become  electric 
by  friction,  although  the  degree  to  which  this  is  manifested  differs  widely. 
There  is  no  line  of  distinction  among  minerals,  dividing  them  into  positively 
electric  and  negatively  electric ;  for  both  electrical  states  may  be  presented  by 
different  varieties  of  the  same  species,  and  by  the  same  variety  in  different 
states.     The  gem&  are  in  general  positively  electric  only  when  polished;  the 
diamond,  however,  exhibits  positive  electricity  whether  polished  or  not.     It  is 
a  familiar  fact  that  the  electrification  of  amber  upon  friction  was  early  observed 
(600  B.  C.),  and  indeed  the  Greek  name  (^Xe/crpo*/)  later  gave  rise  to  the 
word  electricity. 

438.  Pyro-electricity.  —  The  simultaneous  development  of  positive  and 
negative  charges  of  electricity  on  different  parts  of  the  same  crystal  when  its 
temperature  is  suitably  changed  is  called  pyro-electricity.     Crystals  exhibiting 
such  phenomena  are  said  to  be  pyro-electric.     This  phenomenon  was  first 
observed  in  the  case  of  tourmaline,  which  is  rhombohedral-hemimorphic  in 
crystallization,  and  it  is  particularly  marked  with  crystals  belonging  to  groups 
of  relatively  low  symmetry,  especially  those  of  the  hemimorphic  type.     It  is 
possible,  of  course,  only  with  non-conductors.     This  subject  was  early  inves- 
tigated by  Riess  and  Rose  (1843),  later  by  Hankel,  also  by  C.  Friedel,  Kundt. 
and  others  (see  literature). 

In  all  cases  it  is  true  that  directions  of  like  crystallographic  symmetry 
show  charges  of  like  sign,  while  unlike  directions  may  exhibit  opposite  charges. 
Substances  not  crystallized  cannot  show  pyro-electricity.  A  few  of  the  many 
possible  examples  will  serve  to  bring  out  the  most  essential  points. 

Boracite  (isometric-tetrahedral,  p.  66)  on  heating  exhibits  +  electricity  on 
one  set  of  tetrahedral  faces  and  —  electricity  on  the  other.  Cf.  Fig.  619. 

Tourmaline  (rhombohedral-hemimorphic,  p.  109)  shows  opposite  charges  at 
the  opposite  extremities  of  the  vertical  axis  corresponding  to  its  hemimorphic 
crystallization.  In  this  and  in  other  similar  cases,  the  extremity  which 

*  On  the  conductivity  of  minerals,  see  Beijerinck,  Jb.  Min.,  Beil.-Bd.,  11,  403,  1898. 


CHARACTERS   DEPENDING   UPON   ELECTRICITY   AND   MAGNETISM  307 

becomes  positive  on  heating  has  been  called  the  analogous  pole,  and  that  which 
becomes  negative  has  been  called  the  antilogous  pole. 

Calamine  and  struvite  (orthorhombic-hemimorphic,  p.  126)  exhibit  phenom- 
ena analogous  to  those  of  tourmaline. 

Quartz  (rhombohedral-trapezohedral,  p.  112)  shows  +  electricity  on  heating 
at  the  three  alternate  prismatic  edges  and  —  electricity  at  the  three  remaining 
edges;  the  distribution  for  right-handed  crystals  is  opposite  to  that  of  left- 
handed.  Twins  may  exhibit  a  high  degree  of  complexity.  Cf.  Figs.  620,  621. 

Axinite  (triclinic,  p.  144),  when  heated  to  120°  or  130°,  has  an  analogous 

619  620  621 


pole  (Riess  &  Rose)  at  the  solid  angle  rxM';  the  antilogous  pole  at  the  angle 
mr'M'  near  plane  n. 

A  very  convenient  and  simple  method  for  investigating  the  phenomena  is 
the  following,  which  is  due  to  Kundt:  First  heat  the  crystal  or  section  care- 
fully in  an  air-bath;  pass  it  several  times  through  the  flame  of  an  alcohol 
lamp  and  then  place  it  on  a  little  upright  cylinder  of  brass  to  cool.  While 
cooling,  a  mixture  of  red  lead  and  sulphur  finely  pulverized  and  previously 
agitated  is  dusted  over  it  through  a  fine  cloth  from  a  suitable  bellows.  The 
positively  electrified  red  lead  collects  on  the  parts  having  a  negative  charge, 
and  the  negatively  electrified  sulphur  on  those  with  a  positive  charge.  This  is 
illustrated  by  Figs.  619-621,  and  still  better  by  the  illustrations  given  by 
Kundt  and  others.  (Cf.  Plate  III  of  Groth,  Phys.  Kryst.,  1905.) 

439.  Piezoelectricity.  —  The  name  piezo-electricity  has  been  given  to 
the  development  of  electrical  charges  on  a  crystallized  body  by  pressure.     This 
is  shown  by  a  cleavage  mass  of  calcite,  also  by  topaz.     This  phenomenon  is 
most  interesting  where  a  relation  can  be  established  between  the  electrical 
excitement  and  the  molecular  structure,  as  is  conspicuously  true  with  quartz, 
tourmaline,  and  some  other  species. 

This  subject  has  been  investigated  by  Hankel,  Curie,  and  others,  and 
discussed  theoretically  by  Lord  Kelvin  (see  literature).  Hankel  has  also 
employed  the  term  actino-electricity ',  or,  better,  photo-electricity,  for  the  phe- 
nomenon of  producing  an  electrical  condition  by  the  influence  of  direct 
radiation;  fluorite  is  a  conspicuous  example. 

440.  Thermo-electricity.  —  The  contact  of  two  unlike  metals  in  gen- 
eral results  in  electrifying  one  of  them  positively  and  the  other  negatively.     If, 
further,  the  point  of  contact  be  heated  while  the  other  parts,  connected  with 
a  wire,  are  kept  cool,  a  continuous  current  of  electricity  —  shown,  for  example, 
by  a  suitable  galvanometer  —  is  set  up  at  the  expense  of  the  heat-energy  sup- 
plied.    If,  on  the  other  hand,  the  point  of  junction  is  cooled,  a  current  is  set 
up  in  the  reverse  direction.     This  phenomenon  is  called  thermo-electricity , 


308  PHYSICAL   MINERALOGY 

and  two  metals  so  connected  constitute  a  thermo-electric  couple.  Further  it 
is  found  that  different  conductors  can  be  arranged  in  order  in  a  table  —  a 
so-called  thermo-electric  series  —  according  to  the  direction  of  the  current  set 
up  on  heating  and  according  to  the  electromotive  force  of  this  current.  Among 
the  metals,  bismuth  (+)  and  antimony  (—)  stand  at  the  opposite  ends  of  the 
series;  the  current  passes  through  the  connecting  wire  from  antimony  to 
bismuth. 

This  subject  is  so  far  important  for  mineralogy,  as  it  was  shown  by  Bunsen 
that  the  natural  metallic  sulphides  stand  farther  off  in  the  series  than  bismuth 
and  antimony,  and  consequently  by  them  a  higher  electromotive  force  is 
produced.  The  thermo-electrical  relations  of  a  large  number  of  minerals  were 
determined  by  Flight. 

It  was  early  observed  that  some  minerals  have  varieties  which  are  both  -f- 
and  —  .  Rose  attempted  to  establish  a  relation  between  the  positive  and 
negative  pyritohedral  forms  of  pyrite  and  cobaltite,  and  the  positive  or  nega- 
tive thermo-electrical  character.  Later  investigations  by  Schrauf  and  Dana 
have  shown,  however,  that  the  same  peculiarity  belongs  also  to  glaucodot, 
tetradymite,  skutterudite,  danaite,  and  other  minerals,  and  it  is  demonstrated 
by  them  that  it  cannot  be  dependent  upon  crystalline  form,  but  rather  upon 
chemical  composition. 

LITERATURE  * 
Pyro-electricity,  etc. 

Rose.     Tourmaline.     Pogg.  Ann.,  39,  285,  1836. 

Riess  and  Rose.     Pogg.  Ann.,  59,  353,  1843:  61.  659,  1844. 

Kobell.     Pogg.  Ann.,  118,  594,  1863. 

Hankel.  Pogg.  Ann.,  49,  493;  50,  237,  1840;  61,  281,  1844.  Many  important  papers 
in  Abhandl.  K.  Sachs.  Ges.,  1865  and  later;  also  Wied.  Ann.,  2,  66,  1877;  11,  269,  1880, 
etc. 

J.  and  P.  Curie.     C.  R.,  91,  294,  383,  1880;  92,  186,  350,  1881;  93,  204,  1882. 

Kundt.     Ber.  Ak.  Berlin,  421,  1883;  Wied.  Ann.,  20,  592,  1893. 

Kolenko.     Quartz.     Zs.  Kr.,  9,  1,  1884. 

C.  Friedel.     Sphalerite,  etc.     Bull.  Soc.  Min.,  2,  31,  1879. 

C.  Friedel  and  Curie.     Sphalerite,  boracite.     Bull.  Soc.  Min.,  6.  191,  1883. 

Mack.     Boracite.     Zs.  Kr.,  8,  503,  1883. 

Voigt.     Abhandl.  Ges.  Gottingen,  36,  99,  1890. 

Kelvin.     Phil.  Mag.,  36,  331,  453,  1893. 

G.  S.  Schmidt.     Photo-electricity  of  fluorite.     Wied.  Ann.,  62,  407,  1897. 

Thermo-electricity 

Marbach.    C.  R.,  45,  705,  1857. 

Bunsen.     Pogg.  Ann.,  123,  505,  1864. 

Friedel.    Ann.  Ch.  Phys.,  17,  79,  1869;  C.  R.,  78,  508,  1874. 

Rose.     Pyrite  and  cobaltite.     Pogg.  Ann.,  142,  1,  1871. 

Schrauf  and  E.  S.  Dana.     Ber.  Ak.  Wien,  69  (1),  142,  1874;  Am.  J.  Sc.,  8,  255,  1874. 

2.     MAGNETISM 

441.  Magnetic  Minerals.  Natural  Magnets.  —  A  few  minerals  in  their 
natural  state  are  capable  of  being  attracted  by  a  strong  steel  magnet;  they 
are  said  to  be  magnetic.  This  is  conspicuously  true  of  magnetite,  the  magnetic 
oxide  of  iron;  also  of  pyrrhotite  or  magnetic  pyrites,  and  of  some  varieties  of 
native  platinum  (especially  the  variety  called  iron-platinum). 

A  number  of  other  minerals,  as  hematite,  franklinite,  etc.,  are  in  some 

*  See  Liebisch  Phys.  Krystallographie,  1891,  for  a  full  discussion  of  the  topics  briefly 
touched  upon  in  the  preceding  pages,  also  for  references  to  original  articles. 


CHARACTERS   DEPENDING   UPON    ELECTRICITY   AND   MAGNETISM  309 

cases  attracted  by  a  steel  magnet,  but  probably  in  most  if  not  all  cases  because 
of  admixed  magnetite  (but  see  Art.  443).  Occasional  varieties  of  the  three 
minerals  mentioned  above,  as  the  lodestone  variety  of  magnetite,  exhibit  them- 
selves the  attracting  power  and  polarity  of  a  true  magnet.  They  are  then 
called  natural  magnets.  In  such  cases  the  magnetic  polarity  has  probably  been 
derived  from  the  inductive  action  of  the  earth,  which  is  itself  a  huge  magnet. 

442.  Paramagnetism.     Diamagnetism.  —  In   a  very  strong  magnetic 
field,  as  that  between  the  poles  of  a  very  powerful  electromagnet,  all  minerals, 
as  indeed  all  other  substances,  are  influenced  by  the  magnetic  force.     Accord- 
ing to  their  behavior  they  are  divided  into  two  classes,  the  paramagnetic  and 
diamagnetic;  those  of  the  former  appear  to  be  attracted,  those  of  the  latter  to 
be  repelled.     For  purposes  of  experiment  the  substance  in  question,  in  the 
form  of  a  rod,  is  suspended  on  a  horizontal  axis  between  the  poles  of  the  magnet. 
If  paramagnetic,  it  takes  a  position  parallel  to  the  magnetic  axis;  if  diamag- 
netic, it  sets  transversely  to  it.     Iron,  cobalt,  nickel,  manganese,  platinum  are 
paramagnetic;    silver,  copper,  bismuth  are  diamagnetic.     Among  minerals 
compounds  of  iron  are  paramagnetic,  as  siderite,  also  diopside;  further,  beryl, 
dioptase.     Diamagnetic  species  include  calcite,  zircon,  wulfenite,  etc. 

By  the  use  of  a  sphere  it  is  possible  to  determine  the  relative  amount  of 
magnetic  induction  in  different  directions  of  the  same  substance.  Experiment 
has  shown  that  in  isometric  crystals  the  magnetic  induction  is  alike  in  all 
directions;  that  in  those  optically  uniaxial,  there  is  a  direction  of  maximum 
and,  normal  to  it,  one  of  minimum  magnetic  induction;  that  in  biaxial 
crystals,  there  are  three  unequal  magnetic  axes,  the  position  of  which  may  be 
determined.  In  other  words,  the  magnetic  relations  of  the  three  classes  of 
crystals  are  analogous  to  their  optical  relations. 

443.  Corresponding  to  the  facts  just  stated,  that  all  compounds  of  iron 
are   paramagnetic,  it  is  found  that  a  sufficiently  powerful  electromagnet 
attracts  all  minerals  containing  iron,  though,  except  in  the  cases  given  in  Art. 
441,  a  bar  magnet  has  no  sensible  influence  upon  them;  hence  the  efficiency 
of  the  electromagnetic  method  of  separating  ores. 

Plucker  *  determined  the  magnetic  attraction  of  a  number  of  substances 
compared  with  iron  taken  as  100,000.  For  example,  for  magnetite  he  obtained 
40,227;  for  hematite,  crystallized,  533,  massive,  134;  limonite,  71;  pyrite,  150. 

LITERATURE 

Magnetism 

Plucker.  Pogg.  Ann.,  72,  315,  1847;  76,  576,  1849;  77,  447,  1849;  78,  427,  1849;  86, 
1,  1852. 

Plucker  and  Beer.     Pogg.  Ann.,  81,  115,  1850;  82,  42,  1852. 

Faraday.  Phil.  Trans.,  1849-1857,  and  Experimental  Researches,  Series  XXII, 
XXVI,  XXX. 

W.  Thomson  (Lord  Kelvin).  Theory  of  Magnetic  Induction.  Brit.  Assoc.,  1850,  pt.  2, 
23;  Phil.  Mag.,  1,  177,  1851,  etc.  Reprint  of  Papers  on  Electrostatics  and  Magnetism, 
1872. 

Tyndall.  Phil.  Mag.,  2,  165,  1851;  10,  153,  257,  1855;  11,  125,  1856;  Phil.  Trans., 
1855,  1.  Researches  on  diamagnetism  and  magne-crystallic  action.  London,  1870. 

Knoblauch  and  Tyndall.  Pogg.  Ann.,  79,  233;  81,  481,  1850  (Phil.  Mag.,  36,  37, 
1850). 

Rowland  and  Jacques.     Bismuth,  Calcite.     Am.  J.  Sc.,  18,  360,  1879. 

Tumlirz.     Quartz.     Wied.  Ann.,  27,  133,  1886. 

Koenig.     Wied.  Ann.,  31,  273,  1887. 

Stenger.     Calcite.     Wied.  Ann.,  20,  304,  1883;  35,  331,  1888. 

*  Pogg.  Ann.,  74,  343,  1848. 


310  PHYSICAL   MINERALOGY 


VI.   TASTE  AND   ODOR 

In  their  action  upon  the  senses  a  few  minerals  possess  taste,  and  others 
under  some  circumstances  give  off  odor. 

444.  Taste  belongs  only  to  soluble  minerals.     The  different  kinds  of 
taste  adopted  for  reference  are  as  follows : 

1.  Astringent:  the  taste  of  vitriol. 

2.  Sweetish  astringent:  taste  of  alum. 

3.  Saline:  taste  of  common  salt. 

4.  Alkaline:  taste  of  soda. 

5.  Cooling:  taste  of  saltpeter. 

6.  Bitter:  taste  of  Epsom  salts. 

7.  Sour:  taste  of  sulphuric  acid. 

445.  Odor.  —  Excepting  a  few  gaseous  and  soluble  species,  minerals 
in  the  dry  unchanged  state  do  not  give  off  odor.     By  friction,  moistening  with 
the  breath,  and  the  elimination  of  some  volatile  ingredient  by  heat  or  acids, 
odors  are  sometimes  obtained  which  are  thus  designated : 

1.  Alliaceous:    the  odor  of  garlic.     Friction  of  arsenopyrite  elicits  this 
odor;  it  may  also  be  obtained  from  arsenical  compounds  by  means  of  heat. 

2.  Horse-radish  odor:  the  odor  of  decaying  horse-radish.     This  odor  is 
strongly  perceived  when  the  ores  of  selenium  are  heated. 

3.  Sulphurous:  friction  elicits  this  odor  from  pyrite,  and  heat  from  many 
sulphides. 

4.  Bituminous:  the  odor  of  bitumen. 

5.  Fetid:  the  odor  of  sulphureted  hydrogen  or  rotten  eggs.     It  is  elicited 
by  friction  from  some  varieties  of  quartz  and  limestone. 

6.  Argillaceous:  the  odor  of  moistened  clay.     It  is  obtained  from  serpen- 
tine and  some  allied  minerals,  after  moistening  them  with  the  breath;  others, 
as  pyrargillite,  afford  it  when  heated. 

446.  Feel.  —  The  FEEL  is  a  character  which  is  occasionally  of  some 
importance;  it  is  said  to  be  smooth  (sepiolite),  greasy  (talc),  harsh,  or  meager, 
etc.     Some  minerals,  in  consequence  of  their  hygroscopic  character,  adhere  to 
the  tongue  when  brought  in  contact  with  it. 


PART  III.    CHEMICAL  MINERALOGY 


GENERAL  PRINCIPLES  OF  CHEMISTRY  AS  APPLIED 

TO  MINERALS 

447.  Minerals,   as  regards  their  chemical  constitution,   are  either  the 
uncombined  elements  in  a  native  state,  or  definite  compounds  of  these  elements 
formed  in  accordance  with  chemical  laws.     It  is  the  object  of  Chemical  Min- 
eralogy to  determine  the  chemical  composition  of  each  species;  to  show  the 
chemical  relations  of  different  species  to  each  other  where  such  exist;  and  also 
to  explain  the  methods  of  distinguishing  different  minerals  by  chemical  means. 
It  thus  embraces  the  most  important  part  of  Determinative  Mineralogy. 

In  order  to  understand  the  chemical  constitution  of  minerals,  some  knowl- 
edge of  the  fundamental  principles  of  Chemical  Philosophy  is  required;  and 
these  are  here  briefly  recapitulated. 

448.  Chemical  Elements.  —  Chemistry  recognizes  about  eighty  sub- 
stances which  cannot  at  will  be  decomposed,  or  divided  into  others,  by  any 
process  of  analysis  at  present  known ;  these  substances  are  called  the  chemical 
elements.     A  list  of  them  is  given  in  a  later  article  (452) ;   common  examples 
are:  Oxygen,  nitrogen,  hydrogen,  chlorine,  gold,  silver,  sodium,  etc. 

449.  Atom.     Molecule.  —  The  study  of  the  chemical  properties  of  sub- 
stances and  of  the  laws  governing  their  formation  has  led  to  the  belief  that 
there  is  for  each  element  a  definite,  indivisible  mass,  which  is  the  smallest 
particle  which  can  play  a  part  in  chemical  reactions;  this  indivisible  unit  is 
called  the  atom. 

With  some  rare  exceptions,  the  atom  cannot  exist  alone,  but  unites  by  the 
action  of  what  is  called  chemical  force,  or  chemical  affinity,  with  other  atoms 
of  the  same  or  different  kind  to  form  the  molecule.  The  molecule,  in  the 
chemical  senso,  may  be  defined  as  the  smallest  particle  into  which  a  given 
kind  of  substance  can  be  subdivided  without  undergoing  chemical  decomposi- 
tion. For  example,  two  atoms  of  hydrogen  unite  to  form  a  molecule  of  hydro- 
gen gas.  Again,  one  atom  of  hydrogen  and  one  of  chlorine  form  a  molecule 
of  hydrochloric  acid  gas;  two  atoms  of  hydrogen  and  one  of  sulphur  form 
a  molecule  of  the  gas  hydrogen  sulphide. 

450.  Atomic  Weight.  —  The  atomic  weight  of  an  element  is  the  weight, 
or,  better  expressed,  the  mass  of  its  atom  compared  with  that  of  the  element 
hydrogen  taken  as  the  unit  or  with  the  weight  of  an  atom  of  oxygen  taken  as 
16.     Of  the  methods  by  which  the  relation  between  the  masses  of  the  atoms  is 
determined  it  is  unnecessary  here  to  speak ;  the  results  that  have  been  obtained 
are  given  in  the  table  on  p.  312. 

311 


312 


CHEMICAL   MINERALOGY 


451.  Symbol.     Formula.  —  The  symbol  of  an  element  is  the  initial 
letter,  or  letters,  often  of  its  Latin  name,  by  which  it  is  represented  when 
expressing  in  chemical  notation  the  constitution  of  substances  into  the  compo- 
sition of  which  it  enters.     Thus  O  is  the  symbol  of  oxygen,  H  of  hydrogen,  Cl 
of  chlorine,  Fe  (from  ferrum)  of  iron,  Ag  (from  argentum)  of  silver,  etc.     Fur- 
ther, this  symbol  is  always  understood  to  indicate  that  definite  amount  of  the 
given  element  expressed  by  its  atomic  weight;  in  other  words,  it  represents  one 
atom.     If  twice  this  quantity  is  involved,  that  is,  two  atoms,  this  is  indicated 
by  a  small  subscript  number  written  immediately  after  the  symbol.     Thus, 
Sb2S3  means  a  compound  consisting  of  two  atoms  of  antimony  and  three  of 
sulphur,  or  of  2  X  120  parts  by  weight  of  antimony  and  3  X  32  of  sulphur. 

This  expression,  Sb2S3,  is  called  the  formula  of  the  given  compound,  since 
it  expresses  in  briefest  form  its  composition.  Similarly  the  formula  of  the 
mineral  albite  is  NaAlSisOg. 

Strictly  speaking,  such  formulas  are  merely  empirical  formulas,  since  they 
express  only  the  actual  result  of  analysis,  as  giving  the  relative  number  of 
atoms  of  each  element  present,  and  make  no  attempt  to  represent  the  actual 
constitution.  A  formula  developed  with  the  latter  object  in  view  is  called  a 
rational,  structural,  or  constitutional  formula  (see  Art.  469). 

452.  Table  of  the  Elements.  —  The  following  table  gives  a  list  of  all 
the  definitely  established  elements  with  their  accepted  symbols  and  also  their 
atomic  weights.* 

Of  the  elements  given  in  this  list  —  more  than  eighty  in  all  —  only  a  very 
small  number,  say  twelve,  play  an  important  part  in  making  up  the  crust  of 
the  earth  and  the  water  and  air  surrounding  it.  The  common  elements  con- 
cerned in  the  composition  of  minerals  are:  Oxygen,  sulphur,  silicon,  alu- 
minium, iron,  calcium,  magnesium,  sodium,  potassium.  Besides  these,  hydro- 
gen is  present  in  water,  nitrogen  in  the  air,  and  carbon  in  all  animal  and 
vegetable  substances.  Only  a  very  few  of  the  elements  occur  as  such  in  nature, 
as  native  gold,  native  silver,  native  sulphur,  etc. 

Of  the  elements,  oxygen,  hydrogen,  nitrogen,  chlorine,  and  fluorine  are 
gases;  bromine  is  a  volatile  liquid;  mercury  is  also  a  liquid,  but  the  others 
are  solids  under  ordinary  conditions. 


0  =  16 

Symbol          At.  Weieht 

'    Symbol 

0=16 

At.    Wpio-h 

Aluminium,  Aluminum 

Al 

27-1 

Columbium,  see  Niobium 

Antimony  (Stibium) 

Sb 

120-2 

Copper  (Cuprum) 

Cu 

63-6 

Argon 
Arsenic 

A 

As 

39-9 
74-9 

Dysprosium 
Erbium 

Dy 
Er 

162-5 
1677 

Barium 

Ba 

137-4 

Europium 

Eu 

152-0 

Beryllium.  Glucinum 

Be 

(or  Gl)     9-1 

Fluorine 

F 

19-0 

Bismuth 

Bi 

208-0 

Gadolinium 

Gd 

157-3 

Boron 

B 

11-0 

Gallium 

Ga 

69-9 

Bromine 

Br 

79-9 

Germanium 

Ge 

72-5 

Cadmium 

Cd 

112-4 

Glucinum,  see  Beryllium 

Caesium 

Cs 

132-8 

Gold  (Aurum) 

Au 

197-2 

Calcium 

Ca 

40-1 

Helium 

He 

4-0 

Carbon 

C 

12-0 

Holmium 

Ho 

163-5 

Cerium 

Ce 

140-2 

Hydrogen 

H 

1-0 

Chlorine 

Cl 

35-5 

Indium 

In 

114-8 

Chromium 

Cr 

52-0 

Iodine 

I 

126*9 

Cobalt 

Co 

59-0 

Iridium 

Ir 

193-1 

*  These  correspond  in  value  to  those  commonly  accepted,  and  are  given  accurate  to  one 
decimal  place. 


GENERAL  PRINCIPLES  OF  CHEMISTRY  AS  APPLIED  TO  MINERALS  313 


Symbol 

Iron  (Ferrum)                    Fe 

0=16 
At.  Weight 

55-8 

Ruthenium 

Symbol 

Ru 

0=16 
At.  Weight 

1017 

Krypton 

Kr 

82-9 

Samarium 

Sa 

150-4 

Lanthanum 

La 

139-0 

Scandium 

Sc 

44-1 

Lead  (Plumbum) 

Pb 

207-2 

Selenium 

Se 

79-2 

Lithium 

Li 

6-9 

Silicon 

Si 

28-3- 

Lutecium 

Lu 

175-0 

Silver  (Argentum) 

Ag 

107-9 

Magnesium 

Mg 

24-3 

Sodium  (Natrium) 

Na 

23-0 

Manganese 

Mn 

54-9 

Strontium 

Sr 

87-6 

Mercury  (Hydrargyrum) 

Hg 

200-6 

Sulphur 

S 

32-0 

Molybdenum 

Mo 

96-0 

Tantalum 

Ta 

181-5 

Neodymium 

Nd 

144-3 

Tellurium 

Te 

127-5 

Neon 

Ne 

20-2 

Terbium 

Tb 

159-2 

Nickel 

Ni 

58-7 

Thallium 

Tl 

204-0 

Niobium 

Nb 

93-1 

Thorium 

Th 

232-4 

Niton 

Nt 

222-4 

Thulium 

Tm 

168-5 

Nitrogen 

N 

14-0 

Tin  (Stannum) 

Sn 

1187 

Osmium 

Os 

190-9 

Titanium 

Ti 

48-1 

Oxygen 
Palladium 

O 
Pd 

16-0 
106-7 

Tungsten  (Wolframium) 
Uranium 

W 
U 

184-0 
238-2 

Phosphorus 

P 

31:0 

Vanadium 

V 

51-0 

Platinum 

Pt 

195-2 

Xenon 

Xe 

130-2 

Potassium  (Kalium) 

K 

39-1 

Ytterbium 

Yb 

173-5 

Praseodymium 

Pr 

140-9 

Yttrium 

Yt 

887 

Radium 

Ra 

226-0 

Zinc 

Zn 

65-4 

Rhodium 

Rh 

102-9 

Zirconium 

Zr 

90-6 

Rubidium 

Rb 

85-5 

453.  Metals  and  Non-metals.  —  The  elements  may  be  divided  into 
two  more  or  less  distinct  classes,  the  metals  and  the  non-metals.     Between 
the  two  lie  a  number  of  elements  sometimes  called  the  semi-metals.     The 
metals,  as  gold,  silver,  iron,  sodium,  are  those  elements  which,  physically 
described,  possess  to  a  more  or  less  perfect  degree  the  fundamental  characters 
of  the  ideal  metal,  viz.:   malleability,  metallic  luster  (and  opacity  to  light), 
conductivity  for  heat  and  electricity;   moreover,  chemically  described,  they 
commonly  play  the  part  of  the  positive  or  basic  element  in  a  simple  compound, 
as  later  denned  (Arts.  462-465).     The  non-metals,  as  sulphur,  carbon,  silicon, 
etc.,  also  the  gases,  as  oxygen,  chlorine,  etc.,  have  none  of  the  physical  charac- 
ters alluded  to:  they  are,  if  solids,  brittle,  often  transparent  to  light-radiation, 
are  poor  conductors  for  heat  and  electricity.     Chemically  expressed,  they 
usually  play  the  negative  or  acid  part  in  a  simple  compound. 

The  so-called  semi-metals,  or  metalloids,  include  certain  elements,  as 
tellurium,  arsenic,  antimony,  bismuth,  which  have  the  physical  characters  of 
a  metal  to  a  less  perfect  degree  (e.g.,  they  are  more  or  less  brittle);  and,  more 
important  4  han  this,  they  often  play  the  part  of  the  acidic  element  in  the 
compound  into  which  they  enter.  These  points  are  illustrated  later. 

It  is  to  be  understood  that  the  distinctions  between  the  classes  of  the 
elements  named  cannot  be  very  sharply  applied.  Thus  the  typical  metallic 
characters  mentioned  are  possessed  to  a  very  unequal  degree  by  the  different 
substances  classed  as  metals;  for  example,  by  silver  and  tin.  Corresponding 

to  this  a  number  of  the  true  metals,  as  tin  and  manganese,  play  the  part  of  an 

U  in 

acid  in  numerous  salts.  Further,  the  mineral  magnetite,  FeFe2O4,  is  often 
described  as  an  iron  ferrate;  so  that  in  this  compound  the  same  element  would 
play  the  part  of  both  acid  and  base. 

454.  Positive  and  Negative  Elements.  —  It  is  common  to  make  a  dis- 
tinction between  the  electro-positive  and  electro-negative  element  hi  a  compound. 


314  CHEMICAL  MINERALOGY 

The  passage  of  a  sufficiently  strong  electrical  current  through  a  chemical  com- 
pound in  many  cases  results  in  its  decomposition  (or  electrolysis)  into  its  ele- 
ments or  parts.  In  such  cases  it  is  found  that  for  each  compound  the  atoms 
of  one  element  collect  at  the  negative  pole  (the  cathode)  and  those  of  the  other 
at  the  positive  pole  (the  anode).  The  former  is  called  the  electro-positive 
element  and  the  latter  the  electro-negative  element.  Thus  in  the  electrolysis 
of  water  (H20)  the  hydrogen  collects  at  the  cathode  and  is  hence  called  posi- 
tive, and  the  oxygen  at  the  anode  and  is  called  negative.  Similarly,  in  hydro- 
chloric acid  (HC1)  the  hydrogen  is  thus  shown  to  be  positive,  the  chlorine 
negative.  This  distinction  is  also  carried  to  complex  compounds,  as  copper 
sulphate  (CuSO4),  which  by  electrolysis  is  broken  into  Cu,  which  is  found  to  be 
electro-positive,  and  SO4  (the  last  separates  into  SO3,  forming  H2SC>4  and  free 
oxygen). 

For  reasons  which  will  be  explained  later,  the  positive  element  is  said  to 
play  the  basic  part,  the  negative  the  acidic.  The  metals,  as  already  stated,  in 
most  cases  belong  to  the  former  class,  the  non-metals  to  the  latter,  while  the 
semi-metals  may  play  both  parts. 

It  is  common  in  writing  the  formula  to  put  the  positive  or  basic  element 
first,  thus  H2O,  H2S,  HC1,  H2SO4,  Sb2S3,  As2O3,  AsH3,  NiSb,  FeAs2.  Here 
it  will  be  noted  that  antimony  (Sb)  and  arsenic  (As)  are  positive  in  some  of 
the  compounds  named  but  negative  in  the  others. 

455.  Periodic  Law.  —  In  order  to  understand  the  relations  of  the 
chief  classes  of  chemical  compounds  represented  among  minerals,  as  still  more 
their  further  subdivision,  down  finally  to  the  many  isomorphous  groups  — 
groups  of  species  having  analogous  composition  and  closely  similar  form,  as 
explained  in  Art.  471  —  the  fundamental  relations  and  grouping  of  the  ele- 
ments must  be  understood,  especially  as  developed  of  recent  years  and  shown 
in  the  so-called  Periodic  Law. 

Although  the  subject  can  be  only  briefly  touched  upon,  it  will  be  useful  to 
give  here  the  general  distribution  of  the  elements  into  Groups  and  Series,  as 
presented  in  the  Principles  of  Chemistry  (Engl.  Ed.,  1891)  of  D.  Mendeleeff, 
to  whom  is  due  more  than  any  one  else  the  development  of  the  Periodic  Law. 
When  the  elements  are  arranged  according  to  the  values  of  their  atomic  weights 
it  is  seen  that  they  fall  more  or  less  into  groups  consisting  of  eight  elements 
each,  or  double  groups  containing  sixteen  elements.  The  corresponding 
members  of  each  group  show  similar  chemical  characters.  The  table  given 
below  will  illustrate  these  relationships.  For  the  thorough  explanation  of 
this  subject,  more  particularly  as  regards  the  periodic  or  progressive  relation 
between  the  atomic  weights  and  various  properties  of  the  elements,  the  reader 
is  referred  to  the  work  above  mentioned  or  to  one  of  the  many  other  excellent 
modern  text-books  of  chemistry. 

The  relations  of  some  of  the  elements  of  the  first  group  are  exhibited  by 
the  isomorphism  (see  Art.  471,  also  the  description  of  the  various  groups  and 
species  here  referred  to,  which  are  given  in  Part  IV  of  this  work)  of  NaCl, 
KC1,  AgCl;  or  again  of  LiMnP04  and  NaMnPO4,  etc.  In  the  second  group, 
reference  may  be  made  to  the  isomorphism  of  the  carbonates  and  sulphates 
(p.  322)  of  calcium,  barium,  and  strontium;  while  among  the  sulphides,  ZnS, 
CaS,  and  HgS  are  doubly  related.  In  the  third  group,  we  find  boron  and 
aluminium  often  replacing  one  another  among  silicates.  In  the  fourth  group, 
the  relations  of  silicon  and  titanium  are  shown  in  the  titano-silicates,  while 
the  compounds  Ti02,  SnO2,  Pb02  (and  MnO2),  also  ZrSiO4  and  ThSi04,  have 


GENERAL  PRINCIPLES  OF  CHEMISTRY  AS  APPLIED  TO  MINERALS  315 


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316  CHEMICAL   MINERALOGY 

closely  similar  form.  In  the  fifth  group,  many  compounds  of  arsenic,  anti- 
mony, and  bismuth  are  isomorphous  among  metallic  compounds,  while  the 
relations  of  phosphorous,  vanadium,  arsenic,  also  antimony,  are  shown  among 
the  phosphates,  vanadates,  arsenates,  and  antimonates;  again  the  mutual 
relations  of  the  niobates  and  tantalates  are  to  be  noted. 

In  the  sixth  group,  the  strongly  acidic  elements,  sulphur,  selenium, 
tellurium,  are  all  closely  related,  as  seen  in  many  sulphides,  selenides,  tellu- 
rides;  further,  the  relations  of  sulphur  and  chromium,  and  similarly  of  both 
of  these  to  molybdenum  and  tungsten,  are  shown  among  many  artificial  sul- 
phates, chromates,  molybdates,  and  tungstates. 

In  the  seventh  group  the  relations  of  the  halogens  are  too  well  understood 
to  need  special  remark.  In  the  eighth  group,  we  have  Fe,  Co,  Ni  alloyed  in 
meteoric  iron,  and  their  phosphates  and  sulphates  are  in  several  cases  closely 
isomorphous;  further,  the  relation  of  the  iron  series  to  that  of  the  platinum 
series  is  exhibited  in  the  isomorphism  of  FeS2,  FeAsS,  FeAs2,  etc.,  with  PtAs2 
and  probably  RuS2. 

456.  Combining   Weight.  —  Chemical   investigation   proves   that   the 
mass  of  a  given  element  entering  into  a  compound  is  always  proportional 
either  to  its  atomic  weight  or  to  some  simple  multiple  of  this;   the  atomic 
weight  is  hence  also  called  the  combining  weight.     Thus  in  rock  salt,  sodium 
chloride,  the  masses  involved  of  sodium  and  chlorine  present  are  found  by 
analysis  to  be  equal  to  39'4  and  60'6  in  100  parts,  and  these  numbers  are  in 
proportion  to  23  :  35*4,  the  atomic  weights  of  sodium  and  chlorine;  hence  it  is 
concluded  that  one  atom  of  each  is  present  in  the  compound.     The  formula  is, 
therefore,  NaCl.     In  calcium  chloride,  by  the  same  method  the  masses  pres- 
ent are  found  to  be  proportional  to  39'9  :  70*8,  that  is,  to  39'9   :  2  X  35'4; 
hence  the  formula  is  CaCl2. 

Still  again,  a  series  of  compounds  of  nitrogen  with  oxygen  is  known  in  which  the  ratios 
of  the  masses  of  the  two  elements  are  as  follows:  (1)  28  : 16,  (2)  14  : 16,  (3)  28  :  48,  (4)  14  :  32, 
(5)  28  :  80.  It  is  seen  at  once  that  these  must  have  the  formulas  (1)  N2O;  (2)  NO,  (3)  N2O3, 
(4)  NO2,  (5)  N2O6.  On  the  contrary,  atmospheric  air  which  contains  these  elements  in 
about  the  ratio  of  76 '8  to  23 '2  cannot  be  a  chemical  compound  of  these  elements,  since 
(aside  from  other  considerations)  these  numbers  are  not  in  the  ratio  of  n  X  14  :  m  X  16 
where  n  and  m  are  simple  whole  numbers. 

457.  Molecular  Weight.  —  The  molecular  weight  is  the  weight  of  the 
molecule  of  the  given  substance,  expressed  in  terms  of  the  mass  of  the  hydro- 
gen atom  as  unit.     The  molecular  weight  of  hydrogen  is  2  because  the  mole- 
cule can  be  shown  to  consist  of  two  atoms.     The  molecular  weight  of  hydro- 
chloric acid  (HC1)  is  36*4,  of  water  vapor  (H2O)  18,  of  hydrogen  sulphide 
(H2S)  34. 

Since,  according  to  the  law  of  Avagadro,  like  volumes  of  different  gases 
under  like  conditions  as  to  temperature  and  pressure  contain  the  same  number 
of  molecules,  it  is  obvious  that  the  molecular  weight  of  substances  in  the  form 
of  gas  can  be  derived  directly  from  the  relative  density  or  specific  gravity. 
If  the  density  is  referred  to  hydrogen,  whose  molecular  weight  is  2,  it  will 
be  always  true  that  the  molecular  weight  is  twice  the  density  in  the  state  of  a 
gas  and  vice  versa.  Thus  the  observed  density  of  carbon  dioxide  (CO2)  is  22, 
hence  its  molecular  weight  must  be  44.  It  is  this  principle  that  makes  it 
possible  in  the  case  of  a  gas  to  fix  the  constitution  of  the  molecule  when  the 
ratio  in  number  of  the  atoms  entering  into  it  has  been  determined  by  analysis. 
In  the  case  of  solids,  where  the  constitution  of  the  molecule  in  general  cannot 


GENERAL  PRINCIPLES  OF  CHEMISTRY  AS  APPLIED  TO  MINERALS  317 

be  fixed,  it  is  best,  as  already  stated,  to  write  the  molecular  formula  in  its 
simplest  form,  as  NaAlSi3Os  for  albite.  The  sum  of  the  weights  of  the  atoms 
present  is  then  taken  as  the  molecular  weight. 

458.  Valence.  —  The  valence  of  an  element  is  given  by  a  number 
representing  the  capacity  of  its  atoms  to  combine  with  the  atoms  of  some 
unit  element  like  hydrogen  or  chlorine.     Thus,  using  the  examples  of  Art. 
456,  in  NaCl,  since  one  atom  of  sodium  unites  with  one  of  chlorine,  its 
valence  is  one;   or,  in  other  words,  it  is  said  to   be  univalent.     Further, 
calcium  (as  in  CaCl2),  also  barium,  etc.,  are  bivalent;  aluminium  is  triva- 
lent;  silicon   is   tetravalent,    etc.     The  valence  may  be  expressed  by  the 
number  of  bonds  by  which  one  element  in  a  compound  is  united  to  another, 
thus: 

Na-Cl,  Ba  =  Cl2,  Au=Cl3,  SniiCU,  etc. 

A  considerable  number  of  the  elements  show  a  different  valence  in  different 
compounds.  Thus  both  Sb203  and  Sb2O5  are  known;  also  FeO  and  Fe2p3; 
CuCl  and  CuCl2.  These  possible  variations  are  indicated  in  the  following 
table  which  gives  the  valences  for  the  common  elements. 

Univalent:  H,  Cl,  Br,  I,  F;  Li,  Na,  K,  Rb,  Cs,  Ag,  Hg,  Cu,  Au. 

Bivalent:  O,  S,  Se,  Te;  Be,  Mg,  Ca,  Sr,  Ba,  Pb,  Hg,  Cu,  Zn,  Co,  Ni,  Fe, 
Mn,  Cr,  C,  Sn. 

Trivalent:  B,  Au,  Al,  Fe,  Mn,  Cr,  Co,  Ni,  N,  P,  As,  Sb,  Bi. 

Tetravalent:  C,  Si,  Ti,  Zr,  Sn,  Mn,  Pb. 

Pentavalent:  N,  P,  As,  Sb,  V,  Bi,  Nb,  Ta. 

459.  Chemical   Reactions.  —  When   solutions    of   two    chemical    sub- 
stances are  brought  together,  in  many  cases  they  react  upon  each  other  with 
the  result  of  forming  new  compounds  out  of  the  elements  present;  this  phe- 
nomenon is  called  a  chemical  reaction.     One  of  the  original  substances  may  be 
a  gas,  and  in  many  cases  similar  results  are  obtained  from  a  liquid  and  a  solid, 
or  less  often  from  two  solids. 

For  example,  solutions  of  sodium  chloride  (NaCl)  and  silver  nitrate 
(AgNO3)  react  on  each  other  and  yield  silver  chloride  (AgCl)  and  sodium 
nitrate  (NaNO3).  This  is  expressed  in  chemical  language  as  follows: 

NaCl  +  AgNO3  =  AgCl  +  NaN03. 

This  is  a  chemical  equation,  the  sign  of  equality  meaning  that  equal  weights 
are  involved  both  before  and  after  the  reaction. 

Again,  hydrochloric  acid  (HC1)  and  calcium  carbonate  (CaCO3)  yield 
calcium  chloride  (CaCl2)  and  carbonic  acid  (H2CO3) ;  which  last  breaks  up 
into  water  (H2O)  and  carbon  dioxide  (CO2),  the  last  going  off  as  a  gas  with 
effervescence.  Hence 

CaCO3  +  2HC1  =  CaCl2  +  H2O  +  C02. 

460.  Radicals.  —  A  compound  of  two  or  more  elements  according  to 
their  relative  valence  in  which  all  their  bonds  are  satisfied  is  said  to  be  satu- 
rated.    This  is  true  of  H2O,  or,  as  it  may  be  written,  H— O—H.     If,  however, 
one  or  more  bonds  is  left  unsatisfied,  the  resulting  combination  of  elements  is 
called  a  radical.     Thus  —  O  — H,  called  briefly  hydroxyl,  is  a  common  radical, 
having  a  valence  of  one,  or,  in  other  words,  univalent ;  NH4  is  again  a  univalent 
radical;   so,  too,  (CaF),  (MgF)  or  (A10).     Radicals  often  enter  into  a  com- 
pound like  a  simple  element;  for  example,  in  ammonium  chloride,  NH4C1,  the 
univalent  radical  NH4  plays  the  same  part  as  the  univalent  element  Na  in 
NaCl.     In  the  chemical  composition  of  mineral  species,  the  commonest  radical 


318  CHEMICAL   MINERALOGY 

is  hydroxyl  ( — 0 — H)  already  defined.     Other  examples  are  (CaF)  in  apatite 
(see  Art.  471),  (MgF)  in  wagnerite,  (A1O)  in  many  basic  silicates,  etc. 

461.  Chemical  Compound.  —  A  chemical  compound  is  a  combination 
of  two  or  more  elements  united  by  the  force  of  chemical  attraction.     It  is 
always  true  of  it,  as  before  stated  (Art.  456),  that  the  elements  present  are 
combined  in  the  proportion  of  their  atomic  weights  or  some  simple  multiples 
of  these.     A  substance  which  does  not  satisfy  this  condition  is  not  a  compound, 
but  only  a  mechanical  mixture. 

Examples  of  the  simpler  class  of  compounds  are  afforded  by  the  oxides,  or 
compounds  of  oxygen  with  another  element.  Thus,  among  minerals  we  have 
Cu2O,  cuprous  oxide  (cuprite);  ZnO,  zinc  oxide  (zincite);  A1203,  alumina 
(corundum);  SnO2,  tin  dioxide  (cassiterite) ;  SiO2,  silicon  dioxide  (quartz); 
As2O3,  arsenic  trioxide.(arsenolite). 

Another  simple  class  of  compounds  are  the  sulphides  (with  the  selenides, 
tellurides,  arsenides,  antimonides,  etc.),  compounds  in  which  sulphur  (selen- 
ium, tellurium,  arsenic,  antimony,  etc.)  plays  the  same  part  as  oxygen  in  the 
oxides.  Here  belong  Cu2S,  cuprous  sulphide  (chalcocite) ;  ZnS,  zinc  sulphide 
(sphalerite);  PbTe,  lead  telluride  (altaite);  FeS2,  iron  disulphide  (pyrite); 
Sb2S3,  antimony  trisulphide  (stibnite). 

462.  Acids.  —  The  more  complex  chemical  compounds,  an  understanding 
of  which  is  needed  in  a  study  of  minerals,  are  classed  as  acids,  bases,  and 
salts;  the  distinctions  between  them  are  important. 

An  acid  is  a  compound  of  hydrogen,  or  hydroxyl,  with  a  non-metallic 
element  (as  chlorine,  sulphur,  nitrogen,  phosphorus,  etc.),  or  a  radical  con- 
taining these  elements.  When  dissolved  in  water  they  all  give  the  positive 
hydrogen  ion  and  a  negative  ionic  substance  such  as  Cl,  SO4,  etc.  The 
hydrogen  atoms  of  an  acid  may  be  replaced  by  metallic  atoms;  the  result 
being  then  the  formation  of  a  salt  (see  Art.  464).  Acids  in  general  turn  blue 
litmus  paper  red  and  have  a  sharp,  sour  taste.  The  following  are  familiar 
examples: 

HC1,  hydrochloric  acid, 

HNO3,  nitric  acid. 

H2CO3,  carbonic  acid. 

H2S04,  sulphuric  acid. 

H2Si03,  metasilicic  acid. 

H3PO4,  phosphoric  acid. 

H4Si04,  orthosilicic  acid. 

It  is  to  be  noted  that  with  a  given  acid  element  several  acids  are  possible. 
Thus  normal,  or  orthosilicic,  acid  is  H4SiO4,  in  which  the  bonds  of  the  ele- 
ment silicon  are  all  satisfied  by  the  hydroxyl  (HO).  But  the  removal  of  one 
molecule  of  water,  H2O,  from  this  gives  the  formula  H2SiO3,  or  metasilicic 
acid. 

Acids  which,  like  HN03,  contain  one  atom  of  hydrogen  that  may  be 
replaced  by  a  metallic  atom  (e.g.,  in  KNO3)  are  called  monobasic.  If,  as  in 
H2CO3  and  H2SO4,  there  are  two  atoms  or  a  single  bivalent  atom,  (e.g.,  in 
CaC03,  BaSO4)  the  acids  are  dibasic.  Similarly,  H3PO4  is  tribasic,  etc. 

Most  acids  are  liquids  (or  gases),  and  hence  acids  are  represented  very 
sparingly  among  minerals;  B(OH)3,  boric  acid  (sassolite),  is  an  illustration. 

463.  Bases.  —  The  bases,  or  hydroxides,  as  they  are  also  called,  are 
compounds  which  may  be  regarded  as  formed  of  a  metallic  element  (or  radical) 


GENERAL  PRINCIPLES  OF  CHEMISTRY  AS  APPLIED  TO  MINERALS  319 

and  the  univalent  radical  hydroxyl,  —  (OH) ;  or,  in  other  words,  of  an  oxide 
with  water.  Thus  potash,  K2O,  and  water,  H2O,  form  2K(OH),  or  potassium 
hydroxide;  also  CaO  +  H2O  similarly  give  Ca(OH)2,  or  calcium  hydroxide. 
In  general,  when  soluble  in  water,  bases  give  an  alkaline  reaction  with  turmeric 
paper  or  red  litmus  paper,  and  they  also  neutralize  an  acid,  as  explained  in 
the  next  article.  Further,  the  bases  yield  water  on  ignition,  that  is,  at  a 
temperature  sufficiently  high  to  break  up  the  compound. 

Among  minerals  the  bases  are  represented  by  the  hydroxides,  or  hydrated 
oxides,  as  Mg(OH)2,  magnesium  hydrate  (brucite);  A1(OH)2,  aluminium 
hydrate  (gibbsite);  also,  (A1O)(OH),  diaspore,  etc. 

464.  Salts.  —  A  third  class  of  compounds  are  the  salts;   these  may  be 
regarded  as  formed  chemically  by  the  reaction  of  a  base  upon  an  acid,  or,  in 
other  words,  by  the  neutralization  of  the  acid.     Thus  calcium  hydrate  and  sul- 
phuric acid  give  calcium  sulphate  and  water: 

Ca(OH)2  -f  H2S04  =  CaSO4  +  2H2O. 

Here  calcium  sulphate  is  the  salt,  and  in  this  case  the  acid,  sulphuric  acid,  is 
said  to  be  neutralized  by  the  base,  calcium  hydroxide.  It  is  instructive  to 
compare  the  formulas  of  a  base,  an  acid,  and  the  corresponding  salt,  as 
follows : 

Base,  Ca(OH)2;      Acid,  H2S04;      Salt,  CaS04. 

Here  it  is  seen  that  a  salt  may  be  simply  described  as  formed  from  an  acid  by 
the  replacement  of  the  hydrogen  atom,  or  atoms,  by  a  metallic  element  or 
radical. 

465.  Typical    Salts.  —  The    commonest    types    of    salts    represented 
among  minerals  are  the  following: 

Chlorides:  salts  of  hydrochloric  acid,  HC1;  as  AgCl,  silver  chloride  (cerar- 
gyrite). 

Nitrates:  salts  of  nitric  acid,  HN03;   as  KNO3,  potassium  nitrate  (niter). 

Carbonates:  salts  of  carbonic  acid,  H2C03;  as  CaC03,  calcium  carbonate 
(calcite  and  aragonite). 

Sulphates:  salts  of  sulphuric  acid,  H2S04;  as  CaS04,  calcium  sulphate 
(anhydrite). 

Phosphates:  salts  of  phosphoric  acid,  H3P04;  as  Ca3(PO4)2,  calcium  phos- 
phate. 

Silicates:  several  classes  of  salts  are  here  included.  The  most  common  are 
the  salts  of  metasilicic  acid,  H2SiO3;  as  MnSi03,  manganese  metasilicate 
(rhodonite).  Also  salts  of  orthosilicic  acid,  H4Si04;  as  Mn2Si04,  manganese 
orthosilicate  (tephroite) . 

Numerous  other  classes  of  salts  are  also  included  among  mineral  species; 
their  composition,  as  well  as  that  of  complex  salts  of  the  above  types,  is 
explained  in  the  descriptive  part  of  this  work. 

466.  Normal,  Acid,  and  Basic  Salts.  —  A  neutral  or  normal  salt  is  one 
in  which  the  basic  element  completely  neutralizes  the  acid,  or,  in  other  words, 
one  of  the  type  already  given  as  examples,  in  which  all  the  hydrogen  atoms  of 
the  acid  have  been  replaced  by  metallic  atoms  or  radicals.     Thus,  K2SO4  is 
normal  potassium  sulphate,  but  HKSO4,  on  the  other  hand,  is  acid  potassium 
sulphate,  since  in  the  acid  H2SO4  only  one  of  the  bonds  is  taken  by  the  basic 
element  potassium.     Salts  of  this  kind  are  called  acid  salts.     The  formula  in 


320  CHEMICAL   MINERALOGY 

such  cases  may  be  written  *  as  if  the  compound  consisted  of  a  normal  salt  and 
an  acid;  thus,  for  the  example  given,  K2SO4 .  H2SO4. 

A  basic  salt  is  one  in  which- the  acid  part  of  the  compound  is  not  sufficient 
to  satisfy  all  the  bonds  of  the  base.  Thus  malachite  is  a  basic  salt  —  basic 

carbonate   of   copper  —  its   composition   being   expressed   by   the   formula 

_  f^r\ 
Cu2(OH)2C03.     This  may  be  written  CuCO3 .  Cu(OH)2,  or  (Cu2)  =  ^g^ 

The  majority  of  minerals  consist  not  of  simple  salts,  as  those  noted  above,  but 
of  more  or  less  complex  double  salts  in  which  several  metallic  elements  are 
present.  Thus  common  grossular  garnet  is  an  orthosilicate  containing  both 
calcium  and  aluminium  as  bases;  its  formula  is  Ca3Al2(SiO4)3. 

467.  Sulpho-salts.  —  The  salts  thus  far  spoken  of  are  all  oxygen  salts. 
There  are  also  others,  of  analogous  constitution,  in  which  sulphur  takes  the 
place  of  the  oxygen;  they  are  hence  called  sulpha-salts.     Thus  normal  sulph- 
arsenious  acid  has  the  formula  H3AsS3,  and  the  corresponding  silver  salt  is 
AgsAsS3,  the  mineral  proustite.     Similarly  the  silver  salt  of  the  analogous 
antimony  acid  is  Ag3SbS3,  the  mineral  pyrargyrite.     From  the  normal  acids 
named,  a  series  of  other  hypothetical  acids  may  be  derived,  as  HAsS2,  H4As2S5, 
etc. ;  these  acids  are  not  known  to  exist,  but  their  salts  are  important  minerals. 
Thus  zinkenite,  PbSb2S4,  is  a  salt  of  the  acid  H2Sb2S4,  and  jamesonite,  Pb2Sb2S5, 
of  the  acid  H4Sb2S5,  etc. 

468.  Water  of  Crystallization.  —  As  stated  in  Art.  463,  the  hydroxides, 
or  bases,  and  further  basic  salts -in  general,  yield  water  when  ignited.     Thus 
calcium  hydroxide  Ca(OH)2  breaks  up  on  heating  into  CaO  and  H2O,  as 
expressed  in  the  chemical  equation 

2Ca(OH)2  =  2CaO  +  H20. 

So  also  the  basic  cupric  carbonate,  malachite,  Cu2(OH)2C03,  yields  water  on 
ignition;  and  the  same  is  true  of  the  complex  basic  orthosilicates,  like  zoisite, 
whose  formula  is  (HO)Ca2Al3(Si04)3.  It  is  not  to  be  understood,  however,  in 
these  or  similar  cases,  that  water  as  such  is  present  in  the  substance. 

On  the  other  hand,  there  is  a  large  number  of  mineral  compounds  which 
yield  water  readily  when  heated,  and  in  which  the  water  molecules  are  regarded 
as  present  as  so-called  water  of  crystallization.  Thus,  the  formula  of  gypsum 
is  written 

CaSO4  +  2H2O, 

and  the  molecules  of  water  (2H2O)  are  considered  as  water  of  crystallization. 
So,  too,  in  potash  alum,  KA1(S04)2  +  12H2O,  the  water  is  believed  to  play  the 
same  part. 

469.  Formulas  of  Minerals.  —  The  strictly  empirical  formula  expresses 
the  kinds  and  numbers  of  atoms  of  the  elements  present  in  the  given  com- 
pound, without  attempting  to  show  the  way  in  which  it  is  believed  that  the 
atoms  are  combined.     Thus,  in  the  case  of  zoisite  the  empirical  formula  is 
HCa2Al3Si3Oi3.     While  not  attempting  to  represent  the  structural  formula 
(which  will  not  be  discussed  here),  it  is  convenient  in  certain  cases  to  indicate 
the  atoms  which  there  is  reason  to  believe  play  a  peculiar  relation  to  each  other. 
Thus  the  same  formula  written  (HO)Ca2Al3(SiO4)3  shows  that  it  is  regarded  as 
a  basic  orthosilicate,  in  other  words,  a  basic  salt  of  orthosilicic  acid,  H4SiO4. 

*  This  early  form  of  writing  the  composition  explains  the  name  often  given  to  the  com- 
pound, namely,  in  this  case,  "bisulphate  of  potash." 


GENERAL  PRINCIPLES  OF  CHEMISTRY  AS  APPLIED  TO  MINERALS  321 

Again,  the  empirical  formula  of  common  apatite  is  Ca5FP3Oi2 ;  but  if  this 
is  written  (CaF)Ca4(PO4)3,  it  shows  that  it  is  regarded  as  a  phosphate  of  the 
acid  H3PO4,  that  is,  H^PO^s,  in  which  the  nine  hydrogen  atoms  are  replaced 
by  four  Ca  atoms  together  with  the  univalent  radical  (CaF).  In  another  kind 
of  apatite  the  radical  (CaCl)  enters  in  the  same  way.  Similarly  to  this  the 
formula  of  pyromorphite  is  (PbCl)Pb4(PO4)3,  of  vanadinite  (PbCl)Pb4(VO4)3. 

Further,  it  is  often  convenient  to  employ  the  method  of  writing  the  form- 
ulas in  vogue  under  the  old  dualistic  system.  For  example, 

CaO.CO2  for  CaCO3, 
3CaO  .  A12O3 .  3SiO2  for  Ca3Al2Si3Oi2, 
3Ag2S  .  Sb2S3  for  Ag3SbS3,  etc. 

It  is  no  longer  believed,  however,  that  the  molecular  groups  CaO,  A1203,  etc., 
actually  exist  in  the  molecule  of  the  substance.  But  in  part  because  these 
groups  are  what  analysis  of  the  substance  affords  directly,  and  in  part  because 
so  easily  retained  in  the  memory,  this  method  of  writing  is  still  often  used. 

470.  Calculation  of  a  Formula  from  an  Analysis.  —  The  result  of  an 
analysis  gives  the  proportions,  in  a  hundred  parts  of  the  mineral,  of  either  the 
elements  themselves,  or  of  their  oxides  or  other  compounds  obtained  in  the 
chemical  analysis.  In  order  lo  obtain  the  atomic  proportions  of  the  elements : 

Divide  the  percentages  of  the  elements  by  the  respective  ATOMIC  WEIGHTS; 
or,  for  those  of  the  oxides:  Divide  the  percentage  amounts  of  each  by  their 
MOLECULAR  WEIGHTS;  then  find  the  simplest  ratio  in  whole  numbers  for  the 
numbers  thus  obtained.  . 

Example.  —  An  analysis  of  bournonite  from  Wolfsberg  gave  C.  Bromeis  the  results  under 
(1)  below.  These  percentages  divided  by  the  respective  atomic  weights,  as  indicated,  give 
the  numbers  under  (2).  Finally  the  ratio  of  these  numbers  gives  very  nearly  1  :  3  :  1  :  1. 
Hence  the  formula  derived  is  CuPbSbS3.  The  theoretical  values  called  for  by  the  formula 
are  added  under  (4). 

(1)  (2)  (3)  (4) 

Sb  24'34  -r-  120     =  0'203  1  247 

S  1976  •*•    32     =  0'617  3  19'8 

Pb  42-88  -5-  206-4  =  0'208  1  42'5 

Cu  13-06  -r-    63-2  =  0-207  1  13'0 

100-04  lOO'O 

Second  Example.  —  The  mean  of  two  analyses  of  a  garnet  from  Alaska  gave  Kountze  the 
results  under  (1)  below.  Here,  as  usual,  the  percentage  amounts  of  the  several  molecular 
groups  (SiO2,  A12O3,  etc.)  are  given  instead  of  those  of  the  elements.  These  amounts 
divided  by  the  respective  niolecular  weights  give  the  numbers  under  (2).  In  this  case  the 
amounts  of  the  protoxides  are  taken  together  and  the  ratio  thus  obtained  is  3 '09  :  1  :  2  "92, 
which  corresponds  approximately  to  the  formula  3FeO.Al2O3.3SiO2,  or  Fe3Al2(SiO4)3.  The 
magnesium  in  this  garnet  would  ordinarily  be  explained  by  the  presence  of  the  pyrope 
molecule  (Mg3Al2[SiO4]3)  together  with  the  simple  almandite  molecule  whose  composition 
is  given  above. 

(1)  (2)  (3) 

SiO2  39-29  -5-    60   =  0'655  3'09 

A12O3  21-70  -5-  102   =  0-212  1 

Fe203  tr. 

FeO  30-82  H- 71 -9  =  0'429 

MnO  1-51  -f-  70-8  =  0'022  L.A1Q  9.Q9 

MgO  5-26  -^40     =  0-132   l 

CaO  1-99  -J-  55-9  =  0'036 

100-57 

It  is  necessary,  when  very  small  quantities  only  of  certain  elements  (as  MnO,  MgO,  CaO 
above)  are  present,  to  neglect  them  in  the  final  formula,  reckoning  them  in  with  the  elements 


322  CHEMICAL  MINERALOGY 

which  they  replace,  that  is,  with  those  of  the  same  quanti valence.  The  degree  of  corre- 
spondence between  the  analysis  and  the  formula  deduced,  if  the  latter  is  correctly  assumed, 
depends  entirely  upon  the  accuracy  of  the  former. 

i  !  471.  Isomorphism.  —  Chemical  compounds  which  have  an  analogous 
composition  and  a  closely  related  crystalline  form  are  said  to  be  isomorphous. 
This  phenomenon,  called  ISOMORPHISM,  was  first  clearly  brought  out  by  Mit- 
scherlich. 

Many  examples  of  groups  of  isomorphous  compounds  will  be  found  among 
the  minerals  described  in  the  following  pages.  Some  examples  are  mentioned 
here  in  order  to  elucidate  the  subject. 

In  the  brief  discussion  of  the  periodic  classification  of  the  chemical  ele- 
ments of  Art.  455,  attention  has  been  called  to  the  prominent  groups  among 
the  elements  which  form  analogous  compounds.     Thus  calcium,  barium,  and 
strontium,  and  also  lead,  form  the  two  series  of  analogous  compounds, 
Aragonite  Group  Barite  Group 

CaCO3,  aragonite.          Also        CaSO4,  anhydrite. 

BaC03,  witherite.  BaS04,  barite. 

SrCO3,  strontianite.  SrS04,  celestite. 

PbCO3,  cerussite,  PbSO4,  anglesite. 

Further,  the  members  of  each  series  crystallize  in  closely  similar  forms.  The 
carbonates  are  orthorhombic,  with  axial  ratios  not  far  from  one  another;  thus 
the  prismatic  angle  approximates  to  60°  and  120°,  and  corresponding  to  this 
they  all  exhibit  pseudo-hexagonal  forms  due  to  twinning.  The  sulphates  also 
form  a  similar  orthorhombic  series,  and  though  anhydrite  deviates  somewhat 
widely,  the  others  are  close  together  in  angle  and  in  cleavage. 

Again,  calcium,  magnesium,  iron,  zinc,  and  manganese  form  a  series  of  car- 
bonates with  analogous  composition  as  shown  in  the  list  of  the  species  of 
the  Calcite  Group  given  on  p.  437.  This  table  brings  out  clearly  the  close 
relation  in  form  between  the  species  named. 

Further  it  is  also  generally  true  with  an  isomorphous  series  that  the  various 
molecules  may  enter  in  greater  or  less  degree  into  the  constitution  of  one  of  the 
members  of  the  series  without  causing  any  marked  change  in  the  crystal 
characters.  For  instance,  in  the  Calcite  Group,  calcite  itself  may  contain 
small  percentages  of  MgCO3,  FeCO3  and  MnCO3.  These  different  molecules 
may  assume  in  the  crystal  structure  of  the  mineral  the  same  functions  as  the 
corresponding  amounts  of  CaC03  which  they  have  replaced.  The  molecules 
of  magnesite  and  siderite,  MgCO3  and  FeCO3,  may  replace  each  other  in  any 
proportion  and  the  same  is  true  with  siderite  and  rhodochrosite,  MnC03. 
Various  intermediate  mixtures  of  these  latter  molecules  have  been  described 
and  given  distinctive  names  to  which  definite  formulas  have  been  assigned.  It 
is  doubtful,  however,  if  these  compounds  have  any  real  existence  but  merely 
represent  certain  points  in  the  complete  isomorphous  series  that  lies  between 
the  end  members.  Dolomite,  CaMg(CO3)2,  on  the  other  hand,  is  a  definite 
compound  and  not  an  isomorphous  mixture  of  CaCO3  and  MgCO3.  It  may, 
however,  contain  varying  amounts  of  FeCO3,  MnCO3  and  also  an  excess  of 
CaCO3  or  MgCO3,  all  of  which  enter  the  regular  molecule  in  the  form  of 
isomorphous  replacements. 

The  Apatite  Group  forms  another  valuable  illustration  since  in  it  are 
represented  the  analogous  compounds,  apatite  and  pyromorphite,  both  phos- 
phates, but  respectively  phosphates  of  calcium  and  lead;  also  the  analogous 


GENERAL  PRINCIPLES  OF  CHEMISTRY  AS  APPLIED  TO  MINERALS  323 

lead  compounds  pyromorphite,  mimetite,  and  vanadinite  respectively  lead 
phosphate,  lead  arsenate,  and  lead  vanadate.  Further,  in  all  these  compounds 
the  radical  (RC1)  or  (RF)  enters  in  the  same  way  (see  Art.  469).  Thus  the 
formulas  for  the  two  kinds  of  apatite  and  that  for  pyromorphite  are  as  follows : 

(CaF)Ca4(P04)3,  (CaCl)Ca4(PO4)3,          (PbCl)Pb4(PO4)3. 

Some  of  the  more  important  isomorphous  groups  are  mentioned  below.  For  a  discus- 
sion of  them,  as  well  as  of  many  others  that  might  be  mentioned  here,  reference  must  be 
made  to  the  descriptive  part  of  this  work. 

Isometric  System.  —  The  Spinel  group,  including  spinel,  MgAl2O4;  also  magnetite, 
chromite,  franklinite,  gahnite,  etc.  The  Galena  group,  as  galena,  PbS;  argentite,  Ag->S, 
etc.  The  Garnet  group,  as  grossularite,  CasAiiSiiOn,  etc. 

Tetragonal  System.  —  Rutile  group,  including  rutile,  TiO2,'  cassiterite,  SnC>2.  The 
Scheelite  group,  including  scheelite,  CaWO4;  stolzite,  PbW04;  wulfenite,  PbMoO4. 

Hexagonal  System.  —  Apatite  group,  already  mentioned,  including  apatite,  pyromor- 
phite, mimetite,  and  vanadinite.  Corundum  group,  corundum,  A12O3;  hematite,  FesOs. 
Calcite  group,  already  mentioned.  Phenacite  group,  etc. 

Orthorhombic  System.  —  Aragonite  group,  and  Barite  group,  both  mentioned  above. 
Chrysolite  group,  (Mg,Fe)2SiO4;  Topaz  group,  etc. 

Monodinic  System.  —  Copperas  group,  including  melanterite,  FeSO4  +  THizO;  bieberite, 
CoSO4  +  7H2O,  etc.  Pyroxene  and  Amphibole  groups,  and  the  Mica  group. 

Monodinic  and  Triclinic  Systems.  —  Feldspar  group. 

472.  Isomorphous  Mixtures.  —  It  is  important  to  note  that  the  inter- 
mediate compounds  in  the  case  of  an  isomorphous  series,  such  as  those  spoken 
of  in  the  preceding  article,  often  show  a  distinct  gradation  in  crystalline  form, 
and  more  particularly  in  physical  characters  (e.g.,  specific  gravity,  optical 
properties,  etc.).    This  is  illustrated  by  the  species  of  the  calcite  group  already 
referred  to;  also  still  more  strikingly  by  the  group  of  the  triclinic  feldspars  as 
fully  discussed  under  the  description  of  that  group.     See  further  Art.  424. 

The  feldspars  also  illustrate  two  other  important  points  in  the  subject, 
which  must  be  briefly  alluded  to  here.  The  triclinic  feldspars  have  been  shown 
by  Tschermak  to  be  isomorphous  mixtures  of  the  end  compounds  in  varying 
proportions : 

Albite,  NaAlSi3O8.  Anorthite,  CaAl2Si2O8. 

Here  it  is  seen  that  these  compounds  have  not  an  analogous  composition  in  the 
narrow  sense  previously  illustrated,  and  yet  they  are  isomorphous  and  form  an 
isomorphous  series.  Other  examples  of  this  are  found  among  the  pyroxenes, 
the  scapolites,  etc. 

Further,  the  Feldspar  group  in  the  broader  sense  includes  several  other 
species,  conspicuously  the  monoclinic  orthoclase,  KAlSi3Os,  which,  though 
belonging  to  a  different  system,  still  approximates  closely  in  form  to  the 
triclinic  species. 

473.  Variation  in  Composition  of  Minerals.     Isomorphous  Replacement 
and  Solid  Solution.  —  The  idea  that  a  mineral  must  rigidly  conform  in  its 
chemical  composition  to  a  theoretical  composition  derived  from  its  formula 
can  no  longer  be  strictly  held.     It  is  true  that  the  majority  of  minerals  do  show 
a  close  correspondence  to  that  theory,  commonly  within  the  limits  of  possible 
errors  in  the  analyses.     On  the  other  hand,  many  minerals  show  slight  and 
certain   ones   considerable   variations   from   their  theoretical   compositions. 
These  variations. can  usually  be  explained  by  the  principle  of  isomorphism. 
An  instructive  example  is  the  case  of  sphalerite.     Note  in  the  analyses  quoted 
below  how  the  percentages  of  zinc  diminish  and  those  of  iron  correspondingly 
increase.     It  is  evident  from  these  analyses  that  iron,  and  in  a  much  smaller 


324  CHEMICAL   MINERALOGY 

degree  other  metals,  may  enter  into  the  chemical  compound  and  while  replac- 
ing the  zinc  perform  the  same  function  as  it,  in  the  crystalline  structure  of  the 
mineral.  The  iron  is  therefore  spoken  of  as  being  isomorphous  with  the  zinc 
or  the  iron  sulphide  molecule  as  isomorphous  with  the  zinc  sulphide  molecule. 
There  is  no  definite  ratio  between  the  amounts  of  the  iron  and  zinc  that  may 
be  present  but  there  is  a  constant  ratio  (1  :  1)  between  the  sum  of  the  atoms 
of  the  metals  and  the  atoms  of  sulphur.  That  is,  although  the  composition 
may  vary,  the  atomic  ratios  and  the  crystalline  structure  remain  constant.  In 
some  cases  this  interchange  between  elements  or  radicals  may  be  complete, 
in  other  cases  there  may  be  distinct  limitations  to  the  amount  by  which  any 
element  or  radical  may  be  replaced  by  another.  For  instance  in  sphalerite 
the  maximum  percentage  of  the  isomorphous  iron  seems  to  be  about  16  to 
18  per  cent. 

Colorless  Sphalerite  Brown  Sphalerite  Black  Sphalerite 

S  32.93  S  33.36  S  33.25 

Zn          66.69  Zn          63.36  Zn          50.02 

Fe  0.42  Fe  3.60  Fe  15.44 

moi  100.32  Cd        0.30 

100.02 

Further,  we  have  cases  where  a  compound  may,  in  a  certain  sense,  dissolve 
another  unrelated  substance  and  form  what  is  known  as  a  solid  solution. 
This  kind  of  phenomenon  is  well  recognized  among  artificial  salts  and  has 
recently  been  definitely  proved  with  certain  minerals.  For  instance,  it  has 
been  shown  experimentally  that  the  artificial  iron  sulphide,  FeS,  correspond- 
ing to  pyrrhotite,  can  dissove  an  excess  of  sulphur  up  to  about  6  per  cent. 
Natural  pyrrhotite  always  contains  an  excess  of  sulphur  over  that  required  by 
the  formula,  FeS,  and  various  formulas  such  as  Fe7S8,  FenSn+i,  etc.,  have  been 
assigned  to  the  mineral.  This  extra  sulphur  in  the  mineral  varies  in  amount 
but  also  has  as  its  maximum  about  6  per  cent.  In  view  of  the  experimental 
data  there  is  no  doubt  but  that  pyrrhotite  should  be  considered  as  the  mono- 
sulphide  of  iron  containing  varying  small  amounts  of  excess  sulphur  in  the 
form  of  a  solid  solution. 

Another  case  of  solid  solution  is  undoubtedly  shown  by  nephelite  which 
commonly  contains  a  small  excess  of  SiO2.  It  is  very  probable  that  further 
investigation  will  show  that  many  minerals  have  this  power  of  holding  in 
solid  solution  small  amounts  of  foreign  substances  and  that  many  hitherto 
inexplicable  discrepancies  in  their  analyses  may  be  explained  in  this  way. 
Such  an  assumption  should  not  be  made,  however,  without  convincing  proof 
of  its  probability,  since  many  analytical  discrepancies  are  undoubtedly  due  to 
either  faulty  analyses  or  to  impure  material. 

474.  Colloidal  Minerals  or  Mineral  Gels.*  —  It  has  been  recognized 
recently  that  our  amorphous  hydrated  minerals  frequently  do  not  conform  in 
their  analyses  to  the  usually  accepted  formulas  and  cannot  be  regarded  in  the 
strict  sense  as  definite  chemical  compounds.  They  show  rather  the  proper- 
ties of  solid  colloids  or  as  they  are  commonly  called  mineral  gels.  A  colloidal 
solution  may  be  conceived  as  being  intermediate  in  its  characters  between  a 
true  solution  and  the  case  where  the  mineral  material  is  definitely  in  suspen- 

*  For  a  resume  of  the  subject  of  gel  minerals  and  a  complete  bibliography  reference  is 
made  to  articles  by  Marc  and  Himmelbauer,  Fortschritte  Min.  Krist.  Pet.,  3,  11,  33,  1913. 


GENERAL  PRINCIPLES  OF  CHEMISTRY  AS  APPLIED  TO  MINERALS  325 

sion  in  a  liquid.  It  is  probable  that  all  gradations  between  these  two  extremes 
may  occur.  The  mineral  gels,  or  hydrogels,  as  they  are  sometimes  called, 
since  water  is  the  liquid  involved,  are  apparently  formed  from  such  colloidal 
solutions  by  some  process  of  coagulation.  They  are  considered  therefore  to 
consist  of  a  micro-heterogeneous  mixture  of  excessively  minute  particles  of 
mineral  material  and  water. 

These  mineral  gels  are  formed  at  low  temperatures  and  pressures  and  are 
characteristically  found  among  the  products  of  rock  weathering  and  in  the 
oxidized  zone  of  ore  deposits.  Some  of  them  also  occur  in  hot  spring  deposits. 
These  minerals  ordinarily  assume  botryoidal,  reniform  or  stalactitic  shapes, 
although,  when  the  conditions  of  formation  do  not  permit  free  growth,  they 
may  be  earthy  or  dendritic.  Frequently  a  mineral  originally  colloidal  may 
become  more  or  less  crystalline  in  character  through  a  molecular  rearrange- 
ment and  develop  a  fibrous"  or  foliated  structure.  These  have  been  designated 
as  meta-colloids. 

One  important  character  of  the  gel  minerals  is  their  power  to  adsorb  foreign 
materials.  If  through  some  change  in  condition  one  of  these  hydrogels  should 
lose  a  part  of  its  water  content  the  remaining  material  would  have  a  finely 
divided  and  porous  structure  exactly  adapted  to  exert  a  strong  power  of 
adsorption.  Consequently,  although  in  many  cases  the  main  mass  of  the 
mineral  may  have  a  composition  closely  similar  to  some  definite  crystallized 
mineral,  it  will  commonly  show  a  considerable  range  in  composition  due  both 
to  the  non-molecular  relations  of  the  contained  water  and  to  this  secondary 
adsorption.  Common  mineral  gels  or  substances  derived  from  them  are  opal, 
bauxite,  psilomelane,  various  members  of  the  phosphate  and  arsenate  groups, 
etc.  As  suggested  above,  gel  varieties  of  minerals  that  occur  also  in  crystal- 
line forms  are  thought  to  exist.  For  example  some  authors  speak  of  bauxite 
as  the  gel  form  of  hydrargillite,  stilpnosiderite  as  the  gel  form  of  goethite, 
chrysocolla  of  dioptase,  and  further  give  new  names,  such  as  gelvariscite, 
gelpyrophyllite,  etc.,  to  the  gel  phases  of  the  corresponding  crystalline  minerals. 

475.  Dimorphism.  Isodimorphism.  —  A  chemical  compound,  which 
crystallizes  in  two  forms  genetically  distinct,  is  said  to  be  dimorphous;  if  in 
three,  trimorphous,  or  in  general  pleomorphous.  This  phenomenon  is  called 

DIMORPHISM  Or  PLEOMORPHISM. 

An  example  is  given  by  the  compound  calcium  carbonate  (CaCO3),  which 
is  dimorphous :  appearing  as  calcite  and  as  aragonite.  As  calcite  it  crystallizes 
in  the  rhombohedral  class  of  the^  hexagonal  system,  and,  unlike  as  its  many 
crystalline  forms  are,  they  may  be  all  referred  to  the  same  fundamental  axes, 
and,  what  is  more,  they  have  all  the  same  cleavage  and  the  same  specific 
gravity  (27)  and,  of  course,  the  same  optical  characters.  As  aragonite,  cal- 
cium carbonate  appears  in  orthorhombic  crystals,  whose  optical  characters 
are  entirely  different  from  those  of  calcite;  moreover,  the  specific  gravity  of 
aragonite  (2'9)  is  higher  than  that  of  calcite  (27). 

Many  other  examples  might  be  given:  Titanium  dioxide  (TiO2)  is  tri- 
morphous, the  species  being  called  rutile,  tetragonal  (c  =  0'6442),  G.  =  4*25; 
octahedrite,  tetragonal  (c  =  1778),  G.  =  3 '9;  and  brookite,  orthorhombic, 
G.  =  4' 15.  Carbon  appears  in  two  forms,  in  diamond  and  graphite.  Other 
familiar  examples  are  pyrite  and  marcasite  (FeS2),  sphalerite  and  wurtzite 
(ZnS),  etc. 

When  two  or  more  analogous  compounds  are  at  the  same  time  isomorphous 
and  dimorphous,  they  are  said  to  be  isodimbrphous,  and  the  phenomenon  is 


326  CHEMICAL   MINERALOGY 

called  ISODIMORPHISM.  An  example  of  this  is  given  in  the  Pyrite  and  Mar- 
casite  groups  described  later.  Thus  we  have  in  the  isometric  Pyrite  Group, 
pyrite,  FeS2,  smaltite,  CoAs2;  in  the  orthorhombic  Marcasite  Group,  marcas- 
ite,  FeS2,  safflorite,  CoAs2,  etc. 

476.  Chemical   and   Microchemical  Analysis.  —  The   analysis   of  min- 
erals is  a  subject  treated  of  in  chemical  works,  and  need  not  be  touched  upon 
here  except  so  far  as  to  note  the  convenient  use  of  certain  qualitative  methods, 
as  described  in  the  later  part  of  this  chapter. 

Of  more  importance  are  the  microchemical  methods  applicable  to  sections 
under  the  microscope  and  often  yielding  decisive  results  with  little  labor. 
This  subject  has  been  particularly  developed  by  Boricky,  Haushofer,  Behrens, 
Streng,  and  others.  Reference  is  made  to  the  discussion  by  Rosenbusch. 
(Mikr.  Phys.,  1904,  p.  435  et  seq.),  to  Johannsen  (Manual  of  Pet.  Methods, 
559,  et  seq.,  including  a  bibliography).  Microchemical  methods  used  upon 
polished  surfaces  of  opaque  minerals  are  described  by  Murdock  (Micro. 
Deter.  Opaque  Min.,  1916)  and  by  Davy-Farnham  (Micro.  Exam,  of  the 
Ore  Min.,  1920). 

477.  Mineral    Synthesis.  —  The    occurrence    of    certain    mineral    com- 
pounds (e.g.,  the  chrysolites)  among  the  products  of  metallurgical  furnaces 
has  long  been  noted.     But  it  has  only  been  in  recent  years  that  the  formation 
of  artificial  minerals  has  been  made  the  subject  of  minute  systematic  experi- 
mental study.     In  this  direction  the  French  chemists  have  been  particularly 
successful,  and  now  it  may  be  stated  that  the  majority  of  common  minerals  — 
quartz,  the  feldspars,  amphibole,  mica.  etc.  —  have  been  obtained  in  crystal- 
lized form.     Even  the  diamond  has  been  formed  in  minute   crystals  by 
Moissan.     These  studies  are  obviously  of  great  importance  particularly  as 
throwing  light  upon  the  method  of  formation  of  minerals  in  nature.     The 
chief  results  of  the  work  thus  far  done  are  given  in  the  volumes  mentioned  in 
the  Introduction,  p.  4. 

478.  Alteration  of  Minerals.    Pseudomorphs.  —  The   chemical   altera- 
tion of  mineral  species  under  the  action  of  natural  agencies  is  a  subject  of 
great  importance  and  interest,  particularly  when  it  results  in  the  change  of  the 
original  composition  into  some  other  equally  definite   compound.     A  crystal- 
lized mineral  which  has  thus  suffered  change  so  that  its  form  no  longer  belongs 
to  its  chemical  composition  has  already  been  defined  (Art.  273,  p.  183)  as  a 
pseudomorph.     It  remains  to  describe  more  fully  the  different  kinds  of  pseudo- 
morphs.     Pseudomorphs  are  classed  under  several  heads : 

1.  Pseudomorphs  by  substitution. 

2.  Pseudomorphs  by  simple  deposition,  and  either  by  (a)  incrustation  or 
(b)  infiltration. 

3.  Pseudomorphs  by  alteration;  and  these  may  be  altered 

(a)  without  a  change  of  composition,  by  paramorphism; 

(b)  by  the  loss  of  an  ingredient; 

(c)  by  the  assumption  of  a  foreign  substance; 

(d)  by  a  partial  exchange  of  constituents. 

1.  The  first  class  of  pseudomorphs,  by  substitution,  embraces  those  cases 
where  there  has  been  a  gradual  removal  of  the  original  material  and  a  cor- 
responding and  simultaneous  replacement  of  it  by  another,  without,  however, 
any  chemical  reaction  between  the  two.  A  common  example  of  this  is  a  piece 
of  fossilized  wood,  where  the  original  fiber  has  been  replaced  entirely  by 


CHEMICAL   EXAMINATION   OF    MINERALS  327 

silica.  The  first  step  in  the  process  was  the  filling  of  the  pores  and  cavities 
by  the  silica  in  solution,  and  then  as  the  woody  fiber,  by  gradual  decomposi- 
tion, disappeared  the  silica  further  took  its  place.  Other  examples  are  quartz 
after  fluorite,  calcite,  and  many  other  species;  cassiterite  after  orthoclase; 
native  copper  after  aragonite,  etc. 

2.  Pseudomorphs  by  incrustation  form  a  less  important  class.     Such  are 
the  crusts  of  quartz  formed  over  fluorite.     In  most  cases  the  removal  of  the 
original  mineral  has  gone  on  simultaneously  with  the  deposition  of  the  second, 
so  that  the  resulting  pseudomorph  is  properly  one  of  substitution.     In  pseudo- 
morphs  by  infiltration  a  cavity  made  by  the  removal  of  a  crystal  has  been 
filled  by  another  mineral. 

3.  The  third  class  of  pseudomorphs,  by  alteration,  includes  a  considerable 
proportion  of  the  observed  cases,  of  which  the  number  is  very  large.     Con- 
clusive evidence  of  the  change  which  has  gone  on  is  often  furnished  by  a 
nucleus  of  the  original  mineral  in  the  center  of  the  altered  crystal  —  e.g.,  a 
kernel  of  cuprite  in  a  pseudomorphous  octahedron  of  malachite;    also  of 
chrysolite  in  a  pseudomorphous  crystal  of  serpentine,  etc. 

(a)  An  example  of  paramorphism  —  that  is,  of  a  change  in  molecular  con- 
stitution without  change  of  chemical  substance  —  is  furnished  by  the  change 
of  aragonite  to  calcite  (both  CaCO3)  at  a  certain  temperature ;  also  the 
paramorphs  of  rutile  after  brookite  (both  TiO2)  from  Magnet  Cove,  Arkansas. 

(6)  An  example  of  the  pseudomorphs  in  which  alteration  is  accompanied 
by  a  loss  of  ingredients  is  furnished  by  crystals  of  native  copper  in  the  form 
of  cuprite. 

(c)  In  the  change  of  cuprite  to  malachite  —  e.g.,  the  familiar  crystals  from 
Chessy,  France  —  an  instance  is  afforded  of  the  assumption  of  an  ingredient  — 
viz.,  carbon  dioxide  (and  water).     Pseudomorphs  of  gypsum  after  anhydrite 
occur  where  there  has  been  an  assumption  of  water  alone. 

(d)  A  partial  exchange  of  constituents  —  in  other  words,  a  loss  of  one  and 
gain  of  another  —  takes  place  in  the  change  of  feldspar  to  kaolin,  in  which  the 
potash  silicate  disappears  and  water  is  taken  up;  pseudomorphs  of  limonite 
after  pyrite  or  siderite,  of  chlorite  after  garnet,  pyromorphite  after  galena, 
are  other  examples. 

The  chemical  processes  involved  in  such  changes  open  a  wide  and  impor- 
tant field  for  investigation.  Their  study  has  served  to  throw  much  light  on 
the  chemical  constitution  of  mineral  species  and  the  conditions  under  which 
they  have  been  formed.  For  the  literature  of  the  subject  see  the  Introduc- 
tion, p.  4  (Blum,  Bischof,  Roth,  etc.). 


CHEMICAL   EXAMINATION   OF   MINERALS 

479.  The  complete  investigation  of  the  chemical  composition  of  a  min- 
eral includes,  first,  the  identification  of  the  elements  present  by  qualitative 
analysis,  and,  second,  the  determination  of  the  relative  amounts  of  each  by 
quantitative  analysis,  from  which  last  the  formula  can  be  calculated.  Both 
processes  carried  out  in  full  call  for  the  equipment  of  a  chemical  laboratory. 
An  approximate  qualitative  analysis,  however,  can,  in  many  cases,  be  made 
quickly  and  simply  with  few  conveniences.  The  methods  employed  involve 
either  (a)  the  use  of  acids  or  other  reagents  "  in  the  wet  way,"  or  (6)  the  use 


328  CHEMICAL   MINERALOGY 

of  the  blowpipe,  or  of  both  methods  combined.     Some  practical  instructions 
will  be  given  applying  to  both  cases. 

EXAMINATION   IN  THE  WET  WAY 

480.  Reagents,   etc.  —  The   most   commonly   employed   chemical   re- 
agents are  the  three  mineral  acids,  hydrochloric,  nitric,  and  sulphuric  acids. 
To  these  may  be  added  ammonium  hydroxide,  also  solutions  of  barium  chlo- 
ride, silver  nitrate,  ammonium  molybdate,  ammonium  oxalate;   finally,  dis- 
tilled water  in  a  wash-bottle. 

A  few  test-tubes  are  needed  for  the  trials  and  sometimes  a  porcelain  dish 
with  a  handle  called  a  casserole;  further,  a  glass  funnel  and  filter-paper. 
The  Bunsen  gas-burner  (p.  330)  is  the  best  source  of  heat,  though  an  alcohol 
lamp  may  take  its  place.  It  is  unnecessary  to  remark  that  the  use  of  acids 
and  the  other  reagents  requires  much  care  to  avoid  injury  to  person  or  clothing. 

In  testing  the  powdered  mineral  with  the  acids,  the  important  points  to  be 
noted  are:  (1)  the  degree  of  solubility,  and  (2)  the  phenomena  attending  entire 
or  partial  solution;  that  is,  whether  (a)  a  solution  is  obtained  quietly,  without 
effervescence,  and,  if  so,  what  its  color  is;  or  (6)  a  gas  is  evolved,  producing 
effervescence;  or  (c)  an  insoluble  constituent  is  separated  out. 

481.  Solubility.  —  In  testing  the  degree  of  solubility  hydrochloric  acid 
is  most  commonly  used,  though  in  the  case  of  many  metallic  minerals,  as  the 
sulphides  and  compounds  of  lead  and  silver,  nitric  acid  is  required.     Less 
often  sulphuric  acid  and  aqua  regia  (nitro-hydrochloric  acid)  are  resorted  to. 

The  trial  is  usually  made  in  a  test-tube,  »and  in  general  the  fragment  of 
mineral  to  be  examined  should  be  first  carefully  pulverized  in  an  agate 
mortar.  In  most  cases  the  heat  of  the  Bunsen  burner  must  be  employed. 

(a)  Many  minerals  are  completely  soluble  without  effervescence;    among 
these  are  some  of  the  oxides,  as  hematite,  limonite,  gothite,  etc.;   some  sul- 
phates, many  phosphates  and  arsenates,  etc.     Gold  and  platinum  are  soluble 
only  in  aqua  regia  or  nitro-hydrochloric  acid. 

A  yellow  solution  is  usually  obtained  if  much  iron  is  present;  a  blue  or 
greenish  blue  solution  (turning  deep  blue  on  the  addition  of  ammonium  hy- 
droxide in  excess)  from  compounds  of  copper;  pink  or  pale  rose  from  cobalt,  etc. 

(b)  Solubility  with  effervescence  takes   place  when  the  mineral   loses   a 
gaseous  ingredient,  or  when  one  is  generated  by  the  mutual  reaction  of  acid 
and  mineral.     Most  conspicuous  here  are  the  carbonates,  all  of  which  dissolve 
with  effervescence,  giving  off  the  odorless  gas  carbon  dioxide  (C02),  though 
some  of  them  only  when  pulverized,  or,  again,  on  the  addition  of  heat.     In 
applying  this  test  dilute  hydrochloric  acid  is  employed. 

Hydrogen  sulphide  (H2S)  is  evolved  by  some  sulphides  when  dissolved  in 
hydrochloric  acid:  this  is  true  of  sphalerite,  stibnite,  etc.  This  gas  is  readily 
recognized  by  its  offensive  odor. 

Chlorine  is  evolved  by  oxides  of  manganese  and  also  chromic  and  vanadic 
acid  salts  when  dissolved  in  hydrochloric  acid. 

Nitrogen  dioxide  (NO2)  is  given  off,  in  the  form  of  red  suffocating  fumes, 
by  many  metallic  minerals,  and  also  some  of  the  lower  oxides  (cuprite,  etc.), 
when  treated  with  nitric  acid. 

(c)  The  separation  of  an  insoluble  ingredient  takes  place:    With  many 
silicates,  the  silica  separating  sometimes  as  a  fine  powder,  and  again  as  a  jelly; 
in  the  latter  case  the  mineral  is  said  to  gelatinize  (sodalite,  analcite).     In  order 
to  test  this  point  the  finely  pulverized  silicate  is  digested  with  strong  hydro- 


CHEMICAL   EXAMINATION   OF   MINERALS  329 

chloric  acid,  and  the  solution  afterward  slowly  evaporated  nearly  to  dryness. 
With  a  considerable  number  of  silicates  the  gelatinization  takes  place  only 
after  the  mineral  has  been  previously  fused;  while  some  others,  which  ordi- 
narily gelatinize,  are  rendered  insoluble  by  ignition. 

With  many  sulphides  (as  pyrite)  a  separation  of  sulphur  takes  place  when 
they  are  treated  with  nitric  acid. 

Some  compounds  of  titanium  and  tungsten  are  decomposed  by  hydro- 
chloric acid  with  the  separation  of  the  oxides  of  the  elements  named  (TiO2, 
WO3) .  The  same  is  true  of  salts  of  molybdic  and  vanadic  acids,  only  that  here 
the  oxides  are  soluble  in  an  excess  of  the  acid. 

Compounds  containing  silver,  lead,  and  mercury  give  with  hydrochloric 
acid  insoluble  residues  of  the  chlorides.  These  compounds  are,  however, 
soluble  in  nitric  acid. 

When  compounds  containing  tin  are  treated  with  nitric  acid,  the  tin 
dioxide  (SnO2)  separates  as  a  white  powder.  A  corresponding  reaction  takes 
place  under  similar  circumstances  with  minerals  containing  arsenic  and 
antimony. 

Insoluble  Minerals.  —  A  large  number  of  minerals  are  not  sensibly  attacked 
by  any  of  the  acids.  Among  these  may  be  named  the  following  oxides: 
corundum,  spinel,  chromite,  diaspore,  rutile,  cassiterite,  quartz;  also  cerar- 
gyrite;  many  silicates,  titanates,  tantalates,  and  niobates;  some  of  the  sul- 
phates, as  barite,  celestite;  many  phosphates,  as  xenotime,  lazulite,  childrenite, 
amblygonite;  also  the  borate,  boracite. 

482.  Examination  of  the  Solution.  —  If  the  mineral  is  difficultly,  or 
only  partially,  soluble,  the  question  as  to  solubility  or  insolubility  is  not  always 
settled  at  once.     Partial  solution  is  often  shown  by  the  color  given  to  the 
liquid,  or  more  generally  by  the  precipitate  yielded,  for  example,  on  the  addi- 
tion of  ammonium  hydroxide  to  the  liquid  filtered  off  from  the  remaining 
powder.     The  further  examination  of  the  solution  yielded,  whether  from  par- 
tial or  complete  solution,  after  the  separation  by  filtration  of  any  insoluble 
residue,  requires  the  systematic  laboratory  methods  of  qualitative  analysis. 

It  may  be  noted,  however,  that  in  the  case  of  sulphates  the  presence  of 
sulphur  is  shown  by  the  precipitation  of  a  heavy  white  powder  of  barium 
sulphate  (BaSOO  when  barium  chloride  is  added.  The  presence  of  silver  in 
solution  is  shown  by  the  separation  of  a  white  curdy  precipitate  of  silver 
chloride  (AgCl)  upon  the  addition  of  any  chlorine  compound;  conversely,  the 
same  precipitate  shows  the  presence  of  chlorine  when  silver  nitrate  is  added 
to  the  solution. 

Again,  phosphorus  may  be  detected  if  present,  even  in  small  quantity, 
in  a  nitric  acid  solution  of  a  mineral  by  the  fine  yellow  powder  which  separates, 
sometimes  after  standing,  when  ammonium  molybdate  has  been  added. 

EXAMINATION  BY  MEANS  OF  THE  BLOWPIPE* 

483.  The  use  of  the  blowpipe,  in  skilled  hands,  gives  a  quick  method  of 
obtaining  a  partial  knowledge  of  the  qualitative  composition  of  a  mineral. 
The  apparatus  needed  includes  the  following  articles : 

*  The  subject  of  the  blowpipe  and  its  use  is  treated  very  briefly  in  this  place.  The 
student  who  wishes  to  be  fully  informed  not  only  in  regard  to  the  use  of  the  various  instru- 
ments, but  also  as  to  all  the  valuable  reactions  practically  useful  in  the  identification  of 
minerals,  should  consult  a  manual  on  the  subject.  The  Brush-Penfield  Manual  of  Deter- 
minative Mineralogy,  with  an  introduction  on  Blowpipe  Analysis,  is  particularly  to  be 
recommended. 


330 


CHEMICAL   MINERALOGY 


622 


Blowpipe,  lamp,  forceps,  preferably  with  platinum  points,  platinum  wire, 
charcoal,  glass  tubes;  also  a  small  hammer  with  sharp  edges,  a  steel  anvil  an 
inch  or  two  long,  a  horseshoe  magnet,  a  small  agate  mortar,  a  pair  of  cutting 
pliers,  a  three-cornered  file. 

Further,  test-paper,  both  turmeric  and  blue  litmus  paper;  a  little  pure 
tin-foil;  also  in  small  wooden  boxes  the  fluxes:  borax  (sodium  tetraborate) , 
soda  (anhydrous  sodium  carbonate),  salt  of  phosphorus  or  microcosmic  salt 
(sodium-ammonium  phosphate),  acid  potassium  sulphate  (HKS04);  also  a 
solution  of  cobalt  nitrate  in  a  dropping  bulb  or  bottle;  further,  the  three  acids 
mentioned  in  Art.  480. 

484.  Blowpipe  and  Lamp.  —  A  good  form  of  blowpipe  is  shown  in  Fig. 
622.  The  air-chamber,  at  a,  is  essential  to  stop  the  condensed  moisture  of 
the  breath,  the  tip  (6),  which  is  removable,  is  usually  of  brass,  (c)  is  a  remov- 
able mouthpiece  which  may  or  may  not  be  used  as  preferred. 

The  most  convenient  form  of  lamp  is  that  furnished  by  an  ordinary  Bunsen 
gas-burner  *  (Fig.  623),  provided  with  a  tube,  6,  which  when  inserted  cuts  off 
the  air  supply  at  a;  the  gas  then  burns  at  the  top  with  the 
usual  yellow  flame.  This  flame  should  be  one  to  one  and 
a  half  inches  high.  The  tip  of  the  blow-pipe  is  held  near 
(or  just  within  the  flame,  see  beyond),  and  the  air  blown 
through  it  causes  the  flame  to  take  the  shape  shown  in 
Fig.  625. 

It  is  necessary  to  learn  to  blow  continuously,  that  is,  to 
keep  up  a  blast  of  air  from  the  compressed  reservoir  in 
the  mouth-cavity  while  respiration 
is  maintained  through  the  nose. 
To  accomplish  this  successfully  and 
at  the  same  time  to  produce  a  clear 
flame  without  unnecessary  fatiguing 
effort  calls  for  some  practice. 

When  the  tube,  6,  is  removed,  the 
gas  burns  with  a  colorless  flame  and 
is  used  for  heating  glass  tubes,  test- 
tubes,  etc. 

485.  Forceps.  Wire.  —  The  for- 
ceps (Fig.  624)  are  made  of  steel, 
nickel-plated,  and  should  have  a  spring 
strong  enough  to  support  firmly  the 
small  fragment  of  mineral  between  the 
platinum  points  at  d.  The  steel  points 
at  the  other  end  are  used  to  pick  up  small  pieces  of  minerals,  but  must  not  be 
inserted  in  the  flame.  Care  must  be  taken  not  to  injure  the  platinum  by  allow- 
ing it  to  come  in  contact  with  the  fused  mineral,  especially  if  this  contains 
antimony,  arsenic,  lead,  etc.  Cheaper  forceps,  made  of  steel  wire,  etc.,  while 
not  so  convenient,  will  also  serve  reasonably  well. 

A  short  length  of  fairly  stout  platinum  wire  to  be  used  in  the  making  of 
bead  tests  should  be  available.  A  similar  length  of  finer  wire  for  making 
flame  tests  is  also  desirable. 


*  Instead  of  this,  a  good  stearin  candle  will  answer,  or  an  oil  flame  with  flat  wick. 


CHEMICAL   EXAMINATION    OF   MINERALS  331 

486.  Charcoal.  —  The  charcoal  employed  should  not  snap  and  should 
yield  but  little  ash;  the  kinds  made  from  basswood,  pine  or  willow  are  best. 
It  is  most  conveniently  employed  in  rectangular  pieces,  say  four  inches  long, 
an  inch  wide,  and  three-quarters  of  an  inch  in  thickness.     The  surface  must 
always  be  perfectly  clean  before  each  trial. 

487.  Glass  Tubes.  —  The   glass  tubes  should   be   preferably  of  two 
grades;   a  hard  glass  tubing  with  about  5  mm.  interior  diameter  to  be  cut  in 
five  inch  lengths  and  used  in  open  tube  tests  and  a  soft  glass  tubing  with  about 

624     3  mm.  interior  diameter  to  be  in  about  six  inch  lengths,  each  length 
yielding  two  closed  tubes. 

488.  Blowpipe  Flame.  —  The  blowpipe  flame,  shown  in  Fig.  625, 
consists  of  three  cones :  an  inner  of  a  blue  color,  c,  a  second  pale  violet 
cone,  b,  and  an  outer   invisible  cone,  a.     The   cone  c   consists   of 
unburned  gas   mixed   with  air   from  the  blowpipe.     There  is   no 
625  combustion  in  this  cone  and 

therefore  no  heat.     The  cone 
b  is  the  one  in  which  combus- 
tion is  taking  place.  This  cone 
contains     carbon    monoxide 
which  is  a   strong  reducing 
agent,  see  below.     Cone  a  is  merely  a 
gas   envelope   composed   of  the  final 

products    of     combustion,    C02    and 
Blowpipe  Flame  R^      The  ^  ^  mogt  intense  near 

the  tip  of  the  cone  6,  and  the  mineral  is  held  at  this  point  when  its  fusibility 
is  to  be  tested. 

The  point  o,  Fig.  625,  is  called  the  OXIDIZING  FLAME  (O.F.) ;  it  is  character- 
ized by  the  excess  of  the  oxygen  of  the  air  and  has  hence  an  oxidizing  effect 
upon  the  assay.  This  flame  is  best  produced  when  the  jet  of  the  blowpipe 
is  inserted  a  very  little  in  the  gas  flame;  it  should  be  entirely  non-lu- 
minous. 

The  cone  6  is  called  the  REDUCING  FLAME  (R.F.);  it  is  characterized  by 
the  excess  of  the  carbon  or  hydrocarbons  of  the  gas,  which  at  the  high  tem- 
perature present  tend  to  combine  with  the  oxygen  of  the  mineral  brought  into 
it  (at  r),  or,  in  other  words,  to  reduce  it.  The  best  reducing  flame  is  produced 
when  the  blowpipe  is  held  a  little  distance  from  the  gas  flame;  it  should  retain 
the  yellow  color  of  the  latter  on  its  upper  edge. 

489.  Methods  of  Examination.  —  The  blowpipe  investigation  of  min- 
erals includes  their  examination,  (1)  in  the  forceps,  (2)  in  the  closed  and  the 
open  tubes,  (3)  on  charcoal  or  other  support,  and  (4)  with  the  fluxes  on  the 
platinum  wire. 

1.     EXAMINATION  IN  THE  FORCEPS 

490.  Use  of  the  Forceps.  —  Forceps  are  employed  to  hold  the  fragment 
of  the  mineral  while  a  test  is  made  as  to  its  fusibility;  also  when  the  presence 
of  a  volatile  ingredient  which  may  give  the  flame  a  characteristic  color  is  tested 
for,  etc. 

The  following  practical  points  must  be  regarded:  (1)  Metallic  minerals,  especially  those 
containing  arsenic  or  antimony,  which  when  fused  might  injure  the  platinum  of  the  forceps, 


332  CHEMICAL   MINERALOGY 

should  first  be  examined  on  charcoal;  *  (2)  the  fragment  taken  should  be  thin,  and  as 
small  as  can  conveniently  be  held,  with  its  edge  projecting  well  beyond  the  points;  (3)  when 
decrepitation  takes  place,  the  heat  must  be  applied  slowly,  or,  if  this  does  not  prevent  it, 
the  mineral  may  be  powdered  and  a  paste  made  with  water,  thick  enough  to  be  held  in  the 
forceps  or  on  the  platinum  wire;  or  the  paste  may,  with  the  same  end  in  view,  be  heated  on 
charcoal;  (4)  the  fragment  whose  fusibility  is  to  be  tested  must  be  held  in  the  hottest  part 
of  the  flame,  just  beyond  the  extremity  of  the  blue  cone. 

491.  Fusibility.  —  All  grades  of  fusibility  exist  among  minerals,  from 
those  which  fuse  in  large  fragments  in  the  flame  of  the  candle  (stibnite,  see 
below)  to  those  which  fuse  only  on  the  thinnest  edges  in  the  hottest  blowpipe 
flame  (bronzite) ;   and  still  again  there  are  a  considerable  number  which  are 
entirely  infusible  (e.g.,  corundum). 

The  exact  determination  of  the  temperature  of  fusion  is  not  easily  accom- 
plished (cf  Art.  431  p.  304),  and  for  purposes  of  determination  of  species  it  is 
unnecessary.  The  approximate  relative  degree  of  fusibility  is  readily  fixed  by 
referring  the  mineral  to  the  following  scale,  suggested  by  von  Kobell: 

1.  Stibnite.  4.   Actinolite. 

2.  Natrolite  (or  Chalcopyrite).  5.   Orthoclase. 

3.  Almandite  Garnet.  6.   Bronzite. 

492.  In  connection  with  the  trial  of  fusibility,  the  following  phenomena 
may  be  observed:   (a)  coloration  of  the  flame  (see  Art.  493);    (b)  swelling  up 
(stilbite),  or  exfoliation  of  the  mineral  (vermiculite) ;   or  (c)  glowing  without 
fusion  (calcite);    and  (d)  intumescence,  or  a  spirting  out  of  the  mass  as  it 
fuses  (scapolite). 

The  color  of  the  mineral  after  ignition  is  to  be  noted;  and  the  nature  of 
the  fused  mass  is  also  to  be  observed,  whether  a  clear  or  blebby  glass  is 
obtained,  or  a  black  slag;  also  whether  the  bead  or  residue  is  magnetic  or  not 
(due  to  iron,  less  often  nickel,  cobalt),  etc. 

The  ignited  fragment,  if  nearly  or  quite  infusible,  may  be  moistened  with 
the  cobalt  solution  and  again  ignited,  in  which  case,  if  it  turns  blue,  this 
indicates  the  presence  of  aluminium  (as  with  cyanite,  topaz,  etc.) ;  but  note 
that  zinc  silicate  (calamine)  also  assumes  a  blue  color.  If  it  becomes  pink, 
this  indicates  a  compound  of  magnesium  (as  brucite). 

Also,  if  not  too  fusible,  it  may,  after  treatment  in  the  forceps,  be  placed 
upon  a  strip  of  moistened  turmeric  paper,  in  which  case  an  alkaline  reaction 
proves  the  presence  of  an  alkali,  sodium,  potassium;  or  an  alkaline  earth, 
calcium,  barium,  strontium. 

493.  Flame  Coloration.  —  The  color  often  imparted  to  the  outer  blow- 
pipe flame,  while  the  mineral  held  in  the  forceps  is  being  heated,  makes  pos- 
sible the  identification  of  a  number  of  the  elements. 

The  colors  which  may  be  produced,  and  the  substances  to  whose  presence 
they  are  due,  are  as  follows: 

Color  Substance 

Carmine-red Lithium. 

Purple-red Strontium. 

Orange-red Calcium. 

Yellow. Sodium. 

Yellowish  green Barium. 

Siskine-green Boron. 

*  Arsenic,  antimony,  and  easily  reducible  metals  like  lead,  also  copper,  form  more  or 
less  fusible  alloys  with  platinum. 


CHEMICAL   EXAMINATION   OF   MINERALS  333 

Emerald-green Oxide  of  copper. 

Bluish  green Phosphoric  acid  (phosphates). 

Greenish  blue Antimony. 

Whitish  blue Arsenic. 

Azure-blue Chloride  of  copper;  also  selenium. 

Violet Potassium. 

A  yellowish  green  flame  is  also  given  by  the  oxide  or  sulphide  of  molybdenum;  a  bluish 
green  flame  (in  streaks)  by  zinc;  a  pale  bluish  flame  by  tellurium;  a  blue  flame  by  lead. 

494.  Notes.  —  The  presence  of  soda,  even  in  small  quantities,  produces  a  yellow  flame, 
which  (except  in  the  spectroscope)  more  or  less  completely  masks  the  coloration  of  the 
flame  due  to  other  substances,  e.g.,  potassium.     A  filter  of  blue  glass  held  in  front  of  the 
flame  will  shut  out  the  monochromatic  yellow  of  the  sodium  flame  and  allow  the  charac- 
teristic violet  color  of  the  potassium  to  be  observed.     Silicates  are  often  so  difficultly 
decomposed  that  no  distinct  color  is  obtained  even  when  the  substance  is  present;  in  such 
cases  (e.g.,  potash  feldspar)  the  powdered  mineral  may  be  fused  on  the  platinum  wire  with 
an  equal  volume  of  gypsum,  when  the  flame  can  be  seen  (at  least  through  blue  glass). 
Again,  a  silicate  like  tourmaline  fused  with  a  mixture  of  fluorite  and  acid  potassium  sul- 
phate yields  the  characteristic  green  flame  of  boron.     Phosphates  and  borates  give  the 
green  flame  in  general  best  when  they  have  been  pulverized  and  moistened  with  sulphuric 
acid.     Moistening  with  hydrochloric  acid  makes  the  coloration  in  many  cases  (as  with  the 
carbonates  of  calcium,  barium,  strontium)  more  distinct. 

2.   HEATING  IN  THE  CLOSED  AND  OPEN  TUBES 

495.  The  tubes  are  useful   chiefly  for  examining  minerals  containing 
volatile  ingredients,  given  off  at  the  temperature  of  the  gas  flame. 

In  the  case  of  the  closed  tube,  the  heating  goes  on  practically  uninfluenced 
by  the  air  present,  since  this  is  driven  out  of  the  tube  in  the  early  stages  of 
the  process.  In  the  open  tube,  on  the  other  hand,  a  continual  stream  of  hot 
air,  that  is,  of  hot  oxygen,  passes  over  the  assay,  tending  to  produce  oxidation 
and  hence  often  materially  changing  the  result. 

496.  Closed  Tube.  —  A  small  fragment  is  inserted,  or  a  small  amount 
of  the  powdered  mineral  —  in  this  case  with  care  not  to  soil  the  sides  of  the 
tube  —  and  heat  is  applied  by  means  of  the  ordinary  Bunsen  flame.     The 
presence  of  a  volatile  ingredient  is  ordinarily  shown  by  the  deposit,  or  subli- 
mate, upon  the  tube  at  some  distance  above  the  assay  where  the  tube  is  rela- 
tively cool. 

Independent  of  this,  other  phenomena  may  be  noted,  namely:  decrepita- 
tion, as  shown  by  fluorite,  calcite,  etc.;  glowing,  as  exhibited  by  gadoliriite; 
phosphorescence,  of  which  fluorite  is  an  example;  change  of  color  (limonite), 
and  here  the  color  of  the  mineral  should  be  noted  both  when  hot,  and  again 
after  cooling;  fusion;  giving  off  oxygen,  as  mercuric  oxide;  yielding  acid  or 
alkaline  vapors,  which  should  be  tested  by  inserting  a  strip  of  moistened 
litmus  or  turmeric  paper  in  the  tube. 

Of  the  sublimates  which  form  in  the  tube,  the  following  are  those  with 
which  it  is  most  important  to  be  familiar: 

Substance  Sublimate  in  the  Closed  Tube 

Water  (H20) Colorless  liquid  drops. 

Sulphur  (S) ; Red  to  deep  yellow,  liquid ;  pale  yellow,  solid. 

Tellurium  dioxide  (TeO2) Pale  yellow  to  colorless,  liquid;  colorless  or  white,  solid. 

Arsenic  sulphide  (As2S3) Dark  red,  liquid;  reddish  yellow,  solid. 

Antimony  oxysulphide  (Sb2S2O)     Black  to  reddish  brown  on  cooling,  solid. 

Arsenic  (As) Black,  brilliant  metallic  to  gray  crystalline,  solid 

Mercury  sulphide  (HgS) Deep  black,  red  when  rubbed  very  fine. 

Mercury  (Hg) Gray  metallic  globules. 

In  addition  to  the  above:  Tellurium  gives  black  fusible  globules;  selenium  the  same,  but 


334  CHEMICAL   MINERALOGY 

in  part  dark  red  when  very  small;  the  chloride  of  lead  and  oxides  of  arsenic  and  antimony 
give  white  solid  sublimates. 

497.  Open  Tube.  —  The  small  fragment  is  placed  in  the  tube  about 
an  inch  from  the  lower  end,  the  tube  being  slightly  inclined  (say  20°),  but  not 
enough  to  cause  the  mineral  to  slip  out,  and  heat  applied  beneath.     The  cur- 
rent of  air  passing  upward  through  the  tube  during  the  heating  process  has  an 
oxidizing  effect.     The  special  phenomena  to  be  observed  are  the  formation  of 
a  sublimate  and  the  odor  of  the  escaping  gases.     The  acid  or  alkaline  character 
of  the  vapors  is  tested  for  in  the  same  way  as  with  the  closed  tube.     The 
most  common  gas  to  be  obtained  in  this  way  is  sulphur  dioxide,  S02,  when 
sulphides  are  being  oxidized.     This  gas  is  to  be  recognized  by  its  irritating, 
pungent  odor  and  its  acid  reaction  upon  moistened  blue  litmus  paper. 

The  more  important  sublimates  are  as  follows: 

Substance  Sublimate  in  the  Open  Tube 

Arsenic  trioxide  (AsaOa) White,  crystalline,  volatile. 

Antimony  antimonate  (Sb2O4)  Straw-yellow,  hot;  white,  cold.  Infusible,  non-volatile, 

amorphous,  settling  along  bottom  of  tube.  Obtained 
from  compounds  containing  sulphur  as  stibnite,  also  the 
sulphantimonites  (e.g.,  bournonite)  as  dense  white  fumes. 
Usually  accompanied  by  the  following: 

Antimony  trioxide  (Sb2O3) . . .  White,  crystalline,  slowly  volatile,  forming  as  a  ring  on 

walls  of  tube. 

Tellurium  dioxide  (TeO2) White  to  pale  yellow  globules. 

Selenium  dioxide  (SeO2) White,  crystalline,  volatile. 

Molybdenum  trioxide  (MoO3)     Pale  yellow,  hot;  white,  cold. 

Mercury  (Hg) Gray  metallic  globules,  easily  united  by  rubbing. 

It  is  also  to  be  noted  that  if  the  heating  process  is  too  rapid  for  full  oxidation,  subli- 
mates, like  those  of  the  closed  tubes,  may  be  formed,  especially  with  sulphur  (yellow), 
arsenic  (black),  arsenic  sulphide  (orange),  mercury  sulphide  (black),  antimony  oxysulphide 
(black  to  reddish  brown). 

3.   HEATING  ON  CHARCOAL 

498.  The  fragment  (or  powder)  to  be  examined  is  placed  near  one  end  of 
the  piece  and  this  so  held  that  the  flame  passes  along  its  length.     If  the 
mineral  decrepitates,  it  may  be  powdered,  mixed  with  water,  and  then  the 
material  employed  as  a  paste. 

The  reducing  flame  is  employed  if  it  is  desired  to  reduce  a  metal  (e.g.., 
silver,  copper)  from  its  ores :  this  is  the  common  case.  If,  however,  the  min- 
eral is  to  be  roasted,  that  is,  heated  in  contact  with  the  air  so  as  to  oxidize  and 
volatilize,  for  example,  the  sulphur,  arsenic,  antimony  present,  the  oxidizing 
flame  is  needed  and  the  mineral  should  be  in  powder  and  spread  out. 

The  points  to  be  noted  are  as  follows : 

(a)  The  odor  given  off  after  short  heating.     In  this  way  the  presence  of 
sulphur,  arsenic  (garlic  or  alliaceous  odor),  and  selenium  (odor  of  decayed 
horseradish)  may  be  recognized. 

(b)  Fusion.  —  In  the  case  of  the  salts  of  the  alkalies  the  fused  mass  is 
absorbed  into  the  charcoal;  this  is  also  true,  after  long  heating,  of  the  car- 
bonates and  sulphates  of  barium  and  strontium.     (Art.  501.) 

(c)  The  Sublimate.  —  By  this  means  the  presence  of  many  of  the  metals 
may  be  determined.     The  color  of  the  sublimate,  both  near  the  assay  (N)  and 
at  a  distance  (D) ,  as  also  when  hot  and  when  cold,  is  to  be  noted. 

The  important  sublimates  are  the  following: 


CHEMICAL   EXAMINATION    OF   MINERALS  335 

Substance  Sublimate  on  Charcoal 

Arsenic  trioxide  (As2O3) White,  very  volatile,  distant  from  the  assay;  also 

garlic  fumes. 

Antimony  oxides  (SbaOe  and  Sb2C>4)     Dense  white,  volatile;   forms  near  the  assay. 

Zinc  oxide  (ZnO) Canary-yellow,  hot;  white,  cold;  moistened  with 

cobalt  nitrate  and  ignited  (O.F.)  becomes  green. 

Molybdenum  trioxide  (MoO3) Pale  yellow,  hot;  yellow,  cold;  touched  for  a  moment 

with  the  R.F.  becomes  azure-blue.  Also  a  copper- 
red  sublimate  (MoO2)  near  the  assay. 

Lead  oxide  (PbO) Dark  yellow,  hot;  pale  yellow,  cold.  Also  (from 

sulphides)  dense  white  (resembling  antimony),  a 
mixture  of  oxide,  sulphite,  and  sulphate  of  lead. 

Bismuth  trioxide  (I^Os) Dark  orange-yellow  (N),  paler  on  cooling;  also  bluish 

white  (D).  See  further,  p.  338. 

Cadmium  oxide  (CdO) Nearly  black  to  reddish  brown  (N)  and  orange-yellow 

(D) ;  often  iridescent. 

To  the  above  are  also  to  be  added  the  following: 

Selenium  dioxide,  SeO2,  sublimate  steel-gray  (N)  to  white  tinged  with  red  (D) ;  touched 
with  R.F.  gives  an  azure-blue  flame;  also  an  offensive  selenium  odor. 

Tellurium  dioxide,  TeOz,  sublimate  dense  white  (N)  to  gray  (D);  in  R.F.  volatilizes 
with  green  flame. 

Tin  dioxide,  SnO2,  sublimate  faint  yellow  hot  to  white  cold;  becomes  bluish  green 
when  moistened  with  cobalt  solution  and  ignited. 

Silver  (with  lead  and  antimony),  sublimate  reddish 

(d)  The  Infusible  Residue.  —  This  may  (1)  glow  brightly  in  the  O.F.,  indi- 
cating the  presence  of  calcium,  strontium,  magnesium,  zirconium,  zinc,  or  tin. 
(2)  It  may  give  an  alkaline  reaction  after  ignition:  alkaline  earths.  (3)  It 
may  be  magnetic,  showing  the  presence  of  iron  (or  nickel).  (4)  It  may  yield 
a  globule  or  mass  of  a  metal  (Art.  499) . 

499.  Reduction  on  Charcoal.  —  In  many  cases  the  reducing  flame  alone 
suffices  on  charcoal  to  separate  the  metal  from  the  volatile  element  present, 
with  the  result  of  giving  a  globule  or  metallic  mass.  Thus  silver  is  obtained 
from  argentite  (Ag2S)  and  cerargyrite  (AgCl) ;  copper  from  chalcocite  (Cu2S) 
and  cuprite  (Cu20),  etc.  The  process  of  reduction  is  always  facilitated  by  the 
use  of  sodium  carbonate  or  borax  as  a  flux,  and  this  is  in  many  cases  (sulph- 
arsenites,  etc.)  essential. 

The  finely  pulverized  mineral  is  intimately  mixed  with  two  or  three  times 
its  volume  of  soda,  and  a  drop  of  water  added  to  form  a  paste.  This  is  placed 
in  a  cavity  in  the  charcoal,  and  subjected  to  a  strong  reducing  flame.  More 
soda  is  added  as  that  present  sinks  into  the  coal,  and,  after  the  process  has 
been  continued  some  time,  a  metallic  globule  is  often  visible,  or  a  number  of 
them,  which  can  be  removed  and  separately  examined.  If  not  distinct,  the 
remainder  of  the  flux,  the  assay,  and  the  surrounding  coal  are  cut  out  with  a 
knife,  and  the  whole  ground  up  in  a  mortar,  with  the  addition  of  a  little  water. 
The  charcoal  is  carefully  washed  away  and  the  metallic  globules,  flattened  out 
by  the  process,  remain  behind.  Some  metallic  oxides  are  very  readily  reduced, 
as  lead,  while  others,  as  copper  and  tin,  require  considerable  skill  and  care. 

The  metals  obtained  (in  globules  or  as  a  metallic  mass)  may  be:  copper, 
color  red;  bismuth,  lead-gray,  brittle;  gold,  yellow,  not  soluble  in  nitric  acid; 
silver,  white,  soluble  in  nitric  acid,  the  solution  giving  a  silver  chloride  pre- 
cipitate (p.  340);  tin,  white,  harder  than  silver,  soluble  in  nitric  acid  with 
separation  of  white  powder  (Sn02);  lead,  lead-gray  (oxidizing),  soft  and 
fusible.  The  coatings  (see  the  list  of  sublimates  above)  often  serve  to  identify 
the  metal  present. 


336  CHEMICAL   MINERALOGY 

500.  Detection  of  Sulphur  in  Sulphates.  —  By  means  of  soda  on  char- 
coal the  presence  of  sulphur  in  the  sulphates  may  be  shown,  in  the  following 
manner.     Fuse  the  powdered  mineral  with  soda  and  charcoal  dust.     The 
latter  acting  as  a  strong  reducing  agent  changes  the  sulphate  to  a  sulphide 
with  the  formation  of  sodium  sulphide.     When  the  fused  mass  is  placed  with 
a  drop  of  water  upon  a  clean  silver  surface  a  black  or  yellow  stain  of  silver 
sulphide  will  be  formed.     A  similar  reaction  would  of  course  be  obtained  from 
a  sulphide.     The  latter  can  however  be  readily  distinguished  by  roasting  in 
the  open  tube  or  upon  charcoal  and  noting  the  formation  of  SO2. 

4.   TREATMENT  ON  THE  PLATINUM  WIRE 

501.  Use  of  the  Fluxes.  —  The  three  common  fluxes  are  borax,  salt  of 
phosphorus,  and  carbonate  of  soda  (p.  330).     They  are  generally  used  with  the 
platinum  wire,  less  often  on  charcoal  (see  p.  335) .     If  the  wire  is  employed  it 
must  have  a  small  loop  at  the  end;  this  is  heated  to  redness  and  dipped  into 
the  powdered  flux,  and  the  adhering  particles  fused  to  a  bead;  this  operation 
is  repeated  until  the  loop  is  filled.     Sometimes  in  the  use  of  soda  the  wire  may 
at  first  be  moistened  a  little  to  cause  it  to  adhere. 

When  the  bead  is  ready,  it  is,  while  hot,  brought  in  contact  with  the  pow- 
dered mineral,  some  of  which  will  adhere  to  it,  and  then  the  heating  process 
may  be  continued.  Very  little  of  the  mineral  is  in  general  required,  and  the 
experiment  should  be  commenced  with  a  minute  quantity  and  more  added  if 
necessary.  The  bead  must  be  heated  successively  first  in  the  oxidizing  flame 
(O.F.)  and  then  in  the  reducing  flame  (R.F.),  and  in  each  case  the  color  noted 
when  hot  and  when  cold.  The  phenomena  connected  with  fusion,  if  it  takes 
place,  must  also  be  observed. 

Minerals  containing  sulphur  or  arsenic,  or  both,  must  be  first  roasted  (see  p.  334)  till 
these  substances  have  been  volatilized.  If  too  much  of  the  mineral  has  been  added  and  the 
bead  is  hence  too  opaque  to  show  the  color,  it  may,  while  hot,  be  flattened  out  with  the 
hammer,  or  d'rawn  out  into  a  wire,  or  part  of  it  may  be  removed  and  the  remainder  diluted 
with  more  of  the  flux . 

With  salt  of  phosphorus,  the  wire  should  be  held  above  the  flame  so  that  the  escaping 
gases  may  support  the  bead ;  this  is  continued  till  quiet  fusion  is  attained. 

It  is  to  be  noted  that  the  colors  vary  much  with  the  amount  of  material  present ;  they 
are  also  modified  by  the  presence  of  other  metals. 

502.  Borax.  -  -  The  following  list  enumerates  the  different  colored  beads 
obtained  with  borax,  both  in  the  oxidizing  (O.F.)  and  reducing  flames  (R.F.), 
and  also  the  metals  to  the  presence  of  whose  oxides  the  colors  are  due.     Com- 
pare further  the  reactions  given  in  the  list  of  elements  (Art.  504). 

Color  in  Borax  Bead  Substance 

1.  OXIDIZING  FLAME 

Colorless,  or  opaque  white.  . .     Silica,  calcium,  aluminium;  also  silver,  zinc,  etc. 

Iron,  cold  —  (pale  yellow,  hot,  if  in  small  amount). 
Ked,  red-brown  to  brown Chromium  (CrO3),  hot  —  (yellowish  green,  cold). 

Manganese  (Mn2O3),  amethystine-red —  (violet,  hot). 

Iron  (Fe2O3),  hot  —  (yellow,  cold)  —  if  saturated. 

Nickel  (NiO)  red-brown  to  brown,  cold—  (violet,  hot). 

Uranium  (UO3),  hot  —  (yellow,  cold). 

Green Copper  (CuO),  hot  —  (blue,  cold,  or  bluish  green  if  highly 

saturated). 

Chromium  (CrO3),  yellowish  green,  cold  —  (red,  hot). 


CHEMICAL   EXAMINATION   OF   MINERALS  337 

Yellow Iron  (Fe2O3),  hot  —  (pale  yellow  to  colorless,  cold)  —  but 

red-brown  and  yellow  if  saturated. 

Uranium  (UOs),  hot,  if  in  small  amount;  paler  on  cooling. 
Chromium  (CrO3),  hot  and  in  small  amount  —  (yellowish 
green,  cold). 

Blue Cobalt  (CoO),  hot  and  cold. 

Copper  (CuO),  cold  if  highly  saturated —  (green,  hot). 

Violet ,. .     Nickel  (NiO),  hot  —  (red-brown,  cold). 

Manganese  (Mn2O3),  hot —  (amethystine-red,  cold). 

2.   REDUCING  FLAME  (R.F.) 

Colorless Manganese  (MnO),  or  a  faint  rose  color. 

Red Copper  (Cu2O,  with  Cu),  opaque  red. 

Green Iron  (FeO),  bottle-green. 

Chromium  (CrjOs),  emerald-green. 

Uranium  (U^Os),  yellowish  green  if  saturated. 

Blue Cobalt  (CoO),  hot  and  cold. 

Gray,  turbid Nickel  (Ni). 

503.  Salt  of  Phosphorus.  —  This  flux  gives  for  the  most  part  reactions 
similar  to  those  obtained  with  borax.  The  only  cases  enumerated  here  are 
those  which  are  distinct,  and  hence  those  where  the  flux  is  a  good  test. 

With  silicates  this  flux  forms  a  glass  in  'which  the  bases  of  the  silicate  are 
dissolved,  but  the  silica  itself  is  left  insoluble.  It  appears  as  a  skeleton  readily 
seen  floating  about  in  the  melted  bead. 

The  colors  of  the  beads,  and  the  metals  to  whose  oxides  these  are  due,  are : 

Color  Substance 

Red : Chromium  in  O.F.,  hot  —  (fine  green  when  cold). 

Green Chromium  in  O.F.  and  R.F.,  when  cold  —  (red  in  O.F.,  hot). 

Molybdenum  in  R.F.,  dirty  green,  hot;  fine  green,  cold  —  (yellow-green 

in  O.F.). 

Uranium  in  R.F.,  cold;  yellow-green,  hot. 

Vanadium,  chrome-green  in  R.F.,  cold —  (brownish  red,  hot).     In  O.F., 
dark  yellow,  hot,  paler  on  cooling. 

Yellow Molybdenum,  yellowish  green  in  O.F.,  hot,  paler  on  cooling  —  (in  R.F., 

dirty  green,  hot;  fine  green,  cold). 
Uranium  in  O.F. ,  hot;  yellowish  green,  cold  —  (in  R.F. ,  yellowish  green, 

hot;  green,  cold). 
Vanadium  in  O.F.,  dark  yellow,  hot,   paler  on  cooling  —  (in  R.F., 

brownish  red,  hot;  chrome-green,  cold). 

Violet Titanium  (TiO2)  in  R.F.,  yellow,  hot.     (Also  in  O.F.,  yellow,  hot;  color- 
cold.) 


CHARACTERISTIC  REACTIONS  OF  THE  IMPORTANT  ELEMENTS  AND  OF  SOME 

OF  THEIR  COMPOUNDS 

504.  The  following  list  contains  the  most  characteristic  reactions,  chiefly 
before  the  blowpipe  and  in  some  cases  also  in  the  wet  way,  'of  the  different 
elements  and  their  oxides.  It  is  desirable  for  every  student  to  gain  familiarity 
with  them  by  trial  with  as  many  minerals  as  possible.  Many  of  them  have 
already  been  briefly  mentioned  in  the  preceding  pages.  For  a  thoroughly  full 
description  of  these  and  other  characteristic  tests  (blowpipe  and  otherwise) 
reference  should  be  made  to  the  volume  by  Brush  and  Penfield  referred  to  on 
p.  329. 

It  is  to  be  remembered  that  while  the  reaction  of  a  single  substance  may 
be  perfectly  distinct  if  alone,  the  presence  of  other  substances  may  more  or 


338  CHEMICAL   MINERALOGY 

less  entirely  obscure  these  reactions;  it  is  consequently  obvious  that  in  the 
actual  examination  of  minerals  precautions  have  to  be  taken,  and  special 
methods  have  to  be  devised,  to  overcome  the  difficulty  arising  from  this  cause. 
These  will  be  gathered  from  the  "pyrognostic  characters"  (Pyr.)  given  in  con- 
nection with  the  description  of  each  species  in  the  Fourth  Part  of  this  work. 

Aluminium,  —  The  presence  of  aluminium  in  most  infusible  minerals,  containing  a  con- 
siderable amount,  may  be  detected  by  the  blue  color  which  they  assume  when,  after  being 
heated,  they  are  moistened  with  cobalt  solution  and  again  ignited  (e.g.,  cyanite,  andalusite, 
etc.).  Very  hard  minerals  (as  corundum)  must  be  first  finely  pulverized.  The  test  is  not 
conclusive  with  fusible  minerals  since  a  glass  colored  blue  by  cobalt  oxide  may  be  formed. 
It  is  to  be  noted  that  the  infusible  calamine  (zinc  silicate)  also  assumes  a  blue  color  when 
treated  with  cobalt  nitrate.  From  solutions  aluminium  will  be  precipitated  as  a  flocculent 
white  or  colorless  precipitate  on  the  addition  of  ammonium  hydroxide  in  excess. 

Antimony.  —  Antimonial  minerals  roasted  on  charcoal  give  dense  white  odorless  fumes; 
metallic  antimony  and  its  sulphur  compounds  give  in  the  open  tube  a  white  sublimate  of 
oxide  of  antimony  (see  p.  334).  Antimony  sulphide  (stibnite),  also  many  sulpharitimonites, 
give  in  a  strong  heat  in  the  closed  tube  a  sublimate  of  antimony  oxysulphide,  black  when 
hot,  brown-red  when  cold.  See  also  p.  333. 

In  nitric  acid,  compounds  containing  antimony  deposit  white  insoluble  metantimonic 
acid. 

Arsenic.  —  Arsenides,  sulpharsenites,  etc.,  give  off  fumes  when  roasted  on  charcoal, 
usually  easily  recognized  by  their  peculiar  garlic  odor.  In  the  open  tube  they  give  a  white, 
volatile,  crystalline  sublimate  of  arsenic  trioxide.  In  the  closed  tube  arsenic  sulphide 
gives  a  sublimate  dark  brown-red  when  hot,  and  red  or  reddish  yellow  when  cold;  arsenic 
and  some  arsenides  yield  a  black  mirror  of  metallic  arsenic  in  the  closed  tube.  In  arsenates 
the  arsenic  can  be  detected  by  the  garlic  odor  yielded  when  a  mixture  of  the  powdered 
mineral  with  charcoal  dust  and  sodium  carbonate  is  heated  (R.F.)  on  charcoal. 

Barium.  —  A  yellowish  green  coloration  of  the  flame  is  given  by  all  barium  salts,  except 
the  silicates;  an  alkaline  reaction  is  usually  obtained  after  intense  ignition. 

In  solution  the  presence  of  barium  is  proved  by  the  heavy  white  precipitate  (BaSO4) 
formed  upon  the  addition  of  dilute  sulphuric  acid. 

Bismuth.  —  On  charcoal  alone,  or  better  with  soda,  bismuth  gives  a  very  characteristic 
orange-yellow  sublimate;  brittle  globules  of  the  reduced  metal  are  also  obtained  (with 
soda).  Also  when  treated  with  3  or  4  times  the  volume  of  a  mixture  in  equal  parts  of 
potassium  iodide  and  sulphur,  and  fused  on  charcoal,  a  beautiful  red  sublimate  of  bismuth 
iodide  is  obtained;  near  the  mineral  the  coating  is  yellow. 

Boron.  —  Many  compounds  containing  boron  (borates,  also  the  silicates,  datolite,  dan- 
burite,  etc.)  tinge  the  flame  intense  yellowish  green,  especially  if  moistened  with  sulphuric 
acid.  For  some  .silicates  (as  tourmaline)  the  best  method  is  to  mix  the  powdered  mineral 
with  one  part  powdered  fluorite  and  two  parts  potassium  bisulphate.  The  mixture  is 
moistened  and  placed  on  platinum  wire.  At  the  moment  of  fusion  the  green  color  appears, 
but  lasts  but  an  instant. 

A  clilute  hydrochloric  acid  solution  containing  boron  gives  a  reddish  brown  color  to 
turmeric  paper  which  has  been  moistened  with  it  and  then  dried  at  100°;  the  color  changes 
to  black  when  ammonia  is  poured  on  the  paper. 

Cakium.  —  Many  calcium  minerals  (carbonates,  sulphates,  etc.)  give  an  alkaline  reaction 
on  turmeric  paper  after  being  ignited.  A  yellowish  red  color  is  given  to  the  flame  by  some 
compounds  (e.g.,  calcite  after  moistening  with  HG1) ;  the  strontium  flame  is  a  much  deeper 
red. 

In  weakly  acid  or  alkaline  solutions  calcium  is  precipitated  as  oxalate  by  the  addition  of 
ammonium  oxalate. 

Cadmium.  —  On  charcoal  with  soda,  compounds  of  cadmium  give  a  characteristic  sub- 
limate of  the  reddish  brown  oxide. 

Carbonates.  —  All  carbonates  effervesce  with  dilute  hydrochloric  acid,  yielding  the  odor- 
less gas  CO2  (e.g.,  calcite);  many  require  to  be  pulverized,  and  some  need  the  addition  of 
heat  (dolomite,  sidente).  Carbonates  of  lead  should  be  tested  with  nitric  acid. 

LMprides.  —  If  a  small  portion  of  a  mineral  containing  chlorine  (a  chloride,  also  pyro- 
morphite,  etc.)  is  added  to  the  bead  of  salt  of  phosphorus,  saturated  with  copper  oxide,  the 
bead  when  heated  is  instantly  surrounded  with  an  intense  purplish  flame  of  copper  chloride. 

In  solution  chlorine  gives  with  silver  nitrate  a  white  curdy  precipitate  of  silver  chloride 
which  darkens  in  color  on  exposure  to  the  light;  it  is  insoluble  in  nitric  acid,  but  entirely 
soluble  m  ammonia. 


CHEMICAL   EXAMINATION    OF   MINERALS  339 

Chromium.  —  Chromium  gives  with  borax  a  bead  which  (O.F.)  is  yellow  to  red  (hot)  and 
yellowish  green  (cold)  and  R.F.  a  fine  emerald-green.  With  salt  of  phosphorus  in  O.F. 
the  bead  is  dirty  green  (hot)  and  clear  green  (cold);  in  R.F.  the  same.  Cf.  Vanadium 
beyond  (also  pp.  336,  337). 

Cobalt.  —  A  beautiful  blue  bead  is  obtained  with  borax  in  both  flames  from  minerals 
containing  cobalt.  Where  sulphur  or  arsenic  is  present  the  mineral  should  first  be 
thoroughly  roasted  on  charcoal. 

Copper.  —  On  charcoal,  at  least  with  soda,  metallic  copper  can  be  reduced  from  most  of 
its  compounds.  In  the  case  of  sulphides  the  powdered  mineral  should  be  roasted  first  in 
order  to  eliminate  the  major  part  of  the  sulphur  before  fusion  with  soda.  With  borax  it 
gives  (O.F.)  a  green  bead  when  hot,  becoming  blue  when  cold;  also  (R.F.),  if  saturated,  an 
opaque  red  bead  containing  Cu2O  and  often  Cu  is  obtained.  Copper  chloride,  obtained  by 
moistening  the  mineral  with  hydrochloric  acid  (in  the  case  of  sulphides  the  mineral  should 
be  previously  roasted)  yields  a  vivid  azure-blue  flame;  copper  oxide  gives  a  green  flame. 

Most  metallic  compounds  are  soluble  in  nitric  acid.  Ammonia  in  excess  produces  an 
intense  blue  color  in  the  solution. 

Fluorine.  —  Heated  in  the  closed  tube  with  potassium  bisulphate  and  powdered  glass 
produces  a  white  sublimate  of  SiO2.  This  sublimate  and  the  hydrofluosilicic  acid  present 
form  a  volatile  combination.  But  if  the  lower  end  of  the  tube  is  broken  off  and  the  open  tube 
then  dipped  in  a  test  tube  of  water  so  that  the  acid  is  removed,  the  deposit  of  SiO2  which 
will  appear  when  the  tube  is  dried  will  be  found  to  be  no  longer  volatile. 

Heated  gently  in  a  platinum  crucible  with  sulphuric  acid,  many  compounds  (e.g., 
fluorite)  give  off  hydrofluoric  acid,  which  corrodes  the  exposed  parts  of  a  glass  plate  placed 
over  it  which  has  been  coated  with  wax  and  then  scratched. 

Iron.  —  Minerals  which  contain  even  a  small  amount  of  iron  yield  a  magnetic  mass 
when  heated  in  the  reducing  flame.  With  borax  iron  gives  a  bead  (O.F.)  which  is  yellow 
to  brownish  red  (according  to  quantity)  while  hot,  but  is  colorless  to  yellow  on  cooling; 
R.F.  becomes  bottle-green  (see  pp.  336',  337). 

Lead.  —  With  soda  on  charcoal  a  malleable  globule  of  metallic  lead  is  obtained  from  lead 
compounds;  the  coating  has  a  yellow  color  near  the  as§ay;  the  sulphide  gives  also  a  white 
coating  (PbSO3)  farther  off  (p.  335).  On  being  touched  with  the  reducing  flame  the  coat- 
ing disappears,  tingeing  the  flame  azure-blue. 

In  solutions  dilute  sulphuric  acid  gives  a  white  precipitate  of  lead  sulphate;  when 
delicacy  is  required  an  excess  of  the  acid  is  added,  the  solution  evaporated  to  dryness,  and 
water  added;  the  lead  sulphate,  if  present,  will  then  be  left  as  a  residue. 

Lithium.  —  Lithium  gives  an  intense  carmine-red  to  the  outer  flame,  the  color  somewhat 
resembling  that  of  the  strontium  flame  but  is  deeper;  in  very  small  quantities  it  is  evident 
in  the  spectroscope. 

Magnesium.  —  Moistened,  after  heating,  with  cobalt  nitrate  and  again  ignited,  a  pink 
color  is  obtained  from  some  infusible  compounds  of  magnesium  (e.g.,  brucite).  In  solution 
the  addition  of  ammonium  hydroxide  in  large  excess  and  a  little  hydrogen  sodium  phos- 
phate produces  a  white  granular  precipitate  of  NH4MgPO4.  Elements  precipitated  by 
ammonium  hydroxide  or  ammonium  oxalate  should  be  removed  first. 

Manganese.  —  With  borax  manganese  gives  a  bead  violet-red  (O.F.),  and  colorless  (R.F.). 
With  soda  (O.F.)  it  gives  a  bluish  green  bead;  this  reaction  is  very  delicate  and  may  be 
relied  upon,  even  in  presence  of  almost  any  other  metal. 

Mercury.  —  In  the  closed  tube  a  sublimate  of  metallic  mercury  is  yielded  when  the 
mineral  is  heated  with  dry  sodium  carbonate.  In  the  open  tube  the  sulphide  gives  a  mirror 
of  metallic  mercury;  in  the  closed  tube  a  black  lusterless  sublimate  of  HgS,  red  when 
rubbed,  is  obtained. 

Molybdenum.  —  On  charcoal  molybdenum  sulphide  gives  near  the  assay  a  copper-red 
stain  (O.F.),  and  beyond  a  white  coating  of  the  oxide;  the  former  becomes  azure-blue  when 
for  a  moment  touched  with  the  R.F.  The  salt  of  phosphorus  bead  (O.F.)  is  yellowish 
green  (hot)  and  nearly  colorless  (cold);  also  (R.F.)  a  fine  green. 

Nickel.  —  With  borax,  nickel  oxide  gives  a  bead  which  (O.F.)  is  violet  when  hot  and 
red-brown  on  cooling;  (R.F.)  the  glass  becomes  gray  and  turbid  from  the  separation  of 
metallic  nickel. 

Niobium  (Columbium).  —  An  acid  solution  boiled  with  metallic  tin  gives  a  blue  color. 
The  reactions  with  the  fluxes  are  not  very  satisfactory. 

Nitrates.  —  These  detonate  when  heated  on  charcoal.  Heated  in  a  tube  with  sulphuric 
acid  they  give  off  red  fumes  of  nitrogen  dioxide  (NO2). 


been 


Phosphorus.  —  Most  phosphates  impart  a  green  color  to  the  flarne,  especially  after  having 
n  moistened  with  sulphuric  acid,  though  this  test  may  be  rendered  unsatisfactory  by 


340  CHEMICAL  MINERALOGY 

the  presence  of  other  coloring  agents.  If  they  are  used  in  the  closed  tube  with  a  fragment 
of  metallic  magnesium  or  sodium,  and  afterward  moistened  with  water,  phosphureted 
hydrogen  is  given  off,  recognizable  by  its  disagreeable  odor. 

A  few  drops  of  a  nitric  acid  solution,  containing  phosphoric  acid,  produce  in  a  solu- 
tion of  ammonium  molybdate  a  pulverulent  yellow  precipitate  of  ammonium  phospho- 
molybdate. 

Potassium.  —  Potash  imparts  a  violet  color  to  the  flame  when  alone.  The  flame  is  best 
observed  through  a  blue  glass  filter  which  will  eliminate  the  sodium  flame  color  which  will 
almost  invariably  be  present.  It  is  best  detected  in  small  quantities,  or  when  soda  or 
lithia  is  present,  by  the  aid  of  the  spectroscope.  See  also  p.  333. 

Selenium.  —  On  charcoal  selenium  fuses  easily,  giving  off  brown  fumes  with  a  peculiar 
disagreeable  organic  odor;  the  sublimate  on  charcoal  is  volatile,  and  when  heated  (R.F.) 
gives  a  fine  azure-blue  flame. 

Silicon.  —  A  small  fragment  of  a  silicate  in  the  salt  of  phosphorus  bead  leaves  a  skeleton 
of  silica,  the  bases  being  dissolved. 

If  a  silicate  in  a  fine  powder  is  fused  with  sodium  carbonate  and  the  mass  then  dissolved 
in  hydrochloric  acid  and  evaporated  to  dryness,  the  silica  separates  as  a  gelatinous  mass  and 
on  evaporation  to  dryness  is  made  insoluble.  When  strong  hydrochloric  acid  is  added  and 
then  water  to  the  dry  residue  in  the  test  tube,  the  bases  are  dissolved  and  the  silica  left 
behind. 

Many  silicates,  especially  those  which  are  hydrous,  are  decomposed  by  strong  hydro- 
chloric acid,  the  silica  separating  as  a  powder  or,  after  evaporation,  as  a  jelly  (see  p.  328). 

Silver.  —  On  charcoal  in  O.F.  silver  gives  a  brown  coating.  A  globule  of  metallic  silver 
may  generally  be  obtained  by  heating  on  charcoal  in  O.F.,  especially  if  soda  is  added. 
Under  some  circumstances  it  is  desirable  to  have  recourse  to  cupellation. 

From  a  solution  containing  any  salt  of  silver,  the  insoluble  chloride  is  thrown  down 
when  hydrochloric  acid  is  added.  This  precipitate  is  insoluble  in  acid  or  water,  but  entirely 
so  in  ammonia.  It  changes  color  on  exposure  to  the  light. 

Strontium.  —  Compounds  of  strontium  are  usually  recognized  by  the  fine  crimson-red 
which  they  give  to  the  blowpipe  flame;  many  yield  an  alkaline  reaction  after  ignition. 
(Cf.  barium.) 

Sodium.  —  Compounds  containing  sodium  in  large  amount  give  a  strong  yellow  flame. 

Sulphur,  Sulphides,  Sulphates.  —  In  the  closed  tube  some  sulphides  give  off  sulphur;  in 
the  open  tube  they  yield  sulphur  dioxide,  which  has  a  characteristic  odor  and  reddens  a 
strip  of  moistened  litmus  paper.  In  small  quantities,  or  in  sulphates,  sulphur  is  best 
detected  by  fusion  on  charcoal  with  soda  and  charcoal  dust.  The  fused  mass,  when  sodium 
sulphide  has  thus  been  formed,  is  placed  on  a -clean  silver  coin  and  moistened;  a  distinct 
black  stain  on  the  silver  is  thus  obtained  (the  precaution  mentioned  on  p.  336  must  be 
exercised). 

A  solution  of  a  sulphate  in  hydrochloric  acid  gives  with  barium  chloride  a  white  insoluble 
precipitate  of  barium  sulphate. 

Tellurium.  —  Tellurides  heated  in  the  open  tube  give  a  white  or  grayish  sublimate, 
fusible  to  colorless  drops  (p.  334).  On  charcoal  they  give  a  white  coating  and  color  the 
R.F.  green. 

Tin.  —  Minerals  containing  tin  (e.g.,  cassiterite),  when  heated  on  charcoal  with  soda  or 
potassium  cyanide,  yield  metallic  tin  in  minute  globules;  these  are  malleable,  but  harder 
than  silver.  Dissolved  in  nitric  acid,  white  insoluble  stannic  oxide  separates  out. 

Titanium.  —  Titanium  gives  in  the  R.F.  with  salt  of  phosphorus  a  bead  which  is  violet 
when  cold.  Fused  with  sodium  carbonate  and  dissolved  with  hydrochloric  acid,  and 
heated  with  a  piece  of  metallic  tin,  the  liquid  takes  a  violet  color,  especially  after  partial 
evaporation. 

Tungsten.  —  Tungsten  oxide  gives  a  blue  color  to  the  salt  of  phosphorus  bead  (R.F.). 
Fused  and  treated  as  titanium  (see  above)  with  the  addition  of  zinc  instead  of  tin,  gives  a 
fine  blue  color. 

Uranium.  —  Uranium  compounds  give  to  the  salt  of  phosphorus  bead  (O.F.)  a  greenish 
yellow  bead  when  cool;  also  (R.F.)  a  fine  green  on  cooling  (p.  337). 

Vanadium.  —  With  borax  (O.F.)  vanadates  give  a  bead  yellow  (hot)  changing  to  yellow- 
ish green  and  nearly  colorless  (cold) ;  also  (R.F.)  dirty  green  (hot),  fine  green  (cold).  With 
£r«i  PhosPhorus  (O.F.)  a  yellow  to  amber  color  (thus  differing  from  chromium);  also 
(R.F.)  fine  green  (cold). 

Zinc.  —  On  charcoal  in  the  reducing  flame  compounds  of  zinc  give  a  coating  which  is 
yellow  while  hot  and  white  on  cooling,  and  moistened  by  the  cobalt  solution  and  again 
heated  becomes  a  fine  green.  Note,  however,  that  the  zinc  silicate  (calamine)  becomes  blue 
when  heated  after  moistening  with  cobalt  solution. 


CHEMICAL   EXAMINATION    OF   MINERALS  341 

Zirconium.  —  A  dilute  hydrochloric  acid  solution,  containing  zirconium,  imparts  an 
orange-yellow  color  to  turmeric  paper,  moistened  by  the  solution. 

DETERMINATIVE  MINERALOGY 

505.  Determinative  Mineralogy  may  be  properly  considered  under  the 
general  head  of  Chemical  Mineralogy,  since  the  determination  of  minerals 
depends  mostly  upon  chemical  tests.  But  crystallographic  and  all  the  physi- 
cal characters  have  also  to  be  carefully  observed. 

There  is  but  one  exhaustive  way  in  which  the  identity  of  an  unknown 
mineral  may  in  all  cases  be  fixed  beyond  question,  and  that  is  by  the  use  of  a 
complete  set  of  determinative  tables.  By  means  of  such  tables  the  mineral  in 
hand  is  referred  successively  from  a  general  group  into  a  more  special  one, 
until  at  last  all  other  species  have  been  eliminated,  and  the  identity  of  the  one 
given  is  beyond  doubt. 

A  careful  preliminary  examination  of  the  unknown  mineral  should,  how- 
ever, always  be  made  before  final  recourse  is  had  to  the  tables.  This  examina- 
tion will  often  suffice  to  show  what  the  mineral  in  hand  is,  and  in 
any  case  it  should  not  be  omitted,  since  it  is  only  in  this  way  that  a 
practical  familiarity  with  the  appearance  and  characters  of  minerals  can  be 
gained. 

The  student  will  naturally  take  note  first  of  those  characters  which  are  at 
once  obvious  to  the  senses,  that  is:  crystalline  form,  if  distinct;  general  struc- 
ture, cleavage,  fracture,  luster,  color  (and  streak),  feel;  also,  if  the  specimen  is 
not  too  small,  the  apparent  weight  will  suggest  something  as  to  the  specific 
gravity.  The  characters  named  are  of  very  unequal  importance.  Structure, 
if  crystals  are  not  present,  and  fracture  are  generally  unessential  except  in 
distinguishing  varieties;  color  and  luster  are  essential  with  metallic,  but 
generally  very  unimportant  with  nonmetallic,  minerals.  Streak  is  of  impor- 
tance only  with  colored  minerals  and  those  of  metallic  luster  (p.  247) .  Crystal- 
line form  and  cleavage  are  of  the  highest  importance,  but  may  require  careful 
study. 

The  first  trial  should  be  the  determination  of  the  hardness  (for  which  end 
the  pocket-knife  is  often  sufficient  in  experienced  hands).  The  second  trial 
should  be  the  determination  of  the  specific  gravity.  Treatment  of  the  pow- 
dered mineral  with  acids  may  come  next;  by  this  means  (see  pp.  328,329)  a 
carbonate  is  readily  identified,  and  also  other  results  obtained.  Then  should 
follow  blowpipe  trials,  to  ascertain  the  fusibility;  the  color  given  to  the  flame, 
if  any;  the  character  of  the  sublimate  given  off  in  the  tubes  and  on  charcoal; 
the  metal  reduced  on  the  latter;  the  reactions  with  the  fluxes,  and  other  points 
as  explained  in  the  preceding  pages. 

How  much  the  observer  learns  in  the  above  way,  in  regard  to  the  nature 
of  his  mineral,  depends  upon  his  knowledge  of  the  characters  of  minerals  in 
general,  and  upon  his  familiarity  with  the  chemical  behavior  of  the  various 
elementary  substances  with  reagents  and  before  the  blowpipe  (pp.  338  to  341). 
If  the  results  of  such  a  preliminary  examination  are  sufficiently  definite  to 
suggest  that  the  mineral  in  hand  is  one  of  a  small  number  of  species,  reference 
may  be  made. to  their  full  description  in  Part.  IV  of  this  work  for  the  final 
decision. 

A  number  of  tables,  in  which  the  minerals  included  are  arranged  according 
to  their  crystalline  and  physical  characters,  are  added  in  the  Appendix.  They 


342  CHEMICAL  MINERALOGY 

will  In  many  cases  aid  the  observer  in  reaching  a  conclusion  in  regard  to  a 
specimen  in  hand. 

The  first  of  these  tables  gives  lists  of  minerals  arranged  primarily  accord- 
ing to  their  principle  basic  elements  and  secondarily  according  to  their  acid 
radicals. 

The  second  of  these  tables  is  intended  to  include  all  well-defined  species, 
grouped  according  to  the  crystalline  system  to  which  they  belong  and  arranged 
under  each  system  in  the  order  of  their  specific  gravities;  the  hardness  is  also 
added  in  each  case.  The  relative  importance  of  the  individual  species  is  shown 
by  the  type  employed.  Following  this  are  minor  tables  enumerating  species 
characterized  by  some  one  of  the  prominent  crystalline  forms;  that  is,  those 
crystallizing  in  cubes,  octahedrons,  rhombohedrons,  etc.  Other  tables  give 
the  names  of  species  prominent  because  of  their  cleavage;  structure  of 
different  types;  hardness;  luster;  the  various  colors,  etc.  The  student  is 
recommended  to  make  frequent  use  of  these  tables,  not  simply  for  aid  in  the 
identification  of  specimens,  but  rather  because  they  will  help  him  in  the 
difficult  task  of  learning  the  prominent  characters  of  the  more  important 
minerals. 


PART  IV.   DESCRIPTIVE  MINERALOGY 


506.  Scope  of  Descriptive  Mineralogy.  —  It  is  the  province  of  De- 
scriptive Mineralogy  to  describe  each  mineral  species,  as  regards:    (1)  form 
and  structure;    (2)  physical  characters;    (3)  chemical  composition  including 
blowpipe  and  chemical  tests;   (4)  occurrence  in  nature  with  reference  to  geo- 
graphical distribution  and  association  with  other  species;   also  in  connection 
with  the  above  to  show  how  it  may  be  distinguished  from  other  species.     Fur- 
ther, it  should  classify  mineral  species  into  more  or  less  comprehensive  groups 
according  to  those  characters  regarded  as  most  essential.     Other  points  which 
may  or  may  not  be  included  are  the  investigation  of  the  methods  of  origin  of 
minerals;   the  changes  that  they  undergo  in  nature  and  the  results  of  such 
alteration;  also  the  methods  by  which  the  same  compounds  may  be  made  in 
the  laboratory;  finally,  the  uses  of  minerals  as  ores,  for  ornament  and  in  the 
arts. 

507.  Scheme  of  Classification.  —  The  method  of  classification  adopted 
in  this  work,  and  the  one  which  can  alone  claim  to  be  thoroughly  scientific,  is 
that  which  places  similar  chemical  compounds  together  in  a  common  class  and 
which  further  arranges  the  mineral  species  into  groups  according  to  the  more 
minute  relations  existing  between  them  in  chemical  composition,  crystalline 
form  and  other  physical  properties. 

Upon  this  basis  there  are  recognized  eight  distinct  chemical  classes,  begin- 
ning with  the  Native  Elements;  these  are  enumerated  on  the  following  page. 
Under  each  of  these,  sections  of  different  grades  are  made,  also  based  on  chem- 
ical relationships.  Finally,  the  mineral  species  themselves  are  arranged,  as 
far  as  possible,  in  isomorphous  groups,  including  those 'which  have,  at  once, 
analogous  chemical  composition  and  similar  crystallization  (see  Art.  471).  It 
is  unnecessary  to  take  the  space  here  to  develop  the  entire  scheme  of  classi- 
fication in  detail,  since  a  survey  of  the  successive  sub-classes  under  any  one  of 
the  divisions  will  make  the  principles  followed  entirely  clear.  A  few  remarks, 
only,  are  added  for  sake  of  illustration. 

Under  the  Oxides,  for  example,  the  classification  is  as  follows:  First,  the 
Oxides  of  silicon  (quartz,  tridymite,  opal).  Second,  the  Oxides  of  the  semi- 
metals,  tellurium,  arsenic,  antimony,  bismuth,  also  molybdenum,  tungsten. 
Third,  the  Oxides  of  the  metals,  as  copper,  zinc,  iron,  manganese,  tin,  etc. 
The  third  section  is  then  subdivided  into  the  anhydrous  and  hydrous  species. 
Further,  the  former  fall  into  the  four  divisions :  Protoxides,  RoO  and  RO ;  Ses- 
quioxides,  R2O3;  Intermediate  oxides,  RO,R2O3;  Dioxides,  RO2.  Under  each 
of  these  heads  come  finally  the  individual  species,  arranged  so  far  as  possible 
in  isomorphous  groups.  Thus  we  have  the  Hematite  group,  the  Rutile  group, 
etc. 

343 


344  DESCRIPTIVE   MINERALOGY 

In  regard  to  the  various  classes  of  salts  it  may  be  stated  that,  in  general, 
they  are  separated  into  anhydrous,  acid,  basic  and  hydrous  sections;  the 
special  subdivisions  called  for,  however,  vary  in  the  different  cases. 

For  an  explanation  of  the  abbreviations  used  in  the  description  of  species,  see  p.  5. 

SCHEME   OF   CLASSIFICATION 

I.  NATIVE  ELEMENTS. 
II.  SULPHIDES,  SELENIDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES. 

III.  Sulpho-salts.  —  SULPHARSENITES,  SULPHANTIMONITES,  SULPHO- 

BISMUTHITES. 

IV.  Haloids.  —  CHLORIDES,  BROMIDES,  IODIDES  J  FLUORIDES. 

V.  OXIDES. 

VI.    Oxygen  Salts. 

1.  CARBONATES. 

2.  SILICATES,  TITANATES. 

3.  NIOBATES,  TANTALATES. 

4.  PHOSPHATES,  ARSENATES,  VANADATES;     ANTIMONATES. 

NITRATES. 
6.  BORATES.    URANATES. 

6.  SULPHATES,  CHROMATES,  TELLURATES. 

7.  TUNGSTATES,  MOLYBDATES. 

VII.   Salts  of  Organic  Acids:   Oxalates,  Mellates,  etc. 
VIII.  HYDROCARBON  COMPOUNDS. 

I.   NATIVE   ELEMENTS 

The  NATIVE  ELEMENTS  are  divided  into  the  two  distinct  sections  of  the 
Metals  and  the  Non-metals,  and  these  are  connected  by  the  transition  class  of 
the  Semi-metals.  The  distinction  between  them  as  regards  physical  characters 
and  chemical  relations  has  already  been  given  (Art.  453) . 

The  only  non-metals  present  among  minerals  are  carbon,  sulphur,  and 
selenium;  the  last,  in  one  of  its  allotropic  forms,  is  closely  related  to  the 
semi-metal  tellurium. 

The  native  semi-metals  form  a  distinct  group  by  themselves,  since  all 
crystallize  in  the  rhombohedral  class  of  the  hexagonal  system  with  a  funda- 
mental angle  differing  only  a  few  degrees  from  90°,  as  shown  in  the  following 
list: 

Tellurium,  rrr  =  93°    3'.          Arsenic,  rr'    =  94°  54'. 
Antimony,  rr'  =  92°  53'.          Bismuth,  rr'  =  92°  20'. 

An  artificial  form  of  selenium  is  known  with  metallic  luster  and  rhombo- 
hedral in  crystallization,  with  rr'  =  93°.  Zinc  (also  only  artif .)  is  rhombohe- 
dral (rr'  =  93°  46')  and  connects  the  semi-metals  to  the  true  metals.  Metallic 
tantalum  has  been  described  in  cubic  crystals. 

Among  the  metals  the  isometric  GOLD  GROUP  is  prominent,  including  gold, 
silver,  copper,  mercury,  amalgam  (AgHg),  and  lead. 


NATIVE    ELEMENTS 


345 


Another  related  isometric  group  includes  the  metals  platinum,  iridium, 
palladium,  and  iron.  An  allot ropic  form  of  palladium  and  also  iridosmine 
(IrOs)  are  both  rhombohedral. 

DIAMOND. 

Isometric,  tetrahedral,  but  with  the  +  and  —  forms  usually  equally  devel- 
oped and  not  to  be  distinguished  from  each  other.  Commonly  showing  octahe- 
dral, hexoctahedral,  and  other  forms ;  faces  frequently  rounded  or  striated  and 
with  triangular  depressions  (on  o(lll)).  Twins  common  with  tw.  pi.  0(111). 
Crystals  often  distorted.  In  spherical  forms;  massive. 

627  628 


Cleavage:  o( 111)  highly  perfect.  Fracture  conchoidal.  Brittle.  H.  =  10. 
G.  =  3-516-3-525  crystals.  Luster  adamantine  to  greasy.  Color  white  or 
colorless;  occasionally  various  pale  shades  of  yellow,  red,  orange,  green,  blue, 
brown;  rarely  deeply  colored;  sometimes  black.  Usually  transparent;  also 
translucent,  opaque.  Refractive  and  dispersive  power  high;  index  n  =  2-4195. 
(See  Art.  328.) 

Var.  --  1 .  Ordinary.  In  crystals  usually  with  rounded  faces  and  varying  from  those 
which  are  colorless  and  free  from  flaws  (first  water)  through  many  faint  shades  of  color, 
yellow  being  the  most  common;  often  full  of  flaws  and  hence  of  value  only  for  cutting  pur- 
poses. 

2.  Bort  or  Boort;   rounded  forms  with  rough  exterior  and  radiated  or  confused  crystal- 
line structure. 

3.  Carbonado  or  Carbon;   black  diamond.     Massive,  crystalline,  granular  to  compact, 
without  cleavage.     Color  black  or  grayish  black.     Opaque.     Obtained  chiefly  from  Bahia, 
Brazil. 

Comp.  —  Pure  carbon;  the  variety  carbonado  yields  on  combustion  a  slight 
ash. 

Pyr.,  etc.  —  Unaffected  by  heat  except  at  very  high  temperatures,  when  (in  an  oxygen 
atmosphere)  it  burns  to  carbon  dioxide  (CO2) ;  out  of  contact  with  the  air  transformed  into 
a  kind  of  coke.  Not  acted  upon  by  acids  or  alkalies. 

Diff.  —  Distinguished  (e.g.,  from  quartz  crystal)  by  its  extreme  hardness  and  brilliant 
adamantine  luster;  the  form,  cleavage,  and  high  specific  gravity  are  also  distinctive  charac- 
ters; it  is  optically  isotropic ;  transparent  to  X-rays. 

Artif.  —  Minute  diamonds  have  been  formed  artificially  in  several  ways.  Moissan 
first  produced  them  by  dissolving  carbon  in  molten  iron  and  then  cooling  the  mass  suddenly 
under  pressure;  they  have  been  formed  by  dissolving  graphite  in  fused  olivine  or  artificial 
magnesium  silicate  melts;  they  have  been  formed  when  an  electric  current  was  passed 
through  an  iron  spiral  embedded  in  carbon  while  under  high  pressure  in  an  atmosphere  of 
hydrogen. 

Obs.  —  The  diamond  occurs  chiefly  in  alluvial  deposits  of  gravel,  sand,  or  clay,  asso- 
ciated with  quartz,  gold,  platinum,  zircon,  octahedrite,  rutile,  brookite,  hematite,  ilmenite, 
and  also  andalusite,  chrysoberyl,  topaz,  corundum,  tourmaline,  garnet,  etc.;  the  associated 
minerals  being  those  common  in  granitic  rocks  or  granitic  veins.  Also  found  in  quartzose 


346  DESCRIPTIVE   MINERALOGY 

conglomerates,  and  further  in  connection  with  the  laminated  granular  quartz  rock  or 
quartzose  hydromica  schist,  itacolumite,  which  in  thin  slabs  is  more  or  less  flexible.  This 
rock  occurs  at  the  mines  of  Brazil  and  the  Ural  Mts.;  and  also  in  Georgia  and  North  Caro- 
lina, where  a  few  diamonds  have  been  found. 

It  has  been  reported  as  occurring  in  situ  in  a  pegmatite  vein  in  gneiss  at  Bellary  in 
India.  It  occurs  further  in  connection  with  an  eruptive  peridotite  in  South  Africa  and  in  a 
similar  formation  in  Pike  County,  Ark.  It  has  been  noted  as  grayish  particles  forming  one 
per  cent  of  the  meteorite  which  fell  at  Novo-Urei,  Russia,  Sept.  22,  1886;  also  in  the  form 
of  black  diamond  (H.  =  9)  in  the  meteorite  of  Carcote,  Chile;  in  the  meteoric  iron  of 
Canon  Diablo,  Ariz. 

India  was  the  chief  source  of  diamonds  from  very  early  times  down  to  the  discovery  of 
the  Brazilian  mines ;  the  yield  is  now  small.  Of  the  localities,  that  in  southern  India,  in  the 
Madras  presidency,  included  the  famous  "Golconda  mines."  The  diamond  deposits  of 
Brazil  have  been  worked  since  the  early  part  of  the  18th  century,  and  have  yielded  very 
largely,  although  at  the  present  time  the  amount  obtained  is  small.  The  most  important 
region  was  that  near  Diamantina  in  the  province  of  Minas  Geraes;  also  from  Bahia,  etc. 

The  discovery  of  diamonds  in  South  Africa  dates  from  1867.  They  were  first  found  in 
the  gravel  of  the  Vaal  river;  they  occur  from  Potchefstroom  down  to  the  junction  with  the 
Orange  river,  and  along  the  latter  as  far  as  Hope  Town.  More  recently  they  have  been 
found  in  gravels  in  the  Somabula  Forest,  Rhodesia  and  at  Liideritzbucht,  German  South 
West  Africa.  These  river  diggings  are  now  of  much  less  importance  than  the  dry  diggings, 
discovered  in  1871. 

The  latter  are  chiefly  in  Griqualand-West,  south  of  the  Vaal  river,  on  the  border  of  the 
Orange  Free  State.  There  are  here  near  Kimberley  a  number  of  limited  areas  approxi- 
mately spherical  or  oval  in  form,  with  an  average  diameter  of  some  200  to  300  yards,  of 
which  the  Kimberley,  De  Beer's,  Dutoitspan  and  Bultfpntein  mines  are  the  most  important. 
A  circle  3£  miles  in  diameter  encloses  these  four  principal  mines.  The  general  structure  is 
similar:  a  wall  of  nearly  horizontal  black  carbonaceous  shale  with  upturned  edges  enclos- 
ing the  diamantiferous  area.  The  upper  portion  of  the  deposit  consists  of  a  friable  mass  of 
little  coherence  of  a  pale  yellow  color,  called  the  "yellow  ground."  Below  the  reach  of 
atmospheric  influences,  the  rock  is  more  firm  and  of  a  bluish  green  or  greenish  color;  it  is 
called  the  "blue  ground"  or  simply  "the  blue."  This  consists  essentially  of  a  serpentinous 
breccia:  a  base  of  hydrated  magnesian  silicate  penetrated  by  calcite  and  opaline  silica  and 
enclosing  fragments  of  bronzite,  diallage,  also  garnet,  magnetite,  and  ilmenite,  and  less 
commonly  smaragdite,  pyrite,  zircon,  etc.  The  diamonds  are  rather  abundantly  dissemi- 
nated through  the  mass,  in  some  claims  to  the  amount  of  4  to  6  carats  per  cubic  yard.  The 
original  rock  seems  to  have  been  a  peculiar  type  of  peridotite.  These  areas  are  believed 
to  be  volcanic  pipes,  and  the  occurrence  of  the  diamonds  is  obviously  connected  with  the 
eruptive  outflow,  they  having  probably  been  brought  up  from  underlying  rocks.  Other 
important  mines,  similar  in  character  to  those  near  Kimberley,  are  the  Jagersfontein  mine 
in  Orange  Free  State  and  the  Premier,  near  Pretoria,  Transvaal. 

The  South  African  mines  up  to  the  beginning  of  1914  are  estimated  to  have  yielded 
about  120  million  carats  (26  tons)  of  diamonds  valued  at  nearly  900  million  dollars. 

Diamonds  are  also  obtained  in  Borneo,  associated  with  platinum,  etc.;  in  Australia, 
and  the  Ural  Mts. 

In  the  United  States  a  few  stones  have  been  found  in  gravels  in  N.  C.,  Ga.,  Va,,  Col., 
Cal.  and  Wis.  Reported  from  Idaho  and  from  Oregon  with  platinum.  In  1906  diamonds 
were  found  in  Pike  County,  Ark.,  both  loose  in  the  soil  and  enclosed  in  a  peridotite  rock. 
Considerable  exploration  work  has  been  done  at  this  locality  and  probably  between  two 
and  three  thousand  stones  found.  The  stones  have  been  of  good  color  but  usually  small. 

Some  of  the  famous  diamonds  of  the  world  with  their  weights  are  as  follows:  the  Kohi- 
noor,  which  weighed  when  brought  to  England  186  carats,  and  as  recut  as  a  brilliant,  106 
carats;  the  Orloff,  194  carats;  the  Regent  or  Pitt,  137  carats;  the  Florentine  or  Grand 
Duke  of  Tuscany,  133  carats.  The  "Star  of  the  South"  found  in  Brazil  weighed  before 
and  after  cutting  respectively  254  and  125  carats.  Also  famous  because  of  the  rarity  of 
their  color  are  the  green  diamond  of  Dresden,  40  carats,  and  the  deep  blue  Hope  diamond 
from  India,  weighing  44  carats. 


at  the  Premier  mine.  It  was  named  the  Cullinan  and  was  presented  by  the  Transvaal 
Assembly  to  King  Edward  VII  of  England.  When  found  it  weighed  3,025  carats  or  over 
li  Ibs.  It  has  since  been  cut  into  105  separate  stones,  the  two  largest  weighing  516  and  309 


NATIVE    ELEMENTS  347 

carats,  respectively,  being  the  largest  cut  stones  in  existence.  The  history  of  the  above 
stones  and  of  others  is  given  in  many  works  on  gems. 

Use.  —  In  addition  to  its  use  as  a  gem,  the  diamond  is  extensively  used  as  an  abrasive. 
Crystal  fragments  are  used  to  cut  glass.  The  fine  powder  is  employed  in  grinding  and 
polishing  gem  stones.  The  noncrystalline,  opaque  varieties,  especially  the  carbonado,  are 
used  in  the  bits  of  diamond  drills.  The  diamond  is  also  used  in  wire  drawing  and  in  the 
making  of  tungsten  filaments  for  electric  lights. 

CLIFTONITE.  —  Carbon  in  minute  cubic  and  cubo-octahedral  crystals.  H.  =  2'5. 
G.  =  2' 12.  Color  and  streak  black;  from  the  Youndegin,  West  Australia,  meteoric  iron, 
found  in  1884,  and  other  meteoric  irons. 

GRAPHITE.     Plumbago.     Black  Lead. 

Rhombohedral.  In  six-sided  tabular  crystals.  Commonly  in  embedded 
foliated  masses,  also  columnar  or  radiated;  scaly  or  slaty;  granular  to  con> 
pact;  earthy. 

Cleavage:  basal,  perfect.  Thin  laminae  flexible,  inelastic.  Feel  greasy. 
H.  =  1-2.  G  =  2'09-2'23.  Luster  metallic,  sometimes  dull,  earthy.  Color 
iron-black  to  dark  steel-gray.  Opaque.  A  conductor  of  electricity. 

Comp.  —  Carbon,  like  the  diamond;  often  impure  from  the  presence  of 
ferric  oxide,  clay,  etc. 

Pyr.,  etc.  At  a  high  temperature  some  graphite  burns  more  easily  than  diamond, 
other  varieties  less  so.  B.B.  infusible.  Unaltered  by  acids. 

Diff.  —  Characterized  by  its  extreme  softness  (soapy  feel);  iron-black  color;  metallic 
luster;  low  specific  gravity;  also  by  infusibility.  Cf.  molybdenite,  p.  360. 

Artif.  —  It  is  a  common  furnace  product  being  formed  from  the  fuel.  It  is  produced 
extensively  by  heating  coke  in  the  electric  furnace. 

Obs.  —  Graphite  is  most  commonly  formed  through  the  metamorphism  of  carbona- 
ceous deposits  and  is  most  frequently  found  in  metamorphic  rocks,  contact  metamorphic 
deposits,  etc.  Coal  beds  may  be  largely  converted  into  graphite  by  intense  metamorphism 
It  is  not  always  of  organic  origin,  however,  as  is  shown  by  its  occurrence  in  meteorites,  in 
pegmatite  deposits  and  as  a  magmatic  separation  in  various  igneous  rocks.  Frequently  its 
origin  is  obscure.  Found  as  beds  and  embedded  masses,  as  laminae  or  scales  in  granite, 
gneiss,  mica  schist,  quartzite,  crystalline  limestone.  The  deposits  of  crystalline  graphite 
which  are  of  the  greatest  commercial  importance  have  formed  as  veins  along  rock  fractures. 

Important  localities  are:  Island  of  Ceylon  from  which  the  largest  part  of  the  world's 
supply  comes;  Passau  district  in  Bavaria;  southern  Bohemia;  Korea;  Madagascar; 
Sonora  in  Mexico ;  eastern  Ontario  and  adjacent  portions  of  Quebec  in  Canada.  The  most 
productive  locality  in  the  United  States  is  in  the  eastern  and  southeastern  Adirondack 
region  in  Essex,  Warren,  Saratoga  and  Washington  Counties,  N.  Y.  It  occurs  here  in 
graphitic  quartzites,  with  quartz  in  small  veins  running  through  gneiss  and  in  pegmatite 
veins.  Also  found  in  metamorphosed  Carboniferous  rocks  near  Providence  and  Tiverton, 
R.  I.;  in  granite  and  schists  in  Clay,  Chilton  and  Coqsa  Counties,  Ala.;  as  amorphous 
graphite  near  Raton,  N.  M.;  in  irregular  veins  near  Dillon,  Mon.;  near  Turret,  Chaff ee 
Co.,  Col. 

Use.  —  Its  chief  uses  are  for  making  crucibles  and  other  refractory  products,  in  lubri- 
cants, paint,  «tove  polish,  "lead"  pencils  and  for  foundry  facings. 

The  name  black  lead,  applied  to  this  species,  is  inappropriate,  as  it  contains  no  lead. 
The  name  graphite,  of  Werner,  is  derived  from  ypa<t>cu>,  to  write,  alluding  to  its  use  for 
pencils. 

QUISQUEITE.  —  A  black  lustrous  material  composed  chiefly  of  carbon  and  sulphur  from 
the  vanadium  ores  of  Minasragra,  Peru. 

SULPHUR. 

Orthorhombic.     Axes  a  :  b  :  c  =  0'8131  :  1  :  1-9034. 

Crystals  commonly  acute  pyramidal;  sometimes  thick  tabular  ||  c(001). 
See  also  Fig.  79,  p.  47.  Also  massive,  in  reniform  shapes,  incrusting,  stalac- 
titic  and  stalagmitic;  in  powder. 

Cleavage:  c(001),  m(110),  'p(lll)  imperfect.  Fracture  conchoidal  to 
uneven.  Rather  brittle  to  imperfectly  sectile.  H.  =  1/5-2 -5.  G.  =  2 '05- 


348  DESCRIPTIVE   MINERALOGY 

2-09.     Luster   resinous.     Color   sulphur-yellow,    straw-    and   honey-yellow, 

yellowish  brown,  greenish,  reddish  to 

629  630  yellowish  gray.     Streak  white.    Trans- 

parent to  translucent.  A  non-con- 
ductor of  electricity;  by  friction  neg- 
atively electrified.  A  poor  conductor 
of  heat.  Optically  +  .  Double  refrac- 
tion strong.  Ax.  plane  ||  6(010). 
Bx  _L  c(001).  Dispersion  p  <  v. 
2  V  =  69°5'.  Refractive  indices, 
a  =  1-958,  j8  =  2-038,  7  =  2 -245. 

Comp.    -  -  Pure    sulphur;      often 
contaminated    with     clay,    bitumen, 
and  ofher  impurities. 

Sulphur  may  also  be  obtained  in  the  laboratory  in  other  allotropic  forms;  a  monoclinic 
form  is  common. 

Pyr.,  etc.  —  Melts  at  108°  C.,  and  at  270°  burns  with  a  bluish  flame  yielding  sulphur 
dioxide.     Insoluble  in  water,  and  not  acted  on  by  the  acids,  but  soluble  in  carbon  disulphide. 
Diff.  —  Readily  distinguished  by  the  color,  fusibility  and  combustibility. 
Obs.  —  The  great  repositories  of  sulphur  are  either  beds  of  gypsum  and  the  associate 
rocks,  or  the  regions  of  active  and  extinct  volcanoes. 

Sulphur  may  have  several  different  modes  of  origin.  At  times  it  is  a  volcanic  sublimate 
formed  by  reactions  between  sulphur  dioxide  and  hydrogen  sulphide  gases.  It  occurs  fre- 
quently around  mineral  springs  where  it  has  been  formed  by  the  incomplete  oxidation  of 
hydrogen  sulphide.  Where  such  waters  act  upon  limestone  rocks  both  gypsum  and  sul- 
phur may  be  formed.  In  a  small  way  it  is  formed  in  many  coal  deposits  and  elsewhere  by 
the  slow  decomposition  of  pyrite  and  other  sulphides. 

Found  in  large  amounts  on  the  Island  of  Sicily,  often  in  fine  crystals  and  associated 
with  celestite,  calcite,  aragonite,  gypsum,  and  barite.  Important  deposits  are  found  in 
the  volcanic  districts  of  Japan,  Hawaii,  Mexico,  and  western  South  America.  In  the 
United  States  the  most  productive  deposits  are  in  Louisiana  and  Texas.  In  Calcasieu 
Parish,  Louisiana,  a  bed  of  sulphur  100  ft.  in  thickness  is  found  at  a  depth  of  between  300 
and  400  ft.  It  is  underlain  by  beds  of  gypsum  and  salt.  A  similar  deposit  occurs  near 
Freeport  in  Brazoria  Co.,  Texas.  It  is  found  in  numerous  other  Western  localities;  Utah, 
at  Sulphurdale,  Beaver  Co.,  in  a  rhyolitic  tuff;  Wy.,  in  limestones  near  Cody  and  Ther- 
mopolis  and  about  the  fumeroles  of  the  Yellowstone  Park;  Nev.,  in  Esmeralda  Co.  near 
Luning  and  Cuprite,  near  Rosebud,  Humbolt  Co.,  sometimes  in  crystals  and  at  Eureka, 
Eureka  Co.;  Cal.,  in  Colusa,  Lake,  San  Bernadino  and  other  Counties,  at  the  geysers  of 
Napa  Valley,  Sonoma  Co.,  on  Lassen  Peak,  Tehema  Co.;  Col.,  at  Vulcan,  Gunnison  Co., 
and  in  Mineral  Co. 

Use.  —  In  manufacture  of  sulphuric  acid,  in  the  process  of  making  paper  from  wood 
pulp,  in  making  matches,  gun  powder,  fireworks,  insecticides,  for  vulcanizing  rubber,  for 
medicinal  purposes,  etc.  Sulphuric  acid  is  now  largely  derived  from  the  oxidation  of 
pyrite. 

Selensulphur.  —  Contains  sulphur  and  selenium,  orange-red  or  reddish  brown;  from 
the  islands  Vulcano  and  Lipari. 

ARSENIC. 

Rhombohedral.  Generally  granular  massive;  sometimes  reticulated, 
reniform,  stalactitic. 

Cleavage:  c(0001)  highly  perfect.  Fracture  uneven  and  fine  granular. 
Brittle.  H.  =  3'5.  G.  =  5'63-573.  Luster  nearly  metallic.  Color  and 
streak  tin-white,  tarnishing  to  dark  gray. 

Comp.  —  Arsenic,  often  with  some  antimony,  and  traces  of  iron,  silver, 
gold,  or  bismuth. 

•  Pyf'  ~~  *:i'B>«.on  cnarcoal  volatilizes  without  fusing,  coats  the  coal  with  white  arsenic 
tnoxide,  and  affords  a  garlic  odor;  the  coating  treated  in  R.F.  volatilizes,  tingeing  the 
flame  blue.  In  the  closed  tube  gives  a  volatile  sublimate  of  arsenic. 


NATIVE    ELEMENTS  349 

Micro.  —  In  polished  section  shows  white  color  similar  to  galena.  Smooth  surface. 
With  HNOs  slowly  effervesces,  turning  dark.  Changes  color  in  same  way  with  Feds. 
Unaffected  by  KCN  and  HC1. 

Obs.  —  Occurs  in  veins  in  crystalline  rocks  and  the  older  schists,  often  accompanied  by 
ores  of  antimony,  the  ruby  silvers,  realgar,  sphalerite,  and  other  metallic  minerals.  Thus 
in  the  silver  mines  of  Saxony;  also  Andreasberg,  Harz  Mts.,  Germany;  Joachimstal  and 
Pfibram,  Bohemia;  in  Hungary;  Norway;  Zmeov,  Siberia;  Prov.  Echizen,  Japan,  etc. 
Abundant  at  Chanarcjllo,  Chile.  In  the  United  States  sparingly  at  Haverhill  and  Jackson, 
N.  H.;  near  Leadville,  Col.;  Washington  Camp,  Santa  Cruz  Co.,  Ariz.  In  Canada  at 
Watson  Creek,  British  Columbia;  Montreal,  Quebec. 

Use.  —  An  ore  of  arsenic. 

Allemontite.  —  Arsenical  Antimony,  SbAs3.  In  reniform  masses.  G.  =  6'203.  Luster 
metallic.  Color  tin-white  or  reddish  gray.  From  Allemont,  France;  Pfibram,  Bohemia, 
etc. 

Tellurium.  Rhombohedral.  In  prismatic  crystals;  commonly  columnar  to  fine-gran- 
ular massive.  Perfect  prismatic  cleavage.  H.  =  2-2'5.  G.  =  6'2.  Luster  metallic. 
Color  and  streak  tin- white.  B.B.  wholly  volatile.  In  warm  concentrated  sulphuric  acid 
gives  red  solution.  From  Transylvania,  West  Australia,  and  a  number  of  places  in 
Colorado. 

ANTIMONY. 

Rhombohedral.  Generally  massive,  lamellar  and  distinctly  cleavable; 
also  radiated;  granular. 

Cleavage:  c(0001)  highly  perfect;  also  other  cleavages.  Fracture  uneven; 
brittle.  H  =  3-3'5.  G.  =  6'65-672.  Luster  metallic.  Color  and  streak 
tin-white. 

Comp.  —  Antimony,  containing  sometimes  silver,  iron,  or  arsenic. 

Pyr.  —  B.B.  on  charcoal  fuses  very  easily  and  is  wholly  volatile  giving  a  white  coating. 
The  white  coating  tinges  the  R.F.  bluish  green.  Crystallizes  readily  from  fusion. 

Obs.  —  Occurs  near  Sala  in  Sweden;  Andreasberg  in  the  Harz  Mts.,  Germany;  Alle- 
mont, Dauphine,  France;  Pfibram,  Bohemia;  Mexico;  Chile;  Borneo.  In  the  United 
States,  at  Warren,  N.  J.,  rare;  in  Kern  Co.,  and  at  South  Riverside,  Cal.  At  South  Ham, 
Quebec;  Prince  William  parish,  York  Co.,  New  Brunswick. 

Use.  —  An  ore  of  antimony. 

BISMUTH. 

Rhombohedral.     Usually  reticulated,  arborescent;  foliated  or  granular. 

Cleavage:  c(0001)  perfect.  Sectile.  Brittle,  but  when  heated  somewhat 
malleable.  H.  =  2-2*5.  G.  =  970-9-83.  Luster  metallic.  Streak  and 
color  silver-white,  with  a  reddish  hue;  subject  to  tarnish.  Opaque. 

Comp.  —  Bismuth,  with  traces  of  arsenic,  sulphur,  tellurium,  etc. 

Pyr.,  etc.  —  B.B.  on  charcoal  fuses  very  easily  and  entirely  volatilizes,  giving  a  coating 
orange-yellow  while  hot,  lemon-yellow  on  cooling.  With  potassium  iodide  and  sulphur 
B.B.  on  charcoal  gives  a  brilliant  red  coating.  Dissolves  in  nitric  acid;  subsequent  dilu- 
tion causes  a  white  precipitate.  Crystallizes  readily  from  fusion. 

Micro.  —  In  polished  section  shows  creamy  white  color  with  pink  tinge.  Smooth  and 
metallic  surface.  With  HC1  slowly  darkens  and  dissolves.  Rapidly  darkens  with  effer- 
vescence with  HNO3  and  aqua  regia. 

Obs.  —  Occurs  in  veins  in  gneiss  and  other  crystalline  rocks  and  clay  slate,  accom- 
panying various  ores  of  silver,  cobalt,  lead  and  zinc.  Thus  at  the  mines  of  Saxony  and 
Bohemia,  etc.;  Meymac,  Correze,  France.  Also  at  Modum,  Norway;  at  Falun,  Sweden. 
In  Cornwall  and  Devonshire;  near  Copiapo,  Chile;  Bolivia. 

Occurs  at  Monroe,  Conn.;  Brewer's  mine,  Chesterfield  district,  S.  C.;  near  Cummins 
City,  and  elsewhere  in  Col.  Abundant  with  silver  ores  at  Cobalt,  Ontario. 

Use.  —  An  ore  of  bismuth. 

Zinc.  —  Probably  does  not  occur  in  the  native  state.  In  the  laboratory  it  is  obtained 
in  hexagonal  prisms  with  tapering  pyramids;  also  in  complex  crystalline  aggregates.  It 
also  appears  to  crystallize  in  the  isometric  system,  at  least  in  various  alloys. 

Tantalum.     Isometric.     In   cubic   crystals   and   fine    grains.     Color   grayish   yellow. 


350 


DESCRIPTIVE   MINERALOGY 


Found  containing  small  amounts  of  niobium  in  the  gold  washings  of  the  Ural  and  Altai 
Mis. 

Gold  Group 
GOLD. 

Isometric.     Distinct  crystals  rare,  0(111)  most  common,  also  d(110)  and 
ra(311);   crystals  often  elongated  in  direction  of  an  octahedral   axis,  giving 
rise  to'rhombohedral-like   forms,  and   arborescent  shapes;    also    in   plates 
flattened  ||  o(lll),  and  branching  at  60°  parallel  either  to  the  edges  or  diag- 
onals of  an  o  face  (see  pp.  172,  173).     Twins:  tw.  plane  o.     Skeleton  crystals 


633 


634 


common;  edges  salient  or  rounded;  in  filiform,  reticulated,  dendritic  shapes. 
Also  massive  and  in  thin  laminae;  often  in  flattened  grains  or  scales. 

Cleavage  none.  Fracture  hackly.  Very  malleable  and  ductile. 
H.  =  2*5-3.  G.  =  15-6-19-3,  19'33  when  pure.  Luster  metallic.  Color 
and  streak  gold-yellow,  sometimes  inclining  to  silver-white  and  rarely  to 
orange-red.  Opaque. 

Comp.  —  Gold,  but  usually  alloyed  with  silver  in  varying  amounts  and 
sometimes  containing  also  traces  of  copper  or  iron. 

Var.  —  1.  Ordinary.  Containing  up  to  16  p.  c.  of  silver.  Color  varying  accordingly 
from  deep  gold-yellow  to  pale  yellow,  and  specific  gravity  from  19'3  to  15'5.  The  ratio  of 
gold  to  silver  of  3  :  1  corresponds  to  15'1  p.  c.  silver.  For  G.  =  17'6,  Ag  =  9  p.  c.; 
G.  =  16'9,  Ag  =  13'2;  G.  =  14'6,  Ag  =  38'4.  The  purest  gold  which  has  been  described 
is  that  from  Mount  Morgan,  in  Queensland,  which  has  yielded  99'7  to  99'8  of  gold,  the 
remainder  being  copper  with  a  little  iron;  silver  is  present  only  as  a  minute  trace. 

2.  Argentiferous;  Electrum.  Color  pale  yellow  to  yellowish  white;  G  =  15'5-12'5. 
Ratio  for  the  gold  and  silver  of  1  :  1  corresponds  to  36  p.  c.  of  silver;  1|  :  1,  to  26  p.  c.; 
2  :  1,  to  21  p.  c.;  1\  :  1,  to  18  p.  c.  The  word  in  Greek  means  also  amber;  and  its  use  for 
this  alloy  probably  arose  from  the  pale  yellow  color  it  has  as  compared  with  gold. 

Varieties  have  also  been  described  containing  copper  up  to  20  p.  c.  from  the  Ural  Mts.; 
palladium  to  10  p .  c.  (porpezite),  from  Porpez,  Brazil;  bismuth,  including  the  black  gold  of 
Australia  (maldonite);  also  rhodium  (?). 

Pyr.,  etc.  — B.B.  fuses  easily  (at  1100°  C.).  Not  acted  on  by  fluxes.  Insoluble  in 
any  single  acid;  soluble  in  aqua  regia,  the  separation  not  complete  if  more  than  20  p.  c. 
Ag  is  present. 

Diff.  —  Readily  recognized  (e.g.,  from  other  metallic  minerals,  also  from  scales  of  yel- 
low mica)  by  its  malleability  and  high  specific  gravity,  which  last  makes  it  possible  to  sepa- 
rate it  from  the  gangue  by  washing ;  distinguished  from  chalcopyrite  and  pyrite  since  both 
sulphides  are  brittle  and  soluble  in  nitric  acid. 

Micro.  —  In  polished  section  shows  a  golden  yellow  color  with  a  smooth,  metallic  sur- 
face. Unaffected  by  reagents  except  KCN,  with  which  it  quickly  darkens  and  its  surface 
becomes  rough. 

Obs.  —  Gold  is  widely  distributed  in  the  earth's  crust.  It  has  been  found  in  various 
igneous  rocks,  more  commonly  in  the  acid  types,  and  sometimes  in  visible  particles.  It 
occurs  in  sedimentary  rocks  and  quite  frequently  in  connection  with  metamorphic  rocks. 


NATIVE    ELEMENTS  351 

It  is  a  constituent  of  sea  water.     It  is  most  frequently  found  in  notable  amounts  in  quartz 
veins  and  in  the  various  forms  of  placer  deposits. 

The  gold,  when  occurring  in  quartz,  is  often  irregularly  distributed,  in  strings,  scales, 
plates,  and  in  masses  which  are  sometimes  an  agglomeration  of  crystals.  Frequently  the 
scales  are  invisible  to  the  naked  eye.  The  associated  minerals  are:  pyrite,  which  far  exceeds 
in  quantity  all  others,  and  is  generally  auriferous;  next,  chalcopyrite,  galena,  sphalerite,  arsen- 
opyrite,  each  frequently  auriferous;  often  tetradymite  and  other  tellurium  ores,  native 
bismuth,  native  arsenic,  stibnite,  cinnabar,  magnetite,  hematite;  sometimes  barite,  scheelite, 
apatite,  fluorite,  siderite,  chrysocolla.  The  quartz  at  the  surface,  or  in  the  upper  part  of  a 
vein,  is  usually  cellular  and  rusted  from  the  more  or  less  complete  disappearance  of  the 
pyrite  and  other  sulphides  by  decomposition;  but  below,  it  is  commonly  solid. 

The  gold  of  the  world  wasearly  gathered,  not  directly  from  the  quartz  veins  (the  "quartz 
reefs"  of  Australia  and  Africa),  but  from  the  gravel  and  sand  deposited  in  the  valleys  in 
auriferous  regions,  or  on  the  slopes  of  the  mountains  or  hills,  whose  rocks  contain  in  some 
part,  and  generally  not  far  distant,  gold  bearing  veins.  Such  deposits  are  known  as  placer 
deposits.  The  gold  is  obtained  by  some  method  involving  the  use  of  a  current  of  water 
and  the  separation  of  the  gold  from  the  sand  and  gravel  by  means  of  its  high  specific  gravity. 
These  hydraulic  methods  have  been  very  extensively  used  in  California  and  Alaska  and 
indeed  most  of  the  gold  of  the  Ural  Mts.,  Brazil,  Australia,  and  many  other  gold  regions 
has  come  from  such  alluvial  washings.  At  the  present  time,  however,  placer  deposits  are 
much  less  depended  upon  and  in  many  regions  all  the  gold  is  obtained  directly  from  the  rock. 

The  alluvial  gold  is  usually  in  flattened  scales  of  different  degrees  of  fineness,  the  size 
depending  partly  on  the  original  condition  in  the  quartz  veins,  and  partly  on  the  distance 
to  which  it  has  been  transported  and  assorted  by  running  water.  The  rolled  masses  when 
of  some  size  are  called  nuggets;  in  rare  cases  these  occur  very  large  and  of  great  value.  The 
Australian  gold  region  has  yielded  many  large  nuggets;  one  of  these  found  in  1858  weighed 
184  pounds,  and  another  (1869)  weighed  190  pounds.  In  the  auriferous  sands,  crystals  of 
zircon  are  very  common;  also  garnet  and  cyanite  in  grains;  often  also  monazite,  diamond, 
topaz,  corundum,  iridosmine,  platinum. 

Besides  the  free  gold  of  the  quartz  veins  and  gravels,  much  gold  is  also  obtained  from 
auriferous  sulphides  or  the  oxides  produced  by  their  alteration,  especially  pyrite',  also 
arsenopyrite,  chalcopyrite,  sphalerite,  marcasite,  etc.  The  only  minerals  containing  gold  in 
combination  are  the  rare  tellurides  (sylvanite,  calaverite,  etc.). 

Gold  is  widely  distributed  over  the  earth.  It  occurs  under  many  different  conditions 
and  with  many  different  rocks,  being,  however,  more  commonly  associated  with  the  acid 
types.  A  brief  summary  of  the  more  important  districts  follows. 

Europe.  The  gold  deposits  of  Europe  are  to  be  found  chiefly  in  three  great  districts, 
namely  the  Ural  mountains,  eastern  Hungary  and  a  less  important  Alpine  district  reaching 
from  Carinthia  through  the  Austrian  Tyrol^and  the  Italian  Alps  to  the  Pyrenees.  There 
are  three  gold  districts  in  Hungary.  Two  of  these  are  of  minor  importance  and  lie  one  to* 
the  north  of  Buda-Pesth  and  the  other  near  the  Galician  frontier.  The  third  district, 
which  is  the  most  important  district  in  Europe,  is  in  Transylvania,  lying  in  the  southeastern 
portion  of  the  Bihar  mountains.  Its  important  centers  are  Offenbanya,  Verespatak,  Nagyag 
(largely  tellurides),  Boicza  and  Ruda. 

Asia.  In  Siberia  gold  is  found  on  the  eastern  slope  of  the  Ural  mountains  for  a  distance 
of  500  miles.  The  important  districts  from  north  to  south  are  Bogoslov,  Nizhni  Tagilsk, 
Beresov  and  other  localities  near  Ekaterinburg,  Syserstk  and  Kyshtimsk,  the  Miask  dis- 
trict including  Zlatoust  and  Mt.  Ilmen,  Kotchkar  and  at  the  southern  limit  of  the  fields, 
Orsk.  Siberia  also  has  the  important  placer  districts  in  Tomsk,  which  include  Altai  and 
Marinsk,  and  in  Yeniseisk,  the  Atchinsk,  Minusinsk  and  the  north  and  south  Yenisei  dis- 
tricts. .  Farther  east  there  are  deposits  in  Transbaikalia  and  the  Lena  district  in  Yakutsk. 
In  India  the  chief  districts  are  the  Kolar  field  near  Bangalore  in  Mysore  and  the  Gadag 
and  Hutti  districts  a  little  further  north.  Gold  has  been  mined  in  China  in  Chili,  Shantung 
Weihaiwei,  Szechuen,  Yuman  and  Fo-Kien.  In  Manchuria  on  the  Lua.u-tung  Peninsula. 
In  Korea  principally  at  Unsan.  Gold-quartz  veins,  many  of  which  have  been  worked  for 
a  long  time,  occur  on  a  number  of  the  Japanese  islands. 

•  Australasia.  The  most  important  districts  in  New  Zealand  lie  on  the  Hauraki  Penin- 
sula with  the  Waihi  mine  as  the  most  famous.  Other  districts  are  the  West  Coast  area  on 
the  western  slopes  of  the  Alps  of  the  South  Island  and  the  Otago  area.  In  Queensland  the 
districts  of  Charter  Towers  and  the  Mount  Morgan  mine  are  important.  There  are  many 
gold  districts  in  New  South  Wales  among  which  are  Hillgrove,  Mount  Bpppy  and  Hill 
End.  Rich  districts  in  Victoria  are  the  Bendigo  and  Ballarat.  The  principal  gold  fields 
of  Tasmania  are  Beaconsfield,  Mathinna  and  the  copper  deposits  at  Mount  Lyell.  The 
chief  gold  field  in  West  Australia  is  near  Kalgoorlie  where  the  ores  are  largely  tellurides. 


352  DESCRIPTIVE   MINERALOGY 

Africa.  Gold  is  found  in  Egypt  in  the  section  between  the  Nile  and  the  Red  Sea.  Some 
of  these  deposits  were  worked  in  very  early  days.  Gold  has  been  produced  for  a  long  time 
from  the  Gold  Coast  district  on  the  Gulf  of  Guinea.  Important  deposits  are  found  in 
Matabeleland  and  Mashonaland  in  Southern  Rhodesia.  The  most  important  gold  district 
in  the  world  is  that  of  the  Witwatersrand  in  the  Transvaal.  The  mines  occur  in  an  east 
and  west  belt,  some  sixty  miles  in  length,  near  Johannesburg.  The  gold  is  found  scattered 
in  small  amounts  through  a  series  of  steeply  dipping  quartz  conglomerate  rocks. 

South  America.  Colonlbia  has  in  the  past  produced  large  amounts  of  gold.  The  chief 
districts  today  are  in  the  states  of  Antioquia  and  Cauca.  Comparatively  small  amounts 
are  produced  at  the  present  time  in  the  other  northern  countries.  The  important  deposits 
of  Brazil  lie  200  miles  to  the  north  of  Rio  de  Janeiro  in  Minas  Geraes  along  the  Sierra  do 
Espinhaco.  The  gold  deposits  in  Chile  lie  chiefly  in  the  coast  ranges  in  the  northern  and 
central  parts  of  the  country. 

Mexico.  While  Mexico  is  chiefly  noteworthy  for  its  silver  output  it  produces  also  con- 
siderable gold.  Important  districts  are  as  follows:  Altar,  Magdalena  and  Arizpe  in  Sonora; 
various  places  in  Chihuahua,  especially  about  Parral,  and  the  Dolores  mine  on  the  western 
border  of  the  state;  the  El  pro  mines  in  the  state  of  Mexico;  the  Pachuca  district  in 
Hidalgo;  also  various  places  in  Guanajuato  and  Zacatecas. 

Canada.  The  three  important  placer  districts  of  Canada  are  the  Klondike  in  Yukon 
Territory  and  the  Atlin  and  Cariboo  in  British  Columbia.  The  most  productive  vein 
deposits  are  found  in  British  Columbia  in  the  West  Kootenay  and  Yale  districts.  Gold  is 
also  found  in  Ontario  and  Nova  Scotia.  ,  - 

United  States.  Gold  occurs  in  the  United  States  chiefly  along  the  mountain  ranges  in 
the  western  states.  Smaller  amounts  have  been  found  along  the  Appalachians  in  the 
states  of  Virginia,  North  and  South  Carolina  and  Georgia.  The  more  important  localities 
in  the  western  states  are  given  below,  the  states  being  arranged  approximately  in  the  order 
of  their  importance.  California.  At  the  present  time  about  two  thirds  of  the  state's  out- 
put comes  from  the  lode  mines  and  one  third  from  placer  deposits.  The  quartz  veins  are 
chiefly  found  in  what  is  known  as  the  Mother-Lode  belt  that  lies  on  the  western  slope  of 
the  Sierra  Nevada  and  stretches  from  Mariposa  County  for  more  than  100  miles  toward 
the  north.  The  veins  occur  chiefly  in  a  belt  of  slates.  The  lode  mines  are  found  chiefly 
in  Amador,  Calaveras,  Kern,  Nevada,  Shasta,  Sierra  and  Tuolumne  Counties.  The 
important  placer  mines  are  located  in  Butte,  Sacramento  and  Yuba  Counties.  About  90 
per  cent  of  the  placer  gold  is  obtained  by  the  use  of  dredges.  Colorado.  Gold  is  mined  in 
various  districts  in  Gilpin  County,  from  the  Leadville  district  and  others  in  Lake  County, 
in  the  region  of  the  San  Juan  mountains  in  the  Sneffels,  Silverton  and  Telluride  districts, 
Cripple  Creek  district  (telluride  ores)  in  Teller  County,  placer  deposits  in  the  Breckenridge 
district  in  Summit  County.  Alaska.  The  most  important  lode  mines  are  in  the  Juneau 
district,  while  the  chief  placer  deposits  are  those  of  Fairbanks  and  Iditarod  in  the  Yukon 
basin  and  the  Nome  district  on  the  Seward  Peninsula.  Nevada.  The  most  important 
districts  are  those  of  Goldfield  in  Esmeralda  County  and  Tonapah  in  Nye  County.  South 
Dakota.  The  output  is  chiefly  from  the  Homestake  mine  at  Lead  in  Lawrence  County. 
Montana.  There  are  various  producing  districts,  the  more  important  being  in  Madison 
(largely  placers),  Deer  Lodge  and  Silver  Bow  Counties.  Arizona.  The  important  counties 
are  Mohave  and  Cochise.  Utah.  Gold  is  produced  chiefly  from  the  Bingham  and  Tintic 
districts  in  Salt  Lake  County  and  from  Juab  County. 

Use.  —  The  chief  ore  of  gold. 

SILVER. 

Isometric.  Crystals  commonly  distorted,  in  acicular  forms,  reticulated  or 
arborescent  shapes;  coarse  to  fine  filiform;  also  massive,  in  plates  or  flattened 
scales. 

Cleavage  none.  Ductile  and  malleable.  Fracture  hackly.  H.  =  2'5-3. 
G.  =  10-1-11 -1,  pure  10*5.  Luster  metallic.  Color  and  streak  silver-white, 
often  gray  to  black  by  tarnish. 

Comp.  —  Silver,  with  some  gold  (up  to  10  p.  c.),  copper,  and  sometimes 
platinum,  antimony,  bismuth,  mercury. 

r  ?y5'?iet,C*  ~B-B-  on  charcoal  fuses  easily  to  a  silver-white  globule,  which  in  O.F.  gives 
a  faint  dark  red  coating  of  silver  oxide;  crystallizes  on  cooling;  fusibility  about  1050°  C. 
Soluble  in  nitric  acid,  and  deposited  again  by  a  plate  of  copper.  Precipitated  from  its 
solutions  by  hydrochloric  acid  in  white  curdy  forms  of  silver  chloride. 


NATIVE    ELEMENTS 


353 


Diff.  —  Distinguished  by  its  malleability,  color  (on  the  fresh  surface),  and  specific 
gravity. 

Micro.  —  In  polished  section  shows  a  creamy  white  color  with  a  metallic,  smooth 
surface.  With  aqua  regia  and  FeCl3  tarnishes  quickly  with  bright  iridescent  color-s 
Blackens  with  HNO?. 

Obs. —  Native  silver  occurs  in  masses,  or  in  arborescent  and  filiform  shapes,  in  veins 
traversing  gneiss,  schist,  porphyry,  and  other  rocks.  Also  occurs  disseminated,  but  usually 
invisibly,  in  native  copper,  galena,  chalcocite,  etc.  It  is  commonly  of  secondary  origin 
having  been  derived  from  the  reduction  of  sulphides  and  other  compounds  of  silver. 

Native  silver  is  found  at  a  great  many  localities,  some  of  the  most  famous  of  which 
follow:  Kongsberg,  Norway,  in  magnificent  specimens  and  in  very  large  masses;  Freiberg 
Schneeberg,  etc.,  in  Saxony;  Pribram  and  Joachimstal  in  Bohemia;  Andreasberg  in  the 
Harz  Mts.,  Germany;  Allemont  in  Dauphine,  France;  at  various  points  in  Cornwall 
England.  At  Chanarcillo  and  other  localities  in  Chile;  in  large  masses  at  Huantaya' 
Peru.  In  many  places  in  Mexico,  especially  at  Batopilas  in  Chihuahua;  in  Zacatecas  and 
Guanajuato.  A  very  important  district  is  at  Cobalt,  Ontario,  where  native  silver  occurs  in 
masses  up  to  1000  pounds  in  weight;  it  occurs  there  associated  with  various  cobalt  and 
nickel  minerals. 

In  the  United  States  it  has  been  found  with  native  copper  in  the  Lake  Superior  copper 
district;  at  Silver  Islet,  Lake  Superior;  at  Butte  and  the  Elkhorn  mine  in  Mon.;  at  the 
Poor  Man's  Lode  in  Idaho;  in  Col.,  with  various  sulphide  deposits,  especially  at  Aspen. 

Use.  —  An  ore  of  silver. 

COPPER. 

Isometric.  The  tetrahexahedron  a  common  form  (Fig.  635) ;  also  in  octa- 
hedral plates.  Distinct  crystals  rare.  Frequently 
irregularly  distorted  and  passing  into  twisted  and 
wirelike  forms;  filiform  and  arborescent.  Massive; 
as  sand.  Twins:  tw.  pi.  o  (111),  very  common, 
often  flattened  or  elongated  to  spear-shaped  forms. 
Cf.  p.  173. 

Cleavage  none.  Fracture  hackly.  Highly  ductile 
and  malleable.  H.  =  2-5-3.  G.  =  8'8-8'9.  Luster 
metallic.  Color  copper-red.  Streak  metallic  shining. 
Opaque.  An  excellent  conductor  for  heat  and 
electricity. 


(410). 


Comp.  —  Pure  copper,  often  containing  some  silver,  bismuth,  mercury, 
etc. 

Pyr.,  etc.  —  B.B.  fuses  readily;  on  cooling  becomes  covered  with  a  coating  of  black 
oxide.  Dissolves  readily  in  nitric  acid,  giving  off  red  nitrous  fumes,  and  produces  a  deep 
azure-blue  solution  with  excess  of  ammonia.  Fusibility  780°  C. 

Micro.  —  In  polished  section  shows  pink  color  with  smooth,  metallic  surface.  With 
cone.  HNp3  dissolves  and  shows  iridescent  tarnish.  With  FeCl3  blackens  and  shows  a 
solution  pit. 

Obs.  —  Copper  is  usually,  if  not  always,  secondary  in  its  origin.  It  has  either  been 
deposited  from  solution  by  some  reducing  agent  which  is  commonly  a  compound  of  iron 
or  by  the  gradual  reduction  of  some  solid  compound.  Pseudomorphs  of  copper  after  cu- 
prite, azurite,  chalcocite,  etc.,  are  well  known.  It  is  associated  with  other  copper  ores, 
especially  cuprite,  malachite  and  azurite  in  the  upper  zone  of  copper  veins;  also  with  the 
sulphides,  chalcopyrite,  chalcocite,  etc.;  often  abundant  in  the  vicinity  of  dikes  of  igneous 
rocks;  also  in  clay  slate  and  sandstone. 

Occurs  in  crystals  at  Bogoslovsk,  Nijni  Tagilsk  and  elsewhere  in  the  Ural  Mts.  In 
Nassau,  Germany.  Common  in  Cornwall,  England.  Occurs  in  Brazil,  Chile,  and  Peru. 
Found  in  pseudomorphs  after  the  pseudo-hexagonal  twins  of  aragonite  at  Corocoro,  Bolivia. 
Abundant  at  Wallaroo,  South  Australia  and  at  Broken  Hill,  New  South  Wales.  Occurs 
at  various  places  in  Mexico. 

Occurs  native  throughout  the  red  sandstone  region  of  the  eastern  United  States,  spar- 
ingly in  Mass.,  Conn.,  and  more  abundantly  in  N.  J.  Near  New  Haven,  Conn.,  a  mass 
was  found  in  the  drift  weighing  nearly  200  pounds;  smaller  isolated  masses  have  also  been 
found.  Found  in  minor  amounts  at  Bisbee,  Ariz,  (in  branching  crystal  groups) ;  at  George- 


354  DESCRIPTIVE   MINERALOGY 

town  N  M  (pseudomorphs  after  azurite) ;  Ducktown,  Tenn.;  Cornwall,  Pa.;  and  Frank- 
lin N  J.  The  most  important  region  in  the  world  for  native  copper  is  the  Lake  Superior 
copper  district  on  the  Keweenaw  peninsula,  northern  Mich.  The  rocks  of  this  district  con- 
sist of  a  series  of  interbedded  lava  flows,  sandst9nes  and  conglomerates  which  dip  steeply 
to  the  northwest.  The  copper  is  obtained  practically  all  in  the  native  state,  sometimes  m 
immense  masses.  It  occurs  as  (1)  a  cement  filling  the  interstices  in  the  sandstone  and 
conglomerate,  sometimes  replacing  in  large  part  the  grains  and  pebbles  themselves,  (2)  fill- 
ing the  amygdaloidal  cavities  in  the  diabase  and  (3)  in  veins  that  traverse  all  kinds  of  rock. 
The  copper  was  probably  brought  into  the  district  by  the  igneous  rocks.  It  is  associated 
with  native  silver,  calcite,  prehnite,  datolite,  analcite,  etc. 
Use.  —  An  ore  of  copper. 

MERCURY.     Quicksilver. 

In  small  fluid  globules  scattered  through  its  gangue.  G  =  13 '6.  Luster 
metallic,  brilliant.  Color  tin-white.  Opaque. 

Comp.  —  Pure  mercury  (Hg) ;  with  sometimes  a  little  silver. 

Pyr.,  etc.  —  B.B.  entirely  volatile,  vaporizing  at  350°  C.  Becomes  solid  at  —  40°  C., 
crystallizing  in  regular  octahedrons  with  cubic  cleavage;  G.  =  14 '4.  Dissolves  in  nitric 

Obs.  —  Mercury  in  the  metallic  state  is  a  rare  mineral,  and  is  usually  associated  with 
the  sulphide  cinnabar,  from  which  the  supply  of  commerce  is  obtained.  The  rocks  afford- 
ing the  metal  and  its  ores  are  chiefly  clay  shales  or  schists  of  different  geological  ages.  Also 
found  in  connection  with  hot  springs.  See  cinnabar. 

LEAD. 

Isometric.  Crystals  rare.  Usually  in  thin  plates  and  small  globular 
masses.  Very  malleable,  and  somewhat  ductile.  H  =  1-5.  G.  =  11*4. 
Luster  metallic.  Color  lead-gray.  Opaque. 

Comp.  —  Nearly  pure  lead;  sometimes  contains  a  little  silver,  also 
antimony. 

Pyr.  —  B.B.  fuses  easily,  coating  the  charcoal  with  a  yellow  to  white  oxide.  Fusi- 
bility 330°  C.  Dissolves  easily  in  dilute  nitric  acid. 

Obs.  —  Of  rare  occurrence.  Found  at  Pajsberg,  Harstig,  and  Langban  in  Sweden; 
similarly  at  Nordmark;  also  in  the  gold  washings  of  the  Ural  Mts.;  reported  elsewhere, 
but  localities  often  doubtful.  In  the  United  States,  occurs  at  Breckinridge  and  Gunnison, 
Col.;  Wood  River  district,  Idaho;  Franklin,  N.  J. 

AMALGAM. 

Isometric.  Common  habit  dodecahedral.  Crystals  often  highly  modified. 
Also  massive  in  plates,  coatings,  and  embedded  grains. 

Cleavage:  dodecahedral  in  traces.  Fracture  conchoidal,  uneven.  Rather 
brittle  to  malleable.  H.  =  3-3'5.  G,  =  1375-14-1.  Luster  metallic,  bril- 
liant. ^Color  and  streak  silver-white.  Opaque. 

Comp.  —  (Ag,Hg),  silver  and  mercury,  varying  from  Ag2Hg3  to  Ag36Hg. 

Var.  —  Ordinary  amalgam,  Ag2Hg3  (silver  26'4  p.  c.)  or  AgHg  (silver  35-0);  also 
Ag5Hg3,  etc.  Arquerite,  Agi2Hg (silver  86 "6);  G.  =  10'8;  malleable  and  soft.  Kongsber- 
gite,  AgasHg  or  Ag36Hg. 

Pvr.,  etc.  —  B.B.  on  charcoal  the  mercury  volatilizes  and  a  globule  of  silver  is  left.  In 
the  closed  tube  the  mercury  sublimes  and  condenses  on  the  cold  part  of  the  tube  in  minute 
globules.  Dissolves  in  nitric  acid.  Rubbed  on  copper  it  gives  a  silvery  luster. 

Obs.  —  From  Germany  in  the  Rhine-Palatinate  at  Moschel-Landsberg  and  at 
Jriednchssegen,  Nassau;  from  Sala,  Sweden;  Kongsberg,  Norwav;  Allemont,  Dauphine", 
France;  Almaden,  Spain;  Chile;  Vitalle  Creek,  British  Columbia  (arquerite). 
.  .  Tm'~  Native  tin  has  been  reported  from  several  localities.  The  only  occurrence 
fairly  above  doubt  is  that  from  the  washings  at  the  headwaters  of  the  Clarence  river,  near 
>ban,  New  bouth  Wales.  It  has  been  found  here  in  grayish  white  rounded  grains,  with 
platinum,  mdosmine,  gold,  cassiterite,  and  corundum 


PLATINUM. 


NATIVE    ELEMENTS  355 

Platinum-Iron  Group 


Isometric.     Crystals  rare;  usually  in  grains  and  scales. 

Cleavage  none.  Fracture  hackly.  Malleable  and  ductile.  H.  =  4-4-5. 
G.  =  14-19  native;  21-22  chem.  pure.  Luster  metallic.  Color  and  streak 
whitish  steel-gray;  shining.  Sometimes  magnetic  and  occasionally  shows 
polarity. 

Comp.  —  Platinum  alloyed  with  iron,  iridium,  rhodium,  palladium, 
osmium,  and  other  metals. 

Most  platinum  yields  from  8  to  15  or  even  18  per  cent  of  iron,  0*5  to  2  p.  c.  palladium, 
1  to  3  p.  c.  each  of  rhodium  and  iridium,  a  trace  of  osmium  and  finally  0'5  to  2  p.  c.  or  more 
of  copper. 

Var.  —  1.  Ordinary.  Non-magnetic  or  only  slightly  magnetic.  G.  =  16'5-18'0  mostly. 
2.  Magnetic.  G.  about  14.  Much  platinum  is  magnetic,  and  occasionally  it  has  polarity. 
The  magnetic  property  seems  to  be  connected  with  high  percentage  of  iron  (iron-platinum), 
although  this  distinction  does  not  hold  without  exception. 

Pyr.,  etc.  —  B.B.  infusible.  Not  affected  by  borax  or  salt  of  phosphorus,  except  in  the 
state  of  fine  dust,  when  reactions  for  iron  and  copper  may  be  obtained.  Soluble  only  in 
heated  aqua  regia. 

Diff.  —  Distinguished  by  its  color,  malleability,  high  specific  gravity,  infusibility  and 
insolubility  in  ordinary  acids. 

Obs.  —  The  platinum  of  commerce  comes  almost  exclusively  from  placer  deposits.  Its 
original  source,  however,  is  in  the  basic  igneous  rocks,  usually  peridotites.  The  associated 
minerals  are  commonly  chrysolite,  serpentine  and  chromite.  Platinum  was  first  found  in 
pebbles  and  small  grains,  associated  with  iridium,  gold,  chromite,  etc.,  in  the  alluvial  de- 
posits of  the  river  Pinto,  in  the  district  of  El  Choco,  Colombia  ;  South  America,  where  it 
received  its  name  platina  (platina  del  Pinto)  from  plala,  silver.  The  greater  part  of  the 
world's  supply  comes  from  Russia  (discovered  in  1822)  where  it  occurs  in  alluvial  material 
in  the  Ural  Mts.  at  Nijni  Tagilsk,  and  with  chromite  in  a  serpentine  probably  derived  from 
a  peridotite;  also  in  the  Goroblagodat  and  Bisersk  districts.  Also  found  in  Borneo;  in 
New  Zealand,  from  a  region  characterized  by  a  chrysolite  rock  with  serpentine;  in  New 
South  Wales,  at  the  Broken  Hill  district,  and  in  gold  washings  at  various  points. 

In  Cal.  in  small  amounts  in  the  gold  placers,  chiefly  in  Trinity  Co.;  at  Port  Orfqrd  in 
Ore.  At  various  points  in  Canada,  the  most  important  being  the  Tulameen  District  in 
British  Columbia 

Use.  —  Practically  the  only  ore  of  platinum. 

Iridium.  Platin-iridium.  Iridium  alloyed  with  platinum  and  other  allied  metals. 
Occurs  usually  in  angular  grains  of  a  silver-white  color.  H.  =  6-7.  G.  =  22 '6-22 '8. 
With  the  platinum  of  the  Ural  Mts.  and  Brazil. 

IRIDOSMINE.     Osmiridium. 

Rhombohedral.     Usually  in  irregular  flattened  grains. 

Cleavage:  c(0001)  perfect.  Slightly  malleable  to  nearly  brittle.  H.  = 
6-7.  G.  =  19-3-21 -12.  Luster  metallic.  Color  tin-white  to  light  steel- 
gray.  Opaque. 

Comp.  —  Iridium  and  osmium  in  different  proportions.  Some  rhodium, 
platinum,  ruthenium,  and  other  metals  are  usually  present. 

Var.  —  1.  Nevyanskite.  H.  =  7;  G.  =  18'8-19'5.  In  flat  scales;  color  tin-white. 
Over  40  p.  c.  of  iridium.  2.  Siserskite.  In  flat  scales,  often  six-sided,  color  grayish  white, 
steel-gray.  G.  =  20-21'2.  .Not  over  30  p.  c.  of  iridium.  Less  common  than  the  light- 
colored  variety. 

Diff.  —  Distinguished  from  platinum  by  greater  hardness  and  by  its  lighter  color. 

Obs.  —  Occurs  with  platinum  in  South  America;  in  the  Ural  Mts.;  in  auriferous  drift 
in  New  South  Wales.  Rather  abundant  in  the  auriferous  beach-sands  of  northern  Cali- 
fornia and  Oregon. 

Palladium.  —  Isometric.     Palladium,    alloyed   with   a   little   platinum   and   iridium. 


356  DESCRIPTIVE   MINERALOGY 

Mostly  in  grains.     H.  =  4'5-5.     G.  =  11 '3-11 '8.     Color  whitish  steel-gray.    Occurs  with 
platinum  in  Brazil;  also  from  the  Ural  Mts. 

Allopalladium.  —  Palladium  under  the  hexagonal-rhombohedral  class  (?).  From  Til- 
kerode  in  the  Harz  Mts.  in  small  hexagonal  tables  with  gold. 

IRON. 

Isometric.     Usually  massive,  rarely  in  crystals. 

Cleavage:  a(  100),  perfect;  also  a  lamellar  structure  ||  0(111)  and  ||  d(110). 
Fracture  hackly.  Malleable.  H.  =  4-5.  G.  =  7-3-7-8.  Luster  metallic. 
Color  steel-gray  to  iron-black.  Strongly  magnetic. 

Var.  —  1.  Terrestrial  Iron.  —  Found  in  masses,  occasionally  of  great  size,  as  well  as 
in  small  embedded  particles,  in  basalt  at  Blaafjeld,  Oyifak  (or  Uifak),  Disko  Island,  West 
Greenland;  also  elsewhere  on  the  same  coast.  This  iron  contains  1  to  2  p.  c.  of  Ni.  In 
small  grains  with  pyrrhotite  in  basalt  from  near  Kassel,  Hesse  Nassau,  Germany.  In 
minute  spherules  in  feldspar  from  Cameron  Township,  Nipissing  Dist.,  Ontario.  Some 
other  occurrences,  usually  classed  as  meteoric,  may  be  in  fact  terrestrial. 

A  nickeliferous  metallic  iron  (FeNi2)  called  awaruite  occurs  in  the  drift  of  the  Gorge 
river,  which  empties  into  Awarua  Bay  on  the  west  coast  of  the  south  island  of  New  Zea- 
land; associated  with  gold,  platinum,  cassiterite,  chromite;  probably  derived  from  a 
partially  serpentinized  peridotite.  Josephinite  is  a  nickel-iron  (FeNia)  from  Oregon,  occur- 
ring in  stream  gravel.  Similar  material  from  near  Lillooet  on  the  Fraser  river,  British  Co- 
lumbia, has  been  called  soucsite.  Native  iron  also  occurs  sparingly  in  some  basalts;  reported 
from  gold  or  platinum  washings  at  various  points. 

2.   Meteoric  Iron.  —  Native  iron  also  occurs  in  most  meteorites,  forming  in  some  cases 
(a)  the  entire  mass  (iron  meteorites) ;   also  (6)  as  a  spongy,  cellular  matrix  in  which  are 
embedded  grains  of  chrysolite  or  other  silicates  (siderolites)}   (c)  in  grains  or  scales  dissemi- 
nated more  or  less  freely  throughout  a  stony  matrix 
636  (meteoric  stones).     Rarely   a   meteorite  consists  of  a 

single  crystalline  individual  with  numerous  twinning 
lamellse  !(o(lll).  Cubic  cleavage  sometimes  observed: 
also  an  octahedral,  less  often  dodecahedral,  lamellar 
structure.  Etching  with  dilute  nitric  acid  (or  iodine) 
commonly  develops  a  crystalline  structure  (called 
Widmanstdtten  figures)  (Fig.  636);  usually  consisting 
of  lines  or  bands  crossing  at  various  angles  according 
to  the  direction  of  the  section,  at  60°  if  ||  0(111), 
90°  |!  a(100),  etc.  They  are  formed  by  the  edges  of 
crystalline  plates,  usually  1 1  o,  of  the  nickeliferous  iron 
of  different  composition  (kamacite,  tcenite,  plessite),  as 
shown  by  the  fact  that  they  are  differently  attacked 
by  the  acid.  Irons  with  cubic  structure  and  with 
twinning  lamellse  have  a  series  of  fine  lines  correspond- 
r«i  •  4.  iv/r<u  AT  TV/T  m& to  those  developed  by  etching  (Neumann  lines) .  A 

loneta  Mt.,  New  Mexico         damascene  luster  is  also  produced  in  some  cases,  due 
to    quadrilateral    depressions.     Some  irons  show    no 
distinct  crystalline  structure  upon  etching. 

The  exterior  of  masses  of  meteoric  iron  is  usually  more  or  less  deeply  pitted  with  rounded 
thumblike  depressions,  and  the  surface  at  the  time  of  fall  is  covered  with  a  film  of  iron  oxide 
in  fane  ridges  showing  lines  of  flow  due  to  the  melting  caused  by  the  heat  developed  by  the 
resistance  of  the  air;  this  film  disappears  when  the  iron  is  exposed  to  the  weather. 

Meteoric  iron  is  always  alloyed  with  nickel,  which  is  usually  present  in  amounts  varying 
rom  5  to  10  p.  c.,  sometimes  much  more;  small  amounts  of  other  metals,  as  cobalt,  man- 


rare.     Cohenite,  sometimes  identified,  is  (Fe,Ni,Co)3C  in  tin-white  crystals. 


Moissanite.  —  CSi.     This  material,  originally  produced  artificially  as  carborundum,  has 
been  found  occurring  naturally  as  small  green  hexagonal  plates  in  the  meteoric  iron  of 


Canon  Diablo,  Ariz 


SULPHIDES,  SELENIDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES  357 

II.   SULPHIDES,   SELENIDES,   TELLURIDES,   ARSENIDES, 
ANTIMONIDES 

The  sulphides,  etc.,  fall  into  two  Groups  according  to  the  character  of  the 
positive  element. 

I.   Sulphides,  Selenides,  Tellurides  of  the  Semi-metals. 
II.   Sulphides,    Selenides,    Tellurides,    Arsenides,  Antimonides  of    the 
Metals. 


I.   Sulphides,  etc.,  of  the  Semi-Metals 

This  section  includes  one  distinct  group,  the  Stibnite  Group,  to  which 
orpiment  is  related ;  the  other  species  included  stand  alone.  637 


REALGAR. 

Monoclinic.     Axes  a  :  b  :  c  = 
mm'",  110  A  HO  =  105°  34'.' 


1-4403  :1  :  0*9729;  0  =  66°  5'. 
rr',  012  A  012  =  47°  57'. 


Crystals  short  prismatic;  striated  vertically.  Also  gran- 
ular, coarse  or  fine;  compact;  as  an  incrustation. 

Cleavage:  6(010)  rather  perfect.  Fracture  small  con- 
choidal.  Sectile.  H.  =  1-5-2.  G.  =  3 '56.  Luster  resinous. 
Color  aurora-red  or  orange-yellow.  Streak  varying  from 
orange-red  to  aurora-red.  Transparent  —  translucent. 

Comp.  —  Arsenic  monosulphide,  AsS  =  Sulphur  29*9,  arsenic  70*1  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  melts  and  gives  a  dark  red  liquid  when  hot  and  a  red- 
dish yellow  solid  when  cold;  in  the  open  tube  (if  heated  very  slowly)  sulphurous  fumes,  and 
a  white  crystalline  sublimate  of  arsenic  trioxide.  B.B.  on  charcoal  burns  with  a  blue  flame, 
emitting  arsenical  and  sulphurous  odors.  Soluble  in  caustic  alkalies. 

Artif .  —  Realgar  is  frequently  noted  as  a  sublimation  product  from  furnaces  roasting 
ores  of  arsenic.  Crystals  are  produced  when  arsenic  sulphide  is  heated  in  a  sealed  tube 
with  a  solution  of  sodium  bicarbonate. 

Obs.  —  Realgar  occurs  usually  in  veins  associated  with  silver  and  lead  ores.  It  has 
been  found  in  volcanic  regions  as  a  sublimation  product.  It  has  also  been  noted  as  a  deposit 
from  hot  spring  waters.  It  is  often  associated  with  orpiment.  It  occurs  at  Felsobdnya, 
Kapnik  and  Nagy^g,  Hungary;  Allchar,  Macedonia.  Binnental,  Switzerland,  in  dolomite. 
In  the  United  States,  at  Mercur,  Utah;  in  the  Norris  Geyser  Basin,  Yellowstone  Park,  as  a 
deposition  from  the  hot  waters.  Found  at  the  Monte  Cristo  mining  district,  Snohomish 
Co.,  Washington;  the  name  realgar  is  from  the  Arabic,  Rahj  al  ghar,  powder  of  the 
mine. 

Use.  —  Was  used  in  fireworks  to  give  a  brilliant  white  light  when  mixed  with  saltpeter 
and  ignited.  The  artificial  material  is  now  used  for  this  purpose. 

ORPIMENT. 

Monoclinic.     Axes  a  :b  :c  =  0'596  :  1  :  0;665,  0  =  90°41'. 

Crystals  small,  rarely  distinct.  Usually  in  foliated  or  columnar  masses; 
sometimes  with  reniform  surface. 

Cleavage:  6(010)  highly  perfect,  cleavage  face  vertically  striated;  a(100) 
in  traces;  gliding-plane  c  (001).  Sectile.  Cleavage  laminae  flexible,  inelastic. 
H.  =  T5-2.  G.  =  3'4-3'5.  Luster  pearly  on  b  (cleavage);  elsewhere 
resinous.  Color  lemon-yellow  of  several  shades;  streak  the  same,  but  paler. 
Subtransparent  —  sub  translucent. 

Comp.  —  Arsenic  trisulphide,  A^Sa  =  Sulphur  39*0,  arsenic  61*0  =  100. 


358 


DESCRIPTIVE   MINERALOGY 


Pyr.,  etc.  —  Same  as  for  realgar,  p.  357. 

Diff.  —  Distinguished  by  its  fine  yellow  color,  pearly  luster,  easy  cleavage,  and  flexi- 
bility when  in  plates. 

Artif .  —  Orpiment  has  been  synthesized  by  heating  solutions  of  arsenic  with  ammo- 
nium sulphocyanate  in  a  sealed  tube;  also  by  the  treatment  under  pressure  of  arsenic  acid 
with  hydrogen  sulphide. 

ObSc  —  Occurs  under  same  conditions  as  realgar  with  which  it  is  commonly  associated. 
It  is  found  in  Hungary  at  Tajowa  in  small  crystals,  in  foliated  and  fibrous  masses  at  Mol- 
dowa,  in  metalliferous  veins  at  Kapnik  and  Felsob&nya;  with  realgar  at  Allchar,  Macedonia. 
A  large  deposit  occurred  near  Julamerk  in  Kurdistan.  Occurs  in  fine  crystals  at  Mercur, 
Utah.  Among  the 'deposits  of  the  Steamboat  Springs,  Nevada;  also  with  realgar  in  the 
Yellowstone  Park. 

The  name  orpiment  is  a  corruption  of  its  Latin  name  auripigmentum,  "golden  paint," 
given  in  allusion  to  the  color,  and  also  because  the  substance  was  supposed  to  contain  gold. 

Use.  —  For  a  pigment,  in  dyeing  and  in  a  preparation  for  the  removal  of  hair  from  skins. 
The  artificial  material  is  largely  used  as  a  substitute  for  the  mineral. 


Stibnite 

Bismuthinite 

Guanajuatite 


Stibnite  Group 

Sb2S3 
Bi2S3 
Bi2Se3 


a  :  b  :  c 

0*9926  :  1  :  1-0179 
0-9679  :  1  :  0'9850 
1  :  1  approx. 


The  species  of  the  Stibnite  Group  crystallize  in  the  orthorhombic  system 
and  have  perfect  brachypinacoidal  cleavage,  yielding  flexible-  laminae. 

The  species  orpiment  is  in  physical  properties  somewhat  related  to  stibnite,  but  is 
mpnoclinic  in  crystallization.  Groth  notes  that  in  a  similar  way,  the  oxide,  As2O3,  is  mono- 
clinic  in  claudetite,  while  the  corresponding  compound,  Sb2O3  (valentinite),  is  orthorhombic. 


STIBNITE.    Antimonite,  Antimony  Glance. 
Orthorhombic.     Axes  a  :  b  :  c  =  0'9926 

mm'",  110  A  110  =  89°  34'. 

ppf,   111  A  111  =  71°  24|'. 

ss',   113  A  113  =  35°  52§'. 

ss'",  113  A  113  =  35°  36'. 


1  :  1-0179. 
bv,  010  A  121  =  35 
br,,  010  A  353  =  40° 
br,  010  A  343  =  46° 
bp,  010  A  111  =  54° 


33' 
36' 


640 


Crystals  prismatic;  striated  or  furrowed  vertically;  often  curved  or  twisted 
(cf.  p.  188).     Common  in  confused  aggregates  or  radiating  groups  of  acicular 

crystals;  massive,  coarse  or  fine 
columnar,  commonly  bladed,  less 
often  granular  to  impalpable. 

Cleavage :  b  (010)  highly 
perfect.  Slightly  sectile.  Frac- 
ture small  sub-conchoidal.  H. 
=  2.  -  G.  =  4-52^-62.  Luster 
metallic,  highly  splendent  on 
cleavage  or  fresh  crystalline  sur- 
faces. Color  and  streak  lead- 
gray,  inclining  to  steel-gray:  sub- 
ject to  blackish  tarnish,  sometimes 
iridescent. 
Hungary  Japan  Comp.  ~  Antimony  trisul- 

antimony  71'4  =  100.     Sometimes  auriferou^also 

p~  fc  Ife^^ 


California 


SULPHIDES,  SELENIDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES    359 

sublimate  which  B.B.  is  non-volatile.  On  charcoal  fuses,  spreads  out,  gives  sulphurous 
fumes,  and  coats  the  coal  white  with  oxide  of  antimony;  this  coating  treated  in  R.F. 
volatilizes  and  tinges  the  flame  greenish  blue.  When  pure,  perfectly  soluble  in  hydrochloric 
acid;  in  nitric  acid  decomposed  with  separation  of  antimony  pentoxide. 

Diff.  —  Distinguished  (e.g.,  from  galena)  by  cleavage,  color,  softness;  also  by  its  fusi- 
bility and  other  blowpipe  characters.  It  is  harder  than  graphite.  Resembles  sometimes 
certain  of  the  rarer  sulphantimonites  of  lead,  but  yields  no  lead  coating  on  charcoal. 

Micro.  —  In  polished  section  shows  white  color  like  galena  with  a  smooth  surface. 
Darkens  with  HNO3  and  aqua  regia;  with  KOH  turns  oranffe-vpllnw  t.n  radish  hrjyvn 

Artif.  —  Stibnite,  like  orpiment,  has  been  artificially  produced  by  heating  in  a  sealed 
tube,  a  solution  of  antimony  with  ammonium  sulphocyanate;  also  by  passing  hydrogen 
sulphide  at  a  red  heat  over  compounds  of  antimony. 

Obs.  —  Stibnite  has  been  noted  in  deposits  of  solf  ataric  origin  but  usually  has  appar- 
ently been  deposited  from  alkaline  solutions  in  intimate  association  with  quartz.  It  is 
found  in  beds  or  veins  in  granite  and  gneiss,  often  accompanied  with  various  other  antimony 
minerals  produced  by  its  alteration.  Also  associated  in  metalliferous  deposits  with  sphal- 
erite, galena,  cinnabar,  barite,  quartz;  sometimes  accompanies  native  gold. 

Stibnite  is  the  most  common  ore  of  antimony  and  is  found  in  quantity  in  many  countries 
but  has  never  been  extensively  mined  in  the  United  States.  In  Europe  it  has  been  found 
in  notable  deposits  at  Wolfsberg,  Harz  Mts.;  at  Braunsdorf  near  Freiberg  in  Saxony;  at 
the  Caspari  mine  near  Arnsberg,  Westphalia;  in  Hungary  at  Felsobanya,  Kremnitz  and 
Kapnik;  at  various  points  in  France.  Groups  of  large  splendent  crystals  have  come 
from  the  antimony  mines  in  the  Province  of  Ivo,  island  of  Shikoku,  Japan.  Important 
deposits  are  located  in  southern  China,  particularly  in  the  Province  of  Hunan.  Mexico  and 
Chile  produce  considerable  antimony  ore. 

In  the  United  States  the  more  important  deposits  are  in  C#l.,  on  Telescope  Peak  in  the 
Panamint  Ra'nge,  in  Kern  County  and  in  the  eastern  part  of  San  Benito  County.  Nev. 
has  several  deposits,  mostly  in  the  northwest  section. 

Use.  —  The  most  important  ore  of  antimony. 

•  Metastibnite.  —  An  dmorphous  brick-red  deposit  of  antimony  trisulphide,  Sb2S3, 
occurring  with  cinnabar  and  arsenic  sulphide  upon  siliceous  sinter  at  Steamboat  Springs, 
Washoe  Co.,  Nev. 

BISMUTHINITE.     Bismuth  Glance. 

Orthorhombic.  Rarely  in  acicular  crystals,  mm"',  110  A  110  =  88°  8'. 
Usually  massive,  foliated  or  fibrous. 

Cleavage:  6(010)  perfect.  Somewhat  sectile.  H.  =  2.  G.  =  6'4-6*5. 
Luster  metallic.  Streak  and  color  lead-gray,  inclining  to  tin-white,  with  a 
yellowish  or  iridescent  tarnish.  Opaque. 

Comp.. —  Bismuth  trisulphide,  Bi2S3  =  Sulphur  18'8,  bismuth  81*2  = 
100.  Sometimes  contains  a  little  copper  and  iron. 

Pyr.,  etc.  —  Fusibility  =  1.  In  the  open  tube  sulphurous  fumes,  and  a  white  sublimate 
which  B.B.  fuses  into  drops,  brown  while  hot  and  opaque  yellow  on  cooling.  On  char- 
coal at  first  gives  sulphurous  fumes;  then  fuses  with  spirting,  and  coats  the  coal  with 
yellow  bismuth  oxide;  with  potassium  iodide  and  sulphur  gives  a  yellow  to  bright  red 
coating  of  bismuth  iodide.  Dissolves  readily  in  hot  nitric  acid,  and  a  white  precipitate 
of  a  basic  salt  falls  on  diluting  with  water. 

Artif.  —  Bismuthinite  has  been  produced  artificially  by  treating  the  volatilized  chlo- 
ride of  bismuth  with  hydrogen  sulphide;  in  crystals  by  heating  bismuth  sulphide  in  a  sealed 
tube  with  an  alkaline  sulphide. 

Micro.  —  In  polished  section  shows  white  color  like  galena  with  a  smooth  surface, 
with  HNO3  blackens,  leaving  a  rough  surface;  with  aqua  regia  slowly  turns  brown. 

Obs.  —  Found  in  Cornwall,  England,  at  Carrock  Fells,  Redruth,  etc. ;  in  France  at 
Meymac,  Correze;  in  Saxony  at  Schneeberg  and  Altenberg;  in  Hesse  at  Bieber;  in  Hun- 
gary at  Rezbany  a  and  Oravicza;  in  Sweden  at  Riddarhyttan ;  in  Bolivia  at  San  Baldamero 
near  Sovata  and  in  the  Chorolque  and  Tazna  districts.  Occurs  in  the  United  States  in  Beaver 
Co.,  Utah;  in  Rowan  and  Jackson  Cos.,  N.  C.;  at  Wicks,  Jefferson  Co.,  Mon.;  Delaware 
Co.,  Pa.;  Haddam,  Conn. 

Use.  —  An  ore  of  bismuth. 

Guanajuatite.  Frenzelite.  Bismuth  selenide,  Bi2Se3,  sometimes  with  a  small  amount 
of  sulphur  replacing  selenium.  In  acicular  crystals;  also  massive,  granular,  foliated  or 
fibrous.  Cleavage:  6(010)  distinct.  H.  =  2'5-3'5.  G.  =  6'25-6'62.  Luster  metallic. 


360  DESCRIPTIVE   MINERALOGY 

Color  bluish  gray.     From  the  Santa  Catarina  mine,  near  Guanajuato,  Mexico.     Noted 
from  Salmon,  Idaho. 

TETRAD  YMITE. 

Rhombohedral.  Crystals  small,  indistinct.  Commonly  in  bladed  forms 
foliated  to  granular  massive. 

Cleavage:  basal,  perfect.  Laminse  flexible;  not  very  sectile.  H.  =  1-5-2; 
soils  paper.  G.  =  7-2-7-6.  Luster  metallic,  splendent.  Color  pale  steel-gray. 

Comp.  —  Consists  of  bismuth  and  tellurium,  with  sometimes  sulphur 
and  a  trace  of  selenium;  the  analyses  for  the  most  part  afford  the  general 
formula  Bi2(Te,  S)8. 

Var.  —  1.  Free  from  sulphur.  Bi2Te3  =  Tellurium  48' 1,  bismuth  51*9.  G.  =  7'642 
from  Dahlonega.  Var.  2.  Sulphurous.  2Bi2Te3 .  Bi2S3  =  Tellurium  36 '4,  sulphur  4 '6, 
bismuth  59'0  =  100.  This  is  the  more  common  variety  and  includes  the  tetradymite  in 
crystals  from  Schubkau. 

Pyr.  —  In  the  open  tube  a  white  sublimate  of  tellurium  dioxide,  which  B.B.  fuses  to 
colorless  drops.  On  charcoal  fuses,  gives  white  fumes,  and  entirely  volatilizes;  tinges  the 
R.F.  bluish  green;  coats  the  coal  at  first  white  (TeO2),  and  finally  orange-yellow  (Bi2O3); 
some  varieties  give  sulphurous  and  selenous  odors. 

Obs.  —  Occurs  in  Hungary  at  Schubkau  near  Schemnitz  at  Rezbanya  and  Orawitza; 
at  Carrock  Fells,  Cumberland,  England.  Occurs  on  Liddell  Creek,  Kaslo  river,  West 
Kootenay,  British  Columbia.  In  the  United  States,  in  Va.,  at  the  Whitehall  gold  mines, 
Spottsylvania  Co.;  in  Davidson  Co.,  N.  C.,  and  in  the  gold  washings  of  Burke  and 
McDowell  counties,  etc.;  near  Dahlonega,  Ga.;  in  Mon.  At  the  Montgomery  mine 
and  near  Bradshaw,  Ariz.  Named  from  TeTp'dvuos,  fourfold,  in  allusion  to  complex  twin 
crystals  sometimes  observed. 

Griinlingite.  —  Bi4TeS3.  Massive.  One  distinct  cleavage.  Color,  gray.  G.  =  7'321. 
From  Cumberland,  England.  Oruetite  is  a  similar  mineral,  Bi8TeS4,  from  Serrania  de 
Ronda,  Spain. 

Joseite.  — A  bismuth  telluride  (Te  80  p.  c.,  also  S  and  Se).  G.  =  7'9.  San  Jose, 
Brazil. 

Wehrlite.  —  A  foliated  bismuth  telluride  (Te  30  p.  c.)  of  doubtful  formula.  G.  =  8'4. 
Deutsch-Pilsen,  Hungary. 

MOLYBDENITE. 

Crystals  hexagonal  in  form,  tabular,  or  short  prisms  slightly  tapering  and 
horizontally  striated.  Commonly  foliated,  massive  or  in  scales;  also  fine 
granular. 

Cleavage:  basal  eminent.  Laminse  very  flexible,  but  not  elastic.  Sectile. 
H.  =  1-1-5.  G.  =  4-7-4-8.  Luster  metallic.  Color  pure  lead-gray;  a 
bluish  gray  trace  on  paper.  Opaque.  Feel  greasy. 

Comp.  —  Molybdenum  disulphide,  MoS2  =  Sulphur  40 -0,  molybdenum 
60-0  =  100. 

Pyr.,  etc.  —  In  the  open  tube  sulphurous  fumes  and  a  pale  yellow  crystalline  sublimate 
of  molybdenum  trioxide  (MoOg).  B.B.  in  the  forceps  infusible,  imparts  a  yellowish  green 
color  to  the  flame;  on  charcoal  the  pulverized  mineral  gives  in  O.F.  a  strong  odor  of  sul- 
phur dioxide  and  coats  the  coal  with  crystals  of  molybdic  oxide,  yellow  while  hot,  white  on 
cooling;  near  the  assay  the  coating  is  copper-red,  and  if  the  white  coating  be  touched  with 
an  intermittent  R.F.,  it  assumes  a  beautiful  azure-blue  color.  Decomposed  by  nitric  acid, 
leaving  a  white  or  grayish  residue. 

Diff.  —  Much  resembles  graphite  in  softness  and  structure  (see  p.  347),  but  has  a  bluer 
trace  on  paper  and  readily  yields  sulphur  fumes  on  charcoal. 

Artif.  —  Molybdenite  has  been  made  artificially  by  adding  molybdic  oxide  to  a  fused 
mixture  of  potassium  carbonate  and  sulphur;  also  by  heating  a  mixture  of  molybdates  and 
lime  in  an  atmosphere  of  hydrochloric  acid  and  hydrogen  sulphide. 

Micro.  —  In  polished  section  shows  grayish  white  color  with  smooth  surface.  Un- 
affected by  reagents. 


SULPHIDES,  SELENIDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES   361 

Obs.  —  Generally  occurs  embedded  in,  or  disseminated  through,  granite,  gneiss,  zircon- 
syenite,  granular  limestone,  and  other  crystalline  rocks.  At  Arendal  and  Laurvik  in 
Norway;  Altenberg,  Saxony;  Zinnwald  and  Schlaggenwald,  Bohemia;  near  Miask,  Ural 
Mts.;  Chessy  in  France;  in  Italy,  on  island  of  Sardinia;  Carrock  Fells,  in  Cumberland;  at 
several  of  the  Cornish  mines.  In  large  crystals  at  Kingsgate,  Glen  Innes,  N.  S.  W. 

In  Me.  at  Blue  Hill  Bay;  in  Conn.,  at  Haddam,  in  gneiss;  in  Ver.,  at  Newport;  in 
N.  H.,  at  Westmoreland;  in  N.  Y.,  two  miles  southeast  of  Warwick;  in  N.  J.,  at  Franklin; 
in  Pa.,  in  Chester,  near  Reading  and  at  Frankford;  near  Concord,  Cabarrus  Co.,  N.  C.;  in 
quartz  vein  at  Crown  Point,  Wash.  Molybdenite  has  been  mined  in  various  places  in 
Ariz.,  Col.,  Nev.,  Mon.,  Tex.,  Utah.  etc.  In  Canada,  at  St.  Jer6me,  Quebec;  in  large  crys- 
tals in  Renfrew  county,  Ontario;  also  in  Aldfield  township,  Pontiac  Co.,  Quebec. 

Named  from  tSoXvpdos,  lead;  the  name,  first  given  to  some  substances  containing  lead, 
later  included  graphite  and  molybdenite,  and  even  some  compounds  of  antimony.  The 
distinction  between  graphite  and  molybdenite  was  established  by  Scheele  in  1778-79. 

Use.  —  An  important  ore  of  molybdenum. 

Tungstenite.  —  Probably  WS2.  Earthy  or  foliated.  Color  and  streak,  dark  lead- 
gray.  H.  =  2'5.  G.  =  7'4.  Found  at  Emma  mine,  Salt  Lake  Co.,  Utah. 

Patronite.  Rizopatronite.  —  Complex  composition,  containing  large  amounts  of  a 
vanadium  sulphide,  perhaps  ¥84.  Amorphous.  Color  black.  Occurs  in  a  complex  mix- 
ture of  mineral  substances  among  which  are  quisqueite  and  bravoite,  at  Minasragra,  Peru. 

II.   Sulphides,  Selenides,  Tellurides,  Arsenides,  Antimonides  of  the 

Metals 

The  sulphides  of  this  second  section  fall  into  four  divisions  depending 
upon  the  proportion  of  the  negative  element  present.  These  divisions  with 
the  groups  belonging  to  them  are  as  follows : 

A.  Basic  Division 

ii 
B.    Monosulphides,  Monotellurides,  etc.,  RjjS,  RS,  etc. 

1.  Galena  Group.     Isometric-normal. 

2.  Chalcocite  Group.     Orthorhombic. 

3.  Sphalerite  Group.     Isometric-tetrahedral. 

4.  Cinnabar — Wurtzite — Millerite  Group.     Hexagonal  and  rhombo- 

hedral. 

C.   Intermediate  Division 

Embraces  Melonite,  Te2S3;  Bornite,  5Cu2S.Fe2S3;  Linnaeite,  €08.00283; 
Chalcopyrite,  Cu2S.Fe2S3;  etc. 

[D.  Disulphides,  Diarsenides,  etc.,  RS2,  RAs2,  etc. 

1.  Pyrite  Group.     Isometric-pyritohedral. 

2.  Marcasite  Group.     Orthorhombic. 


A.   Basic  Division 

The  basic  division  embraces  several  rare  basic  compounds  of  silver,  copper 
or  nickel  chiefly  with  antimony  and  arsenic.  Of  these  the  crystallization  of 
dyscrasite  and  maucherite  only  is  known. 

DYSCRASITE. 

Orthorhombic.  Axes  a  :  b  :  c  =  0-5J75  :  1  :  (V6718.  Crystals  rare,  pseu- 
dohexagonal  in  angles  (mm'",  110  A  110  =  60°  1')  and  by  twinning.  Also 
massive.  Fracture  uneven.  Sectile.  H.  =  3'5-4.  G.  =  9 '44-9 '85.  Luster 


362  DESCRIPTIVE   MINERALOGY 

metallic.  Color  and  streak  silver-white,  inclining  to  tin-white;  sometimes 
tarnished  yellow  or  blackish.  Opaque. 

Comp.  —  A  silver  antimonide,  including  Ag3Sb  =  Antimony  27' 1,  silver 
72 '9  =  100,  and  AgeSb  =  Antimony  157,  silver  84 -3  =  100,  and  perhaps  other 
compounds. 

Analyses  vary  widely,  S9me  conforming  also  to  Agj>Sb,  Ag4(Sb,As)3,  etc.  By  some 
authors  classed  with  chalcocite. 

Pyr.,  etc.  B.B.  on  charcoal  fuses  (1'5)  to  a  globule,  coating  the  coal  with  white  anti- 
mony trioxide  and  finally  giving  a  globule  of  almost  pure  silver.  Soluble  in  nitric  acid, 
leaving  antimony  trioxide. 

Obs.  —  Occurs  near  Wolfach,  Baden;  Andreasberg  in  the  Harz  Mts.,  Germany;  Alle- 
mont,  France.  Noted  at  Cobalt,  Ontario,  Canada.  Also  from  Mexico  arid  Chile.  Named 
from  dvffKpacrts,  a  bad  alloy. 

HENTILITE,  ANIMIKITE.  The  ores  from  Silver  Islet,  Lake  Superior,  apparently  contain 
a  silver  arsenide  (huntilite,  Ag3As?)  and  perhaps  also  a  silver  antimonide  (animikite,  Ag9Sb?), 
the  latter  probably  a  mixture. 

Horsfordite.  A  silver-white,  massive  copper  antimonide,  probably  Cu6Sb  (Sb  24  p.  c.). 
G.  =  8'8.  Asia  Minor,  near  Mytilene. 

Domeykite.  —  Copper  arsenide,  Cu3As.  Reniform  and  botryoidal;  also  massive,  dissem- 
inated. G.  =  7'2-775.  Luster  metallic.  Color  tin-white  to  steel-gray,  readily  tarnished. 
From  several  Chilian  mines;  also  Zwickau,  Saxony.  In  North  America,  with  niccolite 
at  Michipicoten  Island,  Lake  Superior.  Microscopic  examination  shows  this  mineral  to  be 
an  intimate  mixture  of  two  unknown  constituents.  Usually  identical  with  algodonite. 

Mohawkite.  —  Like  domeykite,  Cu3As,  with  Ni  and  Co.  Massive,  fine  granular  to 
compact.  Color  gray  with  faint  yellow  tinge;  tarnishes  to  dull  purple.  H.  =  3'5.  Brittle. 
G.  =  8 '07.  Microscopic  examination,  shows  it  to  be  a  mixture.  From  Mohawk  mine, 
Keweenaw  Co.,  Mich.  Ledouxite  from  the  Mohawk  mine»said  to  be  Cu4As  has  been  shown 
to  be  a  mixture. 

Algodonite.  Copper  arsenide,  Cu6As  (As  16'5  p.  c.);  G.  =  7'62.  Resembles  domey- 
kite.  From  Chile;  also  Lake  Superior.  Microscopic  examination  shows  this  mineral  to  be 
a  mixture  of  two  constituents. 

Whitneyite.  Copper  arsenide,  Cu9As  (As  11'6  p.  e).  G.  =  8'4-8'6.  Color  pale  red- 
dish white.  From  Houghton  Co.,  Mich.;  Sonora,  Lower  California. 

Chilenite.     Perhaps  Ag6Bi.     Copiapo,  Chile. 

COCINERITE.  Copper,  silver  sulphide,  Ci^AgS.  Massive.  Color  silver-gray,  tarnish- 
ing black,  H  =  2'5.  G.  =  6*1.  From  Cocinera  mine,  Ramos,  San  Luis  Potosi,  Mexico. 

Stiitzite.     A  rare  silver  telluride  (Ag4Te?).     Probably  from  Nagyag,  Transylvania. 

Rickardite.  Cu4Te3.  Massive.  H.  =  3'5.  G.  =  7'5.  Color  deep  purple,  dulling  on 
exposure.  Fusible.  Found  at  Vulcan,  Col. 

Maucherite.  Ni3As2.  Tetragonal.  Habit,  square  tabular.  H.  =5.  G.  =  7'83.  Color 
reddish  silver-white  tarnishing  to  gray  copper-red.  Streak  blackish  gray.  Easily  fusible. 
From  Eisleben,  Thuringia.  The  furnace  product,  placodine,  is  identical  wfth  maucherite. 


B.  Monosulphides,  Monotellurides,*  etc.,  R2S,  RS,  ETC. 

1.    Galena  Group.  Isometric. 

Galena                                   PbS  Argentite  Ag2S 

Also,                 (Pb,Cu2)S,  (Cu2,Pb)S  Jalpaite  (Ag,Cu)2S 

Altaite                              PbTe  Hessite  Ag2Te 

Clausthalite                     PbSe  Aguilarite  Ag2Se 
Naumannite               (Ag2,Pb)Se 

The  following,  known  only  in  massive  form,  probably  also  belong  here: 
Berzelianite  Cu2Se  Zorgite  (Pb,Cu2,Ag2)Se? 

Lehrbachite  (Pb,Hg2)Se        t    Crookesite       (Cu,Tl,Ag)2Se 

Eucairite  Cu2Se.Ag2Se 


SULPHIDES,  SELENIDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES  363 


The  GALENA  GROUP  embraces  a  number  of  monosulphides,  etc.,  of  the 
related  metals,  silver,  copper,  lead,  and  mercury.  These  crystallize  in  the 
normal  class  of  the  isometric  system,  and  several  show  perfect  cubic  cleavage. 
These  characters  are  most  distinctly  exhibited  in  the  type  species,  galena. 

GALENA.    GALENITE.    Lead  glance. 

Isometric.  Commonly  in  cubes,  or  cubo-octahedrons,  less  often  octa- 
hedral. Also  in  skeleton  crystals,  reticulated,  tabular.  Twins:  tw.  pi. 
o(lll),  both  contact-  and  penetration-twins  (Figs.  401,  404,  p.  165),  sometimes 
repeated;  twin  crystals  often  tabular  ||  o.  Also  other  tw.  planes  giving  poly- 
synthetic  tw.  lamellae.  Massive  cleavable,  coarse  or  fine  granular,  to  impal- 
pable; occasionally  fibrous  or  plumose. 

641  642 


643 


644 


! 
! 
!  a 


p(221),  w 


Cleavage:  cubic,  highly  perfect;  less  often  octahedral.  Fracture  flat  sub- 
conchoidal  or  even.  H.  =  2-5-275.  G.  =  7*4-7  '6.  Luster  metallic.  Color 
and  streak  pure  lead-gray.  Opaque. 

Comp.  —  Lead  sulphide,  PbS  =  Sulphur  13'4,  lead  86'6  =  100.  Often 
contains  silver,  and  occasionally  selenium,  zinc,  cadmium,  antimony,  bismuth, 
copper,  as  sulphides;  besides,  also,  sometimes  nativ,e  silver  and  gold. 

Var.  —  1.  Ordinary,  (a)  Crystallized;  (6)  somewhat  fibrous  and  plumose;  (c)  cleav- 
able, granular  coarse  or  fine;  (d)  crypto  -crystalline.  The  variety  with  octahedral  cleavage 
is  rare;  in  it  the  usual  cubic  cleavage  is  obtained  readily  after  heating  to  200°  or  300°;  the 
peculiar  cleavage  may  be  connected  with  the  bismuth  usually  present.  One  variety  showing 
octahedral  cleavage  contained  a  small  amount  of  tellurium. 

2.  Argentiferous.     All  galena  is  more  or  less  argentiferous,  and  no  external  characters 
serve  to  distinguish  the  kinds  that  are  much  so  from  those  that  are  not.     The  silver  is 
detected  by  cupellation,  and  may  amount  from  a  few  thousandths  of  one  per  cent  to  one 
per  cent  or  more;  when  mined  for  silver  it  ranks  as  a  silver  ore. 

3.  Containing  arsenic,  or  antimony  ,  or  a  compound  of  these  metals,  as  impurity.     Here 
belong  bleischweif  f  rom  Claustal,  Harz'Mts.,  with  0'22  Sb,  and  steinmannite  from  PHbram, 
Bohemia,  with  both  arsenic  and  antimony. 

Pyr.  —  In  the  open  tube  gives  sulphurous  fumes.  B.B.  on  charcoal  fuses,  emits  sul- 
phurous fumes,  coats  the  coal  yellow  near  the  assay  (PbO)  and  white  with  a  bluish  border 
at  a  distance  (PbSO3,  chiefly),  and  yields  a  globule  of  metallic  lead.  Decomposed  by  strong 
nitric  acid  with  the  separation  of  some  sulphur  and  the  formation  of  lead  sulphate. 

Diff.  —  Distinguished,  except  in  very  fine  granular  varieties,  by  its  cubic  cleavage;  the 
color  and  the  high  specific  gravity  are  characteristic;  also  the  blowpipe  reactions. 

Micro.  —  In  polished  section  shows  white  color  with  smooth  surface  usually  showing 
triangular  pits.  With  HNO3  blackens;  with  FeCl3  becomes  bright,  iridescent. 

Artif.  —  Crystallized  galena  has  been  formed  in  numerous  ways.  In  nature  it  is  appar- 
ently commonly  formed  by  hydrochemical  reactions  perhaps  similar  to  the  following  labora- 
tory methods  :  galena  was  produced  by  allowing  a  mixture  of  lead  chloride,  sodium  bicar- 
bonate and  a  solution  of  hydrogen  sulphide  to  remain  in  a  sealed  tube  for  several  months. 


364  DESCRIPTIVE   MINERALOGY 

Pyrite  or  marcasite  heated  with  a  solution  of  lead  chloride  will  produce  galena;  a  solution  of 
lead  nitrate  when  heated  with  ammonium  sulphydrate  will  yield  galena.  Galena  is  fre- 
quently observed  in  furnace  slags. 

Obs.  —  One  of  the  most  widely  distributed  of  the  metallic  sulphides.  Occurs  in  beds 
and  veins,  both  in  crystalline  and  uncrystalline  rocks.  Very  commonly  found  together  with 
zinc  ores  in  connection  with  limestone  rocks.  It  is  often  associated  with  pyrite,  marcasite, 
sphalerite,  chalcopyrite,  arsenopyrite,  etc.,  in  a  gangue  of  quartz,  calcite,  barite  or  fluorite, 
etc.;  also  with  cerussite,  anglesite,  and  other  salts  of  lead,  which  are  frequent  results  of  its 
alteration.  It  is  also  common  with  gold,  and  in  veins  of  silver  ores. 

A  few  of  the  notable  localities  at  which  galena  has  been  found  are  as  follows: 

At  Freiberg  in  Saxony  in  veins  in  gneiss;  at  Claustal  and  Neudorf,  etc.,  in  the  Harz  Mts., 
and  at  Pribram  in  Bohemia,  it  forms  veins  in  clay  slate;  similarly  in  Styria;  in  limestone 
at  Bleiberg,  Carinthia;  in  Silesia,  Prussia;  at  Gonderbach  near  Laasphe,  Westphalia;  at 
Schemnitz,  Kapnik,  etc.,  Hungary;  Joachimstal,  Bohemia;  at  Poullaouen  and  Huelgoet, 
Brittany,  France;  in  Moresnet  district  in  Belgium;  in  province  of  Cagliari,  Sardinia;  in 
Spain,  in  granite  at  Linares,  also  in  Catalonia,  Grenada,  and  elsewhere;  in  veins  through  the 
graywacke  of  Leadhill,  Scotland,  and  the  contact  hornstones  of  Cornwall;  filling  cavities  in 
the  limestone  of  Derbyshire,  Cumberland,  and  the  northern  districts  of  England,  associated 
with  calcite,  dolomite,  fluorite,  barite,  witherite,  calamine  and  sphalerite;  in  many  places  in 
Australia,  Chile,  Bolivia,  Peru,  etc. 

Extensive  deposits  of  this  ore  in  the  United  States  exist  in  Missouri,  Illinois,  Iowa, 
and  Wisconsin.  The  ore  occurs  usually  filling  cavities  or  chambers»in  stratified  limestone, 
of  different  periods,  from  Silurian  to  Carboniferous.  It  is  associated  with  sphalerite,  smith- 
sonite,  calcite,  pyrite,  etc.  The  Missouri  mines  are  situated  in  three  districts  in  the  southern 
part  of  the  state,  (1)  Southeastern,  chiefly  in  St.  Francis,  Washington  and  Madison  counties, 
(2)  Central,  (3)  Southwestern  or  Joplin  district,  the  latter  producing  chiefly  zinc.  Other 
districts  in  the  upper  Mississippi  Valley  are  found  in  southwestern  Wis.,  eastern  Iowa  and 
northwestern  111.  Also  occurs  in  N.  Y.,  at  Rossie,  St.  Lawrence  Co.,  in  crystals  with  calcite 
and  chalcopyrite;  in  Pa.,  at  Phcenixyille  and  elsewhere.  In  Col.,  at  Leadville  and  Aspen, 
there  are  productive  mines  of  argentiferous  galena,  also  at  Georgetown,  the  San  Juan  dis- 
trict and  elsewhere.  Mined  for  silver  in  the  Cceur  d'Alene  region  in  Idaho;  at  the  Park 
City  and  Tintic  districts  in  Utah. 

The  name  galena  is  from  the  Latin  galena  (ya\i)t>rj),  a  name  'given  to  lead  ore  or  the 
dross  from  melted  lead. 

Use.  —  The  most  important  ore  of  lead  and  frequently  a  valuable  ore  of  silver. 

CUPROPLUMBITE.  A  massive  mineral,  from  Chile,  varying  in  characters  from  galena  to 
those  of  chalcocite  and  covellite;  composition,  Cu2S.2PbS(?).  Material  classed  here  from 
Butte,  Mon.,  gave  formula,  5Cu2S.PbS.  Alisonite  is  massive,  deep  indigo-blue  quickly 
tarnishing;  corresponds  to  3(?u2S.PbS.  From  Mina  Grande,  Chile.  Whether  these  and 
similar  minerals  represent  definite  homogeneous  compounds,  or  only  ill-defined  alteration- 
products,  is  uncertain,  and  if  so  it  is  not  clear  whether  they  should  be  classed  with  isometric 
galena  or  with  orthorhombic  chalcocite. 

Altaite.  Lead  telluride,  PbTe.  Rarely  in  cubic  or  octahedral  crystals,  usually  massive 
with  cubic  cleavage.  G.  =  8 '16.  Color  tin-white,  with  yellowish  tinge  tarnishing  to 
bronze-yellow.  From  the  Altai  Mts.,  with  hessite;  Coquimbo,  Chile;  Cal.,  Col.,  British 
Columbia.  ( 

Clausthalite.  Lead  selenide,  PbSe.  Commonly  in  fine  granular  masses  resembling 
galena.  Cleavage:  cubic.  G.  =  7 '6-8 -8.  Color  lead-gray,  somewhat  bluish.  From 
Claustal,  Harz  Mts.,  Germany;  Cacheuta  mine,  Mendoza  River,  Argentina.  Tilkerodite 
is  a  cobaltiferous  variety. 

Naumannite.  —  Silver-lead  telluride  (Ag2,Pb)Se.  In  cubic  crystals;  also  massive, 
granular,  in  thin  plates.  Cleavage:  cubic.  G.  =  8'0.  Color  and  streak  iron-black. 
From  Tilkerode  in  the  Harz  Mts  ,  Germany. 

ARGENTITE.     Silver  Glance. 

Isometric.  Crystals  often  octahedral,  also  cubic;  often  distorted,  fre- 
quently grouped  in  reticulated  or  arborescent  forms;  also  filiform.  Massive; 
embedded;  as  a  coating. 

Cleavage:  a(100),  d(110)  in  traces.  Fracture  small  subconchoidal.  Per- 
fectly sectile.  H.  =  2-2-5.  G.  =  7'20-7'36.  Luster  metallic.  Color  and 
streak  blackish  lead-gray;  streak  shining.  Opaque. 

Comp.  —  Silver  sulphide,  AgaS  =  Sulphur  12-9,  silver  871  =  100. 


SULPHIDES,  SELENIDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES   365 

Pyr.,  etc.  In  the  open  tube  gives  off  sulphurous  fumes.  B.B.  on  charcoal  fuses  with 
intumescence  in  O.F.,  emitting  sulphurous  fumes,  and  yielding  a  globule  of  silver. 

Diff.  —  Distinguished  from  other  sulphides  by  being  readily  cut  with  a  knife;  also  by 
yielding  metallic  silver  on  charcoal. 

Micro.  —  In  polished  section  shows  grayish  white  color  with  a  smooth  surface  which  is 
easily  scratched.  Turns  brown  with  HNO3,KCN  and  FeCl3;  with  cone.  HC1  tarnished 
iridescent  by  fumes  and  blackened  by  acid. 

Artif.  —  Argentite  is  very  easily  prepared  artificially  and  in  numerous  ways.  Sulphur, 
sulphur  dioxide  or  hydrogen  sulphide  will  act  upon  metallic  silver  or  any  of  its  common 
compounds,  either  in  solution  or  as  solids,  to.  produce  silver  sulphide. 

Obs.  —  Found  at  Freiberg,  etc.,  Saxony;  Andreasberg,  Harz  Mts.,  Germany;  Schemnitz, 
Hungary:  Joachimstal,  Bohemia;  Kongsberg,  Norway;  Sardinia.  In  South  America  at  sil- 
ver mines  in  Chile,  Peru  and  Bolivia.  In  Mexico  in  the  states  of  Chihuahua,  Guanajuato, 
etc.  Important  ore  at  Comstock  Lode,  Tonapah,  etc.,  Nev.;  Aspen,  Leadville,  etc.  Col. 
Found  at  Port  Arthur  on  north  shore  of  Lake  Superior. 

Use.  —  An  important  ore  of  silver. 

JALPAITE  is  a  cupriferous  argentite  from  Jalpa,  Mexico. 

Hessite.  —  Silver  telluride,  Ag2Te.  Isometric.  Usually  massive,  compact  or  fine- 
grained. Cleavage  indistinct.  Somewhat  sectile.  H.  =  2*5-3.  G.  =  8 '31-8 '45.  Color 
between  lead-gray  and  steel-gray.  From  the  Altai  Mts.;  at  Nagyag,  Botes  and  Rezbdnya 
in  Transylvania;  Chile  near  Arqueros,  Coquimbo.  In  Mexico  at  San  Sebastian,  Jalisco. 
In  the  United  States,  Calaveras  Co.,  Cal.;  Boulder  Co.,  Col.;  Utah.  This  species  also 
often  contains  gold  and  thus  graduates  toward  petzite. 

Petzite.  —  (Ag,Au)2Te  with  Ag  :  Au  =  3  :  1.  Massive;  granular  to  compact.  Slightly 
sectile  to  brittle  H.  =  2*5-3.  G.  =  8 '7-9 '02.  Color  steel-gray  to  iron-black ;  tarnishing. 
From  Nagyag,  Transylvania;  Kalgoorlie,  West  Australia;  Yale  District,  British  Columbia; 
Col.;  Poverty  Hill,  Tuolumne  Co.,  and  elsewhere,  Cal. 

Aguilarite.  Silver  selenide,  Ag2S  and  Ag2(S,Se).  In  skeleton  dodecahedral  crystals. 
Sectile.  G.  =  7'586.  Color  iron-black.  From  Guanajuato,  Mexico. 

Berzelianite.  Copper  selenide,  Cu2Se.  In  thin  dendritic  crusts  and  disseminated. 
G.  =  671.  Color  silver-white,  tarnishing.  From  Skrikerum,  Sweden;  Lehrbach,  in  the 
Harz  Mts.,  Germany. 

Lehrbachite.  Selenide  of  lead  amd  mercury,  PbSe  with  HgSe.  Massive,  granular. 
G.  =  7'8.  Color  lead-gray  to  iron-black.  From  Lehrbach,  in  the  Harz  Mts.,  Germany. 

Eucairite.  Cu2Se.Ag2Se.  Massive,  granular.  G.  =  7-50.  Color  between  silver- 
white  and  lead-gray.  From  the  Skirkerum  copper  mine,  Sweden;  also  Chile. 

Zorgite.  —  Selenide  of  lead  and  copper  in  varying  amounts.  Perhaps  a  mixture.  Mas- 
sive, granular  G.  =  7-7 '5.  Color  dark  or  light  lead-gray.  From  the  Harz  Mts.,  Germany; 
Cacheuta,  Argentina. 

Crookesite.  Selenide  of  copper  and  thallium,  also  silver  (1-5  p.  c.),  (Cu,Tl,Ag)2Se. 
Massive,  compact.  G.  =  6*9.  Luster  metallic.  Color  lead-gray.  From  the  mine  of 
Skirkerum,  Sweden. 

Umangite.  CuSe.Cu2Se.  Massive,  fine-granular  to  compact.  H.  =3.  G.  =  5-620. 
Color  dark  cherry-red.  From  La  Rioja,  Argentina. 

2.  Chalcocite  Group 

a  :b  :  c 

Chalcocite                          Cu2S                     0'5822  :  1  0'9701 

Stromeyerite  Ag2S.Cu2S                0'5822  :  1  0.9668 

Sternbergite  Ag2S.Fe4S5                0-5832  :  1  0.8391 

Frieseite                                                       0-5970  :  1  0-7352 

Acanthite                            Ag2S                     0-6886  :  1  0-9944 

The  species  of  the  CHALCOCITE  GROUP  crystallize  in  the  orthorhombic 
system  with  a  prismatic  angle  approximating  to  60°;  they  are  hence  pseudo- 
hexagonal  in  form,  especially  when  twinned.  The  group  is  parallel  to  the 
Galena  Group,  since  Cu2S  appears  in  isometric  form  in  cuproplumbite  and  Ag2S 
also  in  argentite.  Some  authors  include  dyscrasite  here  (see  p.  361). 


366 


DESCRIPTIVE   MINERALOGY 


CHALC0CITE.    Copper  Glance.    Redruthite. 
Orthorhombic.     Axes  a  :  b  :  c  =  0'5822  :  1 
110    A  110  =    60°  25'. 


dd'f  (021)  A  021  =  125°  28'. 
645 


0-9701.      • 

p,  001  A  111  =  62°  35*'. 


pp"r,  111  A  111  =53°- 


646 


647 


Crystals  pseudo-hexagonal  in  angle,  also  by  twinning  (tw.  pi.  w(110)). 
Often  massive,  structure  granular  to  compact  and  impalpable. 

Cleavage:  m(110)  indistinct;  etching  of  orientated  crystals  develops  cleav- 
ages parallel  to  the  three  pinacoids.  Fracture  conchoidal.  Rather  sectile. 
H.  =  2-5-3.  G.  =  5-5-5-8.  Luster  metallic.  Color  and  streak  blackish 
lead-gray,  often  tarnished  blue  or  green,  dull.  Opaque. 

Comp.  —  Cuprous  sulphide,  Cu2S  =  Sulphur  20*2,  copper  79'8  =  100. 
Sometimes  iron  in  small  amount  is  present,  also,  silver. 

Pyr.,  etc.  —  In  the  open  tube  gives  sulphurous  fumes.  B.B.  on  charcoal  melts  to  a 
globule,  which  boils  with  spirting;  the  fine  powder  roasted  at  a  low  temperature  on  charcoal, 
then  heated  in  R.F.,  yields  a  globule  of  metallic  copper.  Soluble  in'nitric  acid. 

Diff.  —  Resembles  argentite  but  much  more  brittle;  bornite  has  a  different  color  on 
the  fresh  fracture  and  becomes  magnetic  B.B. 

Micro.  —  In  polished  section  shows  grayish  or  bluish  white  color  with  smooth  surface. 
With  HNO3  effervesces  and  etches,  turning  more  or  less  blue,  and  develops  cleavage  direc- 
tions; wibh  KCN  blackens  and  etches. 

Artif .  —  Chalcocite  has  been  prepared  artificially  by  heating  the  vapors  of  cuprous 
chloride  and  hydrogen  sulphide  or  by  the  treatment  of  cupric  oxide  with  hydrogen  sulphide; 
also  by  the  heating  of  cupric  solutions  with  ammonium  sulphocyanate  in  a  sealed  tube. 

Obs.  —  Chalcocite  is  an  important  ore  of  copper.  It  is  usually  secondary  in  its  origin, 
being  found  in  the  upper,  enriched  portions  of  copper  veins.  It  is  commonly  associated  with 
chalcopyrite,  bornite,  pyrite,  cuprite,  malachite,  azurite,  etc. 

Cornwall  affords  splendid  crystals,  especially  the  districts  of  Saint  Just,  Camborne,  and 
Redruth  (redruthite).  Occurs  at  Joachimstal,  Bohemia;  Tellemarken,  Norway;  compact 
and  massive  varieties  in  Siberia;  Saxony;  Mte.  Catini  mines  in  Tuscany;  Mexico;  South 
America. 

In  the  United  States,  Bristol,  Conn.,  has  afforded  large  and  brilliant  crystals ;  also  found 
at  Simsbury  and  Cheshire;  at  Schuyler's  mines,  *N.  J.;  in  Nev.,  in  Washoe,  Humboldt, 
Churchill  and  Nye  counties;  at  Clifton,  Ariz.;  in  Mon.,  massive  at  Butte  in  great  amounts. 
Notable  deposit  at  Kennecott,  Copper  River  District,  Alaska.  Found  in  Canada,  with 
chalcopyrite  and  bornite  at  the  Acton  mines  and  elsewhere  in  the  province  of  Quebec. 

Use.  —  An  important  ore  of  copper. 

Stromeyerite.  (Ag,Cu)?S,  or  Ag2S.Cu2S.  Rarely  in  orthorhombic  crystals,  often 
twinned.  Commonly  massive,  compact.  H.  =  2 '5-3.  G.  =  6'15-6'3.  Luster  metallic. 
Color  and  streak  dark  steel-gray.  From  the  Zmeinogorsk  mine,  Siberia;  Silesia;  also  Chile, 
Zacatecas,  Mexico;  Cobalt,  Ontario;  the  Heintzelman  mine  in  Ariz.;  Col. 

Chalmersite.  Cu2S.Fe4S5.  Orthorhombic.  Axial  ratio  near  that  of  chalcocite.  In 
thin  elongated  prisms  vertically  striated.  Twins  cdmmon  with  ra(110)  as  tw.  pi.  resem- 
bling chalcocite.  H.  =  3'5.  G.  =  47.  Color  brass-  to  bronze-yellow.  Strongly  mag- 
netic. From  the  Morro  Velho  gold  mine,  Minas  Geraes,  Brazil. 


SULPHIDES,  SELENIDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES   367 


STERNBERGITE 

Orthorhombic.  Crystals  tabular  ||  c(001).  Commonly  in  fan-like  aggre- 
gations; twins,  tw.  pi.  ra(110).  Cleavage  :  c(001),  highly  perfect.  Thin 
laminae  flexible,  like  tin-foil.  H.  =  1-1*5.  G.  =  4-215.  Luster  metallic. 
Color  pinchbeck-brown.  Streak  black.  Opaque. 

Comp.  —  AgFe2S3  or  Ag2S.Fe4S5  =  Sulphur  30.4,  silver  34.2,  iron  35.4 
=  100. 

Obs.  —  Occurs  with  pyrargyrite  and  stephanite  at  Joachimstal,  Bohemia,  and  Johann- 
georgenstadt,  Saxony. 

FRIESEITE.  Near  sternbergite.  In  thick  tabular  crystals.  H.  =  2 '5;  G.  =  4 '22. 
.Color  dark  gray.  Composition  Ag2Fe5S8.  Occurs  with  marcasite  at  Joachimstal,  Bohemia. 

Acanthite.  Silver  sulphide,  Ag2S,  like  argentite.  In  slender  prismatic  crystals  (or- 
thorhornbic) .  Sectile.  G.  =  7'2-7'3.  Color  iron-black.  Occurs  at  Joachimstal,  Bohemia; 
also  at  Freiberg  and  Schneeberg,  Saxony;  at  Rico,  Col. 

It  has  been  suggested  that  acanthite  may  be  only  argentite  in  distorted  isometric  crys- 
tals. 


Sphalerite  Group. 

Sphalerite  ZnS 

Metacinnabarite         HgS 

Guadalcazarite        (Hg,Zn)S 
Tiemannite  HgSe 


RS.     Isometric-tetrahedral 

Onofrite  Hg(S,Se) 

Alabandite          MnS 
Cotoradoite        HgTe        Massive 


The  SPHALERITE  GROUP  embraces  a  number  of  sulphides,  selenides,  etc., 
of  zinc,  mercury,  and  manganese.  These  are  isometric-tetrahedral  in  crystal- 
lization. * 

SPHALERITE,  ZINC  BLENDE  or  BLENDE.    Black-Jack,  Mock-Lead,  False  Galena. 
Isometric-tetrahedral.     Often  in  tetrahedrons.     Twins  common:   tw.  pi. 

648  649  650 


m  =  (311) 

o(lll);  twinning  often  repeated,  sometimes  as  polysynthetic  lamellae.  Com- 
monly massive  cleavable,  coarse  to  fine  granular  and  compact;  also  foliated, 
sometimes  fibrous  and  radiated  or  plumose;  also  botryoidal  and  other  imita- 
tive shapes.  Cryptocrystalline  to  amorphous,  the  latter  sometimes  as  a 
powder. 

Cleavage:  dodecahedral,  highly  perfect.  Fracture  conchoidal.  Brittle. 
H.  =  3-5-4.  G.  =  3-9-4-1;  4-063  white,  N.  J.  Luster  resinous  to  adaman- 
tine.. Color  commonly  yellow,  brown,  black;  also  red,  green  to  white,  and 
when  pure  nearly  colorless.  Streak  brownish  to  light  yellow  and  white. 
Transparent  to  translucent.  Refractive  index  high:  n  =  2-3692. 

Comp.  —  Zinc  sulphide,  ZnS  =  Sulphur  33,  zinc  67  =  100.  Often  con- 
taining iron  and  manganese,  and  sometimes  cadmium,  mercury  and  rarely  lead 


368  DESCRIPTIVE    MINERALOGY 

and  tin.     Also  sometimes  contains  traces  of  indium,  gallium  and  thallium; 
may  be  argentiferous  and  auriferous. 

Var.  —  1.  Ordinary.  Containing  little  or  no  iron;  from  colorless  white  to  yellowish 
brown,  sometimes  green;  G.  =  4-0-4 '1.  The  red  or  reddish  brown  transparent  crystallizec 
kinds  are  sometimes  called  ruby  blende  or  ruby  zinc.  The  massive  cleavable  forms  are  the 
most  common,  vary  ing  from  coarse  to  fine  granular;  also  cryptocrystalline.  Schalenblende 
is  a  closely  compact  variety,  of  a  pale  liver-brown  color,  in  concentric  layers  with  reniform 
surface;  galena  and  marcasite  are  often  interstratified.  The  fibrous  forms  are  chiefly 
wurtzite.  A  soft  white  amorphous  form  of  zinc  sulphide  occurs  in  Cherokee  Co.,  Kan. 

2.  Ferriferous:  Marmatite.    Containing  10  p.  c.  or  more  of  iron;  dark-brown  to  black; 
G.  =  S'9-4'05.    The  proportion  of  FeS  to  ZnS  varies  from  1  :  5  to  1  :  2,  and  the  last  ratio  is 
that  of  the  christophitc  of  Breithaupt,  a  brilliant  black  sphalerite  from  St.  Christophe  mine, 
at  Breitenbrunn,  having  G.  =  3 '91-3 '923. 

3.  Cadmiferous:    Pribramite,  Przibramite.     The  amount  of  cadmium  present  in  any 
sphalerite  thus  far  analyzed  is  less  than  5  per  cent. 

Pyr.,  etc.  —  Difficultly  fusible.  In  the  open  tube  sulphurous  fumes,  and  generally 
changes  color.  B.B.  on  charcoal,  in  R.F.,  gives  a  coating  of  zinc  oxide,  which  is  yellow  while 
hot  and  white  after  cooling.  If  cadmium  is  present  a  reddish  brown  coating  of  cadmium 
oxide  will  form  first.  With  cobalt  solution  the  zinc  oxide  coating  gives  a  green  color  when 
heated  in  O.F.  Most  varieties,  after  roasting,  give  with  borax  a  reaction  for  iron.  Dissolves 
in  hydrochloric  acid  with  evolution  of  hydrogen  sulphide. 

Diff.  —  Varies  widely  in  color  and  appearance,  but  distinguished  by  the  resinous  luster 
in  all  but  deep  black  varieties;  usually  exhibits  distinct  cleavage;  nearly  infusible  B.B.; 
yields  a  zinc  oxide  coating  on  charcoal. 

Micro.  —  In  polished  section  shows  a  grav'color  with  smooth  surface.  Transparent, 
yellow  to  brown  with  oblique  illumination. /HiVith  HNOs  becomes  slowly  brown,  often 
showing  crystal  structure;  with  aqua  regia  effervesces  and  blackens. 

Arttf .  —  Sphalerite  has  been  artificially  formed  by  heating  zinc  solutions  in  hydrogen 
sulphide  inclosed  in  a  sealed  tube;  also  by  passing  hydrogen  sulphide  over  heated  zinc 
chloride. 

Obs.  —  Sphalerite  is  the  most  important  ore  of  zinc.  It  occurs  in  both  crystalline  and 
sedimentary  rocks,  being  especially  common  in  the  limestones,  where  it  often  occurs  as 
beds  of  considerable  size.  It  is  frequently  associated  with  galena,  also  with  chalcopyrite, 
pyrite,  barite.  fluorite,  siderite,  etc.  Commonly  found  with  silver  ores.  Of  the  two  forms 
of  zinc  sulphide,  sphalerite  is  the  form  which  crystallizes  below  1020°  while  wurtzite  is 
deposited  at  higher  temperatures.  Zinc  sulphide  is  deposited  from  alkaline  solutions  as 
sphalerite;  from  acid  solutions  both  forms  are  deposited,  the  amount  of  sphalerite  increas- 
ing with  the  temperature  while  that  of  wurtzite  increases  with  the  acidity  of  the  solution. 

Some  of  the  chief  localities  for  crystallized  sphalerite  are:  Alston  Moor  in  Cumberland 
and  at  St.  Agnes  and  elsewhere  in  Cornwall,  England;  Andreasberg  and  Neudorf  in  the 
Harz  Mts.,  Freiberg,  and  other  localities  in  Saxony;  Pfibram,  and  Schlackenwald  in  Bohe- 
mia; Kapnik,  Schemnitz  and  Felsobanya,  in  Hungary;  Nagyag  and  Rodna  in  Transyl- 
vania; the  Binnental  in  Switzerland,  isolated  crystals  of  great  beauty,  yellow  to  brown,  in 
cavities  of  dolomite.  A  beautiful  transparent  variety .  yielding  large  cleavage  masses  is 
brought  from  Picos  de  Europa,  Santander,  Spain,  where  it  occurs  in  a  brown  limestone. 
A  similar  variety  with  golden  brown  to  green  colors  from  Chivera  mine,  Cannanea,  Mexico. 
Large  crystals  from  Ani  copper  mines,  Ugo,  Japan.  Fibrous  varieties  (see  wurtzite)  are 
obtained  at  Pribram;  Geroldseck  in  Baden;  Raibl,  Carinthia;  also  in  Cornwall.  The  origi- 
nal marmatite  is  from  Marmato  near  Popayan,  Italy. 

The  important  zinc  ore  districts  of  the  United  States  in  which  sphalerite  is  the  chief 
zinc  mineral  are  found  in  Missouri,  Colorado,  Montana,  Wisconsin,  Idaho  and  Kansas, 
borne  localities  noteworthy  for  the  specimens  they  have  produced  are  as  follows:  In  Conn., 
?in,  i  y'j  N*  J-'  a  white  variety  (cleiophane)  at  Franklin  Furance.  In  Pa.,  at  the 
Wheatley  and  Perkiomen  lead  mines,  in  crystals;  near  Friedensville,  Lehigh  Co.,  a  grayish 
waxy  variety.  In  111.,  near  Rosiclare,  with  galena  and  calcite;  at  Marsden'  diggings,  near 
Galena,  m  stalacites,  with  crystallized  marcasite,  and  galena;  at  Warsaw.  In  Wis.,  at 
Mineral  Point,  in  fine  crystals.  In  Ohio,  at  Tiffin.  In  Mo.,  in  beautiful  crystallizations  with 
galena,  marcasite  and  calcite  at  Joplin  and  other  points  in  the  southwestern  part  of  the  state; 
deposits  here  occur  in  limestone  and  are  of  great  extent  and  value;  also  in  adjoining 
parts  of  Kan.  In  Col.,  at  many  places. 

Named  blende  because,  while  often  resembling  galena,  it  yielded  no  lead,  the  word  in 
German  meaning  blind  or  deceiving.  Sphalerite  is  from  cr0aXepds,  treacherous. 

use.  —  ine  most  important  ore  of  zinc. 


SULPHIDES,  SELENIDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES   369 

Metacinnabarite.  Mercuric  sulphide,  HgS.  In  composition  like  cinnabar,  but  occurs 
in  black  tetrahedral  crystals;  also  massive.  G.  =  77.  In  Cal.,  from  the  Reddington 
mine,  Lake  county,  with  cinnabar,  quartz  and  marcasite;  and  from  San  Joaquin,  Orange 
Co.  Found  also  at  Idria  in  Austria. 

Guadalcazarite.  Near  metacinnabarite,  but  contains  zinc  (up  to  4  p.  c.).  Guadal- 
cazar,  Mexico.  Probably  a  mixture. 

Tiemannite.  Mercuric  selenide,  HgSe.  Isometric-tetrahedral.  Commonly  massive' 
compact.  G.  =  8'19  Utah;  8'30-8'47  Claustal.  Luster  metallic.  Color  steel-gray  to 
blackish  lead-gray.  Streak  nearly  black.  Occurs  at  Claustal  in  the  Harz  Mts.;  Cal.,  in 
the  vicinity  of  Clear  lake;  MarysVale,  Piute  Co.,  Utah. 

Onofrite.     Hg(S,Se)  with  Se  =  4'5  to  6'5  p.  c.     San  Onofre,  Mexico;  Marysvale,  Utah. 

Coloradoite.  Mercuric  telluride,  HgTe.  Massive.  Conchoidal  fracture.  H.  =  2'5. 
G.  =  8'07  (Kalgoorlie).  Color  iron-black.  Originally  found  sparingly  in  Colorado. 
Rather  abundant  at  the  Kalgoorlie  district,  West  Australia.  Material  called  kalgoorlite 
is  a  mixture  of  coloradoite  and  petzite. 

*  Alabandite.  Manganese  sulphide,  MnS.  Isometric-tetrahedral;  usually  granular 
massive.  Cleavage:  cubic,  perfect.  G.  =  3 '95-4 '04.  Luster  submetallic.  Color  iron- 
black.  Streak  green.  Occurs  at  Nagyag,  Transylvania;  Kapnik,  Hungary;  Mexico; 
Peru;  crystallized  and  massive  on  Snake  River,  Summit  county,  Col.;  Tombstone,  Ariz. 

Oldhamite.  Calcium  sulphide,  CaS.  In  pale  brown  spherules  with  cubic  cleavage  in 
the  Busti  meteorite.  Also  noted  in  Allegan  meteorite. 

PENTLANDITE. 

Isometric.  Massive,  granular.  Cleavage:  octahedral.  Fracture  uneven. 
Brittle.  H.  =  3*5^.  G.  =  5-0.  Luster  metallic.  Color  light  bronze- 
yellow.  Streak  light  bronze-brown.  Opaque.  Not  magnetic. 

Comp.  —  A  sulphide  of  iron  and  nickel,  (Fe,Ni)S.  In  part,  2FeS.NiS 
=  Sulphur  36-0,  iron  42-0,  nickel  22-0  =  100. 

Obs.  —  Occurs  with  chalcopyrite  near  Lillehammer,  Norway.  Also  from  Sudbury, 
Ontario,  where  it  is  intimately  associated  with  nickeliferous  pyrrhotite.  It  can  be  dis- 
tinguished from  the  latter  by  its  cleavage. 

4.    Cinnabar-Wurtzite-Millerite  Group.     Rhombohedral   or    Hexagonal 

c 
Cinnabar  HgS       Rhombohedral-Trapezohedral        1*1453 

Covellite  CuS  1-1466 

c  c 

Greenockite       CdS  Hexagonal-Hemimorphic  0*8109  or  0*9364 

Wurtzite  ZnS  "  0*8175        0*9440 


Millerite  NiS  Rhombohedral  0*9883 

Niccolite  NiAs  "  0*8194      0*9462 

Breithauptite      NiSb  0'8586      0*9915 

Arite  Ni(Sb,As) 

Pyrrhotite          FenSw,  etc.  Hexagonal  0*8701      1*0047 

Troilite  FeS 

This  fourth  group  among  the  monosulphides  includes  several  subdivisions, 
as  shown  in  the  scheme  above,  and  the  relations  of  the  species  are  not  in  all 
cases  perfectly  clear.  It  is  to  be  noted  that  the  sulphides  of  mercury  and  zinc, 
already  represented  in  the  sphalerite  group,  appear  here  again. 

If,  as  suggested  by  Groth,  the  prominent  pyramids  of  wurtzite,  greenockite,  etc.,  be 
made  pyramids  of  the  second  series  (e.g.,  x  =  1122,  instead  of  1011),  then  the  values  of  c 
in  the  second  column  are  obtained,  which  correspond  to  millerite.  The  form  of  several  of 
these  species,  however,  is  only  imperfectly  known.  A  rhombohedral  form  for  greenockite 
has  been  suggested. 


370  DESCRIPTIVE   MINERALOGY 

CINNABAR. 

Rhombohedral-trapezohedral.     Axis  c  =  11453. 
rr'  1011  A  1011  =  87°  23'. 
u',  4045  A  4045  =  78°  0£'. 
cr,   0001  A  1C11  =  52°  54'. 

Crystals  usually  rhombohedral  or  thick  tabular  in  habit,  rarely  showing 
trapezohedral  faces;  in  rhombohedral  penetration  twins;  also  acicular  pris- 
matic. In  crystalline  incrustations,  granular,  massive;  sometimes  as  an 
earthy  coating. 

Cleavage:  ra(1010)  perfect.  Fracture  subconchoidal,  uneven.  Some- 
what sectile.  H.  =  2-2;5.  G..=  8-0-8-2.  Luster  adamantine,  inclining  to 
metallic  when  dark-colored,  and  to  dull  in  friable  varieties.  Color  cochineal- 
red,  often  inclining  to  brownish  red  and  lead-gray.  Streak  scarlet.  Trans- 
parent to  opaque.  Optically  +  .  Indices:  o>r  =  2 -82,  er  =  3 '14.  See  Art. 
394. 

Var.  —  1.  Ordinary:  either  (a)  crystallized;  (b)  massive,  granular  embedded  or  com- 
pact; bright  red  to  reddish  brown  in  color;  (c)  earthy  and  bright  red.  2.  Hepatic.  Of  a 
fiver-brown  color,  with  sometimes  a  brownish  streak,  occasionally  slaty  in  structure,  though 
commonly  granular  or  compact. 

Comp. —  Mercuric  sulphide,  HgS  =  Sulphur  13'8,  mercury  86'2  =  100. 
Usually  impure  from  the  admixture  of  clay,  iron  oxide,  bitumen. 

Pyr.  —  In  the  closed  tube  alone  a  black  sublimate  of  mercuric  sulphide,  but  with  sodium 
carbonate  one  of  metallic  mercury.  Carefully  heated  in  the  open  tube  gives  sulphurous 
fumes  and  metallic  mercury,  which  condenses  in  minute  globules  on  the  cold  walls  of  the 
tube.  B.B.  on  charcoal  wholly  volatile,  but  only  when  quite  free  from  gangue. 

Diff.  —  Characterized  by  its  color  and  vermilion  streak,  high  specific  gravity  (reduced, 
however,  by  the  gangue  usually  present),  softness;  also  by  the  blowpipe  characters  (e.g.,  in 
the  closed  tube) .  Resembles  some  varieties  of  hematite  and  cuprite. 

Artif.  —  Cinnabar  has  been  produced  artificially  by  several  methods  which  are,  how- 
ever, in  general  modifications  of  the  two  following  types:  (1)  When  the  black  mercury  sul- 
phide formed  byjthe  direct  union  of  mercury  and  sulphur  is  sublimed,  cinnabar  is  the  prod- 
uct; (2)  the  black  sulphide  when  treated  with  solutions  of  alkaline  sulphides  is  converted 
into  cinnabar.  In  general  cinnabar  is  formed  under  alkaline  conditions  and  metacinnabarite 
under  acidic  conditions. 

Obs.  —  Cinnabar  is  the  only  common  mineral  of  mercury  and  with  rare  exceptions 
constitutes  the  ore  of  the  metal.  It  occurs  in  veins  filling  fissures  and  cavities  in  rocks  which 
are  commonly  sedimentary  in  character,  being  often  slates,  shales,  sandstones  or  limestones. 
While  infrequently  occurring  in  igneous  rocks  such  rocks  are  commonly  near  by  and  are 
thought  to  have  been  the  source  of  the  metal.  Cinnabar  is  deposited  from  hot  alkaline 
solutions  or  as  the  result  of  solfataric  action.  Pyrite  and  marcasite,  sulphides  of  copper, 
stibnite,  realgar,  gold,  etc.,  are  associated  minerals;  calcite,  quartz  or  opal,  also  barite, 
fluorite,  are  gangue  minerals;  a  bituminous  mineral  is  common. 

The  most  important  European  deposits  are  at  Almaden  in  Spain,  and  at  Idria  in  Car- 
niola,  where  it  is  usually  massive;  also  at  Bakmut.in  southern  Russia.  Crystallized  at 
Moschellandsberg  and  Wolf  stein  in  the  Palatinate  and  at  the  mines  of  Mt.  Avala,  near 
Belgrade,  Servia;  at  Ripa  in  Tuscany;  at  Als6sajo,  Hungary;  in  the  Ural  Mts.,  the  Ner- 
chinsk region  in  Transbaikalia;  in  large  twinned  rhombohedrons  from  Province  of  Kwei- 
chow,  China;  Japan;  Mexico;  Huancavelica,  Peru;  Chile. 

In  the  United  States  forms  extensive  mines  in  Cal.,  the  most  important  at  New  Almaden 
and  the  vicinity,  in  Santa  Clara  Co.;  also  at  Altoona,  Trinity  Co.;  it  is  now  forming  by 
solfataric  action  at  Sulphur  Bank,  Cal.,  and  Steamboat  Springs,  Nev.;  has  been  found  in 
southern  Utah;  important  deposits  occur  in  Brewster  Co.,  Texas;  also  mined  in  Nev.  and 
Ariz. 

The  name  cinnabar  is  supposed  to  come  from  India,  where  it  is  applied  to  the  red  resin, 
dragon's  blood.  The  native  cinnabar  of  Theophrastus  is  true  cinnabar;  he  speaks  of  its 
affording  quicksilver.  The  Latin  name  of  cinnabar,  minium,  is  now  given  to  red  lead,  a 
substance  which  was  early  used  for  adulterating  cinnabar,  and  so  got  at  last  the  name. 

Only  comparatively  few  localities  have  furnished  the  mineral  in  quantity. 

Use.  —  The  most  important  ore  of  mercury. 


SULPHIDES,  SELENIDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES  371 

COVELLITE. 

Monoclinic  ?  Pseudohexagonal  through  twinning.  Crystals  usually  thin 
hexagonal  plates.  Often  massive. 

CleaVage:  basal,  perfect.  H.  =  T5-2.  G.  =  4'6.  Luster  submetallic  to 
resinous.  Color  indigo-blue  or  darker.  Often  shows  fine  purple  color  when 
moistened  with  water.  Streak  lead-gray  to  black.  Opaque. 

Comp.  —  Cupric  sulphide,  CuS  =  Sulphur  33'6,  copper  66'4  =  100. 

Pyr.,  etc.  —  Fusible  at  2' 5  yielding  sulphurous  fumes.  After  roasting  and  moistening 
with  hydrochloric  acid  gives  azure-blue  flame.  Much  sulphur  in  C.T. 

Macro.  —  In  polished  section  shows  blue  color  with  smooth  surface.  With  KCN  be- 
comes instantly  deep  violet  which  rubs  off,  leaving  a  yellow  coating  and  rough  surface. 

Artif.  —  Covellite  has  been  prepared  artificially  by  heating  in  sealed  tubes  a  cupric 
solution  with  ammonium  sulphocyanate  and  by  heating  sphalerite  in  a  solution  of  copper 
sulphate. 

Obs.  —  Covellite  is  a  mineral  of  secondary  origin  found  in  the  enriched  portions  of  copper 
sulphide  veins,  associated  with  chalcocite,  bornite,  etc.  Found  in  small  amounts  in  many 
places.  Noteworthy  localities  are  as  follows:  various  places  in  Germany;  in  exceptional 
crystals  at  Bor  in  Timoker  Kreis,  Servia;  on  the  lavas  of  Vesuvius;  in  Chile;  Province  of 
Rikuchu,  Japan.  In  the  United  States  at  the  Butte  district,  Mon.;  Summitville,  Col.; 
La  Sal  district,  Utah;  Kennecott,  Alaska,  etc. 


GREENOCKITE. 

Hexagonal-hemimorphic.  Rarely  in  hemimorphic  crystals;  also  as  a 
coating. 

Cleavage:  a(1120)  distinct,  c(0001)  imperfect.  Fracture  conchoidal. 
Brittle.  H.  =  3-3'5.  G.  =  4'9-5*0.  Luster  adamantine  to  resinous.  Color 
honey-,  citron-,  or  orange-yellow.  Streak  between 
orange-yellow  and  brick-red.  Nearly  transparent. 
Optically  +  .  co  =  2-506,  e  =  2*529. 

Comp.  —  Cadmium  sulphide,  CdS  =  Sulphur  22'3, 
cadmium  77-7  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  assumes  a  carmine-red  color 
white  hot,  fading  to  the  original  yellow  on  cooling.  In  the 
open*  tube  gives  sulphurous  fumes.  B.B.  on  charcoal,  either 
alone  or  with  soda,  gives  in  R.F.  a  reddish  brown  coating. 
Soluble  in  hydrochloric  acid,  affording  hydrogen  sulphide. 

Artif.  —  Greenockite  has  been  prepared  artificially  in  sev- 
eral ways.  Precipitated  cadmium  sulphide  when  fused  with 
potassium  carbonate  and  sulphur  produced  greenockite  crystals;  also  when  cadmium 
sulphate,  calcium  fluoride  and  barium  sulphide  were  fused  together.  Greenockite  is 
formed  when  cadmium  oxide  is  heated  in  sulphur  vapor. 

Obs.  —  Occurs  with  prehnite  at  Bishopton,  Renfrewshire,  and  elsewhere  in  Scotland. 
At  Pfibram  in  Bohemia,  as  a  coating  on  sphalerite;  similarly  at  other  points;  so  too  in  the 
United  States  near  Friedensville,  Pa.,  and  in  the  zinc  region  of  southwestern  Mo.;  in 
Marion  Co.,  Ark.,  it  colors  smithsonite  bright  yellow;  noted  at  Franklin,  N.  J.  Not  un- 
common as  a  furnace  product. 

Use.  —  An  ore  of  cadmium. 

Wurtzite.  Zinc  sulphide,  ZnS,  like  sphalerite,  but  in  hemimorphic  hexagonal  crystals; 
also  fibrous  and  massive.  G.  =  3 '98.  Color  brownish  black.  See  under  sphalerite,  p.  368, 
for  the  conditions  of  its  formation.  From  a  silver-mine  near  Oruro  in  Bolivia;  Portugal; 
at  Mies,  Bohemia;  Peru.  In  crystals  with  sphalerite  and  quartz  at  the  "Original  Butte" 
mine,  Butte,  Mon.  In  crystals  from  Joplin,  Mo.;  from  near  Frisco,  Beaver  Co.,  Utah. 

The  massive  fibrous  forms  of  "Schalenblende"  occur  at  Pfibram,  Bohemia;  Liskeard, 
Cornwall,  etc.  Other  forms,  from  Stolberg,  Wiesloch,  Altenberg,  Germany,  are  in  part 
wurtzite,  in  part  sphalerite. 


372  DESCRIPTIVE   MINERALOGY 

MILLERITE.     Capillary  Pyrites. 

Rhombohedral.  Usually  in  very  slender  to  capillary  crystals,  often  in 
delicate  radiating  groups;  sometimes  interwoven  like  a  wad  of  hair.  Also  in 
columnar  tufted  coatings,  partly  semi-globular  and  radiated.  The  rhombohe- 
dron  (0112)  is  a  gliding  plane  and  artificial  twins  may  be  formed. 

Cleavage  perfect  parallel  to  (1011)  and  (0112).  Fracture  uneven.  Brittle; 
capillary  crystals  elastic.  H.  =  3-3 '5.  G.  =  5 '3-5 '65.  Luster  metallic. 
Color  brass-yellow,  .inclining  to  bronze-yellow,  with  often  a  gray  iridescent 
tarnish.  Streak  greenish  black. 

Comp.  —  Nickel  sulphide,  NiS  =  Sulphur  35'3,  nickel  64-7  =  100. 

Pyr.,  etc.  In  the  open  tube  sulphurous  fumes.  B.B.  on  charcoal  fuses  to  a  globule. 
When  roasted,  gives  with  borax  and  salt  of  phosphorus  a  violet  bead  in  O.F.,  becoming 
gray  in  R.F.  from  reduced  metallic  nickel.  On  charcoal  in  R.F.  the  roasted  mineral  gives 
a  coherent  metallic  mass,  attractable  by  the  magnet.  Most  varieties  also  show  traces  of 
copper,  cobalt,  and  iron  with  the  fluxes. 

Artif .  —  Crystals  of  millerite  have  been  formed  artificially  by  treating  under  pressure  a 
solution  of  nickel  sulphate  with  hydrogen  sulphide. 

Obs.  —  Found  at  Joachimstal  and  Pfibram  in  Bohemia;  in  Germany  at  Johann- 
georgenstadt  and  Freiberg,  Saxony;  Wissen,  Prussia;  in  Cornwall,  England. 

In  the  United  States,  at  Antwerp,  N.  Y.,  in  cavities  in  hematite;  in  Lancaster  Co.,  Pa., 
at  the  Gap  mine,  in  thin  velvety  coatings  of  a  radiated  fibrous  structure.  With  calci'te, 
dolomite  and  fluorite,  forming  delicate  tangled  hair-like  tufts,  in  geodes  in  limestone,  often 
penetrating  the  calcite  crystals,  at  St.  Louis,  Mo.;  similarly  near  Milwaukee,  Wis.  At 
Orford,  Quebec. 

Use.  —  An  ore  of  nickel. 

BEYRICHITE.  NiS  like  millerite,  but  with  lower  specific  gravity  (4  '7).  Laspeyres  con- 
siders all  millerite  as  formed  by  paramorphism  from  beyrichite.  Found  in  Westerwald, 
Rhine-Prussia. 

HAUCHECORNITE.  Perhaps  Ni(Bi,Sb,S).  In  tabular  tetragonal  crystals.  H.  =  5. 
G.  =  6*4.  Color  light  bronze-yellow.  From  Hamm  a.  d.  Sieg,  Germany. 

NICCOLITE.     Copper  Nickel. 

Hexagonal.  Crystals  rare.  Usually  massive,  structure  nearly  impal- 
pable; also  reniform,  columnar;  reticulated,  arborescent.  Fracture  uneven. 
Brittle.  H.  =  5-5'5.  G.  =  7'33-7'67.  Luster  metallic.  Color  pale  cop- 
per-red. Streak  pale  brownish  black.  Opaque. 

Comp.  —  Nickel  arsenide,  NiAs  =  Arsenic  56'1,  nickel  43*9  =  100. 
Usually  contains  a  little  iron  and  cobalt,  also  sulphur;  sometimes  part  of  the 
arsenic  is  replaced  by  antimony,  and  then  it  graduates  toward  breithauptite. 
The  intermediate  varieties  have  been  called  write. 

Pyr.,  etc.  —  In  the  closed  tube  on  intense  ignition  gives  a  faint  sublimate  of  arsenic. 
In  the  open  tube  a  sublimate  of  arsenic  trioxide,  with  a  trace  of  sulphurous  fumes,  the 
assay  becoming  yellowish  green.  On  charcoal  gives  arsenical  fumes  and  fuses  to  a  globule, 
which,  treated  with  borax  glass,  affords,  by  successive  oxidation,  reactions  for  iron,  cobalt, 
and  nickel;  the  antimonial  varieties  give  also  reactions  for  antimony.  Soluble  in  aqua 
regia. 

Obs.  —  Accompanies  cobalt,  silver  and  copper  ores  in  Germany  in  the  Saxon  mines  of 
Annaberg,  Schneeberg,  Mansfield,  etc.;  also  in  Thuringia,  Hesse,  and  in  Styria;  at  Alle- 
mont,  Dauphine,  at  Balen  in  the  Basses  Pyrenees,  France  (arite) ;  at  the  Ko  mines  in  Nord- 
mark,  Sweden;  occasionally  in  Cornwall,  Chile:  abundant  at  Mina  de  la  Rioja,  Oriocha, 
Argentina.  In  the  United  States,  sparingly  at  Franklin  Furnace,  N.  J.,  Silver  Cliff,  Col. 
In  Canada,  at  Cobalt,  Ontario. 

Use.  —  An  ore  of  nickel. 

TEMISKAMITE.  Described  as  having  composition  Ni4As3,  has  been  shown  to  be  a  mix- 
ture of  niccolite,  maucherite  and  a  little  cobaltite. 

Breithauptite.  Nickel  antimonide,  NiSb.  Rarely  in  hexagonal  crystals;  usually 
massive,  arborescent,  disseminated.  G.  =  7'54.  Color  light  copper-fed.  From  Andreas- 
berg  in  the  Harz  Mts.,  Germany. 


SULPHIDES,  SELENIDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES   373 

PYRRHOTITE.     Magnetic  Pyrites. 

Hexagonal,     c  =  0'8701.  652 

cs,  0001  A   1011  =  45°    8'. 

cu,  0001  A  4041  _         =76°    0'.  XC~ 

cy,  0001  A  (20-0-20-3)  =  81°  30*'.  gg 

Twins:  tw.  pi.  s(10ll),  with  vertical  axes  nearly  at     \— 
right  angles  (Fig.  418,  p.  167).     Distinct  crystals  rare, 
commonly  tabular;    also  acute  pyramidal  with  faces 
striated  horizontally.     Usually  massive,  with  granular  structure. 

Parting:  c(0001),  sometimes  distinct.  Fracture  uneven  to  subconchoidal. 
Brittle.  H.  =  3 -5-4-5.  G.  =  4-58-4-64.  Luster  metallic.  Color  between 
bronze-yellow  and  copper-red,  and  subject  to  speedy  tarnish.  Streak  dark 
grayish  black.  Magnetic,  but  varying  much  in  intensity;  sometimes  possess- 
ing polarity. 

Comp.  —  Ferrous  sulphide  containing  variable  amounts  of  dissolved 
sulphur.  Analyses  show  variation  from  FesSe  to  FeieSi?.  Often  also  contains 
nickel.  Fe7S8  =  Sulphur  39'6,  iron  60'4  =  100.  (Cf.  Art.  473,  p.  323.) 

Pyrrhotite  differs  from  troilite  in  containing  more  or  less  of  dissolved  sulphur,  while 
troilite,  occurring  in  meteorites  where  there  is  always  an  excess  of  iron,  may  form  the  pure 
monosulphide. 

Pyr.,  etc.  —  Unchanged  in  the  closed  tube.  In  the  open  tube  gives  sulphurous  fumes. 
On  charcoal  in  R.F.  fuses  to  a  black  magnetic  mass;  in  O.F.  is  converted  into  red  oxide, 
which  with  fluxes  gives  only  an  iron  reaction  when  pure,  but  many  varieties  yield  small 
amounts  of  nickel  and  cobalt.  Decomposed  by  hydrochloric  acid,  with  evolution  of  hydro- 
gen sulphide. 

Diff.  —  Distinguished  by  its  peculiar  reddish  bronze  color;  also  by  its  magnetic  prop- 
erties. 

Micro.  —  In  polished  section  shows  a  cream  color  with  a  shiny  and  pitted  surface. 
With  hot  HC1  tarnishes  quickly,  giving  bright  colors,  then  blackens  and  dissolves;  with  aqua 
regia  effervesces,  becomes  iridescent  in  center  of  drop  and  brown  at  the  edge. 

Artif.  —  Pyrrhptite  has  been  synthesized  by  the  direct  union  of  iron  and  sulphur  and 
also  when  pyrite  is  heated  in  an  atmosphere  of  hydrogen  sulphide  at  550°.  Pyrrhotite 
exists  in  two  crystalline  modifications,  hexagonal  at  ordinary  temperatures  and  ortho- 
rhombic-above  138°. 

Obs.  —  Occurs  at  Kongsberg,  Modum,  Kristiania,  etc.,  in  Norway;  Falun,  Sweden; 
Andreasberg  in  the  Harz  Mts.,  Germany;  Schneeberg,  Saxony;  Leoben  and  Lavantal, 
Carinthia;  Minas  Geraes  in  Brazil,  in  large  tabular  crystals;  the  lavas  of  Vesuvius;  Corn- 
wall. 

In  North  America,  in  Me.,  at  Standish  with  andalusite;  in  Ver.,  at  Stafford,  etc.  In 
N.  Y.,  near  Diana,  Lewis  Co.;  Orange  Co.;  at  Tilly  Foster  mine,  Brewsters.  In  Pa.,  at  the 
Gap  mine,  Lancaster  Co.,  nickeliferous.  In  Tenn .,  at  Ducktown  mines,  abundant.  In 
Canada,  in  large  veins  at  St.  Jerome,  Elizabethtown ,  Ontario;  large  deposit  mined  for  nickel 
at  Sudbury,  Ontario. 

Named  from  irvpporw,  reddish. 

Use.  —  Often  becomes  a  valuable  ore  of  nickel. 

Troilite.  Ferrous  sulphide,  FeS,  occurring  in  nodular  masses  and  in  thin  veins  in 
many  iron  meteorites.  G.  =  4 -75-4*82.  Color  tombac-brown.  Considered  to  be  the  end 
member  of  the  pyrrhotite  series.  See  above. 

C.     Intermediate  Division 

Polydymite.  A  nickel  sulphide,  perhaps  Ni4S8.  In  octahedral  crystals;  frequently 
twinned.  G.  =  4'54-4'81.  Color  gray.  From  Griinau,  Westphalia,  Germany. 

Sychnodymite.  Essentially  (Co,Cu)4S6.  Isometric,  in  small  steel-gray  octahedrons. 
From  the  Siegen  district,  Germany. 


374  DESCRIPTIVE   MINERALOGY 

The  following  species  are  sometimes  regarded  as  Sulpho-salts,  namely, 
Sulpho-ferrites,  etc. 

BORNITE.     Peacock  Ore.     Purple  Copper  Ore.     Variegated  Copper  Ore.     Erubescite. 

Isometric.  Habit  cubic,  faces  often  rough  or  curved.  Twins:  tw.  pi. 
o(lll),  often  penetration-twins.  Crystals  rare.  Usually  massive,  structure 
granular  or  compact. 

Cleavage :  o  (1 1 1) ,  in  traces.  Fracture  small  conchoidal,  uneven.  Brittle. 
H.  =  3.  G.  =  4-9-5-4.  Luster  metallic.  Color  between  copper-red  and 
pinchbeck-brown  on  fresh  fracture,  speedily  iridescent  from  tarnish.  Streak 
pale  grayish  black.  Opaque. 

Comp.  —  A  sulphide  of  copper  and  iron.  Cu5FeS4.  Copper  63-3,  iron 
11-1,  sulphur  25-6=100. 

The  mineral  often  contains  small  amounts  of  chalcocite,  etc.,  and  therefore  shows  con- 
siderable variation  in  its  percentage  composition,  giving  from  50  to  70  p.  c.  of  copper  and 
15  to  6*5  p.  c.  of  iron. 

Pyr.,  etc.  —  In  the  closed  tube  gives  a  faint  sublimate  of  sulphur.  In  the  open  tube 
yields  sulphurous  fumes.  B.B.  on  charcoal  fuses  in  R.F.  to  a  brittle  magnetic  globule. 
The  roasted  mineral  gives  with  the  fluxes  the  reactions  of  iron  and  copper,  and  with  soda 
a  metallic  globule.  Soluble  in  nitric  acid  with  separation  of  sulphur. 

Diff.  —  Distinguished  (e.g.,  from  chalcocite)  by  the  peculiar  reddish  color  on  the  fresh 
fracture  and  by  its  brilliant  tarnish;  B.B.  becomes  strongly  magnetic. 

Micro.  —  In  polished  section  shows  a  pinkish  brown  color  with  smooth  surface.  With 
HNO3  becomes  quickly  golden-brown  with  effervescence. 

Artif.  —  Bornite  has  been  obtained  by  fusing  pyrite,  copper  and  sulphur  together;  by 
heating  a  mixture  of  cuprous,  cupric  and  ferric  oxides  in  hydrogen  sulphide  at  100°  to  200°. 

Obs.  —  Bornite  is  often  a  primary  mineral  of  magmatic  origin,  being  frequently  found 
in  igneous  rocks.  It  is  also  often  a  secondary  mineral,  occurring  with  chalcocite,  etc.,  in 
the  enriched  portions  of  copper  sulphide  veins.  It  is  usually  associated  with  other  copper 
ores,  and  is  a  valuable  ore  of  copper.  Crystalline  varieties  are  found  in  Cornwall,  called  by 
the  miners  "horse-flesh  ore."  Occurs  massive  at  Ross  Island,  Killarney,  Ireland;  Monte 
Catini,  Tuscany;  the  Mansfeld  district,  Germany;  in  Norway,  Sweden,  Siberia,  Silesia, 
and  Hungary.  It  is  the  principal  copper  ore  at  some  Chilian  mines;  also  common  in  Peru, 
Bolivia,  and  Mexico. 

In  the  United  States,  found  at  the  copper  mine  in  Bristol,  Conn.;  massive  at  Mahoopeny, 
near  Wilkesbarre,  Pa.;  in  western  Idaho;  Butte,  Mon.,  etc.  A  common  ore  in  Canada,  at 
the  Acton  and  other  mines. 

Named  after  the  mineralogist  Ignatius  von  Born  (1742-1791). 

Use.  —  An  ore  of  copper. 

Linnaeite.  A  sulphide  of  cobalt,  Co3S4  =  CqS.Co2S3,  analogous  to  the  spinel  group. 
Also  contains  nickel  (var.  siegenite).  Commonly  in  octahedrons;  also  massive.  H.  =  5 '5. 
G.  =  4*8-5.  Color  pale  steel-gray,  tarnishing  copper-red.  Occurs  at  Bastnaes,  etc., 
Sweden;  Mtisen,  near  Siegen,  Prussia;  at  Siegen  (siegenite),  in  octahedrons.  In  the 
United  States  at  Mine  la  Motte,  Mo.;  Mineral  Hill,  Md. 

Daubreelite.  An  iron-chromium  sulphide,  FeS.Cr2S3,  occurring  with  troilite  in  some 
meteoric  irons.  Color  black.  G.  =  5 '01. 

CUBANITE.  Described  as  an  iron-copper  sulphide,  perhaps  CuFe2S4  =  CuS.Fe2S3. 
Examination  of  specimens  from  several  localities  show  it  to  be  a  mixture  of  pyrite  or  pyrrho- 
tite  with  chalcopyrite. 

CARROLITE.  A  copper-c9balt  sulphide,  CuCo2S4  =  CuS.Co2S3.  Isometric;  rarely  in 
octahedrons.  Usually  massive.  G.  =  4*85.  Color  light  steel-gray,  with  a  faint  reddish 
hue.  From  Carroll  Co.,  Md.,  near  Finksburg.  Probably  linnseite  with  intergrown  bornite 
and  chalcopyrite. 

Badenite.  (Co,Ni,Fe)2(As,Bi)3.  Massive  granular  to  fibrous.  G.  =  7'1.  Metallic. 
Color  steel-gray.  Fusible.  From  near  Badeni-Ungureni,  Neguletzul  valley,  Roumania. 

CHALCOPYRITE.    Copper  Pyrites.     Yellow  Copper  Ore. 
Tetragpnal-sphenoidal.     Axis  c  =  0-98525. 
ppf,  111  A  111  =  108°  40'.          PPl,  111  A  111  =  70°  7i'.          ce,  001  A  101  =  44°  34|'. 


SULPHIDES,  SELENIDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES  375 

Crystals  commonly  tetrahedral  in  aspect,  the  sphenoidal  faces  p(lll) 
large,  dull  or  oxidized;  p/111)  small  and  brilliant.  Sometimes  both  forms 
equally  developed,  and  then  octahedral  in  form.  Twins:  (1)  tw.  pi.  p(lll), 


663  654  655  656 


2(201),  8(513) 

resembling  spinel-twins  (Fig.  417,  p.  167);  sometimes  repeated  as  a  five- 
ling  (Fig.  655).  (2)  Tw.  pi.  and  comp.-face  e(101)  (Fig.  656,)  often  in 
repeated  twins.  (3)  Tw.  pi.  w(110),  tw.  axis  c,  complementary  penetration 
twins.  Often  massive,  compact. 

Cleavage:  2(201),  sometimes  distinct;  c(001),  indistinct.  Fracture  un- 
even. Brittle.  H.  =  3*5-4.  G.  =  4-1-4-3.  Luster  metallic.  Color  brass- 
yellow;  often  tarnished  or  iridescent.  Streak  greenish  black.  Opaque. 

Comp.  —  A  sulphide  of  copper  and  iron,  CuFeS2  =  Sulphur  35-0,  cop- 
per 34-5,  iron  30 '5  =  100.  Analyses  often  show  variations  from  this  formula, 
often  due  to  mechanical  admixture  of  pyrite. 

Sometimes  auriferious  and  argentiferous;  also  contains  traces  of  selenium  and  thallium. 

Pyr.,  etc. —  In  the  closed  tube  often  decrepitates,  and  gives  a  sulphur  sublimate,  in  the 
open  tube  sulphurous  fumes.  On  charcoal  fuses  to  a  magnetic  globule;  the  residue  mois- 
tened with  hydrochloric  acid  and  then  touched  with  blowpipe  flame  gives  intense  blue  flame 
color.  Decomposed  by  nitric  acid  giving  free  sulphur  and  a  green  solution;  ammonia  in 
excess  changes  the  green  color  to  a  deep  blue,  and  precipitates  red  ferric  hydroxide. 

Diff.  —  Distinguished  from  pyrite  by  its  inferior  hardness  and  deeper  yellow  color. 
Resembles  gold  when  disseminated  in  minute  grains  in  quartz,  but  differs  in  being  brittle 
and  in  having  a  black  streak;  further  it  is  soluble  in  nitric  acid. 

Micro.  —  In  polished  section  shows  a  bright  brass-yellow  color  with  smooth  surface. 
With  hot  HNO8  tarnishes  and  dissolves.  Unaffected  by  KCN,  differing  from  gold. 

Artif.  —  Chalcopyrite  has  been  artificially  prepared  (1)  by  fusing  pyrite  and  copper 
sulphide  together;  (2)  by  gently  heating  cupric  and  ferric  oxides  in  an  atmosphere  of  hy- 
drogen sulphide. 

Obs. -^Chalcopyrite  is  the  most  common  and  important  mineral  containing  copper. 
It  is  commonly  of  primary  origin  and  from  it,  by  various  alteration  processes,  many  other 
copper  minerals  are  derived.  It  has  repeatedly  been  observed  as  an  original  constituent  of 
igneous  rocks  and  the  ultimate  source  of  the  copper  of  our  ore  deposits  is  to  be  found  in 
rocks  of  this  type.  It  occurs  widely  disseminated  in  metallic  veins  and  nests  in  gneiss  and 
crystalline  schists,  also  in  serpentine  rocks;  often  intimately  associated  with  pyrite,  also 
with  siderite,  tetrahedrite,  etc.,  sometimes  with  nickel  and  cobalt  sulphides,  pyrrhotite,  etc. 
Observed  coated  with  tetrahedrite  crystals  in  parallel  position,  also  as  a  coating  over  the 
latter.  Frequently  associated  with  sphalerite,  its  crystals  often  lying  with  parallel  orienta- 
tion upon  the  latter  mineral. 

Chalcopyrite  is  so  widely  distributed  as  an  ore  mineral  that  it  is  possible  to  mention 
here  only  those  occurrences  which  are  exceptional  either  because  of  their  size  or  because  of 
the  quality  of  the  minerals  found  in  them. 

It  is  the  principal  ore  of  copper  at  the  Cornwall  mines;  there  associated  with  cassiterite, 
galena,  bornite,  chalcocite,  tetrahedrite,  sphalerite.  At  Falun,  Sweden,  it  occurs  in  large 
masses  embedded  in  gneiss.  At  Rammelsberg,  near  Goslar  in  the  Harz  Mts.,  Germany,  it 


376 


DESCRIPTIVE   MINERALOGY 


forms  a  bed  in  argillaceous  schist;  occurs  with  nickel  and  cobalt  ores  in  the  Kupferschiefer 
of  Mansfield.  In  Germany  the  Kurprinz  mine  at  Freiberg  affords  well-defined  crystals; 
also  Horhausen,  Dillenburg,  Neudorf,  Musen.  Common  elsewhere  as  at  Mte.  Catini  in 
Tuscany;  Rio  Tin  to,  Spain;  in  New.  South  Wales;  Chile;  Japan,  etc. 

In  the  United  States  it  is  found  in  large  crystals  associated  with  quartz  at  Ellenville, 
N.  Y.;  in  exceptional  crystals  at  the  French  Creek  mines,  Chester  Co.,  Pa.,  associated  with 
pyrite,  magnetite,  etc.;  in  Mo.,  with  sphalerite  at  Joplin;  at  various  localities  in  Gilpin 
and  other  counties  in  Col.  The  most  important  sulphide  deposits  of  copper  in  many  of 
which  chalcopyrite  is  the  chief  ore  are  found  in  the  states  of  Arizona,  Montana,  Utah, 
Alaska,  Nevada,  New  Mexico,  California,  and  Tennessee. 

In  Canada  there  are  important  copper  deposits  in  British  Columbia,  Ontario  arid  Quebec, 

Use.  —  The  most  important  ore  of  copper. 

Named  from  XO\KOS,  brass,  and  pyrites,  by  Henckel  (1725). 


D.    Bisulphides,  Diarsenides,  etc. 

The  disulphides,  diarsenides,  etc.,  embrace  two  distinct  groups. 


The 


prominent  metals  included  are  the  same  in  both,  viz. :  iron,  cobalt  and  nickel. 
The  groups  present,  therefore,  several  cases  of  isodimorphism,  as  is  shown  in 
the  lists  of  species  below.  These  sulphides  are  all  relatively  hard,  H.  =  5-6; 
they  hence  strike  fire  with  a  steel,  and  this  has  given  the  familiar  name  pyrites 
applied  to  most  of  them.  The  color  varies  between  pale  brass-yellow  and 
tin-white. 

Pyrite  Group.     RS^RAs^RSb^     Isometric-pyritohedral 


Pyrite  FeS2  Gersdorffite 

Arsenoferrite          FeAs2  Corynite 

Cobaltnickelpyrite  (Co,Ni,Fe)S2  Ullmannite 
Hauerite                 MnS2 

[Smaltite       CoAs2,  also  (Co,Ni)As2  Sperrylite 

|  Chloanthite  NiAs2,  also  (Ni,Co)As2  Laurite 
Cobaltite                         CoS2.CoAs2 


NiS2.NiAs2 
NiS2.Ni(As,Sb)j 
NiS2.NiSb2    (isometric- 

tetartohedral) 
PtAs2 
RuS2? 


Marcasite  Group.     RS2,  RAS2,  etc.     Orthorhombic 


a 

07662 
0-6689 


c 

1-2342 

1-2331 


110 A 110 
74°  55' 
67°  33' 


101AI01 
116°  20' 
123°  3' 


0-6773  :  1  :  1-1882      68°  13'       120°  38' 


0-6942  :  1  :  1-1925      69°  32'      119°  35' 


Marcasite  FeS2 

Lollingite  FeAs2 

Leucopyrite          Fe3  As4 
Arsenopyrite        FeS2.FeAs2 

Danaite        (Fe,Co)S2.  (Fe,Co)  As2 
Safflorite  CoAs2 

Rammelsbergite     NiAs2 
Glaucodot      (Co,Fe)S2.  (Co,Fe)  As2 
Alloclasite          (Co,Fe)  (As,Bi)S 
Wolfachite          NiS2.Ni(As,Sb)2 

The  PYRITE  GROUP  includes,  besides  the  compounds  of  Fe,  Co,  Ni,  also 
others  of  the  related  metals  Mn  and  Pt.  The  crystallization  is  isometric- 
pyntohedral. 

The  species  of  the  MARCASITE  GROUP  crystallize  in  the  orthorhombic 
system  with  prismatic  angles  of  about  70°  and  110°  and  a  prominent  macro- 
dome  of  about  60°  and  120°.  Hence  fivefold  and  sixfold  repeated  twins  are 
common  with  several  species,  in  the  one  case  the  prism  and  in  the  other  the 
macrodome  named  being  the  twinning-plane. 


SULPHIDES,  SELENIDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES   377 


Pyrite  Group 

PYRITE.     Iron  Pyrites. 

Isometric-pyritohedral.  Cube  and  pyritohedron  e(210)  the  common 
forms,  the  faces  of  both  often  with  striations  ||  edge  a(100)/e(210),  due  to 
oscillatory  combination  of  these  forms  and  tending  to  produce  rounded  faces; 
pyritohedral  faces  also  striated  J_  to  this  edge;  octahedron  also  common. 
See  Figs.  657-662,  also  Figs.  133-138,  pp.  65,  66.  Twins:  tw.  ax.=  a  crystal 
axis,  usually  penetration-twins  with  parallel  axes  (Fig.  407,  p.  166);  rarely 
contact-twins.  Frequently  massive,  fine  granular;  sometimes  subfibrous 
radiated;  reniform,  globular,  stalactitic. 
657  658 


660 


661 


Cleavage:  a(100),  o(lll),  indistinct.  Fracture  conchoidal  to  uneven. 
Brittle.  H.  =  6-6-5.  G.  =  4-95-5-10;  4-967  Traversella,  5-027  Elba.  Lus- 
ter metallic,  splendent  to  glistening.  -  Color  a  pale  brass-yellow,  nearly  uni- 
form. Streak  greenish  black  or  brownish  black.  Opaque. 

Comp.  —  Iron  disulphide,  FeS2  =  Sulphur  53'4,  iron  46*6  =  100. 

Nickel,  cobalt,  and  thallium,  and  also  copper  in  small  quantities,  sometimes  replace  part 
of  the  iron,  or  else  occur  as  mixtures;  selenium  is  sometimes  present  in  traces.  Gold  is 
sometimes  distributed  invisibly  through  it,  auriferous  pyrite  being  an  important  source  of 
gold.  Arsenic  is1  rarely  present,  as  in  octahedral  crystals  from  French  Creek,  Pa.  (0'2 
p.  c.  As). 

Pyr.,  etc.  —  Easily  fusible,  (2'5-3).  Becomes  magnetic  on  heating  and  yields  sulphur 
dioxide.  Gives  nn  abundant  sublimate  of  sulphur  in  the  closed  tube.  Insoluble  in  hydro- 
chloric acid.  The  fine  powder  is  completely  soluble  in  strong  nitric  acid . 

Diff.  —  Distinguished  from  chalcopyrite  by  its  greater  hardness  and  paler  color;  in 
form  and  specific  gravity  different  from  marcasite,  which  has  also  a  whiter  color. 

Micro.  —  In  polished  section  shows  a  cream  color  with  a  scratched  and  dull  surface. 
With  HNOa  effervesces  slowly  becoming  faintly  brown. 

Alteration.  —  Pyrite  readily  changes  by  oxidation  to  an  iron  sulphate  or  to  the  hy- 
drated  oxide,  limonite,  with  sulphuric  acid  set  free.  Crystals  of  pyrite  which  have  been 
changed  on  their  surfaces  to  limonite  are  common.  This  change  may  continue  until  tho 
original  mineral  has  completely  disappeared.  Large  masses  of  pyrite  lying  near  the  surface 
may  be  altered  to  a  cellular  mass  of  limonite  —  tHe  iron  gossan  of  the  miners  —  while  the 
sulphuric  acid  set  free  travels  downward  and  enters  into  various  important  reactions  with 
the  unaltered  minerals  below.  The  alteration  of  pyrite  to  limonite  may  be  continued  until 
hematite  is  formed. 

Gbs.  —  Experiments  show  that  pyrite  is  formed  in  neutral  or  alkaline  solutions  and  at 
high  temperatures.  Marcasite,  on  the  other  hand,  is  deposited  from  acid  solutions  and 


378  DESCRIPTIVE    MINERALOGY 

is  stable  only  at  temperatures  below  450°  C.  These  sulphides  can  be  formed  through  the 
action  of  hydrogen  sulphide,  although  the  reducing  action  of  carbonaceous  materials  may  also 
at  times  be  of  importance.  Pyrite  occurs  in  rocks  of  all  ages  and  types,  being  most  common 
in  the  metamorphic  and  sedimentary  rocks,  but  it  is  also  frequently  found  as  a  minor  acces- 
sory constituent  of  igneous  rocks.  When  disseminated  in  the  rocks  it  usually  occurs  in 
small  crystals,  cubes,  octahedrons,  pyritohedrons,  etc.,  but  in  veins  it  may  occur  in  crystals 
or  with  a  granular  or  radiating  massive  structure.  At  times  it  is  in  nodular  or  concre- 
tionary forms. 

Pyrite  is  very  widespread  in  its  occurrence,  being  the  most  common  sulphide  mineral. 
At  times  it  is  found  in  very  large  amounts  and  is  mined  for  its  sulphur  content  or  because 
it  contains  small  amounts  of  some  valuable  metal,  like  copper,  gold,  etc.  It  is  frequently 
found  in  crystals  with  a  fine  luster.  Some  of  ^the  more  notable  localities  for  its  occurrence 
are  given  below. 

Important  commercial  deposits  of  pyrite  are  found  in  Norway,  Germany,  France, 
Italy,  Spain  and  Portugal.  The  mines  at  Rio  Tinto,  Spain,  are  especially  noteworthy. 
The  mineral  has  been  mined  in  the  United  States  in  Louisa  and  Prince  William  Cos.,  Va.; 
in  St:  Lawrence  Co.,  N.  Y.;  at  Davis,  Mass.,  etc.  The  following  localities  furnish  exception- 
ally fine  crystallized  specimens:  Cornwall,  England;  Traversella  and  Brosso,  Piedmont 
Italy;  Island  of  Elba;  Ardennes,  France,  in  distorted  cubes;  Minden,  Prussia,  in  inter- 
penetration  twins;  in  various  localities  in  Bohemia,  Hungary,  Germany,  Sweden,  etc.;  at 
Firmeza,  Cuba;  at  French  Creek,  Pa.,  in  pyramids  with  apparently  tetragonal  or  ortho- 
rhombic  symmetry;  at  Rossie  and  Scoharie,  N.  Y.;  Roxbury,  Conn.;  Franklin,  N.  J.; 
Gilpin  Co.  and  at  Leadville,  Col.;  Bin^ham  Canyon,  Utah. 

The  name  pyrite  is  derived  from  irvp,  fire,  and  alludes  to  the  sparks  formed  when  the 
mineral  is  struck  with  a  hammer;  hence  the  early  name  pyrites,  p.  376. 

Use.  —  Pyrite  often  carries  small  amounts  of  copper  or  gold  and  becomes  an  impor- 
tant ore  of  these  metals.  It  is  also  mined  for  its  sulphur  content  which  is  used  in  the  form  of 
sulphur  dioxide  (used  in  the  preparation  of  wood  pulp  for  manufacture  into  paper),  as  sul- 
phuric acid  (used  for  many  purposes,  especially  in  the  purification  of  kerosene  and  in  the 
preparation  of  mineral  fertilizers),  and  as  the  ferrous  sulphate,  copperas  (used  in  dyeing,  in 
inks,  as  a  wood  preservative,  and  as  a  disinfectant). 

Bravdite  (Fe,Ni)S2.  Contains  nearly  20  per  cent  nickel.  In  small  grains  and  crystal 
fragments,  apparently  octahedral.  Pale  yellow  with  a  faint  reddish  tarnish.  Occurs  dis- 
seminated through  the  vanadium  ores  at  Minasragra,  Peru. 

Cobaltnickelpyrite.l  Iron  sulphide  with  about  20  per  cent  cobalt  and  nickel, 
(Co,Ni,Fe)S2.  In  minute  pyritohedral  crystals.  Steel-gray  color.  Gray-black  streak. 
H.  =  5.  G.  =  4-716.  Found. at  Musen,  Germany. 

Arsenoferrite.  Iron  arsenide,  probably  FeAs2.  Isometric-pyritohedral.  In  small 
crystals.  Color  dark  brown.  Fine  splinters  transparent  with  ruby-red  color.  From  the 
Binnental,  Switzerland. 

Hauerite.  —  Manganese  disulphide,  MnS2.  In  octahedral  or  pyritohedral  crystals; 
also  massive.  G.  =  3'46.  Color  reddish  brown  or  brownish  black.  From  Kalinka, 
Hungary;  Raddusa,  Catania,  Sicily. 

SMALTITE-CHLOANTHITE. 

Isometric-pyritohedral.  Commonly  massive;  in  reticulated  and  other 
imitative  shapes. 

Cleavage:  o(lll)  distinct;  a (100)  in  traces.  Fracture  granular  and 
uneven.  Brittle.  H.  =  5'5-6.  .  G.  =  6*4  to  6-6.  Luster  metallic.  Color 
tin-white,  inclining,  when  massive,  to  steel-gray,  sometimes  iridescent,  or 
grayish  from  tarnish.  Streak  grayish  black.  Opaque. 

Comp.  —  SMALTITE  is  essentially  cobalt  diarsenide,  CoAs2  =  Arsenic 
71;8,  cobalt  28-2  =  100.  CHLOANTHITE  is  nickel  diarsenide,  NiAs2  =  Arsenic 
71-9,  nickel  28'1  =  100. 

Cobalt  and  nickel  are  usually  both  present,  and  thus  these  two  species  graduate  into  each 
other,  and  no  sharp  line  can  be  drawn  between  them.  Iron  is  also  present  in  varying 
amount ;  the  variety  of  chloanthite  containing  much  iron  has  been  called  chathamite.  Fur- 
ther sulphur  is  usually  present,  but  only  in  small  quantities.  Many  analyses  do  not  conform 
even  approximately  to  the  formula  RAs2,  the  ratio  rising  from  less  than  1  :  2  to  1  :  2 '5  and 
nearly  1  :  3,  thus  showing  a  tendency  toward  skutterudite  (RAs3),  perhaps  due  to  either 
molecular  or  mechanical  mixture.  Microscopic  examination  of  polished  specimens  shows 


SULPHIDES,  SELENJDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES    379 

probable  zoning  of  different  members  of  the  group.  Material  known  as  keweenawite  is  a 
mixture  of  smaltite,  niccolite  and  domeykite. 

Much  that  has  been  called  smaltite  is  shown  by  the  high  specific  gravity  to  belong  to  the 
orthorhombic  species  safRorite. 

Pyr.,  etc.  —  In  the  closed  tube  gives  a  sublimate  of  metallic  arsenic;  in  the  open 
tube  a  white  sublimate  of  arsenic  trioxide,  and  sometimes  traces  of  sulphur  dioxide.  B.B. 
on  charcoal  gives  a  coating  of  As2O3,  the  arsenical  odor,  and  fuses  to  a  globule,  which, 
treated  with  successive  portions  of  borax-glass,  affords  reactions  for  iron,  cobalt,  and  nickel. 

Obs.  —  Usually  occurs  in  veins,  accompanying  ores  of  cobalt  or  nickel,  and  ores  of 
silver  and  copper;  also,  in  some  instances,  with  niccolite  and  arsenopyrite.  Found  at  the 
Saxon  mines;  Joachimstal,  Bohemia;  Wheal  Sparnon,  Cornwall;  Riechelsdorf,  Hesse, 
Germany;  Tunaberg,  Sweden;  Allemont,  Dauphine,  France;  Cobalt,  Ontario.  In  the 
United  States,  at  Chatham,  Conn.,  the  chathamite  occurs  in  mica  slate,  with  arsenopyrite 
and  niccolite;  at  Franklin  Furnace,  N.  J. 

Use.  —  Ores  of  cobalt  and  nickel. 

COBALTITE. 

Isometric-pyrithohedral.  Commonly  in  cubes,  or  pyritohedrons,  or  com- 
binations resembling  common  forms  of  pyrite.  Also  granular  massive  to 
compact. 

Cleavage:  cubic,  rather  perfect.  Fracture  uneven.  Brittle.  H.  =  5-5. 
G.  =  6-6 -3.  Luster  metallic.  Color  silver-white,  inclined  to  red;  also  steel- 
gray,  with  a  violet  tinge,  or  grayish  black  when  containing  much  iron.  Streak 
grayish  black. 

Comp.  —  Sulpharsenide  of  cobalt,  CoAsS  or  CoS2.CoAs2  =  Sulphur  19'3, 
arsenic  45'2,  cobalt  35'5  =  100. 

Iron  is  present,  and  in  the  variety  ferrocobaltite  in  large  amount. 

Pyr.,  etc.  —  Unaltered  in  the  closed  tube.  In  the  open  tube  gives  sulphurous  fumes, 
and  a  crystalline  sublimate  of  arsenic  trioxide.  B.B.  on  charcoal  gives  off  sulphur  and 
arsenic  oxides,  and  fuses  to  a  magnetic  globule;  with  borax  a  cobalt-blue  color.  Soluble  in 
warm  nitric  acid,  with  the  separation  of  sulphur. 

Obs.  —  Occurs  at  Tunaberg  and  Hakansbo  in  Sweden;  at  the  Nordmark  mines;  also  at 
Skutterud  in  Norway;  at  Schladming,  Styria;  Siegen  in  Westphalia;  Botallack  mine,  near 
St.  Just,  in  Cornwall;  Khetri  mines,  Rajputana,  India;  Cobalt,  Ontario,  Canada. 

Use.  —  An  ore  of  cobalt. 

Gersdorffite.  Sulpharsenide  of  nickel,  NiAsS  or  NiS2.NiAs2.  Iron,  and  sometimes 
cobalt,  replace  more  or  less  of  the  nickel.  Isometric-pyritohedral;  usually  massive. 
H.  =  5*5.  G.  =  5'6-6'2.  Color  silver-white  to  steel-gray.  From  Loos,  Sweden;  the 
Harz  Mts.,  and  Lobenstein,  Reuss-Schleiz,  Germany;  Schladming,  Styria;  Sudbury  and 
Algoma  districts,  Ontario;  Rossland,  British  Columbia. 

CORYNITE  is  near  gersdorffite,  but  contains  also  antimony.  Probably  represents  a  mix- 
ture. From  Olsa,  Carinthia. 

Willyamite.  —  CoS2.NiS2.CoSb2.NiSb2.  Cleavage  cubic.  Color  tin-white  to  steel-gr.ay. 
Broken  Hill  mines,  New  South  Wales. 

Villamaninite.  Sulphide  of  Cu,Ni  with  smaller  amounts  of  Co,Fe.  H  =  4'5. 
G.  =  4-4-4-5.  Color,  iron-black.  In  irregular  groups  of  cubo-octahedral  crystals  and  in 
radiating  nodular  masses.  In  dolomite  from  Carmenes  district,  near  Villamanm,  Prov. 
Leon,  Spain. 

UUmannite.  Sulphantimonide  of  nickel,  NiSbS  or  NiS2.NiSb2;  arsenic  is  usually 
present  in  small  amount.  Isometric-tetartohedral;  both  pyritohedral  and  tetrahedral  forms 
occur.  Usually  massive,  granular.  H.  =  5-5 '5.  G.  =  6 '2-6  7.  Color  steel-gray  to 
silver-white.  Occurs  in  the  mines  of  Siegen,  Prussia;  Lolling,  Carinthia  (tetrahedral); 
Monte  Narba,  Sarrabus,  Sardinia  (pyritohedral). 

KALLILITE.  Ni(Sb,Bi)S  or  NiS2.Ni(Sb,Bi)2.  Massive,  color  light  bluish  gray.  From 
the  Friedrich  mine  near  Schonstein  a.  d.  Sieg,  Germany. 

Sperrylite.  —  Platinum  diarsenide,  PtAs2.  In  minute  cubes,  or  cubo-octahedrons  with 
at  times  small  pyritohedral  or  diploid  faces.  H.  =  6-7.  G.  =  10*6.  Luster  metallic. 
Color  tin-white.  Streak  black.  Found  at  the  Vermillion  mine,  22  miles  west  of  Sudbury, 
Ontario,  Canada;  also  in  Macon  Co.,  N.  C.  Found  associated  with  covellite  at  the  Rambler 
mine,  Medicine  Bow  Mts.,  Wy.  This  is  the  only  known  native  compound  of  platinum. 


380 


DESCRIPTIVE   MINERALOGY 


Laurite.  Sulphide  of  ruthenium  and  osmium,  probably  essentially  RuS2.  In  minute 
octahedrons;  in  grains.  H.  =  7 '5.  G.  =  6 '99.  Luster  metallic.  Color  dark  iron-black. 
From  the  platinum  washings  of  Borneo.  Also  reported  from  Oregon. ^ 

Skutterudite.  Cobalt  arsenide,  CoAs3.  Isometric-pyritohedral.  Also  massive  granu- 
lar. Cleavage:  a(100),  distinct.  H.  =  6.  G.  =  672-6 '86.  Color  between  tin-white 
and  pale  lead-gray.  From  Skutterud,  Norway;  the  Turtmanntal,  Switzerland. 

NICKEL-SKUTTERUDITE.  (Ni,Co,Fe)As3.  Massive,  granular.  Color  gray.  From  near 
Silver  City,  N.  M. 

BISMUTO-SMALTITE.  Co(As,Bi)3.  A  skutterudite  containing  bismuth.  Color  tin- 
white.  G.  =  6 '92.  Zschorlau,  near  Schneeberg,  Saxony. 

Marcasite  Group 

For  the  list  of  species  and  their  relations,  see  p.  376. 
MARCASITE.     White  iron  pyrites. 

Orthorhombic.     Axes  a  :  b  :  c  =  07662  :  1  :  1*2342. 

mm"',  110  A  110  =    74°  55'.  II',  Oil  A  Oil  =  101°  58'. 

ee',       101  A  101  =  116°  20'.  cs,  001  A  111  =    63°  46'. 

Twins:  tw.  pi.  m(110),  sometimes  in  stellate  fivelings  (Fig.  436,  p.  169, 

cf.  Fig.  664);  also  tw. 
pi.  e(101),  less  common, 
the  crystals  crossing  at 
angles  of  nearly  60°. 
Crystals  commonly 
tabular  ||  c(001),  also 
pyramidal;-  the  bra- 
chydomes  striated 
edge 6(010) /c(001).  Of- 
ten massive;  in  stalac- 
tites ;  also  globular,  ren- 
iform,  and  other  imi- 
tative shapes. 

Cleavage:     m(110) 


Folkestone 


rather  distinct;  Z(Oll)  in  traces.  Fracture  uneven.  Brittle.  H.  =  6-6*5. 
G  =  4-85-4-90.  Luster  metallic.  Color  pale  bronze-yellow,  deepening  on 
exposure.  Streak  grayish  or  brownish  black.  Opaque. 

Comp.  —  Iron  disulphide,  like  pyrite,  FeS2  =  Sulphur  53'4,  iron  46'6 
=  100.     Arsenic  is  sometimes  present  in  small  amount. 

Var-  —  The  varieties  named  depend  mainly  on  state  of  crystallization.  Radiated: 
Radiated;  also  the  simple  crystals.  Cockscomb  Pyrite:  Aggregations  of  flattened  twin  crys- 
tals in  crest-like  forms.  Spear  Pyrite:  Twin  crystals,  with  re-entering  angles  a  little  like 
the  head  of  a  spear  in  form.  (Fig.  664.)  Capillary:  In  capillary  crystallizations. 

Pyr.,  etc.  —  Like  pyrite.     Very  liable  to  decomposition,  more  so  than  pyrite. 

Diff.  —  Resembles  pyrite,  but  has  a  lower  specific  gravity,  and  the  color  when  fresh 
e.g.,  after  treatment  with  acid)  is  paler:  when  crystallized  easily  distinguished  by  the  forms. 
ore  subject  to  tarnish  and  final  decomposition  than  pyrite. 

Marcasite  can  be  distinguished  chemically  from  pyrite  by  the  following  methods.  When 
both  minerals  are  finely  powdered  and  treated  with  a  little  concentrated  nitric  acid,  first 
in  the  cold  and  later,  after  vigorous  action  has  ceased,  by  warming,  it  will  be  found  that  in 
the  case  of  pyrite  the  greater  part  of  the  sulphur  of  the  mineral  has  been  oxidized  and  taken 
into  solution  as  sulphuric  acid,  while  in  the  case  of  marcasite  most  of  the  sulphur  has  sep- 
arated in  a  free  state.  The  Stokes  method,  which  can  be  used  quantitatively  to  determine 
the  amounts  of  the  two  minerals  in  a  mixture,  depends  upon  the  difference  in  their  behavior 
when  boiled  with  a  standard  solution  of  ferric  sulphate.  In  the  case  of  pyrite  about  52  per 
cent  pj  the  sulphur  is  oxidized  to  sulphuric  acid,  while  with  marcasite  only  about  12  per  cent 
is  oxidized. 


(e. 
M 


tfr~^  polished  sections  shows  a  cream  color  with  a  scratched  and  dull  surface. 
With  HNO3  slowly  turns  brown  to  black  with  effervescence. 


SULPHIDES,  SELENIDES,  TELLURIDES,  ARSENIDES,  ANTIMONIDES    381 


Alteration.  —  Marcasite  being  relatively  unstable  is  easily  altered.  Specimens  often 
disintegrate  with  the  formation  of  ferrous  sulphate  and  sulphuric  acid.  It  also  alters  to 
pyrite,  limonite,  etc. 

Obs.  —  Marcasite  is  a  much  more  unstable  compound  than  pyrite  and  is  formed  under 
comparatively  limited  conditions.  Experiments  have  shown  that  it  is  deposited  at  tem- 
peratures below  450°  C.  and  in  acid  solutions.  The  higher  the  temperature  the  more  acid 
must  the  solution  contain.  At  ordinary  temperatures  marcasite  may  be  deposited  from 
nearly  neutral  solutions.  Marcasite  is  formed  in  general  under  surface  conditions,  while  in 
deep  veins  where  the  minerals  are  deposited  from  ascending  hot  and  usually  alkaline  waters 
only  pyrite  is  found. 

Marcasite  occurs  abundantly  at  Littmitz  near  Carlsbad,  Bohemia.  Found  at  several 
localities  in  the  Harz  Mts.,  Germany.  In  its  cockscomb  form  occurs  at  Tavistock  in  Devon- 
shire and  as  Spear  Pyrites  in  the  chalk-marl  between  Folkestone  and  Dover,  England.  In 
the  United  States  a  notable  locality  is  at  Galena,  111.,  where  it  occurs  in  stalactites  with 
concentric  layers  of  sphalerite  and  galena.  In  fine  crystals  at  Mineral  Point,  Wis.;  in 
crystals  altered  to  limonite  from  Richland  Co.,  Wis.  Frequently  associated  with  galena, 
sphalerite  and  dolomite  from  the  Joplin  district,  Mo. 

The  word  marcasite,  of  Arabic  or  Moorish  origin  (and  variously  used  by  old  writers,  for 
bismuth,  antimony),  was  the  name  of  common  crystallized  pyrite  among  miners  and  min- 
eralogists in  later  centuries,  until  near  the  close  of  the  eighteenth.  It  was  first  given  to  this 
species  by  Haidinger  in  1845. 

Lb'llingite.  Essentially  iron  diarsenide,  FeAs2,  but  passing  into  FesAs4  (leucopyrite)  ; 
also  tending  toward  arsenopyrite  (FeAsS)  and  safflorite  (CoAs2).  Bismuth  and  antimony 
are  sometimes  present.  Usually  masswe.  H.  =  5-5*5.  G.  =  T'0-7'4  chiefly,  also  6*8. 
Luster  metallic.  Color  between  silver-white  and  steel-gray.  Streak  grayish  black. 
Occurs  in  the  Lolling-Huttenberg  district  in  Carinthia.  Found  also  sparingly  in  a  number 
of  other  districts. 

GEYERITE  is  near  lollingite,  but  contains  sulphur;  from  Geyer,  Saxony. 


ARSENOPYRITE,  or  MISPICKEL. 
Orthorhombic.     Axes  a  :  b  :  c  =  0'6773  : 
mm'",  110  A  110  = 
101  A  101 


uu', 
nnf, 


014  A  014  = 
012  A  012  = 
Oil  A  Oil  = 


1  :  1-1882. 

68°  13'. 
120°  38'. 
33°  5'. 
61°  26'. 
99°  50'. 


665 


Twins:  tw.  pi.  ra(110),  sometimes  repeated  like  marcasite  (Figs.  667  and 
437,  p.  109);  e(101)  cruciform  twins,  also  trillings  (Figs.  432,  433,  p.  169). 
Crystals  prismatic  m(110)  or  flattened  vertically  by  the  oscillatory  combina- 
tion of  brachydomes.  Also  columnar,  straight,  and  divergent;  granular,  or 
compact. 

Cleavage:  ra(110)  rather  distinct;  c(001)  in  faint  traces.  Fracture 
uneven.  Brittle.  H.  =  5*5-6.  G.  =  5'9-6'2.  Luster  metallic.  Color  sil- 
ver-white, inclining  to  steel-gray.  Streak  dark  grayish  black.  Opaque. 

Comp.  —  Sulpharsenide  of  iron,  FeAsS  or  FeS2.FeAs2  =  Arsenic  46 '0,  sul- 


382  DESCRIPTIVE   MINERALOGY 

phur  197,  iron  34 -3  =  100.     Part  of  the  iron  is  sometimes  replaced  by  cobalt, 
as  in  the  variety  danaite  (3  to  9  p.  c.  Co). 

Pyr.,  etc.  —  In  the  closed  tube  may  give  at  first  a  little  yellow  sulphide  of  arsenic  and 
then  a  conspicuous  sublimate  of  metallic  arsenic  which  is  of  bright  gray  crystals  near  the 
heated  end  and  of  a  brilliant  black  amorphous  deposit  farther  away.  In  the  open  tube  gives 
sulphurous  fumes  and  a  white  sublimate  of  arsenic  trioxide.  B.B.  on  charcoal  gives  arsenical 
fumes  and  a  magnetic  globule.  Decomposed  by  nitric  acid  with  the  separation  of  sulphur. 

Diff.  —  Characterized  by  its  hardness  and  "tin-white  color;  closely  resembles  some  of 
the  sulphides  and  arsenides  of  cobalt  and  nickel,  but  identified,  in  most  cases  easily,  by  its 
blowpipe  characters.  Lollingite  does  not  give  a  decided  sulphur  reaction. 

Micro.  —  In  polished  sections  shows  a  white  color  with  scratched  and  dull  surface. 
With  HNO3  darkens  quickly  through  iridescent  colors  to  brown,  showing  rough  surface. 

Obs.  —  Found  principally  in  crystalline  rocks,  its  usual  mineral  associates  being  ores  of 
silver,  lead,  and  tin,  also  pyrite,  chalcopyrite,  and  sphalerite.  Abundant  at  Freiberg,  etc., 
in  Saxony;  at  Andreasberg,  Harz  Mts.,  Germany;  Sala,  Sweden;  Skutterud,  Norway;  at 
several  points  in  Cornwall.  In  crystals  in  the  Binnental,  Switzerland.  Crystals  of  danaite 
from  Sulitjelma,  Finland. 

In  the  United  States,  in  N.  H.,  in  gneiss,  at  Franconia  (danaite).  In  Conn.,  at  Mine 
Hill,  Roxbury,  with  siderite.  In  crystals  at  Canton,  Ga.;  Leadville,  Col.  In  twin  crys- 
tals in  quartz  ore  veins  at  Deloro,  Hastings  Co.,  Ontario. 

The  name  mispickel  is  an  old  German  term  of  doubtful  origin.  Danaite  is  from  J.  Free- 
man Dana  of  Boston  (1793-1827),  who  made  known  the  Franconia  locality. 

Use.  —  An  ore  of  arsenic. 

Safflorite.  Like  smaltite,  essentially  cobalt  diarsenide,  CoAs2.  Form  near  that  of 
arsenopyrite.  Usually  massive.  H.  =  4'5-5.  G.  =  6'9-7*3.  Color  tin-white,  soon  tar- 
nishing. From  Germany  at  Schneeberg,  Saxony;  Bieber,  Hesse;  Wittichen,  Baden; 
from  Tunaberg,  Sweden. 

Rammelsbergite.  Essentially  nickel  diarsenide,  NiAs2,  like  chloanthite.  Crystals 
resembling  arsenopyrite;  also  massive.  G.  =  6'9-7'2.  Color  tin-white  with  tinge  of  red. 
Occurs  at  Schneeberg,  Saxony,  and  at  Riechelsdorf,  Hesse,  Germany. 

Glaucodot.  Sulpharsenide  of  cobalt  and  iron,  (Co,Fe)AsS.  In  orthorhombic  crystals 
(axes,  etc.,  p.  376).  Also  massive.  H.  =  5.  G.  =  $-90-6'01.  Luster  metallic.  Color 
grayish  tin-white.  Occurs  in  the  province  of  Huasco,  Chile;  at  Hakansbo,  Sweden. 
Named  from  yXavnos,  blue,  because  used  for  making  smalt. 

ALLOCLASITE.  Probably  glaucodot  containing  bismuth  and  other  impurities.  Com- 
monly in  columnar  to  hemispherical  aggregates.  H.  =  4'5.  G.  =6'6.  Color  steel-gray. 
From  Orawitza,  Hungary. 

Wolfachite.  Probably  Ni(As,Sb)S,  near  corynite.  In  small  crystals  resembling  arse- 
nopyrite; also  columnar  radiated.  H.  =  4 '5-5.  G.  =  6 "372.  Color  silver-white  to  tin- 
white.  From  Wolfach,  Baden,  Germany. 

Melonite.  A  nickel  telluride,  NiTe2.  In  indistinct  granular  and  foliated  particles. 
Color  reddish  white,  with  metallic  luster.  From  the  Stanislaus  mine,  Cal.;  probably  also 
m  Boulder  Co.,  Col.  Found  at  Worturpa,  New  South  Wales. 


The  following  species  are  tellurides  of  gold,  silver,  etc. 

SYLVANITE.     Graphic  Tellurium. 

_  Monoclinic.  a  :  b  :  c  =  1-6339  : 1  :  M265;  0  =  89°  35'.  Often  in  branch- 
ing arborescent  forms  resembling  written  characters;  also  bladed  and  imper- 
iectly  columnar  to  granular. 

Cleavage:  6(010)  perfect.  Fracture  uneven.  Brittle.  H.  =  1-5-2. 
~'  ~  7 '9-8 -3.  Luster  metallic,  brilliant.  Color  and  streak  pure  steel-era  v 
to  silver-white,  inclining  to  yellow. 

Comp.  —  Telluride  of  gold  and  silver  (Au,Ag)Te2  with  Au  :  Ag  =  1  :  1: 
this  requires:  Tellurium  62-1,  gold  24-5,  silver  134  =  100. 
.  ,Pyr*' ej?- ~  When  a  little  of  the  powdered  mineral  is  heated  in  concentrated  sulphuric 
da  reddish  violet  color  is  given  to  the  solution.     When  treated  with  nitric  acid  is  decom- 

1  leaving  residue  of  rusty  colored  gold.     A  few  drops  of  hydrochloric  acid  added  to  this 


SULPHO-SALTS  383 

solution  yield  an  abundant  precipitate  of  silver  chloride.  In  the  open  tube  gives  a  white  sub- 
limate of  tellurium  dioxide  which  near  the  assay  is  gray;  when  treated  with  the  blowpipe 
flame  the  sublimate  fuses  to  clear  transparent  drops.  B.B.  on  charcoal  fuses  to  a  dark  gray 
globule,  covering  the  coal  with  a  white  coating,  which  treated  in  R.F.  disappears,  giving  a 
bluish  green  color  to  the  flame;  after  long  blowing  a  yellow,  malleable  metallic  globule  is 
obtained. 

Obs.  —  With  gold,  at  OffenMnya,  Transylvania;  also  at  Nagyag.  With  calaverite  at 
Kalgoorlie  district,  West  Australia.  In  CaL,  Calaveras  Co.,  at  the  Melones  and  Stanislaus 
mines.  In  Boulder  Co.,  at  Cripple  Creek  and  elsewhere  in  Col.  Named  from  Transyl- 
vania, where  first  found,  and  in  allusion  to  sylvanium,  one  of  the  names  at  first  proposed 
for  the  metal  tellurium. 

Use.  —  An  ore  of  gold 

Krennerite.  A  telluride  of  gold  and  silver  (Au,Ag)Te2  like  sylyanite.  In  prismatic 
crystals  (orthorhombic),  vertically  striated.  G.  =  8 '353.  Color  silver-white  to  brass- 
yellow.  From  Nagyag,  Transylvania;  Cripple  Creek,  Col. 

Calaverite.  A  gold  telluride,  AuTe2  with  small  amounts  of  silver.  Monoclmic.  In 
small  lath-shaped  crystals  striated  parallel  to  their  length.  Massive  granular  to  crystalline. 
H.  =  2'5.  G:  =  9*043.  Color  silver-white  with  often  a  faint  yellow  tinge.  Tests  similar 
to  those  for  sylvanite  with  smaller  amount  of  silver  showing.  Occurs  with  petzite  at  the 
Stanislaus  mine,  Calaveras  county,  Cal.  An  important  gold  ore  at  the  Cripple  Creek  dis- 
trict, Col.  Found  elsewhere  in  that  state.  Occurs  abundantly  at  Kalgoorlie,  West 
Australia. 

Muthmannite.  (Ag,Au)Te.  In  tabular  crystals  usually  elongated  in  one  direction. 
One  perfect  cleavage  parallel  to  elongation.  H.  =  2 '5.  Color  bright  brass-yellow,  on  fresh 
fracture  gray-white.  Probably  from  Nagyag,  Transylvania.  Empressite,  AgTe,  from  the 
Empress-Josephine  mine,  in  the  Kerber  Creek  District,  Col.,  is  probably  a  gold-free 
variety.  Massive.  H.  =  3-3 '5.  G.  =  7'5.  Color  pale  bronze. 

Nagyagite.  A  sulpho-telluride  of  lead  and  gold;  some  analyses  show  also  about  7  p.  c. 
of  antimony  which  was  probably  due  to  impurities.  Orthorhombic.  Crystals  tabular 
||  6(010);  also  granular  massive,  foliated.  Cleavage:  b  perfect;  flexible.  H.  =  1-1 '5. 
G.  =  6'85-7'2.  Luster  metallic,  splendent.  Streak  and  color  blackish  lead-gray.  Opaque. 
From  Nagyag,  Transylvania;  and  at  Offenbanya.  Reported] from  Colorado  and  Tararu 
Creek,  New  Zealand. 

Oxysulphides 

Here  are  included  Kermesite,  Sb2S2O,  and  Voltzite,  Zn5S40. 

Kermesite.  Pyrostibite.  Antimony  oxysulphide,  Sb2S2O  or  2Sb2S3.Sb2O3.  Mono- 
clinic.  Usually  in  tufts  of  capillary  crystals.  Cleavage:  a(100)  perfect.  H.  =  1-1 -5. 
G.  =  4'5-4'6.  Luster  adamantine.  Color  cherry-red. 

Results  from  the  alteration  of  stibnite.  Occurs  at  Malaczka,  Hungary;  Braunsdorf, 
Saxony:  Allernont,  Dauphine,  France.  At  South  Ham,  Wolfe  Co.,  Quebec,  Canada;  with 
native  antimony  and  stibnite  at  the  Prince  William  mine,  York  Co.,  New  Brunswick. 

Named  from  kermes,  a  name  given  (from  the  Persian  qurmizq,  crimson)  in  the  older 
chemistry  to  red  amorphous  antimony  trisulphide,  often  mixed  with  antimony  trioxide. 

Voltzite.  Zinc  oxysulphide,  Zn6S4O  or  4ZnS.ZnO.  In  implanted  spherical  globules. 
H.  =  4-4'5.  G.  =  3'66-3'80.  Color  dirty  rose-red,  yellowish.  Occurs  near  Pontgibaud, 
Puy-de-D6me,  France;  Joachimstal,  Bohemia;  Marienberg,  Saxony,  Germany. 


IH.   SULPHO-SALTS 

I.   Sulpharsenites,  Sulphantimonites,  Sulphobismuthites. 
H.   Sulpharsenates,  Sulphostannates,  etc. 

I.   Sulpharsenites,  Sulphantimonites,  etc. 

In  these  sulphosalts,  as  further  explained  on  p.  320,  sulphur  takes  the 
place  of  the  oxygen  in  the  commoner  and  better  understood  oxygen  acids  (as 
carbonic  acid,  H2C03,  sulphuric  acid,  H4S04,  phosphoric  acid,  H3PO4,  etc.). 

The  species  included  are  salts  of  the  sulpho-acids  of  trivalent  arsenic, 
antimony  and  bismuth.  The  most  important  acids  are  the  ortho-acids, 


384  DESCRIPTIVE   MINERALOGY 

H3AsS3,  etc.,  and  the  meta-acids,  H2AsS2,  etc.;  but  H4As2S5,  etc.,  and  a  series 
of  others  are  included.  The  metals  present  as  bases  are  chiefly  copper,  silver, 
lead;  also  zinc,  mercury,  iron,  rarely  others  (as  nickel,  cobalt}  in  small  amount. 
In  view  of  the  hypothetical  character  of  many  of  the  acids  whose  salts  are  here 
represented,  there  is  a  certain  advantage,  for  the  sake  of  comparison,  in  writi  ig 
the  composition  after  the  dualistic  method,  RS.As2S3,  2RS.As2S3,  etc. 

As  a  large  part  of  the  species  here  included  are  rare  and  hence  to  be  men- 
tioned but  briefly,  the  classification  can  be  only  partially  developed.  The 
divisions  under  the  first  and  more  important  section  of  sulpharsenites,  etc., 
with  the  prominent  species  under  each,  are  as  follows: 

A.  Acidic  Division.          RS  :  (As,Sb,Bi)2S3  =  1  :  3,  1  :  2,  2  :  3,  3  :  4,  4  :  5. 

B.  Meta-  Division.         RS  :  (As,Sb,Bi)2S3  =  1:1. 

General  formula:  RAs2S4,RSb2S4,RBi2S4.  ;  : 

Zinkenite  Group 

Zinkenite  .  PbS.Sb2S3  Emplectite  CuoS.Bi2S3 

Sartorite  PbS.As2S3  Chalcostibite  Cu2S.Sb2S3,  etc. 

Also 

Miargyrite  Ag2S.Sb2S3  Lorandite  Tl2S.As2S3 

C.  Intermediate  Division.         RS  :  (As,Sb,Bi)2S3  =  5  :  4,  3  :  2,  2  :  1,  5  :  2 
Here  belong 

Plagionite  5PbS.4Sb2S3. 

Schirmerite  3(Ag2,Pb)S.2Bi2S3       Klaprotholite    3Cu2S.2Bi2S3,  etc. 

Jamesonite  Group 

Jamesonite  2PbS.Sb2S3  Cosalite  2PbS.Bi2S3,  etc. 

Dufrenoysite  2PbS.As2S3 

Also  Freieslebenite  5(Ag2,Pb)S.2Sb2S3       Boulangerite    5PbS.2Sb2S3 

D.  Ortho-  Division.  RS  :  (As,Sb,Bi)2S3  =3:1 

General  formula:      R3AsS3,R3SbS3;  R3As2S6,R3Sb2S6,  etc. 

Bournonite  Group 

Bournonite  3(Cu2,Pb)S.Sb2S3        Wittichenite     3Cu2S.Bi2S3 

Seligmannite  3(Cu2,Pb)S.As2S3         LiUianite          3PbS.Bi2S3,  etc. 

Aikmite  3(Pb,Cu2)S.Bi2S3 

Pyrargyrite  Group 

Pyrargyrite  3Ag2S.Sb2S3  Proustite          3Ag2S.As2S3 

E.  Basic  Division.          RS  :  (As,Sb,Bi)2S3  =  4  :  1,  5  :  1,  6  :  1,  9  :  1,  12  :  1 

Tetrahedrite  Group 
Tetrahedrite  4Cu2S.Sb2S3  Tennantite 


SULPHO-SALTS  385 

Jordanite  Group 

Jordanite  4PbS.As2S3  Meneghinite  4PbS.Sb2S3 

Also 

Geocronite  5PbS.Sb2S3  Stephanite  5Ag2S.Sb2S3 

Kilbrickenite  6PbS.Sb2S3  Beegerite  6PbS.Bi2S3 

Polybasite  Group 

Polybasite  9Ag2S.Sb2S3  Pearceite 

Polyargyrite  12Ag2S.Sb2S3 


A.   Acidic  Division 

Eichbergite.  (Cu,Fe)2S.3(Bi,Sb)2S8.  Color  iron-gray.  H.  >  6.  G.  =  5*36.  From 
Eichberg,  Semmering  district,  Austria. 

Livingstonite.  HgS.2Sb2S3.  Resembles  stibnite  in  form.  Color  lead-gray;  streak 
red.  H.  =2.  G.  =  4'81.  From  Huitzuco,  Mexico. 

Histrixite.  5CuFeS2.2Sb2S3.7Bi2S3.  Orthorhombic.  In  radiating  groups  of  prismatic 
crystals.  H.  =  2.  Color  and  streak  steel-gray.  Found  at  Ringville,  Tasmania. 

Chiviatite.     2PbS.3Bi2S3.     Foliated  massive.     Color  lead-gray.     From  Chiviato,  Peru. 

Cuprobismutite.  Probably  3Cu2S.4Bi2S3,  in  part  argentiferous.  Resembles  bismuth- 
inite.  G.  =  6*3-67.  From  Hall  valley,  Park  Co.,  Col. 

Rezbanyite.  4PbS.5Bi2S3.  Fine-granular,  massive.  Color  lead-gray.  G.  =  6' 1-6*4. 
From  Rezbanya,  Hungary. 


B.   Meta-  Division.     RS.As2S3,  RS.Sb2S3,  etc. 

Zinkenite  Group.     Orthorhombic 
ZINKENITE.     Zinckenite. 

Orthorhombic.  Axes  a  :  b  :  c  =  0'5575  : 1  :  0*6353.  Crystals  seldom  dis- 
tinct ;  sometimes  in  nearly  hexagonal  forms  through  twinning.  Lateral  faces 
longitudinally  striated.  Also  columnar,  fibrous,  massive. 

Cleavage  not  distinct.  Fracture  slightly  uneven.  H.  =  3-3*5.  G.  = 
5*30-5*35-  Luster  metallic.  Color  and  streak  steel-gray.  Opaque. 

.  Comp.  —  PbSb2S4  or  PbS.Sb2S3  =  Sulphur  22*3,  antimony  41*8,  lead 
35*9  =  100.  Arsenic  sometimes  replaces  part  of  the  antimony. 

Pyr.,  etc.  —  Decrepitates  and  fuses  very  easily;  in  the  closed  tube  gives  a  faint  subli- 
mate of  sulphur,  and  antimony  trisulphide.  In  the  open  tube  sulphurous  fumes  and  a 
white  sublimate  of  oxide  of  antimony;  the  arsenical  variety  gives  also  arsenical  fumes.  On 
charcoal  is  almost  entirely  volatilized,  giving  a  coating  which  on  the  outer  edge  is  white, 
and  near  the  assay  dark  yellow;  with  soda  in  R.F.  yields  globules  of  lead.  Soluble  in  hot 
hydrochloric  acid  with  evolution  of  hydrogen  sulphide  and  separation  of  lead  chloride  on 
cooling. 

Obs.  —  Occurs  at  Wolfsberg  in  the  Harz  Mts.;  Kinzigtal,  Baden;  Val  Sugana,  Tyrol; 
Oruro,  Bolivia;  Sevier  County,  Ark.;  San  Juan  Co.,  Col. 

Andorite.  Ag2S.2PbS.3Sb2S3.  In  prismatic,  Orthorhombic  crystals.  H.  =  3-3'5. 
G.  =  5*5.  Color  dark  gray  to  black.  From  Felsobanya,  Hungary;  Oruro,  Bolivia. 
Webnerite  and  Sundtite  are  identical  with  andorite. 

Sartorite.  PbS.  As2S3.  In  slender,  striated  crystals,  probably  monoclinic.  G.  =  5'4. 
Color  dark  lead-gray.  Occurs  in  the  dolomite  of  the  Binnental. 

Platynite.  PbS.Bi2Se3.  Rhombohedral.  Basal  and  rhombohedral  cleavages.  H.  = 
2-3.  G.  =  7'98.  Color  like  graphite.  Streak  shining.  In  small  lamellae  in  quartz  at 
Falun,  Sweden. 


386  DESCRIPTIVE   MINERALOGY 

Emplectite.  Cu2S.Bi2S3.  In  thin  striated  prisms.  G.  =  6'3-6'5.  Color  grayish  white 
to  tin-white.  Occurs  in  quartz  at  Schwarzenberg  and  Annaberg,  Saxony. 

Chalcostibite.  Wolfsbergite.  Cu2S.Sb2S3.  In  small  aggregated  prisms;  also  fine 
granular,  massive.  G.  =  475-5 '0.  Color  between  lead-gray  and  iron-gray.  From  Wolfs- 
berg  in  the  Harz  Mts.;  from  Huanchaca,  Bolivia.  Guejarite  from  Spain  is  the  same  species. 

Galenobismutite.  PbS.Bi2S3;  also  with  Ag,Cu.  Crystalline  columnar  to  compact. 
Color  lead-gray  to  tin-white.  G.  =  b'9.  From  Nordmark,  Sweden;  Poughkeepsie  Gulch, 
Col.  (alaskaite,  argentiferous) ;  material  from  Falun,  Sweden,  containing  selenium  has  been 
named  weibullite  and  given  the  formula,  2PbS.Bi4S3Se3. 

Berthierite.  FeS.Sb2S3.  Fibrous  massive,  granular.  G.  =  4'0.  Color  dark  steel- 
gray.  From  Chazelles  and  Martouret,  Auvergne,  France;  Charbes,  Val  de  Ville,  Alsace; 
Braunsdorf,  Saxony,  etc. 

Matildite.  Ag2S.Bi2S3.  In  slender,  prismatic  crystals.  G.  =  6-9.  Color  gray. 
From  Morochoca,  Peru;  Lake]  City,  Col.  PLENARGYRITE,  from  Schapbach,  Baden, 
similar  in  composition,  has  been  shown  to  be  a  mixture. 


Miargyrite.  Ag2S.Sb2S3.  In  complex  monoclinic  crystals,  also  massive.  H.  =  2-2-5. 
G.  =  5'1-5'30.  Luster  metallic-adamantine.  Color  iron-black  to  steel-gray,  in  thin  splin- 
ters deep  blood-red.  Streak  cherry-red.  From  Braunsdorf,  Saxony;  Felsobanya  and 
Nagybanya,  Hungary;  Pfibram,  Bohemia;  Zacatecas,  Mexico;  Bolivia. 

Smithite.  Ag2S.Sb2S3.  Monoclinic.  Crystals  resemble  a  flattened  hexagonal  pyra- 
mid. One  perfect  cleavage.  H.  =  T5^2.  G.  =  4'9.  Color  light  red  changing  to  orange- 
red  on  exposure  to  light.  Streak  vermilion.  From  the  Binnental,  Switzerland. 

Trechmanite.  Ag2S.As2S3.  Rhombohedral,  tetartohedral.  Crystals  minute  with  pris- 
matic habit.  Good  rhombohedral  cleavage.  H.  =  T5-2.  Color  and  streak  scarlet- 
vermilion.  From  the  Binnental,  Switzerland. 

Lorandite.  A  sulpharsenide  of  thallium,  TlAsS2.  Monoclinic.  Color  cochineal-red. 
From  Allchar,  Macedonia;  Rambler  mine,  Encampment,  Wy. 

Vrbaite.  TlAs2SbS5.  Orthorhombic.  H.  =  3'5.  G.  =  5'3.  Color  gray-black  to 
dark  red  in  thin  splinters.  Streak  light  red.  From  Allchar,  Macedonia. 

Hutchinsonite.  (Tl,Ag,Cu)2S.As2S3+PbS.As2S3(?).  Orthorhombic.  In  flattened  rhom- 
bic prisms.  Cleavage  o(100)  good.  H.  =  1-5-2.  G.  =  4'6.  Color  scarlet  to  red.  From 
the  Binnental,  Switzerland. 


C.   Intermediate  Division 

Baumhauerite.  4PbS.3As2S3.  Monoclinic.  In  complex  crystals  with  varied  habit 
One  perfect  cleavage.  H.  =  3.  G.  =  3 -3.  Metallic.  Color  lead  to  steel-gray.  From 
the  Binnental,  Switzerland. 

Schirmerite.  3(Ag2,Pb)S.2Bi2S3.  Massive,  granular.  G.  =  674.  Color  lead-gray. 
Treasury  lode,  Park  Co.,  Col. 

KLAPROTHOLITE.  3Cu2S.Bi2S3.  In  furrowed  prismatic  crystals.  G.  =  4'6.  Color 
steel-gray.  Wittichen,  Baden.  Probably  a  mixture  and  not  a  definite  species. 

Rathite.  3PbS.2As2S3.  Orthorhombic,  in  prismatic  crystals.  Cleavage,  6(010). 
H.  =  3.  G.  =  5'41.  From  the  Binnental,  Switzerland.  Wiltshireite  is  the  same  species. 


Jamesonite  Group.     2RS.As2S3,  2RS.Sb2S3,  etc.     Monoclinic 

JAMESONITE. 

Monoclinic.  QAxes:  a  :  b  :  c  =  0'8316  :  1  :  0-4260.  0  =  88°  36'.  mm'" 
110  A  110  =  79°  28'.  In  acicular  crystals;  common  in  capillary  forms;  also 
fibrous  massive,  parallel  or  divergent;  compact  massive. 

Cleavage:     basal,    perfect.     Fracture    uneven    to    conchoidal.     Brittle. 

-  2-3-  G.  =  5-5-6-0.  Luster  metallic.  Color  steel-gray  to  dark  lead- 
gray.  Streak  grayish  black.  Opaque. 

Comp.  —  Pb2Sb2S5  or  2PbS.Sb2S3  =  Sulphur  197,  antimony  29'5,  lead 


SULPHO-SALTS  387 

50-8  =  100.  Most  varieties  show  a  little  iron  (1  to  3  p.  c.),  and  some  contain 
also  silver,  copper,  and  zinc. 

It  has  been  suggested  that  the  iron  shown  by  the  analyses  is  an  integral  part  of  the 
mineral  and  that  the  formula  should  be  4PbS.FeS.3Sb2S3  and  that  the  usual  jamesonite  for- 
mula, 2PbS.Sb2S3,  belongs  to  the  material  commonly  called  plumosite. 

Pyr.  —  Same  as  for  zinkenite,  p.  385. 

Obs.  —  Occurs  principally  in  Cornwall;  also  in  Siberia;  Hungary;  at  Valentia  d* Al- 
cantara in  Spain;  at  the  antimony  mines  in  Sevier  Co.,  Ark.;  from  Bolivia.  Named  after 
Prof.  Robert  Jameson  of  Edinburgh  (1774-1854). 

The  feather  ore  occurs  at  Wolfsberg,  etc.,  in  the  Harz  Mts.;  Freiberg,  Germany;  Schem- 
nitz,  Hungary;  in  Tuscany,  near  Bottino,  Italy.  These  so-called  feather  ores  may  be  di- 
vided into  flexible  and  brittle,  all  the  latter  being  referred  to  jamesonite  and  the  former  to 
either  zinkenite,  plumosite,  boulangerite,  or  meneghinite. 

Warrenite  has  been  shown  to  probably  be  a  mixture  of  jamesonite  and  zinkenite. 

Dufrenoysite.  2PbS.As2S3.  In  highly  modified  crystals;  also  massive.  Cleavage- 
6(010)  perfect.  H.  =3.  G.  =  5'55-5'57.  Color  blackish  lead-gray.  From  the  Bin- 
nental,  Switzerland,  in  dolomite. 

Cosalite.  2PbS.Bi2S3.  Usually  massive,  fibrous  or  radiated.  G.  =  6'39-675.  Color 
lead-  or  steel-gray.  Cosala,  Province  of  Sinaloa,  Mexico;  Bjelke  mine  (bjelkite),  Nord- 
mark,  Sweden;  Deer  Park,  Wash.;  Col. 

Kobellite.  2PbS.(Bi,Sb)2S3.  Fibrous  radiated  or  granular  massive.  G.  =  6'3.  Color 
lead-gray  to  steel-gray.  From  Hvena,  Sweden;  Ouray,  Col. 

BRONGNIARDITE.  Lead,  silver,  antimony  sulphide.  Shown  in  some  cases  to  be  a 
mixture.  A  doubtful  species. 

Plagionite.  Heteromorphite.  Semseyite.  Lead,  antimony  sulphides  ranging  from 
5PbS4.Sb2S3  to  9PbS.4Sb2S3.  Perhaps  a  morphotropic  series  with  the  vertical  crystallo- 
graphic  axis  increasing  in  length  with  increase  in  the  percentage  of  lead.  Monoclinio. 
G.  =  5'4-5'9.  Plagionite  from  Wolfsberg,  Harz  Mts.;  heteromorphite  from  Arnsberg, 
Westphalia;  semseyite  from  Felsobanya,  Hungary  and  Wolfsberg.  Liveingite  from  the 
Binnental,  Switzerland,  is  said  to  have  the  same  composition  as  plagionite.  Bismuto- 
plagionite,  a  variety  containing  bismuth  instead  of  antimony.  From  Wickes,  Jefferson 
Co.,  Mon. 

SCHAPBACHITE.  A  lead,  silver,  bismuth  sulphide.  From  Schapbach,  Baden.  Shown  to 
be  a  mixture. 


FREIESLEBENITE. 

Monoclinic.  Axes  a  :  b  :  c  =  0-5871  :  1  :  0-9277;  ft  =  87°  46'.  Habit 
prismatic.  G.  =  6-2-6-4.  Luster  metallic.  Color  and  streak  light  steel- 
gray  inclining  to  silver-white,  also  to  blackish  lead-gray. 

Comp.  —  (Pb,Ag2)5Sb4Sii  or  5(Pb,Ag2)S.2Sb2S3. 

Obs.  —  From  Freiberg,  Saxony;  Kapnik  and  Felsobanya,  Hungary;  Hiendelencina, 
Spain;  also  from  the  Augusta  Mt.,  Gunnison  Co.,  Col. 

Diaphorite.  Like  freieslebenite  in  composition  but  orthorhombic  in  form.  G.  =  5'9. 
From  Pfibram,  Bohemia;  Lake  Chelan  district,  Wash. 

BOULANGERITE. 

Orthorhombic.  Axes  a  :  b  :  c  =  0*5527  :  1  :  0*7478.  In  prismatic  or  tabu- 
lar crystals  or  crystalline  plumose  masses;  granular,  compact.  H.  =  2*5-3. 
G.  =  6-18.  Luster  metallic.  Color  bluish  lead-gray;  often  covered  with 
yellow  spots  from  oxidation.  Opaque. 

Comp.  —  Pb5Sb4Sn  or  5PbS.2Sh>S3  =  Sulphur  18'9,  antimony  25*7,  lead 
55-4  =  100. 

Pyr.  —  Same  as  for  zinkenite,  p.  385. 

Obs.  —  In  good  crystals  from  Sala,  Sweden;  Molieres,  Depart,  du  Gard,  France;  at 
Nerchinsk,  Siberia;  Wolfsberg  in  the  Harz  Mts.  Pfibram,  Bohemia;  near  Bottino,  Tus- 
cany, Italy.  Echo  District,  Union  county,  Nev. 

Embrithite  and  plumbostib  are  from  Nerchinsk;  they  correspond  nearly  to  10PbS.3Sb2Sj, 
but  the  material  analyzed  may  not  have  been  quite  pure. 


388 


DESCRIPTIVE   MINERALOGY 


Mullanite.  5PbS.2Sb2S3.  In  slender  orthorhombic  (?)  prisms.  Cleavage,  c(001)  and 
6(010).  Color,  steel-gray.  Streak,  brownish  black  H.  =  3'5.  G  =  6'35.  Found  at 
Gold  Hunter  mine,  near  Mullan,  Idaho,  and  at  Iron  Mountain  mine,  near  Superior,  Mon. 

D.   Ortho-  Division.     3RS.As2S3,  3RS.Sb2S3,  etc. 
Bournonite  Group.     Orthorhombic.     Prismatic  angle  86°  to  87° 


BOURNONITE.    Wheel  Ore. 

Orthorhombic.  Axes:  a  :  b 
mm"'  110  A  110  =  86° 
co,  001  A  101  =  43C 


:  c  =  0-9380 

20' 

43' 


669 


Harz 


Kapnik 

steel-gray, 


1  :  0-8969. 

en,  001  A  Oil  =  41°  53' 

cu,  001  A  112  =  33°  15' 

Twins:  tw.  pi.  ra(110), 
often  repeated,  forming 
cruciform  and  wheel  shaped 
crystals.  Also  massive; 
granular,  compact. 

Cleavage:  6(010)  imper- 
fect; a(100),  c(001)  less 
distinct.  Fracture  sub- 
conchoidal  to  uneven. 
Rather  brittle.  H.  =  2-5-3. 
G.  =  5-7-5-9.  Lustermetal- 
inclining  to  blackish  lead- 


lie,   brilliant.     Color    and    streak 
gray  or  iron-black.     Opaque. 

Comp.  —  (Pb,Cu2)3Sb2S6  or  3(Pb,Cu2)S.Sb2S3  =  PbCuSbS3  (if  Pb  :  Cu2 
=  2:1)  =  Sulphur  19'8,  antimony  247,  lead  42*5,  copper  13*0  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  decrepitates,  and  gives  a  dark  red  sublimate.  In  the 
open  tube  gives  sulphur  dioxide,  and  a  white  sublimate  of  oxide  of  antimony.  B.B.  on  char- 
coal fuses  easily,  and  at  first  coats  the  coal  white;  continued  blowing  gives  a  yellow  coating 
of  lead  oxide;  the  residue,  treated  with  soda  in  R.F.,  gives  a  globule  of  copper.  Decom- 
posed by  nitric  acid,  affording  a  blue  solution,  and  leaving  a  residue  of  sulphur,  and  a  white 
powder  containing  antimony  and  lead. 

Obs.  —  From  Neudorf  in  the  Harz  Mts.;  also  Wolfsberg,  Claustal,  and  Andreasberg; 
Pfibram,  Bohemia;  Kapnik  and  Nagybanya,  Hungary;  Horhausen,  Prussia;  Liskeard, 
Cornwall. 

In  the  United  States  at  the  Boggs  mine,  Yavapai  Co.,  Ariz.;  also  Montgomery  Co.,  Ark.; 
reported  from  San  Juan  Co.,  Col;  Austin,  Ney.  In  Canada,  in  the  township  of  Marmora, 
Hastings  Co.,  and  Darling,  Lanark  Co.,  Ontario. 

Seligmannite.  (Pb,Cu2)3As2S6  isomorphous  with  bournonite.  Orthorhombic.  a  :  b  :  c 
=  0*9233  :  1  :  0'8734.  In  small  complex  crystals.  Commonly  twinned  with  m(110)  as 
tw.  pi.  Color  lead-gray.  Chocolate  streak.  H.  =  3.  Found  at  Lengenbach  quarry, 
Binnental,  Switzerland;  reported  from  Emery,  Mon. 

Aikinite.  2PbS.Cu2S.Bi2S3.  Acicular  crystals;  also  massive.  G.  =  6'l-6'8.  Color 
blackish  lead-gray.  From  Berezov  near  Ekaterinburg,  Ural  Mts. 

Wittichenite.  3Cu2S.Bi2S3.  Rarely  in  crystals  resembling  bournonite;  also  massive. 
G.  =  4*5.  Color  steel-gray  or  tin-white.  Wittichen,  Baden,  etc. 

Stylotypite.  3(Cu2,Ag2,Fe)S.Sb2S3.  In  orthorhombic  crystals,  in  cruciform  twins  like 
bournonite.  G.  =  47-5'2.  Color  iron-black.  Copiapo,  Chile;  Peru. 


Lfflianite.  3PbS.BiSbS3  and  3PbS.Bi2S3.  Orthorhombic.  Crystalline  and  massive. 
Color  steel-gray.  Gladhammar,  Sweden;  Leadville,  Col.  (argentiferous). 

Guitermanite.  Perhaps  3PbS.As2S3.  Massive,  compact.  G.  =  5-94.  Color  bluish 
gray.  Zufii  mine,  Silvertqn,  Col. 

Lengenbachite.  7[Pb,(Ag,Cu)2]S.2As2S3.  Probably  triclinic.  In  thin  blade-shaped 
crystals.  One  perfect  cleavage.  Soft.  G.  =  5*8.  Color  steel-gray.  Streak  black. 
From  the  Lengenbach  quarry,  Binnental,  Switzerland. 


SULPHO-SALTS 


389 


670 


671 


TAPALPITE.  A  sulpho-telluride  of  bismuth  and  silver,  perhaps  3Ag2(S,Te).Bii(S,Te)8. 
Study  of  polished  specimen  shows  it  to  be  a  mixture  of  unknown  components.  Massive, 
granular.  G.  =  7 '80.  Sierra  de  Tapalpa,  Jalisco,  Mexico. 

Pyrargyrite  Group.     Rhombohedral-hemimorphic 
PYRARGYRITE.    Ruby  Silver  Ore.    Dark  Red  Silver  Ore. 

Rhombohedral-hemimorphic.    Axis:  c  =  07892;  0001  A  1011  =  42°20J.' 
ee',  0112  A  1012  =  42°    5'  tw',  2131  A  2311  =  74°  25' 

rrf,  1011  A  1101  =  71°  22'  yyv,  2131  A  3121  =  35°  12' 

Crystals    commonly    prismatic. 
Twins:    tw.  pi.    a(1120),    very    com- 
mon,   the    c    axes    parallel; 
also  common.     Also  massive,  compact. 

Cleavage:  r(1011)  distinct;  e(0112) 
imperfect.  Fracture  conchoidal  to 
uneven.  Brittle.  H.  =  2-5.  G.  =  577- 
5*86;  5-85  if  pure.  Luster  metallic- 
adamantine.  Color  black  to  grayish 
black,  by  transmitted  light  deep  red. 
Streak  purplish  red.  Nearly  opaque,  '<cd^r=J' 
but  transparent  in  very  thin  splinters. 
Optically  -  .  Refractive  indices,  co  =  3'084,  e  =  2-881. 

Comp.  —  Ag3SbS3  or  3Ag2S.Sb?S3  =  Sulphur  17'8,  antimony  22'3,  silver 
59'9  =  100.  Some  varieties  contain  small  amounts  of  arsenic. 

Pyr.,  etc.  —  In  the  closed  tube  fuses  and  gives  a  reddish  sublimate  of  antimony  oxysul- 
phide;  in  the  open  tube  sulphurous  fumes  and  a  white  sublimate  of  oxide  of  antimony. 
B.B.  on  charcoal  fuses  with  spirting  to  a  globule,  coats  the  coal  white,  and  the  assay  is 
conyerted  into  silver  sulphide,  which,  treated  in  O.F.,  or  with  soda  in  R.F..  gives  a  globule 
of  silver.  In  case  arsenic  is  present  it  may  be  detected  by  fusing  the  pulverized  mineral 
with  soda  on  charcoal  in  R.F.  Decomposed  by  nitric  acid  with  the  separation  of  sulphur 
and  of  antimony  trioxide. 

Obs.  —  Occurs  at  Andreasberg  in  the  Harz  Mts.;  Freiberg,  Saxony;  Pfibram  and 
Joachimstal,  Bohemia;  Schemnitz  and  Nagybanya,  Hungary;  Kongsberg,  Norway; 
Gaudalcanal,  Spain;  in  Cornwall.  In  Mexico  it  is  worked  at  Guanajuato  and  elsewhere  as 
an  ore  of  silver.  In  Chile  with  proustite  at  Chanarcillo  near  Copiapo. 

In  Col.,  not  uncommon;  thus  in  Ruby  district,  Gunnison  Co.;  with  sphalerite  in 
Sneffle's  district,  Ouray  Co.,  etc.  In  Nev.,  at  Washoe  in  Daney  Mine;  about  Austin, 
Reese  river;  at  Poorman  lode,  Idaho,  in  masses  with  cerargyrite.  In  N.  M.,  Utah,  and 
Ariz,  with  silver  ores  at  various  points.  At  Cobalt,  Ontario. 

Named  from  wvp,  fire,  and  apyvpos,  silver,  in  allusion  to  the  color. 

PROUSTITE.     Ruby  Silver  Ore.     Light  Red  Silver  Ore. 

Rhombuhedral-hemimorphic.     Axis  c  =  0'8039;_  0001  _A  1011  =  42°  52'. 

ee',  0112  A  1012  =  42°  46'  w',  2131  A  2311  =  74°  39' 

rr',  1011  A  1101  =  72°  12'  Wv,  2131  A  3121  =  35°  18' 

Crystals  often  acute  rhombohedral  or  scalenohedral.     Twins:    tw.  pi. 

w(1014)  and  r(10HX     Also  massive,  compact. 

Cleavage:  r(1011)  distinct.  Fracture  conchoidal  to  uneven.  Brittle. 
H.  =  2-2-5.  G.  =  5-57-5*64;  5'57ifpure.  Luster  admantine.  Color  scarlet- 
vermilion;  streak  same,  also  inclined  to  aurora-red.  Transparent  to  trans- 
lucent. Optically  negative,  co  =  3'084.  e  =  2-881. 

Comp.  —  AgsAsSa  or  3Ag2S.As2S3  =  Sulphur  19'4,  arsenic  15'2,  silver 
65*4  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  fuses  easily,  and  gives  a  faint  sublimate  of  arsenic  tri- 
sulphide;  in  the  open  tube  sulphurous  fumes  and  a  white  crystalline  sublimate  of  arsenic 


390  DESCRIPTIVE   MINERALOGY 

trioxide.  B.B.  on  charcoal  fuses  and  emits  odors  of  sulphur  and  arsenic;  with  soda  in 
R.F.  gives  a  globule  of  silver.  Decomposed  by  nitric  acid,  with  separation  of  sulphur. 

Obs.  —  Occurs  at  Freiberg,  Johanngeorgenstadt,  etc.,  in  Saxony;  Joachimstal,  Bohe- 
mia; in  France  at  Chalanches  in  Dauphine  and  Markirch,  Alsace;  Guadalcanal  in  Spain; 
Sarrabus,  Sardinia;  in  Mexico;  Peru;  Chile,  at  Chanarcillo  in  magnificent  crystallizations. 

In  Col.,  Ruby  distr.,  Gunnison  Co.;  Sheridan  mine,  San  Miguel  Co.;  Yankee  Girl 
mine,  Ouray  Co.;  Montezuma,  Summit  Co.  In  Ariz.,  with  silver  ores  at  various  points. 
In  Nev.,  in  the  Daney  mine,  and  in  Comstock  lode,  rare;  Idaho,  at  the  Poorman  lode. 

Named  after  the  French  chemist,  J.  L.  Proust  (1755-1826). 

Sanguinite.  Near  proustite  in  composition.  In  glittering  scales,  hexagonal  or  rhom- 
bohedral.  From  Chanarcillo,  Chile. 

FALKENHAYNITE.  Perhaps  3Cu2S.Sb2S3.  Massive,  resembling  galena.  From  Joachims- 
tal, Bohemia.  Perhaps  identical  with  stylotypite. 

Pyrostilpnite.  Like  pyrargyrite,  3Ag2S.Sb2S3.  In  tufts  of  slender  (monoclinic)  crys- 
tals. G.  =  4'25.  Color  hyacinth-red.  From  Andreasberg  in  the  Harz  Mts.;  Freiberg, 
Saxony;  Pribram,  Bohemia;  Heazlewood,  Tasmania. 

Samsonite.  2Ag2S.MnS.Sb2S3.  Monoclinic.  Habit  prismatic.  Color,  steel-black,  red 
in -transmitted  light.  Occurs  in  Samson  vein  of  Andreasberg  silver  mines,  Harz  Mts., 
*  Germany.  

E.   Basic  Division 
Tetrahedrite  Group.     Isometric-tetrahedral 

TETRAHEDRITE.     Gray  Copper  Ore.     Fahlerz. 

Isometric-tetrahedral.  Habit  tetrahedral.  Twins:  tw.  pi.  .0(111);  also 
with  parallel  axes  (Fig.  392,  p.  163,  Fig.  408,  p.  166).  Also  massive;  granular, 
coarse  or  fine;  compact. 

672  673  674 


Cleavage  none.  Fracture  subconchoidal  to  uneven.  Rather  brittle. 
H-  =  3-4.  G.  =  4-4-5'L  Luster  metallic,  often  splendent.  Color  between 
flint-gray  and  iron-black.  Streak  like  color,  sometimes  inclining  to  brown 
and  cherry-red.  Opaque;  sometimes  subtranslucent  (cherry-red)  in  very  thin 
splinters. 

Comp.  —  Essentially  Cu8Sb2S7  or  4Cu2S.Sb2S3  =  Sulphur  23-1,  anti- 
mony 24-8,  copper  52'1  =  100. 

Antimony  and  arsenic  are  usually  both  present  and  thus  tetrahedrite  graduates  into  the 
allied  species  tennantite.  There  are  also  varieties  containing  bismuth,  chiefly  at  the  arsen- 
ical end  of  the  series,  rarely  selenium.  Further  the  copper  may  be  replaced  by  iron,  zinc, 
silver,  mercury,  lead,  manganese,  and  rarely  cobalt  and  nickel. 

.      \ar.  —  Ordinary.     Contains  little  or  no  silver.     Color  steel-gray  to  dark  gray  and 
iron-black.     G.  =  4  '75-4*9. 

Argentiferous;   Freibergite.     Contains  3  to  30  p.  c.  of  silver.     Color  usually  steel-gray, 

r.teJ^han  the  ordinary  varieties;  sometimes  iron-black;  streak  often  reddish.     G.  = 
' 


,r. 

4  oo-o'O. 


SULPHO-SALTS  391 

Mercurial;  Schwatzite.  Contains  6  to  17  p.  c.  of  mercury.  Color  dark  gray  to  iron- 
black.  Luster  often  dull.  G.  =  5'10  chiefly. 

Malinowskite,  from  Peru  and  a  similar  variety  from  Arizona,  contain  13-16  p.  c.  of  lead. 

Pyr.,  etc.  —  Differ  in  the  different  varieties.  In  the  closed  tube  alHhe  antimonial  kinds 
fuse  and  give  a  dark  red  sublimate  of  antimony  oxysulphide;  if  much  arsenic  is  present,  a 
sublimate  of  arsenic  trisulphide  first  forms.  In  the  open  tube  fuses,  gives  sulphurous  fumes 
and  a  white  sublimate  of  antimony  oxide;  if  arsenic  is  present,  a  crystalline  volatile  subli- 
mate condenses  with  the  antimony;  if  the  ore  contains  mercury  it  condenses  in  minute 
metallic  globules.  B.B.  on  charcoal  fuses,  gives  a  coating  of  the  oxides  of  antimony  and 
sometimes  arsenic,  zinc,  and  lead;  arsenic  is  detected  by  the  odor  when  the  coating  is  treated 
in  R.F.  The  roasted  mineral  gives  with  the  fluxes  reactions  for  iron  and  copper;  with  soda 
yields  a  globule  of  metallic  copper.  Decomposed  by  nitric  acid,  with  separation  of  sulphur 
and  antimony  trioxide. 

Diff.  —  Distinguished  by  its  form,  when  crystallized,  by  its  deep  black  color  on  fracture 
and  brilliant  metallic  luster.  It  is  harder  than  bournonite  and  much  softer  than  magnetite; 
the  blowpipe  characters  are  usually  distinctive. 

Micro.  —  In  polished  sections  shows  a  grayish  white  color  with  a  smooth  surface. 
Fumes  from  HNO3  tarnish  mineral  slowly  to  a  light  brown.  With  aqua  regia  slowly  effer- 
vesces leaving  a  coating  of  sulphur  and  a  pitted  surface. 

Obs.  —  Often  associated  with  chalcopyrite,  pyrite,  sphalerite,  galena,  and  various  other 
silver,  lead,  and  copper  ores;  also  siderite.  Occurs  at  many  Cornish  mines;  thus  at  the 
Herodsfoot  mine,  Liskeard,  in  tetrahedral  crystals  often  coated  with  iridescent  chalcopyrite; 
the  Levant  mine  near  St.  Just.  In  Germany  from  Andreasberg  and  Claustal  in  the  Harz 
Mts.;  Freiberg,  Saxony;  Dillenburg  and  Horhausen  in  Nassau;  at  Miisen,  Prussia;  various 
mines  in  the  Black  Forest.  From  Pribram,  Bohemia;  Kogel  near  Brixlegg  in  Tyrol, 
Austria;  Kapnik,  Herrengrund,  Hungary.  In  Mexico,  at  Durango,  Guanajuato;  Chile; 
Bolivia,  etc.  The  argentiferous  variety  occurs  especially  at  Freiberg;  Pribram;  HuaUanca 
in  Peru,  and  elsewhere.  The  mercurial  variety  at  Schmolnitz,  Hungary;  Schwatz,  Tyrol; 
valleys  of  Angina  and  Castello,  Tuscany,  Italy. 

In  the  United  States,  tetrahedrite  occurs  at  the  Kellogg  mines,  Ark.  In  Col.,  in  Clear 
Creek,  Summit  and  Gilpin  Cos.;  the  Ulay  mine,  Lake  Co.;  with  pyrargyrite  in  Ruby  dis- 
trict, Gunnison  Co.,  etc.  Much  of  the  Colorado  "gray  copper"  is  tennantite  (see  below). 
In  Nev.,  abundant  in  Humboldt  Co.;  near  Austin  in  Lander  Co.;  Isabella  mine,  Reese 
river.  In  Utah  at  Bingham  Canyon.  In  Ariz,  at  the  Heintzelman  mine;  at  various  points 
in  British  Columbia. 

Use.  —  An  ore  of  copper  and  frequently  ore  of  the  other  metals,  like  silver,  etc.,  that 
it  may  contain. 

TENNANTITE. 

Isometric-tetrahedral.     Crystals  often  dodecahedral.     Also  massive,  com- 
pact.    H.  =  3-4.     G.  =  4-37-4-49.     Color  blackish  lead-gray  to  iron-black. 
Comp.  —  Essentially  Cu8As2S7  or  4Cii2S.As2S3  =  Sulphur  25*5,  arsenic 
17-0,  copper  57'5  =  100. 

Var.  —  Often  contains  antimony  and  thus  graduates  into  tetrahedrite.  The  original 
tennantite  from  Cornwall  contains  only  copper  and  iron.  In  crystals,  habit  dodecahedral. 

Sandbergerite  contains  7  p.  c.  of  zinc.  Fredricite  from  Sweden  has,  besides  copper,  also 
iron,  lead,  silver,  and  tin.  Binnite  from  Binnental,  Switzerland,  is  tennantite. 

Found  at  the  Cornish  mines,  particularly  at  Wheal  Jewel  in  Gwennap,  and  Wheal  Unity 
in  Gwinear;  in  Germany  at  Freiberg,  Saxony,  and  at  the  Wilhelmine  mine  in  the  Spessart;  at 
Skutterud,  Norway.  Near  Central  City,  Idaho  Springs  and  Aspen  in  Col.  At  Butte,  Mon. 
At  Capelton,  Quebec,  Canada.  Named  after  the  chemist,  Smithson  Tennant  (1761-1815). 
See  further  above. 


Jordanite.  4PbS.As2S3  Monoclinic;  often  pseudohexagonal  by  twinning.  G.  =  6'39. 
Color  lead-gray.  From  the  Binnental,  Switzerland;  Nagyag,  Transylvania. 

Meneghinite.  4PbS.Sb2S3.  Orthorhombic.  In  slender  prismatic  crystals;  also  mas- 
sive. G.  =  6'34-6'43.  Color  blackish  lead-gray.  From  Bottino,  Tuscany,  Italy;  Mar- 
ble Lake,  Barrie  Township,  Ontario. 

GOLDFIELDITE.  5Cu2S.(Sb,As,Bi)2(S,Te)3.  As  a  crust.  Color,  dark  lead-gray.  Con- 
choidal  fracture.  H.  =  3-3 '5.  At  Mohawk  mine,  Goldfield,  Nev.  Probably  a  mixture. 


392  DESCRIPTIVE   MINERALOGY 

STEPHANITE.     Brittle  Silver  Ore. 

Orthorhombic.     Axes  a  :  b  :  c  =  0*6292  :  1  :  0'6851. 

mm"'    110  A  110  =  64°  21'  cd,   001  A  021  =  53°  52' 

c8,        001  A  101  =  47°  26'  ch,   001  A  112  =  32°  45' 

ck,        001  A  Oil  =  34°  25'  cP,  001  A  111  =  52°    9' 

675  Crystals  usually  short  prismatic  or  tabular  ||  c(001). 

Twins:  tw.  pi.  w(110),  often  repeated,  pseudo-hexagonal. 
Also  massive,  compact  and  disseminated. 

Cleavage:  6(010),  d(021)  imperfect.  Fracture  sub- 
conchoidal  to  uneven.  Brittle.  H.  =  2-2'5.  G.  =  6'2 
-6*3.  Luster  metallic.  Color  and  streak  iron-black. 
Opaque. 

Comp.  —  Ag5SbS4  or  5Ag2S.Sb2S3  =  Sulphur  16*3,  antimony  15'2,  silver 
68'5  =  100.  . 

Pyr.  —  In  the  closed  tube  decrepitates,  fuses,  and  after  long  heating  gives  a  faint 
sublimate  of  antimony  oxysulphide.  In  the  open  tube  fuses,  giving  off  antimonial  and 
sulphurous  fumes.  B.B.  on  charcoal  fuses  with  projection  of  small  particles,  coats  the  coal 
with  oxide  of  antimony,  which  after  long  blowing  is  colored  red  from  oxidized  silver,  and 
a  globule  of  metallic  silver  is  obtained.  Soluble  in  dilute  heated  nitric  acid,  sulphur  and 
antimony  trioxide  being  deposited. 

Obs.  —  In  veins,  with  other  silver  ores,  at  Freiberg,  Schneeberg,  etc.,  in  Saxony;  Pri- 
bram,  Bohemia;  Schemnitz,  Hungary;  Andreasberg  in  the  Harz  Mts.,  Germany;  Kongs- 
berg,  Norway;  Sarrabus,  Sardinia;  Wheal  Newton,  Cornwall;  Arispe,  Sonora  and  elsewhere, 
Mexico;  Peru;  Chanarcillo,  Chile. 

In  Nev.,  in  the  Comstock  lode,  Reese"  river,  etc.  In  Idaho,  at  the  silver  mines  at  Yankee 
Fork,  Queen's  River  district. 

Named  after  the  Archduke  Stephen,  Mining  Director  of  Austria. 

Geocronite.  5PbS.Sb2S3.  Rarely  in  orthorhombic  crystals  closely  resembling  those 
of  stephanite;  usually  massive,  granular.  G.  =  6 '4.  Color  lead-gray.  From  Sala, 
Sweden;  Val  Castello,  Tuscany.  Kilbrickenite  from  Kilbricken,  Co.  Clare,  Ireland,  is  the 
same  species. 


Beegerite. '  6PbS.Bi2S3.     Massive,  indistinctly  crystallized.      G.  =  7'27.     Color  light 
to  dark  gray.     From  Park  Co.,  Col. 


Ultrabasite.     HAg2S.28PbS.2Sb2S3.3GeS2    Orthorhombic.     Color    and    streak    gray- 
black.     H.  =  5.  G.  =  6.     From  Freiberg,  Germany. 


Polybasite  Group.     9RS2As2S3,  9RS.Sb2S3.     Monoclinic,  pseudo- 

rhombohedral 
POLYBASITE. 

Monoclinic.  Axes  a  :  b  :  c  =  17309  :  1  :  1'5796,  0  =  90°  0'.  Prismatic 
angle  60°  2'.  In  short  six-sided  tabular  prisms,  with  beveled  edges;  c(001) 
faces  with  triangular  striations;  in  part  repeated  twins,  tw.  pi.  m  (110). 

Cleavage:  c(001)  imperfect.  Fracture  uneven.  H.  =  2-3.  G.  =  6'0- 
6'2.  Luster  metallic.  Color  iron-black,  in  thin  splinters  cherry-red.  Streak 
black.  Nearly  opaque. 

Comp.  —  Ag9SbS6  or  9Ag2S.Sb2S3  =  Sulphur  15'0,  antimony  9'4,  silver 
75-6  =  100.  Part  of  the  silver  is  replaced  by  copper;  also  the  antimony  by 
arsenic. 

Pry.,  etc.  —  In  the  open  tube  fuses,  gives  sulphurous  and  antimonial  fumes,  the  latter 
forming  a  white  sublimate,  sometimes  mixed  with  crystalline  arsenic  trioxide.  B.B.  fuses 


SULPHO-SALTS  393 

with  spirting  to  a  globule,  gives  off  sulphurous  (sometimes  arsenical)  fumes,  and  coats  the 
coal  with  antimony  trioxide;  with  long-continued  blowing  some  varieties  give  a  faint  yellow- 
ish white  coating  of  zinc  oxide,  and  a  metallic  globule,  which  with  salt  of  phosphorus  reacts 
for  copper,  and  cupelled  with  lead  gives  pure  silver.  Decomposed  by  nitric  acid. 

Obs.  —  Occurs  in  the  mines  of  Guanajuato,  from  Las  Chipas  and  Arispe,  Sonora, 
Mexico;  at  Tres  Puntos,  desert  of  Atacama,  Chile;  At  Freiberg,  Saxony;  and  Pvibram, 
Bohemia;  at  Sarrabus,  Sardinia.  In  Nev.,  at  the  Reese  mines  and  at  the  Comstock  Lode. 
In  Col,  at  the  Terrible  Lode,  Clear  Creek  Co.,  at  Ouray.  In  Ariz.,  at  the  Silver  King 
mine;  at  Neihart,  Mon. 

Named  from  iro\vs,  many,  and  /3e*<ns,  base,  in  allusion  to  the  basic  character  of  the 
compound. 

Pearceite.  9Ag2S.As2S3.  Monoclinic,  pseudo-rhombohedral.  The  arsenical  variety 
of  polybasite.  From  Aspen,  Col.;  Marysville,  Lewis  and  Clarke  Co.,  Mon. 


Polyargyrite.     12Ag2S.Sb2S3.     In    indistinct    isometric    crystals.     G.  =  6'97.     Color 
iron-black.     Wolfach,  Baden,  Germany. 


II.     Sulpharsenates,  Sulphantimonates ;   Sulpho-stannates,  etc. 

Here  are  included  a  few  minerals,  chiefly  sulpho-salts  of  quintivalent 
arsenic  and  antimony;  also  several  sulpho-stannates  and  rare  sulpho-german- 
ates. 

ENARGITE. 

Orthorhombic.     Axes:  a  :  b  :  c  =  0*8711  :  1  :  0'8248. 

Crystals  usually  small;  prismatic  faces  vertically  striated.  Twins:  tw.  pi. 
#(320)  in  star-shaped  trillings.  Also  massive,  granular,  or  columnar. 

Cleavage  :m(l  10)  perfect;  a(100),  6(010)  distinct;  c(001)  indistinct. 
Fracture  uneven.  Brittle.  H.  =  3.  G.  =  4'43-^'45.  Luster  metallic.  Color 
grayish  black  to  iron-black.  Streak  grayish  black.  Opaque. 

Comp.  —  Cu3AsS4  or  3Cu2S.As2S5  =  Sulphur  32'6,  arsenic  19*1,  copper 
48*3  =  100.  Antimony  is  often  present,  cf.  famatinite. 

Pyr.  —  In  the  closed  tube  decrepitates,  and  gives  a  sublimate  of  sulphur;  at  a  higher 
temperature  fuses,  and  gives  a  sublimate  of  sulphide  of  arsenic.  In  the  open  tube,  heated 
gently,  the  powdered  mineral  gives  off  sulphurous  and  arsenical  fumes,  the  latter  condensing 
to  a  sublimate  containing  some  antimony  oxide.  B.B.  on  charcoal  fuses,  and  gives  a 
faint  coating  of  the  oxides  of  arsenic,  antimony,  and  zinc;  the  roasted  mineral  with  the 
fluxes  gives  a  globule  of  metallic  copper.  Soluble  in  aqua  regia. 

Micro.  —  In  polished  sections  shows  a  white  color  with  a  smooth  surface.  With  KCN 
turns  black  quickly  and  surface  is  etched;  quickly  brown  with  aqua  regia. 

Obs.  —  From  Morococha,  and  Caudalosa,  Peru;  in  Chile  and  Argentina;  Mexico; 
Matzenkopfl,  Brixlegg,  Tyrol,  Austria;  Mancayan,  island  of  Luzon;  Kinkwaseki,  Formosa. 

In  the  United  States,  at  Brewer's  gold  mine,  Chesterfield  dist.,  S.  C. ;  in  Col.,  at  mines 
near  Central  City,  Gilpi'n  Co.;  in  Park  Co.,  at  the  Missouri  mine;  from  Red  Mountain 
district.  In  southern  Utah;  also  in  the  Tintic  district;  Butte,  Mon. 

Clarite,  from  the  Clara  Mine,  Schapback,  Baden,  and  luzonite  from  the  island  of  Luzon, 
Philippines,  are  identical  with  enargite. 

Use.  —  Serves  as  an  ore  of  copper  and  arsenic. 

Famatinite.  3Cu2S.Sb2S5,  isomorphous  with  enargite.  G.  .=  4*57.  Color  gray  with 
tinge  of  copper-red.  From  the  Sierra  de  Famatina,  Argentina;  Goldfield,  Nev. 

Sulvanite.  3Cu2S.V2S5.  Massive.  H.  =  3'5.  G.  =  4'0.  Color  bronze-yellow.  Streak 
nearly  black.  From  near  Burra,  South  Australia. 


Xanthoconite. — 3Ag2S.As2Ss.  In  thin  tabular  rhombohedral  crystals;  also  massive, 
reniform.  G.  =  5.  Color  orange-yellow.  From  Freiberg,  Germany.  Rittingerite  is  the 
same  species. 


394  DESCRIPTIVE   MINERALOGY 

Epiboulangerite.  —  3PbS.Sb2S3.  In  striated  prismatic  needles  and  granular.  G.  = 
6-31.  Color  dark  bluish  gray  to  black.  From  Altenberg,  Saxony,  Germany. 

Epigenite.  —  Perhaps  4Cu2S.3FeS.As2S5.  In  short  prisms  resembling  arsenopyrite. 
Color  steel-gray.  From  Wittichen,  Baden,  Germany. 


STANNITE.     Tin  Pyrites.     Bell-metal  Ore. 

Tetragonal-sphenoidal.  Pseudo  isometric-tetrahedral  through  twinning. 
Twinning,  (1)  always  interpenetrant  with  e(101)  as  tw.  pi.,  (2)  interpenetrant 
with  twin  axis  J_  to  p(lll).  Also  massive,  granular,  and  disseminated,  ^.-i 

Cleavage:  cubic,  indistinct.  Fracture  uneven.  Brittle.  H.  =4.  G.  = 
4 -3-4 -522;  4 -506  Zinnwald.  Luster  metallic.  Streak  blackish.  Color  steel- 
gray  to  iron-black,  the  former  when  pure;  sometimes  a  bluish  tarnish;  often 
yellowish  from  the  presence  of  chalcopyrite.  Opaque. 

Comp.  —  A  sulpho-stannate  of  copper,  iron  and  sometimes  zinc, 
Cu2FeSnS4  or  Cu2S.FeS.SnS2  =  Sulphur  29-9,  tin  27-5,  copper  29'5,  iron  131 
=  100. 

Pyr.,  etc. —  In  the  closed  tube  decrepitates,  and  gives  a  faint  sublimate;  in  the  open 
tube  sulphurous  fumes.  B.B.  on  charcoal  fuses  to  a  globule,  which  in  O.F.  gives  off  sul- 
phur dioxide  and  coats  the  coal  with  tin  dioxide;  the  roasted  mineral  treated  with  borax 
gives  reactions  for  iron  and  copper.  Decomposed  by  nitric  acid,  affording  a  blue  solution, 
with  separation  of  sulphur  and  tin  dioxide. 

Obs.  —  In  Cornwall  formerly  found  at  Wheal  Rock;  and  at  Carn  Brea;  more  recently 
in  granite  at  St.  Michael's  Mount;  also  at  Stenna  Gwynn,  etc.;  at  the  Cronebane  mine,  Co. 
Wicklow,  in  Ireland;  Zinnwald,  in  the  Erzgebirge,  Germany.  Crystallized  at  Oruro, 
Bolivia.  From  the  Black  Hills,  S.  D. 

Argyrodite.  A  silver  sulpho-germanate,  Ag8GeS6  or  4Ag2S.GeS2.  Isometric,  crystals 
usually  indistinct;  at  times  they  show  octahedral  and  dodecahedral  forms  with  frequent 
twinning  according  to  the  Spinel  Law;  also  massive,  compact.  H.  =  2'5.  G.  =  6 '085- 
6*266.  Luster  metallic.  Color  steel-gray  on  a  fresh  fracture,  with  a  tinge  of  red  turning 
to  violet.  From  the  Himmelsfurst  mine,  Freiberg,  Saxony;  from  Colquechaca  and  Aul- 
lagas,  Bolivia. 

Canfieldite.  AggSnSe  or  4Ag2S.SnS2,  the  tin  in  part  replaced  by  germanium.  Iso- 
metric, in  octahedrons  with  d(l  10).  Twins  according  to  Spinel  Law.  G.  =  6 '28.  Luster 
metallic.  Color  black.  Colquechaca,  Bolivia. 

Teallite.  PbSnS2.  Orthorhombic?  In  thin  flexible  folia.  Perfect  basal  cleavage. 
H.  =  1-2.  G.  =  6-4.  Color  blackish  gray.  Streak  black.  Probably  from  Boh' via, 
exact  locality  unknown. 

Franckeite.  Pb5Sn3FeSb2S14  or  3PbSnS2  +  Pb2FeSb2S8.  Massive.  G.  =  5'55.  Color 
blackish  gray  to  black.  Las  Animas,  Bolivia. 

Cylindrite.  Pb3Sn4FeSb2S14  or  3PbSnS2  +  SnFeSb2S8.  H.  =  2'5-3.  G.  =  5'42. 
Luster  metallic.  Color  blackish  lead-gray.  In  cylindrical  forms  separating  under  pressure 
into  distinct  shells  or  folia.  Poopo,  Bolivia. 


IV.  HALOIDS.  —  CHLORIDES,  BROMIDES,   IODIDES; 
FLUORIDES 

I.  Anhydrous  Chlorides,  Bromides,  Iodides;   Fluorides. 
II.   Oxy chloride s ;   Oxyfluorides. 
m.   Hydrous  Chlorides;   Hydrous  Fluorides. 

The  Fourth  Class  includes  the  haloids,  that  is,  the  compounds  with  the 
halogen  elements,  chlorine,  bromine,  iodine,  and  also  the  less  closely  related 
fluorine. 


HALOIDS.  —  CHLORIDES,    BROMIDES,   IODIDES;    FLUORIDES        395 


I.   Anhydrous  Chlorides,  Bromides,  Iodides;   Fluorides 

CALOMEL.     Horn  Quicksilver. 

Tetragonal.  Axis  c  =  17234;  001  A  101  =  59°  52'.  Crystals  sometimes 
tabular  ||  c(001);  also  pyramidal;  often  highly  complex. 

Cleavage:  a (100)  rather  distinct;  also  r(lll).  Fracture  conchoidal. 
Sectile.  H.  =  1-2.  G.  =  6*482.  Luster  adamantine.  Color  white,  yellow- 
ish gray,  or  ash-gray,  also  grayish,  and  yellowish  white,  brown.  Streak  pale 
yellowish  white.  Translucent  —  subtranslucent.  Optically +.  o>  =  T970. 
e  =  2-650. 

Comp.  —  Mercurous  chloride,  HgCl  =  Chlorine  15 -1,  mercury  84 -9  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  volatilizes  without  fusion,  condensing  in  the  cold  part  of 
the  tube  as  a  white  sublimate;  with  soda  gives  a  sublimate  of  metallic  mercury.  B.B.  on 
charcoal  volatilizes,  coating  the  coal  white.  Insoluble  in  water,  but  dissolved  by  aqua 
regia;  blackens  when  treated  with  alkalies. 

Obs.  —  Usually  associated  with  cinnabar.  Thus  at  Moschellandsberg  in  the  Palatinate, 
Germany;  at  Idria  in  Carniola,  Austria;  Almaden  in  Spain;  at  Mt.  Avala  near  Belgrade 
in  Servia.  In  crystals  with  many  forms  from  Terlingua,  Tex. 

Calomel  is  an  old  term  of  uncertain  origin  and  meaning,  perhaps  from  KO\OS,  beautiful, 
and  /zeXi,  honey,  the  taste  being  sweet,  and  the  compound  the  Mercurius  dulcis  of  early 
chemistry;  or  from  /caXos  and  /xeXas,  black. 

Kleinite.  Mercurammonite.  A  mercury  ammonium  chloride  of  uncertain  composition. 
Hexagonal.  Crystals  short  prismatic.  Basal  cleavage.  H.  =  3*5.  G.  =  8'0.  Color 
yellow  to  orange,  darkening  on  exposure.  Volatile.  From  Terlingua,  Tex. 

Nantokite.  Cuprous  chloride,  CuCl.  Granular,  massive.  Cleavage  cubic.  H.  = 
2-2*5.  G.  =  3*93.  Luster  adamantine.  Colorless  to  white  or  grayish.  From  Nantoko, 
Chile;  Broken  Hill,  New  South  Wales. 

Marshite.  Cuprous  iodide,  Cul.  Isometric- tetrahedral.  Cleavage  dodecahedral. 
H.  =  2'5.  G.=5'59.  Color  oil-brown..  n  =  2'346.  Broken  Hill  mines,  New  South  Wales. 


Halite  Group.     RC1,  RBr,  RI.     Isometric 

Halite  NaCl  Embolite 

Sylvite  KC1  Bromyrite 

Sal  Ammoniac  (NH4)C1  lodobromite 

Cerargyrite  AgCl  Miersite 


Ag(Cl,Br) 

AgBr 

Ag(Cl,Br,I) 
Agl 


The  HALITE  GROUP  includes  the  halogen  compounds  of  the  closely  related 
metals,  sodium,  potassium,  and  silver,  also  ammonium  (NH4).  They  crystal- 
lize in  the  isometric  system,  the  cubic  form  being  the  most  common.  Sylvite 
and  sal-ammoniac  are  plagiohedral,  and  the  same  may  be  true  of  the  others. 

HALITE.    COMMON  or  ROCK  SALT. 

Isometric.     Usually  in  cubes;  crystals  sometimes  distorted,  or  with  cavern- 
ous faces.     Also  massive,  granular 
to  compact;  less  often  columnar.  676 

Cleavage:  cubic,  perfect.  Frac- 
ture conchoidal.  Rather  brittle. 
H.  =  2-5.  G.  =  2-1-2-6;  pure 
crystals  2-135.  Luster  vitreous. 
Colorless  or  white  also  yellowish, 
reddish,  bluish,  purplish.  Transpar- 
ent to  translucent.  Soluble;  taste 
saline,  n  =  1-5442.  Highly  dia- 
thermanous. 


396  DESCRIPTIVE    MINERALOGY 

Comp.  -  Sodium  chloride,  NaCl  =  Chlorine  60 -6,  sodium  39 -4  =  100. 
Commonly  mixed  with  calcium  sulphate,  calcium  chloride,  magnesium  chlo- 
ride, and  sometimes  magnesium  sulphate,  which  render  it  liable  to  deliquesce. 

Pyr.,  etc.  —  In  the  closed  tube  fuses,  often  with  decrepitation;  when  fused  on  the 
platinum  wire  colors  the  flame  deep  yellow.  After  intense  ignition  the  residue  gives  an 
alkaline  reaction  upon  moistened  test  paper.  Nitric  acid  solution  gives  precipitate  of 
silver  chloride  upon  addition  of  silver  nitrate.  Dissolves  readily  in  three  parts  of  water. 

Diff.  —  Distinguished  by  its  solubility  (taste),  softness,  perfect  cubic  cleavage. 

Obs.  —  Common  salt  occurs  in  extensive  but  irregular  beds  in  rocks  of  various  ages, 
associated  with  gypsum,  poly  halite,  anhydrite,  carnallite,  clay,  sandstone,  and  calcite; 
also  in  solution  forming  salt  springs'  similarly  in  the  water  of  the  ocean  and  salt  seas. 
The  deposits  of  salt  have  been  formed  by  the  gradual  evaporation  and  ultimate  drying  up 
of  enclosed  bodies  of  salt  water.  Salt  beds  formed  in  this  way  are  subsequently  covered 
by  other  sedimentary  deposits  and  gradually  buried  beneath  the  rock  strata  thus  formed. 
The  salt  strata  range  from  a  few  feet  up  to  more  than  one  hundred  feet  in  thickness  and 
have  been  found  at  depths  of  two  thousand  feet  and  more  beneath  the  earth's  surface. 

The  principal  salt  mines  of  Europe  are  at  Stassfurt,  near  Magdeburg,  Saxony;  Wie- 
liczka,  in  Galicia;  at  Hall,  in  Tyrol,  Austria;  and  along  the  range  through  Reichental  in 
Bavaria,  Hallein  in  Salzburg,  Hallstadt,  Ischl,  and  Ebensee,  in  Upper  Austria,  and  Aussee 
in  Styria;  in  Hungary,  at  Marmoros  and  elsewhere;  Transylvania;  Wallachia,  Galicia, 
and  Upper  Silesia;  in  southern  and  southeastern  Russia;  Vic  and  Dieuze  in  France; 
Valley  of  Cardona  and  elsewhere  in  Spain;  Bex  in  Switzerland;  and  Northwich  in  Cheshire, 
England. 

Salt  also  occurs,  forming  hills  and  covering  extended  plains,  near  Lake  Urumia,  the 
Caspian  Sea,  etc.  In  Algeria;  in  Abyssinia.  In  India  in  enormous  deposits  in  the  Salt 
Range  of  the  Punjab.  In  China  and  Asiatic  Russia;  in  South  America,  in  Peru,  and  at 
Zipaquera  and  Nemocon,  the  former  a  large  mine  long  explored  in  the  Cordilleras  of 
Colombia;  clear  salt  is  obtained  from  the  Cerro  de  Sal,  San  Domingo. 

In  the  United  States,  salt  has  been  found  in  large  amount  in  central  and  western  N.  Y. 
Salt  wells  had  long  been  worked  in  this  region,  but  rock  salt  is  now  known  to  exist  over  a 
large  area  from  Ithaca  at  the  head  of  Cayuga  Lake,  Tompkins  Co.,  and  Canandaigua 
Lake,  Ontario  Co.,  through  Livingston  Co.,  also  Genesee,  Wyoming,  and  Erie  Cos.  The 
salt  is  found  in  beds  with  an  average  thickness  of  75  feet,  but  sometimes  much  thicker  (in 
one  instance  325  feet),  and  at  varying  depths  from  1000  to  2000  feet  and  more;  the  depth 
increases  southward  with  the  dip  of  the  strata.  The  rocks  belong  to  the  Salina  period  of 
the  Upper  Silurian.  Extensive  deposits  of  salt  occur  in  Mich.,  chiefly  in  Saginaw,  Bay, 
Midland,  Isabella,  Detroit,  Wayne,  Manistee  and  Mason  Counties.  Salt  has  also  been 
found  near  Cleveland,  Ohio,  associated  with  gypsum;  in  Kan.;  in  La.,  extensive  beds 
occur  in  the  southern  portion  of  the  state  at  and  in  the  neighborhood  of  Petite  Anse  island. 
Salt  has  also  been  obtained  from  Nev.,  Utah,  Ariz,  and  Cal.  In  Utah  and  Cal.  salt  is 
chiefly  obtained  by  the  evaporation  of  the  waters  of  Great  Salt  Lake  and  the  ocean. 

Brine  springs  are  very  numerous  in  the  Middle  and  Western  States.  Vast  lakes  of  salt 
water  exist  in  many  parts  of  the  world.  The  Great  Salt  Lake  in  Utah  is  2000  square  miles 
in  area;  L.  Gale  found  in  this  water  20 '196  per  cent  of  sodium  chloride.  The  Dead  and 
Caspian  seas  are  salt,  and  the  waters  of  the  former  contain  20  to  26  parts  of  solid  matter  in 
100  parts.  Sodium  chloride  is  the  prominent  salt  present  in  the  ocean. 

Use.  —  The  chief  uses  of  salt  are  for  culinary  and  preservative  purposes.  Soda  ash  is 
also  made  from  it,  being  employed  in  the  manufacture  of  glass,  soap,  bleaching,  prepara- 
tion of  other  sodium  compounds,  etc. 

Villiaumite.  NaF.  Isometric.  In  small  carmine  colored  grains.  Soft.  G.  =  2'8. 
Refractive  index  =  1'33.  Found  in  nepheline-syenite  from  the  Islands  of  Los. 

Huantajayite.  20NaCl.AgCl.  In  cubic  crystals  and  as  an  incrustation.  H.  =  2. 
Wot  sectile.  Color  white.  From  Huantajaya,  Tarapaca,  Chile. 

SYLVITE. 

Isometric-plagiohedral.     Also  in  granular  crystalline  masses;  compact. 

Cleavage:  cubic,  perfect.  Fracture  uneven.  Brittle.  H.  =  2.  G.  = 
1-97-1-99.  Luster  vitreous.  Colorless,  white,  bluish  or  yellowish  red  from 
inclusions.  Soluble;  taste  resembling  that  of  common  salt,  but  bitter. 
n  =  1'490. 

Comp.  —  Potassium  chloride,  KC1  =  Chlorine  47-6,  potassium  52'4  = 
100.  Sometimes  contains  sodium  chloride. 


HALOIDS.  — CHLORIDES,    BROMIDES,    IODIDES;    FLUORIDES        397 

Pyr.,  etc.  —  B.B.  in  the  platinum  loop  fuses,  and  gives  a  violet  color  to  the  outer  flame 
Dissolves  completely  in  water  (saline  taste).  After  ignition  residue  reacts  alkaline  upon 
moistened  test  paper.  Solution  in  nitric  acid  gives  precipitate  of  silver  chloride  with  silver 
nitrate. 

Obs.  —  Occurs  at  Vesuvius,  about  the  fumaroles  of  the  volcano.  Also  in  Germany  at 
Stassfurt,  Saxony;  and  at  Leopoldshall  (leopoldite) ,  Anhalt;  at  Kalusz  in  Galicia. 

Use.  —  A  source  of  potash  compounds  used  as  fertilizers. 

Sal  Ammoniac.  Ammonium  chloride,  NH4C1.  n  =  1'642.  Observed  as  a  white  in- 
crustation about  volcanoes,  as  at  Etna,  Vesuvius,  etc. 

Cerargyrite  Group.     Isometric-Normal 

An  isomorphous  series  of  silver  haloids  in  which  silver  chloride,  bromide 
and  iodide  may  mix  in  varying  proportions.  The  suggestion  has  been  made 
that  the  name  cerargyrite  be  kept  as  the  group  name  and  that  the  different 
sub-species  be  named  as  follows:  chlorargyrite,  AgCl;  bromargyrite,  AgBr: 
embolite,  Ag(Cl,Br);  iodembolite,  Ag(Cl,Br,I). 

CERARGYRITE.     Horn  Silver. 

Isometric.  Habit  cubic.  Twins:  tw.  pi.  o(lll).  Usually  massive  and 
resembling  wax;  sometimes  columnar;  often  in  crusts. 

Cleavage  none.  Fracture  somewhat  conchoidal.  Highly  sectile.  H.  = 
1-1*5.  G.  =  5 -552.  Luster  resinous  to  adamantine.  Color  pearl-gray, 
grayish  green,  whitish  to  colorless,  rarely  violet-blue;  on  exposure  to  the 
light  turns  violet-brown.  Transparent  to  translucent,  n  =  2-0611. 

Comp.  —  Silver  chloride,  AgCl  =  Chlorine,  24-7,  silver  75-3  =  100.  Some 
varieties  contain  mercury. 

Pyr.,  etc.  —  In  the  closed  tube  fuses  without  decomposition.  B.B.  on  charcoal  gives  a 
globule  of  metallic  silver.  Added  to  a  bead  of  salt  of  phosphorus,  previously  saturated 
with  oxide  of  copper  and  heated  in  O.F.,  imparts  an  intense  azure-blue  to  the  flame. 
Insoluble  in  nitric  acid,  but  soluble  in  ammonia. 

Obs.  —  Cerargyrite  and  the  related  minerals  are  products  of  secondary  action  and  are 
commonly  found  in  the  upper  parts  of  silver  deposits.  Descending  waters  containing 
chlorine,  bromine  or  iodine  act  upon  the  oxidation  products  of  the  primary  silver  minerals 
and  so  precipitate'  these  relatively  insoluble  compounds.  Commonly  associated  with 
other  silver  minerals,  with  lead,  copper  and  zinc  ores  and  their  usual  alteration  products. 

The  largest  masses  are  brought  from  Peru,  Chile,  Bolivia,  and  Mexico,  where  it  occurs 
with  native  silver.  Also  once  obtained  from  Johanngeorgenstadt  and  Freiberg,  Saxony; 
occurs  in  the  Altai  Mts.;  at  Kongsberg  in  Norway. 

In  the  United  States,  in  Col.,  near  Leadville,  Lake  Co.;  near  Breckenridge,  Summit  Co., 
and  elsewhere.  In  Nev.  near  Austin,  Lander  Co.;  at  mines  of  Comstock  lode;  Tonapah. 
In  Idaho,  at  the  Poorrnan  mine,  in  crystals;  also  at  various  other  mines.  In  Utah,  in 
Beaver,  Summit  and  Salt  Lake  counties.  At  Tombstone,  Ariz. 

Named  from  /cepas,  horn,  and  apyvpos,  silver. 

Use.  —  An  ore  of  silver. 

Embolite.  Silver  chloro-bromide  Ag(Br,Cl),  the  ratio  of  chlorine  to  bromine  vary- 
ing widely.  Usually  massive.  Resembles  cerargyrite,  but  color  grayish  green  to  yellowish 
green  and  yellow,  n  =  2*15.  Abundant  in  Chile.  Found  also  at  Broken  Hill,  New 
South  Wales;  Tonapah,  Nev.;  Leadville,  Col.,;  Yuma  County,  Ariz.;  Georgetown,  N.  M. 

Bromyrite.  Silver  bromide,  AgBr.  G.  =  5*8-6.  Color  bright  yellow  to  amber-yel- 
low; slightly  greenish,  n  =  2'25.  From  Mexico;  Chile. 

lodobromite.  2AgCl.2AgBr.AgI.  Isometric.  G.  =  5713.  Color  sulphur-yellow, 
greenish,  n  =  2'2.  From  near  Dernbach,  Nassau;  Broken  Hill,  New  South  Wales. 


Miersite.  Silver,  copper  iodide,  4AgI.CuI.  Isometric;  tetrahedral.  G.  =  5'64.  In 
bright  yellow  crystals  from  the  Broken  Hill  Silver  Mines,  New  South  Wales.  Cupro- 
iodargyrite  from  Huantajaya,  Peru,  belongs  here  also. 

lodyrite.     Silver  iodide,  Agl.     Hexagonal-hemimorphic;   usually  in  thin  plates;   pale 


398 


DESCRIPTIVE   MINERALOGY 


yellow  or  green.  G.  =  5'5-57. 
Lake  Valley,  Sierra  Co.,  N.  M. 
Tonapah,  Nev. 


Optically  +  .      co  =  2 '182.     From  Mexico,  Chile,  etc. 
In  crystals  from  Broken  Hill,  New  South  Wales,  and 


ii       ii 

RF2,RC12 


Fluorite  Group. 

The  species  here  included  are  Fluoritel  CaF2T  and  the  rare  Hydrophilite, 
CaCl2.  Both  are  isometric,  habit  cubic.  V^  —4 

FLUORITE  or  FLUOR  SPAR. 

Isometric.  Habit  cubic;  less  frequently  octahedral  or  dodecahedral ; 
forms  /(310),  e(210)  (fluoroids)  common;  also  the  vicinal  form  f  (321-0?), 
producing  striations  on  a(100)  (Fig.  682) ;  hexoctahedron  2(421)  also  common 
with  the  cube  (Fig.  681).  Cubic  crystals  sometimes  grouped  in  parallel 
position,  thus  forming  a  pseudo-octahedron.  Twins:  tw.  pi.  0(111),  com- 


678 


679 


681 


682 


monly  penetration-twins  (Fig.  682).     Also  massive;  granular,  coarse  or  fine- 

rarely  columnar;  compact. 

Cleavage:   o(lll)  perfect.     Fracture  flat-conchoidal;   of  compact  kinds 

splintery.  Brittle.  H.  =  4 
G.  =  3-01-3-25;  318  cryst. 
Luster  vitreous.  Color  white, 
yellow,  green,  rose-  and  crimson- 
red,  violet-blue,  sky-blue,  and 
brown;  wine-yellow,  greenish 
blue,  violet-blue,  most  common; 
red,  rare.  Streak  white. 
Transparent  -  -  subtranslucent. 
Sometimes  shows  a  bluish  fluor- 
escence. Some  varieties  phos- 
phoresce when  heated  (p.  251) 
n  =  1-4339. 
Fluorine  48'9,  calcium  511  =  100. 


A 


Comp. 


-«-.-       Calcium  fluoride,  CaF2  -  nuorme  3 
Oniorme  is  sometimes  present  in  minute  quantities 

ipitates  and  sometimes  phosphoresces.     B.  B.  in  the 
<ne  flame  orange,  to  an  enamel  which  reacts  alkaline 
i  "otassmm  bisulphate  gives  reaction  for  fluorine. 
>rm,  octahedral  cleavage,  relative  softness  (as 
i,  also  with  the  feldspars);    etching  power  when 
effervesce  with  acid  like  calcite 


on  test 


compared  with  certain 
treated  with  sulphuric 


Fused  b  a  closed 


HALOIDS.  —  CHLORIDES,    BROMIDES,    IODIDES;    FLUORIDES        399 


Obs.  —  Fluorite  occurs  most  commonly  as  a  vein  mineral  either  in  deposits  in  which 
it  is  the  chief  constituent  or  as  a  gangue  mineral  with  various  metallic  ores,  especially 
those  of  lead  and  zinc.  It  is  common  in  sedimentary  rocks,  being  often  found  in  dolomites 
and  limestones.  It  is  also  found  as  a  minor  accessory  mineral  in  granite  and  other  acid 
igneous  rocks.  It  occurs  as  a  sublimation  product  in  connection  with  volcanic  rocks. 

In  the  North  of  England,  it  is  the  gangue  of  the  lead  veins,  which  intersect  the  coal 
formation  in  Northumberland,  Cumberland,  Durham,  and  Yorkshire.  In  Derbyshire  it 
is  abundant,  and  also  in  Cornwall,  where  the  veins  intersect  metamorphic  rocks.  The 
Cumberland  and  Derbyshire  localities  especially  have  afforded  magnificent  specimens. 
Common  in  the  mining  district  of  Saxony;  from  Stolberg,  Harz  Mts.;  fine  near  Kongsberg 
in  Norway.  In  the  dolomites  of  St.  Gothard  occurs  in  pink  octahedrons;  from  Brienz, 
Switzerland.  From  Rabenstein,  Tyrol,  Austria.  Rarely  in  volcanic  regions,  as  in  the 
Vesuvian  lava.  In  colorless  transparent  crystals  from  Madoc,  Hastings  Co.,  Ontario, 
Canada. 

Some  localities  in  the  United  States  are,  Trumbull,  Conn,  (chlorophane) ;  Muscolonge 
Lake,  Jefferson  Co.,  N.  Y.,  and  Macomb,  St.  Lawrence  Co.,  both  in  very  large  sea-green 
cubes;  Franklin  Furnace,  N.  J.;  Amelia  Court  House,  Va. ;  Westmoreland,  Ver.  Fluorite 
has  been  mined  in  the  United  States  chiefly  from  Western  Kentucky  and  adjacent  sections 
in  Hardin  and  Pope  counties,  111.  Also  obtained  from  Jamestown,  Boulder  County;  Ever- 
green, Jefferson  County,  and  near  Rosita,  Custer  County,  Col.;  from  ten  miles  north  of 
Deming,  N.  M.;  from  Smith,  Trousdale  and  Wilson  counties,  Tenn.;  from  Castle  Dome 
district,  Ariz. 

Use.  —  As  a  flux  in  the  making  of  steel;  in  the  manufacture  of  opalescent  glass;  in 
enameling  cooking  utensils;  the  preparation  of  hydrofluoric  acid;  sometimes  as  an  orna- 
mental material. 

Hydrophilite.  Chlorocalcite.  Calcium  chloride,  CaCl2.  In  white  cubic  crystals  or 
as  an  incrustation  at  Vesuvius.  Bceumlerite  is  same  material  intergrown  with  halite  and 
tachhydrite  from  Leinetal,  Germany. 

The  following  are  from  Vesuvius:  Chloromagnesite,  MgCl2;  Scacchite.  MnCl2; 
ChloraUuminite,  A1C13.6H2O;  Molysite,  FeCl3;  Chlormanganokalite,  4KCl.MnCl2. 

Sellaite.  Magnesium  fluoride,  MgF2.  In  prismatic  tetragonal  crystals.  H.  =  5. 
G.  =  2 '97-3 15.  Colorless.  Optically  +  .  co  =  1'378.  From  the  moraine  of  theGebrou- 
laz  glacier  in  Savoie,  France.  Belonesite  is  the  same  species. 

Lawrencite.     Ferrous  chloride,  FeCl2.     Occurs  in  meteoric  iron. 

Rinneite.  FeCl2.3KCl.NaCl.  Rhombohedral.  In  coarse  granular  masses.  Prismatic 
cleavage.  H.  =3.  G.  =  2'3.  Colorless,  rose,  violet  or  yellow  when  fresh,  becomes 
brown  on  exposure  due  to  oxidation.  o>  =  1'59.  Easily  fusible.  Astringent  taste. 
Found  in  Germany  at  Nordhausen  and  elsewhere  in  Saxony  and  at  Diekholzen,  Hannover. 

Cotunnite.  Lead  chloride,  PbCl2.  In  acicular  crystals  (orthorhombic)  and  in  semi- 
crystalline  masses.  Soft.  G.  =  5 '24.  Color  white,  yellowish.  Optically  +  .  8  =  2 '2 17. 
From  Vesuvius;  also  Tarapaca,  Chile. 

Tysonite.  Fluoride  of  the  cerium  metals,  (Ce,La,Di)Fs.  In  thick  hexagonal  prisms, 
and  massive.  Cleavage:  c(001),  perfect.  H.  =  4*5-5.  G.  =  6'13.  Color  pale  wax- 
yellow,  changing  to  yellowish  and  reddish  brown.  From  the  granite  of  Pike's  Peak, 
El  Paso  Co.,  Col.  Fluocerite,  from  Osterby,  Sweden,  is  propably  the  same  species. 

Yttrofluorite.  (Ca3,Y2)F6,  near  yttrocerite.  Isometric.  In  granular  masses.  Imperfect 
octahedral  cleavage.  H.  =  4*5.  G.  =  3'55.  Color  yellow,  also  with  brown  or  green 
shades,  n  —  1*46.  Found  in  pegmatite  in  northern  Norway. 

CRYOLITE. 

Monoclinic. 
|8  =  89°  49'. 

mm'",  110  A  1TO  =  88 
cm,  001  A  110  =  89 
cv,  001  A  101  =  55 


683 


Axes  a  :  b  :  c  =  0'9663  :  1  :  1'3882; 


2'. 

52'. 

2'. 


ck,  001  A  T01  =  55°  17'. 
cr,  001  A  Oil  =  54°  14'. 
cp,  001  A  111  =  63°  18'. 

Crystals  often  cubic  in  aspect  and  grouped  in  paral- 
lel position;  often  with  twin  lamellae.  Massive. 

Parting  at  times  due  to  j/winning  lamellae  parallel 
to  c(001),  ra(110)  and  /c(101).  Fracture  uneven. 
Brittle.  H.  =  2'5.  G.  =  2-95-3-0.  Luster 
vitreous  to  greasy;  somewhat  pearly  on  c(001).  Colorless  to  snow-white, 


400 


DESCRIPTIVE   MINERALOGY 


sometimes  reddish  or  brownish  to  brick-red  or  even  black.     Transparent  to 
translucent.     Optically  +.     Mean  index,  1-364.     p_ 

Comp.  —  A  fluoride  of  sodium  and  aluminium^  Na3AlF6  lor  3NaF.AlF3  = 
Fluorine  54*4,  aluminium  12'8,  sodium  32*8  =  !D6>----rAr-nttle  iron  sesqui- 
oxide  is  sometimes  present  as  impurity. 

Pyr.,  etc.  —  Fusible  in  small  fragments  in  the  flame  of  a  candle.  Heated  in  C.  T.  with 
potassium  bisulphate  gives  fluorine  reaction.  In  the  forceps  fuses  very  easily,  coloring 
the  flame  yellow.  On  charcoal  fuses  easily  to  a  clear  bead,  which  on  cooling  becomes 
opaque;  after  long  blowing,  the  assay  spreads  out,  the  fluoride  of  sodium  is  absorbed  by 
the  coal,  a  suffocating  odor  of  fluorine  is  given  off,  and  a  crust  of  alumina  remains,  which, 
when  heated  with  cobalt  solution  in  O.F.,  gives  a  blue  color.  Soluble  in  sulphuric  acid, 
with  evolution  of  hydrofluoric  acid. 

Diff.  —  Distinguished  by  its  extreme  fusibility.  Because  of  its  low  index  of  refraction 
the  powdered  mineral  becomes  almost  invisible  when  placed  in  water.  Its  planes  of  part- 
ing (resembling  cubic  cleavage)  and  softness  are  characteristic. 

Obs.  —  Occurs  in  a  bay  in  Arksukfiord,  in  West  Greenland,  at  Ivigtut  (or  Evigtok), 
about  12  m.  from  the  Danish  settlement  of  Arksuk,  where  it  constitutes  a  large  bed  in 
a  granitic  vein  in  a  gray  gneiss.  Cryolite  and  its  alteration  products,  pachnolite,  thom- 
senolite,  prosopite,  etc.,  also  occur  in  limited  quantity  at  the  southern  base  of  Pike's  Peak, 
El  Paso  county,  Col.,  north  and  west  of  Saint  Peter's  Dome. 

Named  from  Kpvos,  frost,  X«9os,  stone,  hence  meaning  ice-stone,  in  allusion  to  the  trans- 
lucency  of  the  white  masses. 

Use.  —  In  the  manufacture  of  sodium  salts,  certain  kinds  of  glass  and  porcelain,  and 
as  a  flux  in  the  electrolytic  process  for  the  production  of  aluminum. 

Cryolithionite  is  a  variety  of  cryolite  with  half  the  sodium  replaced  by  lithium.  G.  = 
278.  Refractive  index  T34.  Associated  with  cryolite  at  Ivigtut. 

Chiolite.  5NaF.3AlF3.  In  small  pyramidal  crystals  (tetragonal);  also  massive  granu- 
lar. Cleavages,  c(001)  perfect,  p(lll)  distinct.  H.  =  3'5-4.  G.  =  2'84-2'90.  Color 
snow-white.  Optically  — .  co  =  1*349..  From  near  Miask  in  the  Ilmen  Mts.,  Russia; 
also  with  the  Greenland  cryolite. 

Hieratite.  A  fluoride  of  potassium  and  silicon.  In  grayish  stalactitic  concretions; 
isometric.  From  the  fumaroles  of  the  crater  of  Vulcano,  Lipari  Islands. 


ATACAMITE. 
Orthorhombic. 
684  ™ 


II.   Oxychlorides,  Oxyfluorides 


Axes  a  :b  :  c  =  0-6613  :  1  :  07515. 

mm",  110  A  110  =  66°  57'.  rr'"t  111  A  111  =  52°  48'. 

ee',      Oil  A  Oil  =  73°  51'.  mr,    110  A  111  =  36°  16*'. 

Commonly  in  slender  prismatic  crystals,  vertically 
striated.  Twins  according  to  a  complex  law.  (Paratacamite 
is  twinned  atacamite.)  In  confused  crystalline  aggregates; 
also  massive,  fibrous  or  granular  to  compact;  as  sand. 

Cleavage:    6(010)    highly   perfect.     Fracture   conchoidal. 
Brittle.     H.  =  3-3-5.     G.  =  375-377.     Luster  adamantine 
to  vitreous.     Color    bright    green    of    various    shades,  dark 
emerald-green     to     blackish    green.       Streak     apple-green. 
Transparent    to    translucent.      Optically  —  .       a   =    T831 
0  =  T861.  7  =  1-880. 
Comp.  —  Cu2ClH303  or  CuCl2.3Cu(OH)2  =  Chlorine  16'6,  copper  14'9, 
cupnc  oxide  55-8,  water  12-7  =  100. 


on  charcoal  _ . 

owmsn  w.u^  Viiv,  UIMI^I  gioijriBii  wince,   uuiiuiiueu  uiowuig  yieias  a  gioouie  oi  met 
sflv   C?aujngs'  touched  ^h  the  R.F.,  volatilize,  coloring  the  flame  azure-blue. 


In 


HALOIDS.  —  CHLORIDES,    BROMIDES,    IODIDES;     FLUORIDES         401 

Obs.  —  Originally  from  Atacama  in  the  northern  part  of  Chile;  also  found  at  Colla- 
hurasi,  Tarapaca  and  elsewhere  in  Chile  and  Bolivia;  at  Wallaroo  and  Bimbowrie,  in 
South  Australia;  at  Gloncurry,  Queensland;  at  St.  Just  in  Cornwall.  In  the  United 
States,  with  cuprite,  etc.,  at  the  United  Verde  mine,  Jerome,  Ariz. 

Percylite.  A  lead-copper  oxychloride,  perhaps  PbCl2.CuO.H2O.  In  sky-blue  cubes. 
From  Sonora,  Mexico;  Atacama,  Chile;  Bolivia,  etc. 

Boleite.  9PbCl2.8CuO.3AgC1.9H2O.  Tetragonal,  pseudo-isometric.  Twinned  to 
form  pseudo  cubes.  Pseudo-boleite.  5PbCl2.4CuO.6H2O.  Tetragonal.  Cumengite. 
4PbCl2.4CuO.5H2O.  Tetragonal.  Pseudo-boleite  and  cumengite  occur  in  parallel  growth 
upon  crystals  of  boleite.  Boleite  and  pseudo-boleite  have  pearly  luster  on  cleavage,  while 
cumengite  has  not.  All  three  deep  blue  in  color,  the  first  two  showing  a  greenish  tinge  in 
powder.  Found  at  Boleo,  near  Santa  Rosalia,  Lower  California. 

Matlockite.  Lead  oxychloride,  Pb2OCl2.  In  tabular  tetragonal  crystals.  G.  =  7-21. 
Luster  adamantine  to  £  pearly.  Color  yellowish  or  slightly  greenish.  Optically  —  . 
co  =2 '15.  From  Cromford,  near  Matlock,  Derbyshire. 

Mendipite.  Pb2O2Cl2  or  PbCl2.2PbO.  In  fibrous  or  columnar  masses;  often  radiated. 
H.  =2-5-3.  G.  =  7-7'l.  Color  white.  Index,  1'93.  From  the  Mendip  Hills,  Somer- 
setshire, England;  near  Brilon,  Westphalia. 

Lorettoite.  6PbO.PbCl2.  Tetragonal?  Coarse  fibers  or  blades.  Perfect  basal  cleavage. 
G.  =  7-6.  H.  =  3.  Fusible  at  1.  Color  honey-yellow.  Uniaxial,  -.  Indices,  2'37- 
2-40.  From  Loretto,  Tenn. 

Laurionite.  PbClOH  or  PbCl2.Pb(OH)2.  In  minute  prismatic  colorless  crystals  (ortho- 
rhombic),  in  ancient  lead  slags  at  Laurion,  Greece.  Optically  —  .  /3  =  2-116.  Para- 
laurionite.  Same  composition  as  laurionite  but  monoclinic.  From  Laurion.  Rafaelite 
from  Chile  is  the  same  mineral.  Suggested  that  laurionite  is  the  same  as  paralaurionite 
but  owing  to  submicroscopic  twinning  has  apparently  orthorhombic  symmetry.  Fiedlerite, 
associated  with  laurionite,  is  probably  also  a  lead  oxychloride;  in  colorless  monoclinic 
crystals. 

Penfieldite.     Pb3OCl2  or  PbO.2PbCl2.     In  white  hexagonal  crystals.     Laurion,  Greece. 

Daviesite.  A  lead  oxychloride  of  uncertain  composition.  In  minute  colorless  pris- 
matic crystals  (orthorhombic)  from  the  Mina  Beatriz,  Sierra  Gorda,  Atacama,  Chile. 

Schwartzembergite.  Probably  Pb(I,Cl)2.2PbO.  In  druses  of  small  crystals;  also  in 
crusts.  G.  =  6"2.  Color  honey-yellow.  Desert  of  Atacama,  Chile. 

Nocerite.  Perhaps  2(Ca,Mg)F2(Ca,Mg)O(?).  In  white  hexagonal  acicular  crystals 
from  bombs  in  the  tufa  of  Nocera,  Italy. 

Koenenite.  An  oxychloride  of  aluminium  and  magnesium.  Rhombohedral.  Perfect 
cleavage  yielding  flexible  folia.  Very  soft.  G.  =  2'0.  Color  red,  due  to  included  hema- 
tite. From  near  Volpriehausen  in  the  Soiling,  Germany. 

Daubreeite.     An  earthy  yellowish  oxychloride  of  bismuth.     From  Bolivia. 

The  following  are  oxychlorides  of  mercury  from  the  mercury  deposits  at  Terlingua, 
Texas.  Associated  minerals  are  montroydite,  calomel,  native  mercury  and  calcite. 

Eglestonite.  Hg4Cl2O.  Isometric  in  minute  crystals  of  dodecahedral  habit.  Many 
forms  observed.  H.  =  2-3.  G.  =  8' 3.  Luster  adamantine  to  resinous.  Color  brownish 
yellow  darkening  on  exposure  to  black,  n  =  2*49.  Volatile. 

Terlinguaite.  Hg2ClO.  Monoclinic.  In  small  striated  prismatic  crystals  elongated 
parallel  to  the  6-axis.  Many  forms  observed.  Cleavage  perfect.  H.  =  2-3.  G  =  87. 
Luster  adamantine.  Color  sulphur-yellow  changing  to  olive-green  on  exposure. 


III.    Hydrous  Chlorides,  Hydrous  Fluorides,  etc. 

CARNALLITE. 

Orthorhombic.     Crystals  rare.     Commonly  massive,  granular. 

No  distinct  cleavage.  Fracture  conchoidal.  Brittle.  H.  =  1.  G  =  1-60. 
Luster  shining,  greasy.  Color  milk-white,  often  reddish.  Transparent  to 
translucent.  Strongly  phosphorescent.  Optically  +  •  2  V  =  70°.  a  =  1  -466. 
0  =  1-475.  T  =  1-494,  Taste  bitter.  Deliquescent. 

Comp.  —  KMgCl3.6H2O  or  KCl.MgCl2.6H2O  =  Chlorine  38'3,  potas- 
sium 14-1,  magnesium  87,  water  39'0  =  100. 


402  DESCRIPTIVE    MINERALOGY 

Obs.  —  Occurs  at  Stassfurt,  in  beds,  alternating  with  thinner  beds  of  common  salt  and 
kieserite.  In  large  crystals  from  Beienrode,  near  Konigshiitte,  Silesia. 

Use.  —  Carnallite  is  a  source  of  potash  compounds  used  in  fertilizers. 

DOUGLASITE,  associated  with  carnallite,  is  said  to  be  2KCl.FeCl2.2H2O. 

Bischofite.  MgCl2.6H2O.  Crystalline-granular;  colorless  to  white.  Optically  +. 
/3  =  1-507.  From  Leopoldshall  and  Stassfurt,  Prussia. 

Kremersite.  KCl.NH4Cl.FeCl2.H2O.  In  red  octahedrons.  From  Vesuvius  and  Mt. 
Etna,  Sicily. 

Mosesite.  A  mercury-ammonium  compound  containing  chlorine,  sulphur  trioxide  and 
water.  Near  kleinite  in  composition.  Isometric.  Minute  octahedrons.  Spinel  twins. 
H.  =  3  +  .  Color  yellow.  Doubly  refracting  at  ordinary  temperatures.  Found  sparingly 
at  Terlingua,  Texas. 

Erythrosiderite.     2KCl.FeCl3.H2O.    In  red  tabular  crystals.     Vesuvius. 

Tachhydrite.  CaCl2.2MgCl2.12H2O.  In  wax-  to  honey-yellow  masses.  From  Stass- 
furt, Germany. 

Fluellite.  A1F3.H2O.  In  colorless  or  white  rhombic,  pyramids.  Index,  1'47.  From 
Stenna  Gwyn,  Cornwall.  ' 

Prosopite.  CaF2.2Al(F,OH)3.  In  monoclinic  crystals,  or  granular  massive.  H.  =  4'5. 
G.  =  2-88.  Colorless,  white,  grayish.  0  =  1'502.  From  Altenberg,  Saxony;  St.  Peter's 
Dome  near  Pike's  Peak,  Col.;  Utah. 

Pachnolite  and  Thomsenolite,  occurring  with  cryolite  in  Greenland,  Col.,  and  Ural  Mts., 
have  the  same  composition,  NaF.CaF2.AlF3.H2O.  Both  occur  in  monoclinic  prismatic 
crystals;  prismatic  angle  for  pachnolite,  98°  36',  crystal  twins,  orthorhombic  in  aspect. 
/3  =  1-413.  For  thomsenolite,  89°  46',  crystals  often  resembling  cubes,  also  prismatic; 
distinguished  by  its  basal  cleavage;  also  massive.  /3  =  T414. 

Gearksutite.  CaF2.Al(F,OH)3.H2O.  Earthy,  clay-like.  Index,  T448.  Occurs  with 
cryolite. 

Ralstonite.  (Na2,Mg)F2.3Al(F,OH)3.2H2O.  In  colorless  to  white,  isometric,  octa- 
hedrons. H.  =  4-5.  G.  =  2-56-2-62.  n  =  1'43.  With  the  Greenland  cryolite. 

Creedite.  2CaF2.2Al(F,OH)3.CaSO4.2H2O.  Monoclinic.  In  grains,  prismatic  crys- 
tals and  radiating  masses.  Usually  colorless,  rarely  purple.  H.  =  3'5.  G.  =  2*71.  Perfect 
cleavage.  Indices,  1-46-1-49.  2  V  =  64°.  Y  =  b  axis.  Fusible  with  intumescence. 
Soluble  in  acids.  Found  near  Wagon  Wheel  Gap,  Creed  Quadrangle,  Col. 

Tallingite.  A  hydrated  copper  chloride  from  the  Botallack  mine,  Cornwall;  in  blue 
globular  crusts. 

Yttrocerite.  (Y,Er,Ce)F3.5CaF2.H2O.  Massive-eleavable  to  granular  and  earthy. 
H.  =  4-5.  G.  =  3'4.  Color  violet-blue,  gray,  reddish  brown.  From  near  Falun, 
Sweden,  etc. 


V.   OXIDES 

I.    Oxides  of  Silicon, 
n.   Oxides  of  the  Semi-Metals :  Tellurium,  Arsenic,  Antimony,  Bismuth ; 

also  Molybdenum,  Tungsten. 
III.   Oxides  of  the  Metals. 

The  Fifth  Class,  that  of  the  OXIDES,  is  subdivided  into  three  sections, 
according  to  the  positive  element  present.  The  oxides  of  the  non-metal 
silicon  are  placed  by  themselves,  but  it  will  be  noted  that  the  compounds  of 
the  related  element  titanium  are  included  with  those  of  the  metals  proper. 
This  last  is  made  necessary  by  the  fact  that  in  one  of  its  forms  Ti02  is  isomor- 
phous  with  MnO2  and  Pb02. 

A  series  of  oxygen  compounds  which  are  properly  to  be  viewed  as  salts, 
e.g.,  the  species  of  the  Spinel  Group  and  a  few  others,  are  for  convenience  also 
included  in  this  class. 


OXIDES 

I.   Oxides  of  Silicon 


403 


QUARTZ. 

Rhombohedral-trapezohedral. 
rrf,  1011  A  TlOl  =  85°  46'. 
rz,  1011  A  0111  =  46°  16'. 
mr,  1010  A  1011  =  38°  13'. 

685  686 


Axis:  c  =  1-09997. 

mz,  1010  A  0111  =  66°  52'. 
ms,  1010  A  1121  =  37°  58'. 
mx,  1010  A. 5161  =  12°  1'. 

687 


688 


Crystals  commonly  prismauc,  with  the  m(10TO)  faces  horizontally 
striated;  terminated  commonly  by  the  two  rhombohedrons,  r(1011)  and 
2(0111),  in  nearly  equal  development,  giving  the  appearance  of  a  hexagonal 
pyramid;  when  one  rhombohedron  predominates  it  is  in  almost  all  cases  r. 
Often  in  double  six-sided  pyramids  or  quartzoids  through  the  equal  develop- 
ment of  r  and  2;  when  r  is  relatively  large  the  form  then  has  a  cubic  aspect 
(rrf  =  85°  46').  Crystals  frequently  distorted,  when  the  correct  orientation 
may  be  obscure  except  as  shown  by  the  striations  on  m.  Crystals  often  elon- 
gated to  acicular  'forms,  and  tapering  through  the  oscillatory  combination  of 
successive  rhombohedrons  with  the  prism.  Occasionally  twisted  or  bent. 
Frequently  in  radiated  masses  with  a  surface  of  pyramids,  or  in  druses. 

Simple  crystals  are  either  right-  or  left-handed.  On  a  right-handed  crystal  (Fig.  690) 
the  right  trigonal  pyramid,  s(1121),  if  present,  lies  to  the  right  of  the  m  face,  which  is 
below  the  predominating  positive  rhombohedron  r,  and  with  this  belong  the  positive 
right  trapezohedrons,  as  £(5161).  On  a  left-handed  crystal  (Fig.  691),  s  lies  to  the  left 
of  the  m  below  r.  The  right-  and  left-handed  forms  occur  together  only  in  twins.  In  the 
absence  of  trapezohedral  faces  the  striations  on  s  (||  edge  r/m),  if  distinct,  serve  to  dis- 
tinguish the  faces  r  and  z,  and  hence  show  the  right-  and  left-handed  character  of  the 
crystals.  The  right-  and  left-handed  character  is  also  revealed  by  etching  (Art.  286)  and 
by  pyro-electricity  (Art.  438). 

Thermal  study  of  quartz  shows  that  it  exists  in  two  modifications,  known  as  a- 
and  /3-quartz.  a-quartz  is  apparently  hexagonal,  trapezohedral-tetartohedral  and  is 
formed  at  temperatures  below  575°  while  /3-quartz  is  hexagonal,  trapezohedral-hemihedral 
and  forms  at  temperatures  ranging  from  575°  to  800°.  Above  800°  tridymite  is  formed. 
The  crystal  angles  of  a-quartz  change  with  increase  of  temperature  up  to?  575°,  the  inver- 
sion point  to  /3-quartz,  while  beyond  this  point  they  remain  nearly  constant.  In  a  similar 


404 


DESCRIPTIVE    MINERALOGY 


manner  at  this  point  there  is  a  sudden  marked  lowering  of  the  refractive  indices  and  birefrin- 
gence, a-quartz  occurs  in  veins  and  geodes  and  large  pegmatites  while  the  /3  modification 
is  found  in  graphite  granite,  granite  pegmatites,  and  porphyries.  Tridymite  when  heated 
to  about  1470°  passes  over  into  cristobalite.  Quartz,  tridymite  and  cristobalite  are  prob- 
ably to  be  considered  as  polymers  of  the  fundamental  molecule,  SiO2. 

Twins:  (1)  tw.  axis  c,  all  axes  parallel.  (2)  Tw.  pi.  a,  sometimes  called 
the  Brazil  law,  usually  as  irregular  penetration-twins  (Fig.  692).  (3)  Tw.  pi. 
£  (1122),  contact-twins,  the  axes  crossing  at  angles  of  84°  33'_and  with  a  prism 
face  in  common  to  the  two  individuals.  (4)  Tw.  pi.  r(1011).  See  further 
p.  168  and  Figs.  427^429.  Massive  forms  common  and  in  great  variety,  pass- 
ing from  the  coarse  or  fine  granular  and  crystalline  kinds  to  those  which  are 
flint-like  or  cryptocrystalline.  Sometimes  mammillary,  stalactitic,  and  in 
concretionary  forms;  as  sand. 

Cleavage  not  Distinctly  observed;  sometimes  fracture  surfaces  (||  r(1011), 
2(0111)  and  m(1010),  developed  by  sudden  cooling  after  being  heated  (see  Art. 
279).  Fracture  conchoidal  to  subconchoidal  in  crystallized  forms,  uneven  to 
splintery  in  some  massive  kinds.  Brittle  to  tough.  H.  =  7.  G.  =  2-653- 
2-660  in  crystals;  cryptocrystalline  forms  somewhat  lower  (to  2 -60)  if  pure, 
but  impure  massive  forms  (e.g.,  jasper)  higher.  Luster  vitreous,"  sometimes 
greasy;  splendent  to  nearly  dull.  Colorless  when  pure;  often  various  shades 
of  yellow,  red,  brown,  green,  blue,  black.  Streak  white,  of  pure  varieties;  if 
impure,  often  the  same  as  the  color,  but  much  paler.  Transparent  to  opaque. 
Optically  +.  Double  refraction  weak.  Polarization  circular;  right- 
handed  or  left-handed,  the  optical  character 
corresponding  to  right-  and  left-handed 
character  of  crystals,  as  defined  above;  in 
twins  (law  2),  both  right  and  left  forms 
sometimes  united,  sections  then  often 
showing  Airy's  spirals  in  the  polariscope 
(cf.  Art.  394,  p.  270,  and  Fig.  692).  Ro- 
tatory power  proportional  to  thickness  of 
plate.  Refractive  indices  for  the  D  line, 
co  =  1-54418,  e  =  1-55328;  also  rotatory 
power  for  section  of  lmm  thickness,  a  =  21 71 
(D  line).  Pyroelectric;  also  electric  by 
pressure  or  piezo-electric.-  See  Arts.  438, 
439.  On  etching-figures,  see  Arts.  286,  287. 
Comp.  —  Silica,  or  silicon  dioxide, 
=  Oxygen  53'3,  silicon  467  =  100. 


692 


Basal  section  in  polarized  light,  show- 


mg  interpenetration  of  right- and 
left-handed  portions.      Des  Cloi- 


In  massive  varieties  often  mixed  with  a  little  opal 
silica.     Impure  varieties  contain-  iron  oxide,  calcium 
carbonate,  clay,  sand,  and  various  minerals  as  inclusions. 

Artif.  —  Quartz  has  been  produced  artificially  in  numerous  ways.  Recently  crystals 
have  been  obtained  at  temperatures  below  760°  from  melts  containing  dissolved  silica 
which  were  composed  of  (1)  a  mixture  of  potassium  and  lithium  chlorides,  (2)  vanadic 
acid,  (3)  sodium  tungstate.  At  higher  temperatures  tridymite  crystals  formed. 

Var™~A-,  PHENOCRYSTALLINE:  Crystallized,  vitreous  in  luster.  B.  CRYPTOCRYSTAL- 
LINE: Flint-like,  massive. 

The  first  division  includes  all  ordinary  vitreous  quartz,  whether  having  crystalline  faces 
1  he  varieties  under  the  second  are  in  general   acted  upon  somewhat  more  by 
rition    and  by  chemical  agents,  as  hydrofluoric  acid,  than  those  of  the  first.     In  all 
kinds  made  up  of  layers,  as  agate,  successive  layers  are  unequally  eroded. 


OXIDES  405 

A.     PHENOCRYSTALLINE  OR  VITREOUS  VARIETIES 

Ordinary  Crystallized;  Rock  Crystal.  —  Colorless  quarts,  or  nearly  so,  whether  in  dis- 
tinct crystals  or  not.  Here  belong  the  Bristol  diamonds,  Lake  George  diamonds,  Brazilian 
pebbles,  etc.  Some  variations  from  the  common  type  are :  (a)  cavernous  crystals;  (6)  cap- 
quartz  made  up  of  separable  layers  or  caps;  (c)  drusy  quartz,  a  crust  of  small  or  minute 
quartz  crystals;  (d)  radiated  quartz,  often  separable  into  radiated  parts,  having  pyramidal 
terminations;  (e)  fibrous,  rarely  delicately  so,  as  a  kind  from  Griqualand  West,  South 
Africa,  altered  from  crocidolite  (see  cat's-eye  below,  also  crocidolite,  p.  493). 

Asteriated;  Star-quartz.  —  Containing  within  the  crystal  whitish  or  colored  radiations 
along  the  diametral  planes.  Occasionally  exhibits  distinct  asterism. 

Amethystine;  Amethyst.  —  Clear  purple,  or  bluish  violet.  Color  perhaps  due  to  man- 
ganese. 

Rose.  —  Rose-red  or  pink,  but  becoming  paler  on  exposure.  Commonly  massive. 
Luster  sometimes  a  little  greasy.  Color  perhaps  due  to  titanium. 

Yellow;  False  Topaz  or  Citrine.  —  Yellow  and  pellucid;  resembling  yellow  topaz. 

Smoky;  Cairngorm  Stone.  —  Smoky  yellow  to  dark  smoky  brown,  and  often  trans- 
parent; varying  to  brownish  black.  Color  is  probably  due  to  some  organic  compound 
(Forster).  Called  cairngorms  from  the  locality  at  Cairngorm,  southwest  of  Banff,  in 
Scotland.  The  name  morion  is  given  to  nearly  black  varieties. 

Milky.  —  Milk-white  and  nearly  opaque.     Luster  often  greasy. 

Siderite,  or  Sapphire-quartz.  —  Of  indigo  or  Berlin-blue  color;  a  rare  variety. 

Sagenitic.  —  Inclosing  acicular  crystals  of  rutile.  Other  included  minerals  in  acicular 
forms  are:  black  tourmaline;  gothite;  stibnite;  asbestus;  actinolite;  hornblende;  epidote. 

Cat's-eye  exhibits  opalescence,  but  without  prismatic  colors,  especially  when  cut  en  ca- 
bochon,  an  effect  sometimes  due  to  fibers  of  asbestus.  Also  present  in  the  siliceous  pseudo- 
morphs,  after  crocidolite,  called  tiger-eye  (see  crocidolite).  The  highly-prized  Oriental 
cat's-eye  is  a  variety  of  chrysoberyl. 

Aventurine.  —  Spangled  with  scales  of  mica,  hematite,  or  other  mineral. 

Impure  from  the  presence  of  distinct  minerals  distributed  densely  through  the  mass. 
The  more  common  kinds  are  those  .in  which  the  impurities  are:  (a)  ferruginous,  either  red 
or  yellow,  from  anhydrous  or  hydrous  iron  sesquioxide;  (6)  chloritic,  from  some  kind  of 
chlorite;  (c)  actinolitic;  (d)  micaceous;  (e)  arenaceous,  or  sand. 

Containing  liquids  in  cavities.  The  liquid,  usually  water  (pure,  or  a  mineral  solution), 
or  some  petroleum-like  compound.  Quartz,  especially  smoky  quartz,  also  often  contains 
inclusions  of  both  liquid  and  gaseous  carbon  dioxide. 

B.     CRYPTOCRYSTALLINE  VARIETIES 

Chalcedony.  —  Having  the  luster  nearly  of  wax,  and  either  transparent  or  translucent. 
G.  =  2'6-2'64.  Color  white,  grayish,  blue,  pale  brown  to  dark  brown,  black.  Also  of 
other  shades,  and  then  having  other  names.  Often  mammillary,  botryoidal,  stalactitic, 
and  occurring  lining  or  filling  cavities  in  rocks.  It  often  contains  some  disseminated  opal- 
silica.  The  thermal  study  of  chalcedony  shows  that  it  differs  from  quartz  and  may  be 
therefore  a  distinct  species.  The  name  enhydros  is  given  to  nodules  of  chalcedony  con- 
taining water,  sometimes  in  large  amount.  Embraced  under  the  general  name  chalcedony 
is  the  crystalline  form  of  silica  which  forms  concretionary  masses  with  radial-fibrous  and 
concentric  structure,  and  which,  as  shown  by  Rosenbusch,  is  optically  negative,  unlike  true 
quartz.  It  has  n  =  1*537;  G.  =  2'59-2'64.  Often  in  spherulites,  showing  the  spheru- 
litic  interference-figure .  Lussatite  of  Mallard  has  a  like  structure,  but  is  optically  +  and 
has  the  specific  gravity  and  refractive  index  of  opal.  It  may  be  a  fibrous  form  of  tridymite. 
See  also  quartzine,  p.  407. 

Carnelian.  Sard.  —  A  clear  red  chalcedony,  pale  to  deep  in  shade;  also  brownish  red 
to  brown. 

Chrysoprase.  —  An  apple-green  chalcedony,  the  color  due  to  nickel  oxide. 

Prase.  —  Translucent  and  dull  leek-green. 

Plasma.  —  Rather  bright  green  to  leek-green,  and  also  sometimes  nearly  emerald-green, 
and  subtranslucent  or  feebly  translucent.  Heliotrope,  or  Blood-stone,  is  the  same  stone 
essentially,  with  small  spots  of  red  jasper,  looking  like  drops  of  blood. 

Agate.  —  A  variegated  chalcedony.  The  colors  are  either  (a)  banded;  or  (6)  irregu- 
larly clouded ;  or  (c)  due  to  visible  impurities  as  in  moss  agate,  which  has  brown  moss-like 
or  dendritic  forms,  as  of  manganese  oxide,  distributed  through  the  mass.  The  bands  are 
delicate  parallel  lines,  of  white,  pale  and  dark  brown,  bluish  and  other  shades;  they  are 
sometimes  straight,  more  often  waving  or  zigzag,  and  occasionally  concentric  circular. 


406  DESCRIPTIVE    MINERALOGY 

The  bands- are  the  edges  of  layers  of  deposition,  the  agate  having  been  formed  by  a  deposit 
of  silica  from  solutions  intermittently  supplied,  in  irregular  cavities  in  rocks,  and  deriving 
their  concentric  waving  courses  from  the  irregularities  of  the  walls  of  the  cavity.  The 
layers  differ  in  porosity,  and  therefore  agates  may  be  varied  in  color  by  artificial  means, 
and  this  is  done  now  to  a  large  extent  with  the  agates  cut  for  ornament.  There  is  also 
agatized  wood;  wood  petrified  with  clouded  agate. 

Onyx.  —  Like  agate  in  consisting  of  layers  of  different  colors,  white  and  black,  white  and 
red,  etc.,  but  the  layers  in  even  planes,  and  the  banding  straight,  and  hence  its  use  for 
cameos. 

Sardonyx.  —  Like  onyx  in  structure,  but  includes  layers  of  carnelian  (sard)  along  with 
others  of  white  or  whitish,  and  brown,  and  sometimes  black  colors. 

Agate-jasper.  —  An  agate  consisting  of  jasper  with  veinings  of  chalcedony. 

Siliceous -sinter.  —  Irregularly  cellular  quartz,  formed  by  deposition  from  waters  con- 
taining silica  or  soluble  silicates  in  solution.  See  also  under  opal,  p.  408. 

Flint.  —  Somewhat  allied  to  chalcedony,  but  more  opaque,  and  of  dull  colors,  usually 
gray,  smoky,  brown,  and  brownish  black.  The  exterior  is  often  whitish,  from  mixture  with 
lime  or  chalk,  in  which  it  is  embedded.  Luster  barely  glistening,  subvitreous.  Breaks 
with  a  deeply  conchoidal  fracture,  and  a  sharp  cutting  edge.  The  flint  of  the  chalk  forma- 
tion consists  largely  of  the  remains  of  diatoms,  sponges,  and  other  marine  productions. 
The  coloring  matter  of  the  common  kind  is  mostly  carbonaceous  matter.  Flint  implements 
play  an  important  part  among  the  relics  of  early  man. 

Hornstone.  —  Resembles  flint,  but  is  more  brittle,  the  fracture  more  splintery.  Chert 
is  a  term  often  applied  to  hornstone,  and  to  any  impure  flinty  rock,  including  the  jaspers. 

Basanite;  Lydian  Stone,  or  Touchstone.  —  A  velvet-black  siliceous  stone  or  flinty  jasper, 
used  on  account  of  its  hardness  and  black  color  for  trying  the  purity  of  the  precious  metals. 
The  color  left  on  the  stone  after  rubbing  the  metal  across  it  indicates  to  the  experienced 
eye  the  amount  of  alloy.  It  is  not  splintery  like  hornstone. 

Jasper.  —  Impure  opaque. colored  quartz;  commonly  red,  also  yellow,  dark  green  and 
grayish  blue.     Striped  or  riband  jasper  has  the  colors  in  broad  stripes.     Porcelain  jasper  is 
nothing  but  .baked  clay,  and  differs  from  true  jasper  in  being  B.B.  fusible  on  the  edges. 
C.     Besides  the  above  there  are  also: 

Granular  Quartz,  Quartz-rock,  or  Quartzite.  —  A  rock  consisting  of  quartz  grains  very 
firmly  compacted;  the  grains  often  hardly  distinct.  Quartzose  Sandstone,  Quartz-con* 
glomerate.  —  A  rock  made  of  pebbles  of  quartz  with  sand.  The  pebbles  sometimes  are 
jasper  and  chalcedony,  and  make  a  beautiful  stone  when  polished.  Itacolumite,  or  Flexible 
Sandstone.  —  A  friable  sand-rock,  consisting  mainly  of  quartz-sand,  but  containing  a  little 
mica,  and  possessing  a  degree  of  flexibility  when  in  thin  laminae.  Buhrstone,  or  Burrstone. 
—  A  cellular,  flinty  rock,  having  the  nature  in  part  of  coarse  chalcedony. 

Pseudomorphous  Quartz.  —  Quartz  appears  also  under  the  forms  of  many  of  the  mineral 
species,  which  it  has  taken  through  either  the  alteration  or  replacement  of  crystals  of  those 
species.  The  most  common  quartz  pseudomorphs  are  those  of  calcite,  barite,  fluorite,  and 
siderite.  Silicified  wood  is  quartz  pseudomorph  after  wood  (p.  326). 

Pyr.,  etc.  —  B.B.  unaltered;  with  borax  dissolves  slowly  to  a  clear  glass;  with  soda 
dissolves  with  effervescence;  unacted  upon  by  salt  of  phosphorus.  Insoluble  in  hydro- 
chloric acid,  and  only  slightly  acted  upon  by  solutions  of  fixed  caustic  alkalies,  the  crypto- 
crystalline  varieties  to  the  greater  extent.  Soluble  only  in  hydrofluoric  acid.  When  fused 
and  cooled  it  becomes  opal-silica  having  G.  =  2'2. 

Diff.  —  Characterized  in  crystals  by  the  form,  glassy  luster,  and  absence  of  cleavage; 
also  in  general  by  hardness  and  inf usibility. 

Micro.  —  Easily  recognized  in  rock  sections  by  its  low  refraction  ("  low  relief,"  p.  212) 
and  low  birefringence  (e  -  co  =  0'009);  the  interference  colors  in  good  sections  not  rising 
above  yellow  of  the  first  order;  also  by  its  limpidity  and  the  positive  uniaxial  cross  yielded 
by  basal  sections  (p.  270,  note),  which  remain  dark  when  revolved  between  crossed  nicols. 
Commonly  in  formless  grains  (granite),  also  with  crystal  outline  (porphyry,  etc.). 

Obs.  —  Quartz  is  an  essential  component  of  certain  igneous  rocks,  as  granite,  granite- 
porphyry  quartz-porphyry  and  rhyolite  in  the  granite  group;  in  such  rocks  it  is  com- 
nonly  in  tormless  grains  or  masses  filling  the  interstices  between  the  feldspar,  as  the  last 
product  of  crystallization.  Further  it  is  an  essential  constituent  in  quartz-diorite,  quartz- 
diorite  porphyry  and  dacites  in  the  diorite  group;  in  the  porphyries  frequently  in  distinct 
crystals.  It  occurs  also  as  an  accessory  in  other  feldspathic  igneous  rocks,  such  as  syenite 
and  trachyte.  Among  the  metamorphic  rocks  it  is  an  essential  component  of  certain 
varieties  of  gneiss,  of  quartzite,  etc.  It  forms  the  mass  of  common  sandstone.  It  occurs 
as  the  vein-stone  m  various  rocks,  and  forms  a  large  part  of  mineral  veins;  as  a  foreign  min- 


OXIDES  407 

eral  in  some  limestones,  etc.,  making  geodes  of  crystals,  or  of  chalcedony,  agate,  carnelian, 
etc.;  as  embedded  nodules  or  masses  in  various  limestones,  constituting  the  flint  of  the  Chalk 
formation,  the  hornstone  of  other  limestones  —  these  nodules  sometimes  becoming  con- 
tinuous layers;  as  masses  of  jasper  occasionally  in  limestone.  It  is  the  principal  material 
of  the  pebbles  of  gravel-beds,  and  of  the  sands  of  the  seashore,  and  sandbeds  everywhere. 
In  graphic  granite  (pegmatite)  the  quartz  individuals  are  arranged  in  parallel  position  in 
feldspar,  the  angular  particles  resembling  written  characters.  The  quartz  grains  in  a 
fragmental  sandstone  are  often  found  to  have  undergone  a  secondary  growth  by  the  depo- 
sition of  crystallized  silica  with  like  orientation  to  the  original  nucleus.  From  a  general 
study  of  the  chemical  and  mineralogical  character  of  the  rocks  of  the  earth's  crust  it  has 
been  estimated  that  quartz  forms  about  twelve  per  cent  of  their  constituents. 

Switzerland;  Dauphine,  France;  Piedmont,  Italy;  the  Carrara  quarries,  Italy;  and 
numerous  other  foreign  localities  afford  fine  specimens  of  rock  crystal;  also  Japan,  from 
which  are  cut  the  beautiful  crystal  spheres,  in  rare  cases  up  to  6  inches  in  diameter;  also 
interesting  twin  crystals  from  Kai,  Japan;  Bourg  d'Oisans,  Dauphine,  France.  Smoky 
quartz  crystals  of  great  beauty,  and  often  highly  complex  in  form,  occur  at  many  points  in 
the  central  Alps,  also  at  Cairngorm,  Scotland.  The  most  beautiful  amethysts  are  brought 
from  India,  Ceylon,  and  Persia,  Nova  Scotia,  Brazil,  Guanajuato,  Mexico;  inferior  speci- 
mens occur  in  Transylvania.  The  finest  carnelians  and  agates  are  found  in  Arabia,  India, 
Brazil,  Uruguay,  Surinam,  also  formerly  at  Oberstein  and  Saxony.  Scotland  affords 
smaller  but  handsome  specimens  (Scotch  pebbles).  The  banks  of  the  Nile  afford  the 
Egyptian  jasper;  the  striped  jasper  is  met  with  in  Siberia,  Saxony,  and  Devonshire. 

In  N.  Y.,  quartz  crystals  are  abundant  in  Herkimer  Co.,  at  Middleville,  Little  Falls, 
etc.,  loose  in  cavities  hi  the  Calciferous  sand-rock,  or  embedded  in  loose  earth.  Fine 
quartzoids,  at  the  beds  of  hematite  in  Fowler,  Herman,  and  Edwards,  St.  Lawrence  Co., 
also  at  Antwerp,  Jefferson  Co.  On  the  banks  of  Laidlaw  Lake,  Rossie,  large  implanted 
crystals;  at  Ellenville  lead  mine,  Ulster  Co.,  in  fine  groups.  At  Paris,  Me.,  handsome 
crystals  of  brown  or  smoky  quartz.  Beautiful  colorless  crystals  occur  at  Hot  Springs, 
Ark.  Alexander  Co.,  N.  C.,  has  afforded  great  numbers  of  highly  complex  crystals,  with 
rare  modifications.  Fine  crystals  of  smoky  quartz  come  from  the  granite  of  the  Pike's 
Peak  region,  Col.  Geodes  of  quartz  crystals,  also  enclosing  calcite,  sphalerite,  etc.,  are 
common  in  the  Keokuk  limestone  of  the  west. 

Rose  quartz  occurs  at  Hebron,  Albany,  Paris,  Me. ;  Acworth,  N.  H. ;  Southbury,  Conn. ; 
Custer  Co.,  S.  D.  Amethyst,  in  trap,  at  Keweenaw  Point,  Lake  Superior;  Specimen  Mt., 
Yellowstone  Park;  Jefferson  Co.,  Mon.;  in  Pa.,  at  East  Bradford,  Chester,  and  Provi- 
dence (one  fine  crystal  over  7  Ibs.  in  weight),  in  Chester  Co.;  at  the  Prince  vein,  Lake 
Superior;  large  crystals,  near  Greensboro,  N.  C.;  crystallized  green  quartz,  in  talc,  at 
Providence,  Delaware  Co.,  Pa.  Chalcedony  and  agates  abundant  and  beautiful  on  north- 
west shore  of  Lake  Superior.  Red  jasper  is  found  on  Sugar  Loaf  Mt.,  Me.;  in  pebbles  on 
the  banks  of  the  Hudson  at  Troy,  N.  Y.;  yellow,  with  chalcedony,  at  Chester,  Mass. 
Agatized  and  jasperized  wood  of  great  beauty  and  variety  of  color  is  obtained  from  the 
petrified  forest  called  Chalcedony  Park,  near  Carrizo,  Apache  Co.,  Ariz.;  also  from  the 
Yellowstone  Park;  near  Florissant  and  elsewhere  in  Col.;  Amethyst  Mt.,  Utah;  Napa 
Co.,  Cal.  Moss  agates  from  Humboldt  Co.,  Nev.,  and  many  other  points. 

The  word  quartz  is  of  German  provincial  origin.  Agate  is  from  the  name  of  the  river 
Achates,  in  Sicily,  whence  specimens  were  brought,  as  stated  by  Theophrastus. 

Use.  —  In  its  various  colored  forms  as  ornamental  material;  for  abrading  purposes; 
manufacture  of  porcelain,  of  glass;  as  wood  filler;  in  paints,  scouring  soaps,  etc.;  as  sand 
in  mortars  and  Cements;  as  quartzite,  sandstone,  etc.,  for  building  stone,  etc.;  as  an  acid 
flux  in  certain  smelting  operations. 

QUARTZINE  is  a  name  which  has  been  given  to  a  form  of  silica  which  is  present  in 
chalcedony  and  is  inferred  to  be  triclinic  in  crystalline  structure.  Lutecite  belongs  here. 

TRIDYMITE. 

Hexagonal  or  pseudo-hexagonal.  Axis  c  =  1*6530.  Crystals  usually 
minute,  thin  tabular  ||  c(0001);  often  in  twins;  also  united  in  fan-shaped 
groups. 

Cleavage:  prismatic,  not  distinct;  parting  1 1  c,  sometimes  observed.  Frac- 
ture conchoidal.  Brittle.  H.  =  7.  G.  =  2*28-2*33.  Luster  vitreous,  on  c 
pearly.  Colorless  to  white.  Transparent.  Optically  +.  co  =  1*477.  e  = 
1'479.  Often  exhibits  anomalous  refraction  phenomena. 


408  DESCRIPTIVE    MINERALOGY 

Comp.  —  Pure  silica,  SiO2,  like  quartz. 

Tridymite  is  formed  above  800°  C.     See  further  under  Quartz,  p.  403. 

Pyr.,  etc.  —  Like  quartz,  but  soluble  in  boiling  sodium  carbonate. 

Obs.  —  Occurs  chiefly  in  acidic  volcanic  rocks,  rhyolite,  trachyte,  andesite,  liparite, 
less  often  in  dolerite;  usually  in  cavities,  often  associated  with  sanidine,  also  hornblende, 
augite,  hematite;  sometimes  in  opal.  First  observed  in  crevices  and  druses  in  an  augite- 
andesite  from  the  Cerro  San  Cristobal,  near  Pachuca,  Mexico;  later  proved  to  be  rather 
generally  distributed.  Thus  in  trachyte  of  the  Siebengebirge,  Germany;  of  Euganean 
Hills  in  northern  Italy;  Puy  Capucin  (Mont-Dore)  in  Central  France,  etc.  In  the  ejected 
masses  from  Vesuvius  consisting  chiefly  of  sanidine.  In  the  lavas  of  Mt.  Etna,  Sicily,  and 
Mt.  Pelee,  Martinique.  From  Kibosan,  Prov.  Higo,  Japan.  With  quartz,  feldspar, 
fayalite  in  lithophyses  of  Obsidian  cliff,  Yellowstone  Park.  In  the  andesite  of  Mt.  Rainier, 
Washington. 

Named  from  rpiSu/zos,  threefold,  in  allusion  to  the  common  occurrence  in  trillings. 

ASMANITE.  A  form  of  silica  found  in  the  meteoric  iron  of  Breitenbach,  in. very  minute 
grains,  probably  identical  with  tridymite;  by  some  referred  to  the  orthorhombic  system. 

CRISTOBALITE.  Christobalite.  Silica  in  white  octahedrons  (pseudo-isometric?).  G.  = 
2'27.  n  =  1*486.  With  tridymite  in  andesite  of  the  Cerro  S.  Cristobal,  Pachuca,  Mexico, 
Also  noted  in  lava  at  May  en,  Germany,  and  in  meteorites.  For  thermal  relations  to  quartz 
and  tridymite  see  under  quartz,  p.  403. 

MELANOPHLOGITE.  In  minute  cubes  and  spherical  aggregates.  Occurring  with  calcite 
and  celestite  implanted  upon  an  incrustation  of  opaline  silica  over  the  sulphur  crystals  of 
Girgenti,  Sicily.  Consists  of  SiO2  with  5  to  7  p.  c.  of  S03,  perhaps  SiO2  with  SiS2.  The 
mineral  turns  black  superficially  when  heated  B.B. 

OPAL. 

Amorphous.  Massive;  sometimes  small  reniform,  stalactitic,  or  large 
tuberose.  Also  earthy. 

H.  =  5-5-6-5.  G.  =  1-9-2-3;  when  pure  2-1-2-2.  Luster  vitreous,  fre- 
quently subvitreous;  often  inclining  to  resinous,  and  sometimes  to  pearly. 
Color  white,  yellow,  red,  brown,  green,  gray,  blue,  generally  pale;  dark  colors 
arise  from  foreign  admixtures;  sometimes  a  rich  play  of  colors,  or  different 
colors  by  refracted  and  reflected  light.  Streak  white.  Transparent  to  nearly 
opaque,  n  =  1-44-1-45. 

Often  shows  double  refraction  similar  to  that  observed  in  colloidal  substances  due  to 
tension.  The  cause  of  the  play  of  color  in  the  precious  opal  was  investigated  by  Brewster, 
who  ascribed  it  to  the  presence  of  microscopic  cavities.  Behrends,  however,  has  given  a 
monograph  on  the  subject  (Ber.  Ak.  Wien,  64  (1),  1871),  and  has  shown  that  this  explana- 
tion is  incorrect;  he  refers  the  colors  to  thin  curved  lamellae  of  opal  whose  refractive  power 
may  differ  by  O'l  from  that  of  the  mass.  These  are  conceived  to  have  been  originally 
formed  in  parallel  position,  but  have  been  changed,  bent,  and  finally  cracked  and  broken 
in  the  solidification  of  the  groundmass. 

Comp.  —  Silica,  like  quartz,  with  a  varying  amount  of  water,  Si02.nH20. 
The  water  is  sometimes  regarded  as  non-essential. 

The  opal  condition  is  one  of  lower  degrees  of  hardness  and  specific  gravity,  and,  as 
generally  believed,  of  incapability  of  crystallization.  The  water  present  varies  from  2  to  13 
p.  c.  or  more,  but  mostly  from  3  to  9  p.  c.  Small  quantities  of  ferric  oxide,  alumina,  lime 
magnesia,  and  alkalies  are  usually  present  as  impurities. 

Var.  —  Precious  Opal  —  Exhibits  a  play  of  delicate  colors. 

Fire-opal  —  Hyacinth-red  to  honey-yellow  colors,  with  fire-like  reflections,  somewhat 
insed  on  turning. 

Gir'asol.  —  Bluish  white,  translucent,  with  reddish  reflections  in  a  bright  light. 

Common  Opal  —  In  part  translucent;  (a)  milk-opal,  milk-white  to  greenish,  yellowish, 
bluish;  (6)  Resin-opal,  wax-,  honey-  to  ocher-yellow,  with  a  resinous  luster;  (c)  dull  olive- 
green  and  mountain-green ;  (d)  brick-red.  Includes  Semiopal;  (e)  Hydrophane,  a  variety 
which  becomes  more  translucent  or  transparent  in  water. 

Cacholong.  —  Opaque,  bluish  white,  porcelain-white,  pale  yellowish  or  reddish. 

Upal-agate.  —  Agate-like  in  structure,  but  consisting  of  opal  of  different  shades  of  color. 

Memlite.  —  In  concretionary  forms;  opaque,  dull  grayish. 


OXIDES  409 

J asp-opal.  Opal-jasper.  —  Opal  containing  some  yellow  iron  oxide  and  other  impurities, 
and  having  the  color  of  yellow  jasper,  with  the  luster  of  common  opal. 

Wood-opal.  —  Wood  petrified  by  opal. 

Hyalite.  Muller's  Glass.  —  Clear  as  glass  and  colorless,  constituting  globular  concre- 
tions, and  crusts  with  a  globular  or  botryoidal  surface;  also  passing  into  translucent,  and 
whitish.  Less  readily  dissolved  in  caustic  alkalies  than  other  varieties. 

Schaumopal.  —  A  porous  variety  from  the  Virunga  district,  German  East  Africa. 

Fiorite,  Siliceous  Sinter.  —  Includes  translucent  to  opaque,  grayish,  whitish  or  brownish 
incrustations,  porous,  to  firm  in  texture;  sometimes  fibrous-like  or  filamentous,  and,  when 
so,  pearly  in  luster  (then  called  Pearl-sinter)',  deposited  from  the  siliceous. waters  of  hot 
springs. 

Geyserite.  —  Constitutes  concretionary  deposits  about  the  geysers  of  the  Yellowstone 
Park,  Iceland,  and  New  Zealand,s_presenting  white  or  grayish,  porous,  stalactitic,  fila- 
mentous, cauliflower-like  forms,  often  of  great  beauty:  also  compact-massive,  and  scaly- 
massive. 

Float-stone.  —  In  light  porous  concretionary  masses,  white  or  grayish,  sometimes 
cavernous,  rough  in  fracture. 

Tripolite.  —  Formed  from  the  siliceous  shells  of  diatoms  (hence  called  diatomite)  and 
other  microscopic  species,  and  occurring  in  extensive  deposits.  Includes  Infusorial  Earth, 
or  Earthy  Tripolite,  a  very  fine-grained  earth  looking  often  like  an  earthy  chalk,  or  a  clay, 
but  harsh  to  the  feel,  and  scratching  glass  when  rubbed  on  it. 

Pyr.,  etc.  —  Yields  water.  B.B.  infusible,  but  becomes  opaque.  Some  yellow  vari- 
eties, containing  iron  oxide,  turn  red.  Soluble  in  hydrofluoric  acid  somewhat  more  readily 
than  quartz;  also  soluble  in  caustic  alkalies,  but  more  readily  in  some  varieties  than  in 
others. 

Obs.  —  Occurs  filling  cavities  and  fissures  or  seams  in  igneous  rocks,  as  trachyte,  por- 
phyry, where  it  has  probably  resulted  from  the  action  of  hot,  magmatic  waters  upon  the 
silicates  of  the  rocks,  the  liberated  silica  being  deposited  in  the  cavities  in  the  form  of  opal. 
Also  in  some  metallic  veins.  Also  embedded,  like  flint,  in  limestone,  and  sometimes, 
like  other  quartz  concretions,  in  argillaceous  beds;  formed  from  the  siliceous  waters  of 
some  hot  springs;  often  resulting  from  the  mere  accumulation,  or  accumulation  and  partial 
solution  and  solidification,  of  the  siliceous  shells  of  infusoria,  of  sponge  spicules,  etc.,  which 
consist  essentially  of  opal-silica.  The  last  mentioned  is  the  probable  source  of  the  opal 
of  limestones  and  argillaceous  beds  (as  it  is  of  flint  in  the  same  rocks),  and  of  part  of  that 
in  igneous  rocks.  It  exists  in  most  chalcedony  and  flint. 

Precious  opal  occurs  in  porphyry  at  Czerwenitza,  near  Kashau  in  Hungary;  at  Gracias 
a  Dios  in  Honduras;  Queretaro  in  Mexico;  a  beautiful  blue  opal  on  Bulla  Creek,  Queens- 
land; from  White  Cliffs,  New  South  Wales,  as  filling  openings  in  sandstone,  in  fossil  wood, 
in  the  material  of  various  fossil  shells  and  bones  and  in  aggregates  of  radiating  pseudo- 
morphic  crystals.  Fire-opal  occurs  at  Zimapan  in  Mexico;  the  Faroe  Islands;  near  San 
Antonio,  Honduras.  Gem  opal,  often  of  "black  opal"  type,  comes  from  Humboldt  Co., 
Nev.  Common  opal  is  abundant  at  Telkebanya  in  Hungary;  near  Pernstein,  etc.,  in 
Moravia;  in  Bohemia;  Stenzelberg  in  Siebengebirge,  Germany;  in  Iceland.  Hyalite 
occurs  in  amygdaloid  at  Schemnitz,  Hungary;  in  clinkstone  at  Waltsch,  Bohemia;  at  San 
Luis  Potosi,  Mexico;  Kamloops,  British  Columbia. 

In  the  United  States,  hyalite  occurs  sparingly  in  connection  with  the  trap  rock  of  N.  J. 
and  Conn.  A  water-worn  specimen  of  fire-opal  has  been  found  on  the  John  Davis  river, 
in  Crook  Co.,  Ore. 

Common  opal  is  found  at  Cornwall,  Lebanon  Co.,  Pa.;  at  Aquas  Calientes,  Idaho 
Springs,  Col.;  a  white  variety  at  Mokelumne  Hill,  Calaveras  Co.,  Cal.,  and  on  the  Mt. 
Diablo  range.  Geyserite  occurs  in  great  abundance  and  variety  in  the  Yellowstone  region 
(cf.  above);  also  siliceous  sinter  at  Steamboat  Springs,  Nev. 

Use.  —  In  the  colored  varieties  as  a  highly  prized  gem-stone. 


II.  Oxides  of  the  Semi-Metals;  also  Molybdenum,  Tungsten 

Arsenolite.  Arsenic  trioxide,  As2Os.  In  isometric  octahedrons;  in  crusts  and  earthy. 
Colorless  or  white.  G.  =  37.  n  =  1755.  Occurs  with  arsenical  ores. 

Claudetite.    Also  As2O3,  but  monoclinic  in  form.    In  thin  plates. 

Senarmontite.  Antimony  trioxide.  Sb2O3.  In  isometric  octahedrons;  hi  crusts  and 
granular  massive.  G.  =  5;3.  Colorless,  grayish,  n  =  2P087.  Occurs  with  ores  of  anti- 
mony. From  Algeria;  South  Ham,  Quebec. 


410  DESCRIPTIVE   MINERALOGY 

Valentinite.  Sb2O3,  in  prismatic  orthorhombic  crystals.  Index  =  2-34.  From  South 
Ham,  Quebec. 

Bismite.  Bismuth  trioxide,  Bi2O3.  Pulverulent,  earthy;  color  straw-yellow.  From 
Goldfield,  Nevada,  in  minute  silvery  white,  pearly  scales  that  are  hexagonal,  rhombo- 
hedral;  optically  — .  Analyses  of  a  number  of  so-called  bismites  show  them  to  be  bis- 
muth hydroxide  or  other  compounds. 

Tellurite.     Tellurium  dioxide,  TeO2.     In  white  to  yellow  slender  prismatic  crystals. 

Molybdite.  Molybdenum  trioxide,  MoO3.  In  capillary  tufted  forms  and  earthy. 
Color  straw-yellow.  Analyses  of  molybdic  ocher  from  various  localities  show  it  to  be  not 
the  oxide  but  a  hydrous  ferric  molybdate,  Fe2O3.3MO3.7H2O.  Indices,  178-1 '90. 

Tungstite.  Tungsten  trioxide,  WO3.  Pulverulent,  earthy;  color  yellow  or  yellowish 
green.  Indices,  2'09-2'26.  Analysis  of  tungstic  ocher  from  Salmo,  B.  C.,  prove  it  to 
have  the  composition  WO3.H2O;  perhaps  identical  with  meymacite  (a  hydrated  tungstic 
oxide  from  Meymac,  Correze,  France). 

Cervantite.  Sb2O3.Sb2O6.  In  yellow  to  white  acicular  crystals;  also  massive,  pul- 
verulent. 

Stibiconite.  H2Sb2O6.  Massive,  compact.  Color  pale  yellow  to  yellowish  white. 
Index,  1-83. 


HI.   Oxides  of  the  Metals 

A.   ANHYDROUS  OXIDES 
I.  Protoxides,  R2O  and  RO. 

H.   Sesquioxides,  R^Oa. 

ii  in 

m.  Intermediate,  RR-A  or  RO.RgOg,  etc. 
IV.  Dioxides,  RO2. 

The  Anhydrous  Oxides  include,  as  shown  above,  three  distinct  divisions, 
the  Protoxides,  the  Sesquioxides  and  the  Dioxides.  The  remaining  Inter- 
mediate division  embraces  a  number  of  oxygen  compounds  which  are  properly 
to  be  regarded  chemically  as  salts  of  certain  acids  (aluminates,  ferrates,  etc.) ; 
here  is  included  the  well-characterized  SPINEL  GROUP. 

Among  the  Protoxides  the  only  distinct  group  is  the  PERICLASE  GROUP, 
which  includes  the  rare  species  Periclase,  MgO,  Manganosite,  MnO,  and 
Bunsenite,  NiO.  All  of  these  are  isometric  in  crystallization. 

The  Sesquioxides  include  the  well-characterized  HEMATITE  GROUP,  R2O3, 
The  Dioxides  include  the  prominent  RUTILE  GROUP,  R02.  Both  of  these 
groups  are  further  defined  later. 


I.  'Protoxides,  RaO  and  RO 
CUPRITE.    Red  Copper  Ore. 

Isometric-plagiohedral.  Commonly  in  octahedrons;  also  in  cubes  and 
dodecahedrons,  often  highly  modified.  Plagiohedral  faces  sometimes  distinct 
(see  p.  71).  At  times  in  capillary  crystals.  Also  massive,  granular;  some- 
times earthy. 

Cleavage:  o(lll)  interrupted.  Fracture  conchoidal,  uneven.  Brittle. 
H.  =  3*5-4.  G.  =  5'85-6*15.  Luster  adamantine  or  submetallic  to  earthy. 
Color  red,  of  various  shades,  particularly  cochineal-red,  sometimes  almost 
black;  occasionally  crimson-red  by  transmitted  light.  Streak  several  shades 
of  brownish  red,  shining.  Subtransparent  to  subtranslucent.  Refractive 
index,  n  =  2*849. 


OXIDES  411 

Var.  —  1.  Ordinary,  (a)  Crystallized;  commonly  in  octahedrons,  dodecahedrons, 
cubes,  and  intermediate  forms;  the  crystals  often  with  a  crust  of  malachite;  (6)  massive. 

2.  Capillary;   Chalcotrichite.     Plush  Copper  Ore.     In  cap- 
illary or  acicular  crystallizations,  which  are  sometimes  cubes 
elongated  in  the  direction  of  the  cubic  axis. 

3.  Earthy;    Tile  Ore.     Brick-red    or    reddish    brown    and 
earthy,  often  mixed  with  red  oxide  of  iron;  sometimes  nearly 
black.  , 

Comp.  —  Cuprous  oxide,  Cu2O  =  Oxygen  11*2, 
copper  88'8  =  100. 

Pyr.,  etc.  —  Unaltered  in  the  closed  tube.  B.B.  hi  the 
forceps  fuses  and  colors  the  flame  emerald-green.  On  char- 
coal first  blackens,  then  fuses,  and  is  reduced  to  metallic 
copper.  With  the  fluxes  gives  reactions  for  copper.  Soluble 
in  concentrated  hydrochloric  acid,  and  a  strong  solution  when  Arizona 

cooled   and  diluted  with  cold  water  yields  a   heavy,  white 
precipitate  of  cuprous  chloride. 

Diff .  —  Distinguished  from  hematite  by  inferior  hardness,  but  is  harder  than  cinnabar 
and  proustite  and  differs  from  them  in  the  color  of  "the  streak;  reactions  for  copper,  B.B., 
are  conclusive. 

Micro.  —  In  polished  sections  shows  white  with  shining  surface,  usually  pitted.  With 
oblique  illumination,  transparent  deep  red.  With  HNO3  instantly  plated  with  metallic 
copper  which  blackens  and  dissolves.  On  drying  a  thin  film  of  copper  remains.  With  HC1 
darkens  and  is  coated  with  white,  seen  by  oblique  light. 

Obs.  —  Cuprite  is  a  mineral  of  secondary  origin.  It  is  often  formed  as  a  furnace  prod- 
uct and  has  been  rioted  as  a  coating  upon  ancient  copper  or  bronze  objects.  Occurs  at 
Kamsdorf  in  Thuringia;  in  Cornwall,  in  fine  crystals,  at  Wheal  Gorland  and  other  mines; 
in  Devonshire  near  Tavistock;  in  isolated  crystals,  more  or  less  altered  to  malachite,  at 
Chessy,  near  Lyons,  France;  in  the  Ural  Mts.;  South  Australia;  also  abundant  in  Chile, 
Peru,  Bolivia. 

In  the  United  States  observed  at  Somerville,  etc.,  N.  J.;  at  Cornwall,  Lebanon  Co., 
Pa.;  in  the.  Lake  Superior  region.  From  Ariz,  with  malachite,  limonite,  etc.,  at  the  Cop- 
per Queen  mine,  Bisbee,  sometimes  in  fine  crystals;  beautiful  chalcotrichite  at  Morenci; 
at  Clifton,  Graham  Co.,  in  crystals,  and  massive. 

Use. —  An  ore  of  copper. 

Ice.  H2O.  Hexagonal.  Familiarly  known  in  six-rayed  snow  crystals;  also  coating 
ponds  in  whiter,  further  as  glaciers  and  icebergs. 

Periclase  Group 

Periclase.  Magnesia,  MgO.  In  cubes  or  octahedrons,  and  in  grains.  Cleavage  cubic'. 
H.  =6.  G.  =  3'67-3'90.  n  =  174.  Artif.  —  Crystallized  from  a  melt  containing  magne- 
sium chloride  and  silica.  Occurs  in  white  limestone  at  Mte.  Somma,  Vesuvius;  at  the 
Kitteln  manganese  mine,  Nordmark,  Sweden. 

Manganosite  Manganese  protoxide,  MnO.  In  isometric  octahedrons.  Cleavage 
cubic.  H.  =  5-o.  G.  =  5'18.  n  =  2'18.  Color  emerald-green,  becoming  black  on  ex- 
posure. From  Langban  and  Nordmark,  Sweden;  Franklin  Furnace,  N.  J. 

Bunsenite.  Nickel  protoxide,  NiO.  In  green  octahedrons.  From  Johanngeorgen- 
stadt,  Germany. 

Cadmium  oxide.  Isometric.  In  minute  octahedrons.  Forms  a  thin  coating  of  black 
color  and  brilliant  metallic  luster  upon  calamine  from  Monte  Poni,  Sardinia.  Also  formed 
artificially. 


ZINCITE.     Red  Oxide  of  Zinc. 

Hexagonal-hemimprphic.  Axis  c  =  1*5870.  Natural  crystals  rare  (Fig. 
44,  p.  22) ;  usually  foliated  massive,  or  in  coarse  particles  and  grains;  also  with 
granular  structure. 


412  DESCRIPTIVE   MINERALOGY 

Cleavage:  c(0001)  perfect;  prismatic,  sometimes  distinct.  Fracture  sub- 
conchoidal.  Brittle.  H.  =  4-4'5.  G.  =  5-43-57.  Luster  subadamantine. 
Streak  orange-yellow.  Color  deep  red,  also  orange-yellow.  Translucent  to 
subtranslucent.  Optically  +. 

Comp.  —  Zinc  oxide,  ZnO  =  Oxygen  197,  zinc  80*3  =  100.  Manga- 
nese protoxide  is  sometimes  present. 

Pyr.,  etc.  —  B.B.  infusible;  with  the  fluxes,  on  the  platinum  wire,  gives  reactions  for 
manganese,  and  on  charcoal  in  R.F.  gives  a  coating  of  zinc  oxide,  yellow  while  hot,  and 
white  on  cooling.  The  coating,  moistened  with  cobalt  solution  and  treated  in  O.F.,  as- 
sumes a  green  color.  Soluble  in  acids. 

Diff.  —  Characterized  by  its  color,  particularly  that  of  the  streak;  by  cleavage;  by 
reactions  B.B. 

Artif.  —  Zincite  is  often  formed  as  a  furnace  product.  It  is  also  produced  when  zinc 
chloride  and  water  vapor  act  upon  lime  at  red  heat. 

Obs.  —  Occurs  with  franklinite  and  willemite,  at  Sterling  Hill  near  Ogdensburg,  and  at 
Mine  Hill,  Franklin  Furnace,  Sussex  Co.,  N.  J.,  sometimes  in -lamellar  masses  in  pink 
calcite.  Has  been  reported  from  Poland.  A  not  uncommon  furnace  product. 

Use.'  —  An  ore  of  zinc.  „ 

Massicot.  Lead  monoxide,  PbO.  Massive,  scaly  or  earthy.  Color  yellow,  reddish. 
Probably  orthorhombic.  Index,  1735.  Optically—. 

Tenorite.  Cupric  oxide,  CuO.  In  minute  black  scales  with  metallic  luster;  from 
Vesuvius.  Also  black  earthy  massive  (melaconite) ;  occurring  with  ores  of  copper  as  at 
Ducktown,  Tenn.,  and  Keweenaw  Point,  Lake  Superior.  Pitchy  black  material  asso- 
ciated with  cuprite,  chrysocolla  and  malachite  from  Bisbee,  Ariz.,  has  been  called  melano- 
chaldte. 

Paramelaconite  is  essentially  cupric  oxide,  CuO,  occurring  in  black  pyramidal  crystals 
referred  to  the  tetragonal  system.  From  the  Copper  Queen  mine,  Bisbee,  Ariz. 

Montroydite.  HgO.  Orthorhombic.  In  minute  highly  modified  crystals.  H.  = 
T5-2.  Color  and  streak  orange-red.  Index,  2'55.  Volatile.  Found  at  Terlingua,  Tex. 


Hematite  Group.     R203.     Rhombohedral 

rr'  c 

Corundum         A1203  93°  56'  1*3630 

Hematite  Fe2O3  94°     0'  1*3656 

Ilmenite  (Fe,Mg)O.Ti02  Tri-rhombohedral     94°  29'  1*3846 

Pyrophanite       MnO.Ti02  "  94°     5J'  1'3692 

The  HEMATITE  GROUP  embraces  the  sesquioxides  of  aluminium  and  iron. 
These  compounds  crystallize  in  the  rhombohedral  class,  hexagonal  system, 
with  a  fundamental  rhombohedron  differing  but  little  in  angle  from  a  cube. 
Both  the  minerals  belonging  here,  Hematite  and  Corundum,  are  hard. 

To  these  species  the  titanates  of  iron  (and  magnesium)  and  manganese, 
Ilmenite  and  Pyrophanite,  are  closely  related  in  form  though  belonging  to  the 
tri-rhombohedral  class  (phenacite  type) ;  in  other  words,  the  relation  between 
hematite  and  ilmenite  may  be  regarded  as  analogous  to  that  between  calcite 
and  dolomite.  It  is  to  be  noted,  further,  that  hematite  often  contains  tita- 
nium, and  an  artificial  isomorphous  compound,  Ti203,  has  been  described. 
Hence  the  ground  for  writing  the  formula  of  ilmenite  (Fe,Ti)2O3,  as  is  done  by 
some  authors.  It  is  shown  by  Penfield,  however,  that  the  formula  (Fe,Mg)Ti02 
is  more  correct. 


OXIDES 


413 


CORUNDUM. 

Rhombohedral. 

694 


Axisc  =  1-3630. 
695 


697 


cr,  0001  A  1011  =  57°  34' 
en,  0001  A  2243  =  6l°  11' 
rr'  1011  A  1101  =  93°  56' 
nn',  2243  A  2423  =  51°  58' 
w',  4483  A  4843  =  57°  38' 
zz',  2241  A  2421  =  58°  55' 

Twins:  tw.  pi.  r(10ll),  sometimes  penetration-twins;  often  polysynthetic, 
and  thus  producing  a  laminated  structure.  Crystals  usually  rough  and 
rounded.  Also  massive,  with  nearly  rectangular  parting  or  pseudo-cleavage; 
granular,  coarse  or  fine. 

Parting:  c(0001),  sometimes  perfect,  but  interrupted;  also  r(1011)  due 
to  twinning,  often  prominent;  a(1120)  less  distinct.  Fracture  uneven  to 
conchoidal.  Brittle,  when  compact  very  tough.  H.  =9.  G.  =  3-95-4-10. 
Luster  adamantine  to  vitreous;  on  c  sometimes  pearly.  Occasionally  show- 
ing asterism.  Color  blue,  red,  yellow,  brown,  gray,  and  nearly  white;  streak 
uncolored.  Pleochroic  in  deeply  colored  varieties.  Transparent  to  trans- 
lucent. Normally  uniaxial,  negative;  for  sapphire  co  =  17676  to  1*7682  and 
e  =  17594  to  17598.  Often  abnormally  biaxial. 

Var.  —  There  are  three  subdivisions  of  the  species  prominently  recognized  in  the  arts, 
but  differing  only  in  purity  and  state  of  crystallization  or  structure. 

VAR.  1.  SAPPHIRE,  RUBY.  —  Includes  the  purer  kinds  of  fine  colors,  transparent  to 
translucent,  useful  as  gems.  Stones  are  named  according  to  their  colors:  Sapphire  blue; 
true  Ruby,  or  Oriental  Ruby,  red;  Oriental  Topaz,  yellow;  Oriental  Emerald,  green;  Oriental 
Amethyst,  purple.  The  term  sapphire  is  also  often  used  as  a  general  term  to  indicate  corun- 
dum gems  of  any  color  except  red.  A  variety  having  a  stellate  opalescence  when  viewed  in 
the  direction  of  the  vertical  axis  of  the  crystal  is  the  Asteriated  Sapphire  or  Star  Sapphire. 

2.  CORUNDUM.  —  Includes  the  kinds  of  dark  or  dull  colors  and  not  transparent,  colors 
light  blue  to  gray,  brown,  and  black.     The  original  adamantine  spar  from  India  has  a  dark 
grayish  smoky  brown  tint,  but  greenish  or  bluish  by  transmitted  light,  when  translucent. 

3.  EMERY.  —  Includes  granular  corundum,  of  black  or  grayish  black  color,  and  contains 
magnetite  or  hematite  intimately  mixed.     Sometimes  associated  with  iron  spinel  or  hercy- 
nite.     Feels  and  looks  much  like  a  black  fine-grained  iron  ore,  which  it  was  long  considered 
to  be.     There  are  gradations  from  the  evenly  fine-grained  emery  to  kinds  in  which  the  corun- 
dum is  in  distinct  crystals. 

Comp.  —  Alumina,  A12O3  =  Oxygen  47' 1,  aluminium  52'9  =  100.  The 
crystallized  varieties  are  essentially  pure;  analyses  of  emery  show  more  or  less 
impurity,  chiefly  magnetite. 

Artif .  —  Crystallized  corundum  has  been  produced  artificially  in  a  number  of  differ- 
ent ways.  Alumina  dissolved  in  molten  sodium  sulphide,  in  a  fused  mixture  of  a  fluoride 
and  potassium  carbonate  or  in  fused  lead  oxide,  will  separate  out  as  crystallized  corundum. 


414  DESCRIPTIVE   MINERALOGY 

Gem  material  has  been  produced  in  this  way,  colored  red,  with  a  chromium  salt,  or  blue 
by  cobalt.  Crystallized  material  can  also  be  produced  by  fusing  alumina  in  an  electric 
arc.  The  artificial  abrasive,  alundum,  is  made  by  heating  bauxite  to  5000°-6000°  in  an 
electric  furnace.  Pear-shaped  drops  of  gem  material  are  made  by  fusing  together  small 
fragments  of  natural  or  artificial  stones.  Gems  cut  from  them  are  known  as. "recon- 
structed "  stones  and  have  the  crystalline  and  other  physical  properties  of  the  natural 
mineral. 

Pyr.,  etc.  —  B.B.  unaltered;  slowly  dissolved  in  borax  and  salt  of  phosphorus  to  a 
clear  glass,  which  is  colorless  when  free  from  iron;  not  acted  upon  by  soda.  The  finely 
pulverized  mineral,  after  long  heating  with  cobalt  solution,  gives  a  beautiful  blue  color. 
Not  acted  upon  by  acids,  but  converted  into  a  soluble  compound  by  fusion  with  potassium 
bisulphate. 

Diff.  — Characterized  by  its  hardness  (scratching  quartz  and  topaz),  by  its  adaman- 
tine luster,  high  specific  gravity  and  infusibility.  The  massive  variety  with  rhombohedral 
parting  resembles  cleavable  feldspar  but  is  much  harder  and  denser. 

Micro,  —  In  thin  sections  appears  nearly  colorless  with  high  relief  and  low  interfer- 
ence colors. 

Obs.  —  Usually  occurs  in  crystalline  rocks,  as  granular  limestone  or  dolomite,  gneiss, 
granite,  mica  slate,  chlorite  slate.  The  associated  minerals  often  include  some  species  of 
the  chlorite  group,  as  prochlorite,  corundophilite,  margarite,  also  tourmaline,  spinel, 
cyanite,  diaspore,  and  a  series  of  aluminous  minerals,  in  part  produced  from  its  alteration. 
Occasionally  found  as  an  original  constituent  of  igneous  rocks  containing  high  percentages 
of  alumina.  In  the  Ural  Mts.  are  found  an  anorthite  rock  containing  nearly  60  per  cent  of 
corundum,  a  corundum  syenite  with  18  per  cent,  and  a  pegmatite  with  35  per  cent.  A 
corundum  anorthosite  and  corundum  syenites  are  found  in  Canada.  Important  deposits 
of  corundum  in  North  Carolina  and  Georgia  are  associated  with  dunite  rocks.  Rarely 
observed  as  a  contact-mineral.  The  fine  sapphires  are  usually  obtained  from  the  beds  of 
rivers,  either  in  modified  hexagonal  prisms  or  in  rolled  masses,  accompanied  by  grains  of 
magnetite,  and  several  kinds  of  gems,  as  spinel,  etc.  The  emery  of  Asia  Minor  occurs  in 
granular  limestone. 

The  best  rubies  come  from  the  mines  in  Upper  Burma,  north  of  Mandalay,  in  an  area 
covering  25  to  30  square  miles,  of  which  Mogok  is  the  center.  The  rubies  occur  in  situ  in 
crystalline  limestone,  also  in  the  soil  of  the  hillsides  and  in  gem-bearing  gravels  of  the  Irra- 
waddy  River.  Blue  sapphires  are  brought  from  Ceylon  from  the  Ratnapura  and  Rakwena 
districts,  often  as  rolled  pebbles,  also  as  well-preserved  crystals.  Corundum  occurs  in  the 
Carnatic  on  the  Malabar  coast,  on  the  Chantibun  hills  in  Siam,  and  elsewhere  in  the  East 
Indies;  also  near  Canton,  China;  from  Naegi,  Mino,  Japan.  At  St.  Gothard,  Switzerland, 
it  occurs  of  a  red  or  blue  tinge  in  dolomite,  and  near  Mozzo  in  Piedmont,  Italy,  in  white 
compact  feldspar.  Adamantine  spar  is  met  with  in  large,  coarse,  hexagonal  pyramids  in 
Gellivara,  Sweden.  Other  localities  are  in  Bohemia,  near  Petschau,  in  Russia,  in  the 
Ilmen  mountains,  not  far  from  Miask  and  in  the  gold-washings  northeast  of  Zlatoust. 
Corundum,  sapphires,  and  less  often  rubies  occur  in  rolled  pebbles  in  the  diamond  gravels 
on  the  Cudgegong  river,  at  Mudgee  and  other  points  in  New  South  Wales.  Emery  is  found 
in  large  bowlders  at  Naxos,  Nicaria,  and  Samos  of  the  Grecian  islands ;  also  in  Asia  Minor, 
12  m.  E.  of  Ephesus,  near  Gumuchdagh  and  near  Smyrna,  associated  with  margarite, 
chloritoid,  pyrite.  -> 

In  North  America,  in  Mass.,  at  Chester,  with  magnetite,  diaspore,  ripidolite,  'mar- 
garite, etc.,  was  mined  for  use  as  emery.  In  Conn,  near  Litchfield.  In  N.  Y.,  at  Warwick, 
bluish  and  pink,  with  spinel;  Amity,  in  granular  limestone;  emery  with  magnetite  and 
green  spinel  (hercynite)  in  Westchester  Co.,  near  Cruger's  Station,  and  elsewhere.  In 
N.  J.,  at  Newton,  blue  crystals  in  granular  limestone;  at  Vernon,  at  Sparta  and  elsewhere 
in  Sussex  Co.  In  Pa.,  in  Delaware  Co.,  in  Aston,  near  Village  Green,  in  large  crystals;  at 
Mineral  Hill,  in  loose  crystals;  in  Chester  Co.,  at  Unionville,  abundant  in  crystals;  in  large 
crystals  loose  m  the  soil  at  Shimersville,  Lehigh  Co.  In  Va.,  in  the  mica  schists  of  Bull  Mt., 
Patrick  Co. 

Common  at  many  points  along  a  belt  extending  from  Virginia  across  western  North  and 
South  Carolina  and  Georgia  to  Dudleyville,  Alabama;  especially  in  Madison,  Buncombe, 
Haywood,  Jackson,  Macon,  Clay,  and  Gaston  counties  in  N.  C.  The  localities  at  which 
most  work  has  been  done  are  the  Culsagee  mine,  Corundum  hill,  near  Franklin,  Macon  Co., 
ik  U'1!md  26  miles  S  E.  of  this,  at  Laurel  Creek,  Ga.  The  corundum  occurs  in  beds  in 
chrysolite  (and  serpentine)  and  hornblendic  gneiss,  associated  with  a  species  of  the  chlorite 
group,  also  spinel,  etc.,  and  here  as  elsewhere  with  many  minerals  resulting  from  its  altera- 
tion. Some  fine  rubies  have  been  found.  Fine  pink  crystals  of  corundum  occur  at  Hia- 


OXIDES 


415 


wassee,  Towns  Co.,  Ga.  In  Col.,  small  blue  crystals  occur  in  mica  schist  near  Salida 
Chaffee  Co.  Gem  sapphires  are  found  near  Helena,  Mon.,  in  gold-washings  and  in  bars  in 
the  Missouri  river,  especially  the  Eldorado  bar;  at  Yogo  Gulch  on  the  Judith  river  and  at 
other  points  in  the  state.  1  hese  latter  occur  embedded  in  an  igneous  dike  that  cuts  through 
the  limestone  formation.  In  Cat,  in  Los  Angeles  Co.,  in  the  drift  of  San  Francisqueto  Pals. 
In  Canada,  at  Burgess,  Ontario,  red  and  blue  crystals;  in  a  syenite  from  Renfrew  Co 
Ontario. 

Use.  —  Clear  varieties  of  corundum  form  valuable  gem  stones  as  noted  above.  Also 
formerly  largely  used  as  an  abrasive;  at  present  various  artificial  abrasives  are  mostlv 
used  instead.  * 


HEMATITE. 

Rhombohedral.     Axis  c  =  1*3656. 
cr,    0001  A  1011  =  57°  37'. 
rr',  1011  A  1101  =  94°    0'. 
dd',0112  A  1012  =  64°  51'. 


uu',  10T4  A  1104  =  37°  2'. 
nn',  2243  A  2423  =  51°  59'. 
en,  0001  A  2243  =  61°  13'. 


700 


Twins:  tw.  pi.  (1)  c(0001),  penetration-twins;  (2)  r  (0112),  less  common, 
usually  as  polysynthetic  twin- 
ning lamellae,  producing  a  fine 
striation  on  c(0001),  and  giv- 
ing rise  to  a  distinct  parting 
or  pseudo-cleavage  \\  r(1011). 
Crystals  often  thick  to  thin 
tabular  j  \  c,  and  grouped  in  paral- 
lel position  or  in  rosettes;_c  faces 
striated  \\  edge  c/d  (0112)  and 

other  forms  due  to  oscillatory  combination;  also  in  cube-like  rhombohedrons; 
rhombohedral  faces  w(1014)  horizontally  striated  and  often  rounded  over  in 


701 


702 


703 


convex  forms.  Also  columnar  to  granular,  botryoidal,  and  stalactitic  shapes; 
also  lamellar,  laminae  joined  parallel  to  c,  and  variously  bent,  thick  or  thin; 
also  granular,  friable,  earthy  or  compact. 

Parting:  c(0001),  due  to  lamellar  structure;  also  r(1011),  caused  by  twin- 
ning. Fracture  subconchoidal  to  uneven.  Brittle  in  compact  forms;  elastic 
in  thin  laminae;  soft  and  unctuous  in  some  loosely  adherent  scaly  varieties. 
H.  =  5'5-6'5.  G.  =  4'9-5'3;  of  crystals  mostly  5'20-5'25;  of  some  compact 
varieties,  as  low  as  4'2.  Luster  metallic  and  occasionally  splendent;  some- 
times dull.  Color  dark  steel-gray  or  iron-black;  in  very  thin  particles  blood- 
red  by  transmitted  light;  when  earthy,  red.  Streak  cherry-red  or  reddish 
brown.  Opaque,  except  when  in  very  thin  laminae. 

Var.  1.  Specular.  Luster  metallic,  and  crystals  often  splendent,  whence  the  name 
specular  iron.  When  the  structure  is  foliated  or  micaceous,  the  ore  is  called  micaceous 
hematite:  some  of  the  micaceous  varieties  are  soft  and  unctuous.  Some  varieties  are 
magnetic,  but  probably  from  admixed  magnetite  (Arts.  441,  443). 


416  DESCRIPTIVE   MINERALOGY 

2.  Compact  Columnar;  or  fibrous.     The  masses  often  long  radiating;  luster  submetallic 
to  metallic;  color  brownish  red  to  iron-black.     Sometimes  called  red  hematite,  to  contrast  it 
with  limonite  and  turgite.     Often  in  reniform  masses  with  smooth  fracture,  called  kidney  ore. 

3.  Red  Ocherous.     Red  and  earthy.     Reddle  and  red  chalk  are  red  ocher,  mixed  with 
more  or  less  clay. 

4.  Clay  Iron-stone;    Argillaceous  hematite.     Hard,  brownish  black  to  reddish  brown, 
often  in  part  deep  red;   of  submetallic  to  nonmetallic  luster;    and  affording,  like  all  the 
preceding,  a  red  streak.     It  consists  of  oxide  of  iron  with  clay  or  sand,  and  sometimes  other 
impurities. 

Comp.  —  Iron  sesquioxide,  Fe203  =  Oxygen  30,  iron  70  =  100.  Some- 
times contains  titanium  and  magnesium,  and  is  thus  closely  related  to  ilmenite, 
p.  417. 

Pyr.,  etc.  —  B.B.  infusible;  on  charcoal  in  R.F.  becomes  magnetic;  with  borax  gives 
the  iron  reactions.  With  soda  on  charcoal  in  R.F.  is  reduced  to  a  gray  magnetic  powder. 
Slowly  soluble  in  hydrochloric  acid. 

Diff.  —  Distinguished  from  magnetite  by  its  red  streak,  also  from  limonite  by  the  same 
means,  as  well  as  by  its  not  containing  water:  from  turgite  by  its  greater  hardness  and  by 
not  decrepitating  B.B.  It  is  hard  in  all  but  some  micaceous  varieties  (hence  easily  dis- 
tinguished from  the  black  sulphides);  also  infusible,  and  B.B.  becomes  strongly  magnetic. 

Micro.  —  In  polished  sections  shows  white  color  with  a  shining,  pitted  surface.  Un- 
affected by  reagents. 

Artif .  —  Crystals  of  hematite  have  been  made  by  decomposing  ferric  chloride  by  steam 
at  a  high  temperature;  also  by  the  action  of  heated  air  and  hydrochloric  acid  upon  iron. 
Hematite  has  been  crystallized  from  various  artificial  magmas,  which  must  contain  little 
or  no  ferrous  iron. 

Obs.  —  This  ore  occurs  in  rocks  of  all  ages.  The  specular  variety  is  mostly  confined 
to  crystalline  or  metamorphic  rocks,  but  is  also  a  result  of  igneous  action  about  some  vol- 
canoes, as  at  Vesuvius.  Many  of  the  geological  formations  contain  the  argillaceous  variety 
or  clay  iron-stone,  which  is  mostly  a  marsh-formation,  or  a  deposit  over  the  bottom  of 
shallow,  stagnant  water;  but  this  kind  of  clay  iron-stone  (that  giving  a  red  powder)  is 
less  common  than  the  corresponding  variety  of  limonite.  The  beds  that  occur  in  meta- 
morphic rocks  are  sometimes  of  very  great  thickness,  and,  like  those  of  magnetite  in  the 
same  situation,  have  resulted  from  the  alteration  of  stratified  beds  of  ore,  originally  of 
marsh  origin,  which  were  formed  at  the  same  time  with  the  enclosing  rocks,  and  underwent 
metamorphism,  or  a  change  to  the  crystalline  condition,  at  the  same  time. 

Beautiful  crystallizations  of  this  species  are  brought  from  the  island  of  Elba,  which  has 
afforded  it  from  a  very  remote  period;  the  surfaces  of  the  crystals  often  present  an  irised 
tarnish  and  brilliant  luster.  St.  Gothard  in  Switzerland  affords  beautiful  specimens,  com- 
posed of  crystallized  tables  grouped  in  the  form  of  rosettes;  near  Limoges,  France,  in  large 
crystals;  fine  crystals  are  the  result  of  volcanic  action  at  Etna  and  Vesuvius.  Arendal  in 
Norway,  Langban  and  Nordmark  in  Sweden;  Dognacska,  Hungary;  Framont  in  Lorraine, 
Dauphine,  France;  Binnental  and  Tavetsch,  Switzerland;  also  Cleator  Moor  in  Cumber- 
land, and  Minas  Geraes,  Brazil,  afford  splendid  specimens.  Crystals  from  Ascension  Island 
and  from  Cernero  do  Campo,  Brazil.  Red  hematite  occurs  in  reniform  masses  of  a  fibrous 
concentric  structure,  near  Ulverstone  in  Lancashire,  in  Saxony,  Bohemia,  and  the  Harz 
Mts.,  Germany. 

In  North  America,  widely  distributed,  and  sometimes  in  beds  of  vast  thickness  in  rocks  of 
the  Archaean  age.  Very  extensive  and  important  hematite  deposits  are  found  along  the 
southern  and  northwestern  shores  of  Lake  Superior.  The  various  districts  are  known  as 
ranges  and  are  located  as  follows :  The  Marquette  and  Menominee  Ranges  in  northern  Mich., 
the  Penokee-Gogebic  Range  in  Northern  Wis.,  the  Mesabi,  Vermilion  and  Cuyuna  Ranges 
in  Minn.  Another  district,  the  Michipico  en,  is  farther  north  in  Canada.  The  ore  bodies 
are  the  results  of  the  concentration  in  favorable  localities  of  the  iron  content  of  the  original 
sedimentary  rocks.  These  rocks  contained  cherty  iron  carbonates,  pyrite-bearmg  iron 
carbonates  and  ferrous  silicates.  The  ore  bodies  vary  widely  in  form,  many  of  them  lying 
in  trough-like  structures  formed  by  the  deformation  of  an  impervious  rock  strata.  The 
character  of  the  ores  varies  from  hard  specular  hematites  to  soft  earthy  ores.  The  latter 
are  often  mined  by  the  use  of  steam  shovels.  Hematite  is  found  in  Wyoming  in  schist 
formations  in  Lararnie  and  Carbon  Counties. 

In  N.  Y.,  in  Oneida,  Herkimer,  Madison,  Wayne  Cos.,  a  lenticular  argillaceous  variety, 
constituting  one  or  two  beds  in  the  Clinton  group  of  the  Upper  Silurian;  the  same  in  Pa., 
and  as  far  south  as  Ala.,  and  in  Canada,  and  Wis.,  to  the  west;  in  Ala.  there  are  extensive 


OXIDES  417 

beds;  prominent  mines  are  near  Birmingham.  Besides  these  regions  of  enormous  beds, 
there  are  numerous  others  of  workable  value,  either  crystallized  or  argillaceous.  Some  of 
these  localities,  interesting  for  their  specimens,  are  in  northern  N.  Y.,  at  Gouverneur, 
Antwerp,  Hermon,  Edwards,  Fowler,  Canton,  etc.;  Woodstock  and  Aroostoqk,  Me.;  at 
Hawley,  Mass.,  a  micaceous  variety;  in  N.  and  S.  C.  a  micaceou  variety  in  schistose  rocks, 
constituting  the  so-called  specular  schist,  or  itabirite.  Hematite  is  mined  in  Nova  Scotia 
and  Newfoundland. 

Named  hematite  from  cu^a,  blood. 

Use.  —  The  most  important  iron  ore.     Used  also  in  red  paints,  as  polishing  rouge,  etc. 

MARTITE.  Iron  sesquioxide  under  an  isometric  form,  occurring  in  octahedrons  or 
dodecahedrons  like  magnetite,  and  believed  to  be  pseudomorphous  after  magnetite;  perhaps 
in  part  also  after  pyrite.  Parting  octahedral  like  magnetite.  Fracture  conchoidal.  H.  = 
6^7.  G.  =  4 '8-5*3.  Luster  submetallic.  Color  iron-black,  sometimes  with  a  bronzed  tar- 
nish. Streak  reddish  brown  or  purplish  brown.  Not  magnetic,  or  only  feebly  so.  The 
crystals  are  sometimes  embedded  in  the  massive  sesquioxide.  They  are  distinguished  from 
magnetite  by  the  red  streak,  and  very  feeble,  if  any,  action  on  the  magnetic  needle.  Found 
in  the  Marquette  iron  region  south  of  Lake  Superior,  where  crystals  are  common  in  the  ore; 
Monroe,  N.  Y.;  Twin  Peaks,  Milliard  Co.,  Utah;  Digby  Co.,  N.  S.;  at  the  Cerro  de  Mer- 
cado,  Durango,  Mexico,  in  large  octahedrons;  in  the  schists  of  Minas  Gera  s,  Brazil;  near 
Rittersgriin,  Saxony. 

ILMENITE  or  MENACCANITE.     Titanic  Iron  Ore. 

Tri-rhombohedral;  Axis  c  =  1'3846. 

cr,    0001  A  1011  =  57°  58*'. 
rr',  1011  A  TlOl  =  94°  29'. 
en,   0001  A  2243  =  61°  33'. 

Crystals  usually  thick  tabular;  also  acute  rhombohedral.  Often  in  thin 
plates  or  laminae.  Massive, 

compact ;  in  embedded  grains,  704  705 

also  loose  as  sand. 

Fracture  conchoidal.  H. 
-  5-6.  G.  =  4-5-5.  Luster 
submetallic.  Color  iron-black. 
Streak  submetallic,  powder 
black  to  brownish  red. 
Opaque.  Influences  slightly 
the  magnetic  needle. 

Comp.  —  If  normal,  FeTi03  or  FeO,Ti02  =  Oxygen  31-6,  titanium  31-6, 
iron  36 *8  =  100.  Sometimes  written  (Fe,Ti)2O3,  but  probably  to  be  regarded 
as  an  iron  titanate.  Sometimes  also  contains  magnesium  (picrotitanite) , 
replacing  the  ferrous  iron;  hence  the  general  formula  (Fe,Mg)O.Ti02  (Pen- 
field).  (Compare  geikielite,  p.  586.) 

Pyr.,  etc.  —  B.B.  infusible  in  O.F.,  although  slightly  rounded  on  the  edges  in  R.F. 
With  borax  and  salt  of  phosphorus  reacts  for  iron  in  O.F.,  and  with  the  latter  flux  assumes 
a  more  or  less  intense  brownish  red  color  in  R.F.;  this  treated  with  tin  on  charcoal  changes 
to  a  violet-red  color  when  the  amount  of  titanium  is  not  too  small.  The  pulverized  mineral, 
heated  with  hydrochloric  acid,  is  slowly  dissolved  to  a  yellow  solution,  which,  filtered  from 
the  undecomposed  mineral  and  boiled  with  the  addition  of  tin-foil,  assumes  a  beautiful  blue 
or  violet  color.  Decomposed  by  fusion  with  bisulphate  of  sodium  or  potassium. 

Diff.  —  Resembles  hematite,  but  has  a  submetallic,  nearly  black,  streak;  not  magnetic 
like  magnetite. 

Obs.  —  Occurs,  as  an  accessory  component,  in  many  igneous  rocks  in  grams,  assuming 
the  place  of  magnetite,  especially  in  gabbros  and  diorites.  In  these  occurrences,  it  is  often 
found  in  veins  or  large  segregated  masses  near  the  borders  of  the  igneous  rock  where  it  is 
supposed  to  have  formed  by  local  differentiation  or  fractional  crystallization  in  the  molten 
mass.  It  is  also  found  at  tunes  in  metamorphic  rocks.  Some  principal  European  localities 
are  St.  Cristophe,  Dauphine,  France  (cricktonite) ;  Miask  in  the  Ilmen  Mts.  (ilmenite)}  in 


418  DESCRIPTIVE   MINERALOGY 

th'e  form  of  sand  at  Menaccan,  Cornwall  (menaccanite) ;  Gastein  in  Tyrol  (kibdelophane) ; 
Binnental,  Switzerland.  One  of  the  most  remarkable  is  at  Kragero,  Norway,  where  it 
occurs  in  veins  or  bed  3  in  diorite,  which  sometimes  afford  crystals  weighing  over  16  pounds. 
Others  are  Egersund,  Arendal,  Snarum  in  Norway;  St.  Gothard,  Switzerland,  etc. 

Fine  crystals,  sometimes  an  inch  in  diameter,  occur  in  Warwick,  Amity,  and  Monroe, 
Orange  Co.,  N.  Y.;  Litchfield,  Conn,  (washingtonite) .  Crystals  from  Chester  and  Quincy, 
Mass.  Vast  deposits  or  beds  of  titanic  ore  occur  at  Bay  St.  Paul  in  Quebec,  Canada,  in 
tyenite;  also  in  the  Seignory  of  St.  Francis,  Beauce  Co.  Grains  are  found  in  the  gold  sand 
of  California. 

The  titanic  iron  of  massive  rocks  is  extensively  altered  to  a  dull  white  opaque  substance, 
called  leucoxene  by  Gumbel.  This  for  the  most  part  is  to  be  identified  with  titanite. 

Senaite.  (Fe,Mn,Pb)O.TiO2.  Tri-rhombohedral.  H.  =6.  G.  =  5'3.  Color  black. 
Streak  brownish,  black.  Found  in  the  diamond-bearing  sands  of  Diamantina,  Brazil. 

Arizonite.  Fe2O3.3TiO2.  Monoclinic?  Crystal  faces  rough.  H.  =  5'5.  G.  =  4'25. 
Color  dark  steel-gray.  Streak  brown.  Decomposed  by  hot  concentrated  sulphuric  acid. 
Found  with  gadolinite,  25  miles  southeast  of  Hackberry,  Ariz. 

Pyrophanite.  Manganese  titanate,  MnTiOa.  In  thin  tabular  rhombohedral  crystals 
and  scales,  near  ilmenite  in  form  (p.  417).  H.  =t  5.  G.  =  4'537.  Luster  vitreous  to  sub- 
metallic.  Color  deep  blood-red.  Streak  ocher-yellow.  From  the  Harstig  mine,  Pajsberg, 
Sweden. 

SITAPARITE.  9Mn2O3.4Fe2O3.MnO2.3CaO.  Notary stallized.  Good  cleavage.  H.  =•=  7. 
G.  =  5*0.  Color  deep  bronze.  Streak  black.  Weakly  magnetic.  Found  at  Sitapdr, 
District  Chhindwara,  India. 

VREDENBURGITE.  3Mn3O4.2Fe2O3.  Cleavage  parallel  to  octahedron  or  tetragonal 
pyramid.  H.  =  6-5.  G.  =  4 '8.  Color  bronze  to  dark  steel-gray.  Streak  dark  brown. 
Strongly  magnetic.  Completely  soluble  in  acids.  Found  at  Beldongri,  District  Ndgpur 
and  at  Gravidi,  District  Vizagapatam,  India. 


III.  Intermediate  Oxides 

The  species  here  included  are  retained  among  the  oxides,  although  chem- 
ically considered  they  are  properly  oxygen-salts,  aluminates,  ferrates,  manga- 
nates,  etc.,  and  hence  in  a  strict  classification  to  be  placed  in  section  5  of  the 
Oxygen-salts.  The  one  well-characterized  group  is  the  Spinel  Group. 

ii  in  ii     in 

Spinel  Group.     RR204  or  RO.R2O3.     Isometric 

Spinel  MgO.Al2O3 

Ceylomte  (Mg,Fe)O.Al2O3 

Chlorospinel  MgO.  (Al,Fe)2O3 

Picotite  (Mg,Fe)0.(Al,Cr)203 

Hercynite  FeO.Al2O3 

Gahnite  (Automolite)  ZnO.Al2O3 

Dysluite  (Zn,Fe,Mn)0.(Al,Fe)2O3 

Kreittonite  (Zn,Fe,Mg)0.(Al,Fe)2O3 

Magnetite  FeO.Fe2O3 

(Fe,Mg)O.Fe203 

Magnesioferrite  MgO.Fe2O3 

Franklinite  (Fe,Zn,Mn)O.(Fe,Mn)2O3 

Jacobsite  (Mn,Mg)O.(Fe,Mn)2O3 

Chromite  FeO.Cr203 

(Fe,Mg)0.(Cr,Fe)203 


OXIDES 


419 


The  species  of  the  Spinel  Group  are  characterized  by  isometric  crystalli- 
sation, and,  further,  the  octahedron  is  throughout  the  common  form.  All  of 
the  species  are  hard;  those  with  nonmetallic  luster  up  to  7*5-8,  the  others 
from  5*5  to  6*5. 

SPINEL. 

Isometric.  Usually  in  octahedrons,  sometimes  with  dodecahedral  trunca- 
tions, .rarely  cubic.  Twins:  tw.  pi.  and  comp.  face  o(lll)  common  (Fig. 
707),  hence  often  called  spinel-twins;  also  repeated  and  polysynthetic,  pro- 
ducing tw.  lamellae. 

Fracture    conchoidal.     Brittle.     H.  =  8. 


706 


707 


Cleavage:  o(lll)  imperfect. 
G.  =  3'5-4'L  Luster  vitreous; 
splendent  to  nearly  dull.  Color 
red  of  various  shades,  passing  into 
blue,  green,  yellow,  brown  and 
black;  occasionally  almost  white. 
Streak  white.  Transparent  to 
nearly  opaque.  Refractive  index : 
n=  17155. 

Comp.  —  Magnesium     alumin- 
ate,    MgAl2O4    or    MgO.Al2O3  = 
Alumina  71*8,    magnesia    28*2  = 
100.     The  magnesium  may  be  in  part  replaced   by  ferrous  iron  or  man- 
ganese, and  the  aluminium  by  ferric  iron  and  chromium.       ••    . 

Var.  —  RUBY  SPINEL  or  Magnesia  Spinel.  —  Clear  red  or  reddish;  transparent  to 
translucent;  sometimes  subtranslucent.  G.  =  3 '63-3 71.  Compo  ition  normal,  with 
little  or  no  iron,  and  sometimes  chromium  oxide  to  which  the  red  color  has  been  ascribed. 
The  varieties  are:  (a)  Spinel-Ruby,  deep  red;  b)  Balas-Ruby,  rose-red;  (c)  Rubicette, 
yellow  or  orange^red;  (d)  Almandine,  violet. 

CEYLONITE  or  Pleonaste,  Iron-Magnesia  Spinel.  —  Color  dark  green,  brown  to  black, 
mostly  opaque  or  nearly  so.  G.  =  3 '5-3 '6.  Contains  iron  replacing  the  magnesium  and 
perhaps  also  the  aluminium,  hence  the  formula  (Mg,Fe)O.Al2C>3  or  (Mg,Fe)O.(Al,Fe)2O3. 

CHLOROSPINEL  or  Magnesia-Iron  Spinel.  —  Color  grass  green,  owing  to  the  presence  of 
copper.  G.  •=  3'591-3*594.  Contains  iron  replacing  the  aluminium,  MgO.(Al,Fe  3O3. 

PICOTITE  or  Chrome-Spinel.  —  Contains  chromium  and  also  has  the  magnesium  largely 
repla  ed  by  iron  (Mg,Fe)O.(Al,Cr)2O3,  hence  lying  be  ween  spinel  prope  and  chromite. 
G.  =  4 '08.  Color  dark  yellowish  brown  or  greenish  brown  Translucent  to  nearly  opaque. 

Pyr.,  etc.  —  B.B.  alone  infusible.  Slowly  soluble  in  borax,  more  readily  in  salt  of 
phosphorus,  with  which  it  gives  a  reddish  bead  while  hot,  becoming  faint  chrome-green 
on  cooling.  Black  varieties  give  reactions  for  iron  with  the  fluxes.  Soluble  with  difficulty 
in  concentrated  sulphuric  acid.  Decomposed  by  fusion  with  potassium  bisulphate. 

Diff.  —  Distinguished  by  its  octahedral  form,  hardness,  and  inf usibility ;  zircon  Jias  a 
higher  specific  gravity;  the  true  ruby  (p.  413)  is  harder  and  is  distinguished  optically; 
garnet  is  softer  and  fusible. 

Micro.  —  In  thin  section  shows  light  color  and  high  relief.     Isotropic. 

Artif .  —  Artificial  spinel  crystals  may  be  obtained  by  direct  crystallization  from  the 
pure  melt  fused  in  the  electric  arc.  They  also  form  from  melts  of  the  oxides  or  fluorides  of 
magnesium  and  aluminium  dissolved  in  boric  acid.  The  addition  of  chromium  and  iron 
oxides  will  produce  various  colors. 

Obs.  —  Spinel  occurs  embedded  in  granular  limestone,  and  with  calcite  hi  serpentine, 
gneiss,  and  allied  rocks.  Ruby  spinel  is  a  common  associate  of  the  true  ruby.  Common 
spinel  is  often  associated  with  chondrodite.  It  also  occupies  the  cavities  of  masses  ejected 
from  some  volcanoes.  Spinel  (common  spinel,  also  picotite  and  chromite,  occurs  as  an 
accessory  constituent  in  many  basic  igneous  rocks  especially  those  of  the  peridotite  group; 
it  is  the  result  of  the  crystallization  of  a  magma  very  low  in  silica,  high  in  magnesia  and  con- 
taining alumina;  since,  as  in  many  of  the  peridotites  alkalies  are  absent,  feldspars  cannot 
form,  and  the  A12O3  and  Cr2Os  (also  Fe2O3  perhaps)  are  compelled  to  form  spinel  (or  corun- 
dum). The  serpentines  which  yield  spinel  are  altered  peridotites. 


420  DESCRIPTIVE   MINERALOGY 

In  Ceylon,  in  Siam,  and  other  eastern  countries,  occurs  with  beautiful  colors,  as  rolled 
pebbles;  in  0  upper  Burma  with  the  ruby  (cf.  p.  414)*  Plepnaste  is  found  at  Candy,  in 
Ceylon;  at  Aker,  in  Sweden,  a  pale  blue  and  pearl-gray  variety  in  limestone;  small  black 
splendent  crystals  occur  in  the  ancient  ejected  masses  of  Monte  Somma,  Vesuvius;  also  at 
Pargas,  Finland,  with  chondrodite,  etc.;  in  compact  gehlenite  at  Monzoni,  in  the  Fassa 
valley,  Austria. 

From  Amity,  N.  Y.,  to  Andover,  N.  J.,  a  distance  of  about  30  miles,  is  a  region  of  gran- 
ular limestone  and  serpentine,  in  which  localities  of  spinel  abound;  colors,  green,  black, 
brown,  and  less  commonly  red,  along  with  chondrodite  and  other  minerals.  Localities 
are  numerous  about  Warwick,  and  also  at  Monroe  and  Cornwall;  Gouverneur,  2  m.  N.  and 
f  m.  W.  of  Somerville,  St.  Lawrence  Co.;  green,  blue,  and  occasionally  red  varieties  occur 
at  Bolton,  Boxborough,  etc.,  Mass.  Franklin,  N.  J.,  affords  crystals  of  various  shades  of 
black,  blue,  green,  and  red:  Newton,  Sterling,  Sparta,  Hamburgh  and  Vernon,  N.  J.,  are 
other  localities.  With  the  corundum  of  N.  C.  as  at  the  Culsagee  mine,  near  Franklin, 
Macon  Co.;  similarly  at  Dudleyville,  Ala.  Spinel  ruby  at  Gold  Bluff,  Humboldt  Co.,  Cal. 

Good  black  spinel  is  found  in  Burgess,  Ontario;  a  bluish  spinel  having  a  rough  cubic 
form  occurs  at  Wakefield,  Ottawa  Co.;  blue  with  clintonite  at  Daillebout,  Joliette  Co., 
Quebec. 

Use.  —  The  colored  transparent  varieties  are  used  as  gems. 

.  Hercynite.  Iron  Spinel,  FeAl2O4.  Isometric;  massive,  fine  granular.  H.  =  7-5-8. 
G.  =  3  '9  1-3  '95.  Color  black.  From  Ronsberg,  at  the  eastern  foot  of  the  Bohmerwald, 
Bohemia.  A  related  iron-alumina  spinel,  with  about  9  p.  c.  MgO,  occurs  with  magnetite 
and  corundum  in  Cortlandt  township,  Westchester  Co.,  N.  Y.  From  the  tin  drift, 
Moorina,  Tasmania. 

GAHNITE.     Zinc-Spinel. 

Isometric.  Habit  octahedral,  often  with  faces  striated  ||  edge  between 
dodecahedron  and  octahedron;  also  less  commonly  in  dodecahedrons  and 
modified  cubes.-  Twins:  tw.  pi.  0(111). 

Cleavage:  o(lll)  indistinct.  Fracture  conchoidal  to  uneven.  Brittle. 
H.  =  7-5-8.  G.  =  4-0-4-6.  ngr  =  1'82  (Finland).  Luster  vitreous,  or  some- 
what greasy.  Color  dark  green,  grayish  green,  deep  leek-green,  greenish 
black,  bluish  black,  yellowish,  or  grayish  brown;  streak  grayish.  Subtrans- 
parent  to  nearly  opaque. 

Comp.  —  Zinc  aluminate,  ZnAl204  =  Alumina  55-7,  zinc  oxide  44-3  = 
100.  The  zinc  is  sometimes  replaced  by  manganese  or  ferrous  iron,  the 
aluminium  by  ferric  iron. 

Var.  —  AUTOMOLITE,  or  Zinc  Gahnite.  —  ZnAl2O4,  with  sometimes  a  little  iron.  G.  = 
4-1-4  '6.  Colors  as  above  given. 

DYSLUITE,  or  Zinc-Manganese-Iron  Gahnite.  —  (Zn,Fe,Mn)O.(Al,Fe)2O3.  Color  yellow- 
ish brown  or  grayish  brown.  G.  =  4-4*6. 

KREITTONITE,  or  Zinc-Iron  Gahnite.  —  (Zn,Fe,Mg)O.(Al,Fe)2O3.  In  crystals,  and 
granular  massive.  H.  =  7-8.  G.  =  4  '48-4  '89.  Color  velvet-black  to  greenish  black; 
powder  grayish  green.  Opaque. 

Pyr.,  etc.  —  Gives  a  coating  of  zinc  oxide  when  treated  with  a  mixture  of  borax  and 
soda  on  charcoal;  otherwise  like  spinel. 

Obs.  —  Occurs  at  Falun  and  Farila  parish,  Helsingland,  Sweden  (automolite)  ;  Trask- 
bole,  Finland;  at  Tiriola,  Calabria,  Italy;  at  Bodenmais,  Bavaria  (kreittonite)  ',  Minas 
Geraes,  Brazil;  Ambatofisikely,  Madagascar.  In  the  United  States,  at  Franklin  Furnace, 
N.  J.,  with  franklinite  and  willemite;  also  at  Sterling  Hill,  N.  J.  (dysluite);  with  pyrite  at 
Rowe,  Mass.;  at  a  feldspar  quarry  in  Delaware  Co.,  Pa.;  sparingly  at  the  Deake  mica 
mine,  Mitchell  Co.,  N.  C.;  at  the  Canton  Mine,  Ga.;  with  galena,  chalcopyrite,  pyrite  at 
the  Cotopaxi  mine,  Chaffee  Co.,  Col.  In  Canada  at  Raglan,  Renfrew  Co.,  Ontario. 

Named  after  the  Swedish  chemist  Gahn.  The  name  Automolite,  of  Ekeberg,  is  from 
,  a  deserter,  alluding  to  the  fact  of  the  zinc  occurring  in  an  unexpected  place. 


MAGNETITE.     Magnetic  Iron  Ore. 

Isometric.  Most  commonly  in  octahedrons,  also  in  dodecahedrons  with 
faces  striated  ||  edge  between  dodecahedron  and  octahedron  (Fig.  710);  in 
dendrites  between  plates  of  mica;  crystals  sometimes  highly  modified;  cubic 


OXIDES  421 

forms  rare.     Twins:    tw.  pi.  o(lll),  sometimes  as   polysynthetic   twinning 

lamellae,  producing  striations  on  an  octahedral  face  and  often  a  pseudo-cleav- 

708  709  710 


age  (Fig.  474,  p.  176).     Massive  with  laminated  structure;  granular,  coarse 
or  fine;  impalpable. 

Cleavage  not  distinct;  parting  octahedral,  often  highly  developed.     Frac- 
ture subconchoidal  to  uneven.     Brittle.     H.  =  5 '5-6*5. 
G.    =   5-168-5-180,     crystals.       Luster    metallic     and  711 

splendent  to  submetallic  and  rather  dull.  Color  iron- 
black.  Streak  black.  Opaque,  but  in  thin  dendrites 
in  mica  nearly  transparent  and  pale  brown  to  black. 
Strongly  magnetic;  sometimes  possessing  polarity 
(lodestone) . 

ii  in 

Comp.  —  FeFe2O4  or  FeO.Fe2O3  =  Iron  sesquioxide 
69.0,  iron  protoxide  31 '0  =  100;  or,  Oxygen  27-6,  iron 
72 '4  =  100.  The  ferrous  iron  sometimes  replaced  by 
magnesium,  and  rarely  nickel;  also  sometimes  contains 
titanium  (up  to  6  p.  c.  TiO2). 

Var.  —  Ordinary.  —  (a)  In  crystals.  (&)  Massive,  with  pseudo-cleavage,  also  granular, 
coarse  or  fine,  (c)  As  loose  sand,  (d)  Ocherous:  a  black  earthy  kind.  Ordinary  magne- 
tite is  attracted  by  a  magnet  but  has  no  power  6f  attracting  particles  of  iron  itself.  The 
property  of  polarity  which  distinguishes  the  lodestone  (less  properly  written  loadstone)  is 
exceptional. 

Magnesian.  —  G.  =  4-41-4*42;  luster  submetallic;  weak  magnetic;  in  crystals  from 
Sparta,  N.  J.,  and  elsewhere. 

Manganesian.  —  Containing  3'8  to  6 '3  p.  c.  manganese  (Manganmagnetite).  From 
Vester  Silfberg,  Sweden. 

Pyr.,  etc.  —  B.B.  very  difficultly  fusible.  In  O.F.  loses  its  influence  on  the  magnet. 
With  the  fluxes  reacts  like  hematite.  Soluble  in  hydrochloric  acid  and  solution  reacts  for 
both  ferrous  and  ferric  iron. 

Diff.  —  Distinguished  from  other  members  of  the  spinel  group,  as  also  from  garnet,  by 
its  being  attracted  by  the  magnet,  as  well  as  by  its  high  specific  gravity;  franklinite  and 
chromite  are  only  feebly  magnetic  (if  at  all),  and  have  a  brown  or  blackish  brown  streak; 
also,  when  massive,  by  its  black  streak  from  hematite  and  limonite;  much  harder  than 
tetrahedrite. 

Micro.  —  In  polished  sections  shows  white  color  with  a  shining,  pitted  surface..  With 
cone.  HC1  slowly  turns  brown. 

Artif.  —  Magnetite  is  frequently  formed  as  a  furnace  product.  It  is  easily  formed  in 
artificial  magmas  when  they  are  low  in  the  percentage  of  silica.  It  is  formed  by  the 
breaking  down  of  various  minerals  or  by  interreactions  among  minerals  in  processes  simi- 
lar to  those  of  contact  metamorphism. 

Obs.  —  Magnetite  is  mostly  confined  to  crystalline  rocks,  and  is  most  abundant  in 
metamorphic  rocks,  though  widely  distributed  also  in  grainy  in  eruptive  rocks.  It  is  found 
most  abundantly  in  the  ferro-magnesian  rocks,  occurring  at  times  in  large  segregated 


422  DESCRIPTIVE    MINERALOGY 

masses.  These  are  often  highly  titaniferous.  In  the  Archaean  rocks  the  beds  are  of  im- 
mense extent,  and  occur  under  the  same  conditions  as  those  of  hematite.  It  is  an  ingre- 
dient in  most  of  the  massive  variety  of  corundum  called  emery.  The  earthy  magnetite 
is  found  in  bogs  like  bog-iron  ore.-  Occurs  in  meteorites,  and  forms  the  crust  of  meteoric 
irons. 

Present  in  dendrite-like  forms  in  the  mica  of  many  localities  following  the  direction  of 
the  lines  of  the  percussion-figure,  and  perhaps  of  secondary  origin.  A  common  alteration- 
product  of  minerals  containing  iron  protoxide,  e.g.,  present  in  veins  in  the  serpentine 
resulting  from  altered  chrysolite. 

The  beds  of  ore  at  Arendal,  Norway,  and  nearly  all  the  celebrated  iron  mines  of  Sweden, 
consist  of  massive  magnetite,  as  at  Dannemora  and  the  Taberg  in  Smaland.  Falun, 
in  Sweden,  and  Corsica,  afford  octahedral  crystals,  embedded  in  chlorite  slate.  Splendid 
dodecahedral  crystals  occur  at  Nordmark  in  Wermland.  The  most  powerful  native 
magnets  are  found  in  Siberia,  and  in  the  Harz  Mts.,  Germany;  they  are  also  obtained  on 
the  island  of  Elba.  Other  localities  for  the  crystallized  mineral  are  Traversella  in  Piedmont, 
Italy;  Achmatoysk  in  the  Ural  Mts.;  Scalotta,  near  Predazzo,  at  Rothenkopf  and  Wild- 
kreuzjoch,  Austrian  Tyrol;  the  Binnental,  Switzerland;  Sannatake,  Bufen,  Japan. 

In  North  America,  it  constitutes  vast  beds  in  the  Archaean,  in  the  Adirondack  region, 
Warren,  Essex,  and  Clinton  Cos.,  in  Northern  N.  Y.,  while  in  St.  Lawrence  Co.  the  iron 
ore  is  mainly  hematite;  fine  crystals  and  masses  showing"  broad  parting  surfaces  and  yield- 
ing large  pseudo-crystals  are  obtained  at  Port  Henry,  Essex  Co.;  similarly  in  N  J.;  in 
Canada,  in  Hull,  Greenville,  Madoc,  etc.;  at  Cornwall  in  Pa.,  and  Magnet  Cove,  Ark.  It 
occurs  also  in  N.  Y.,  in  Saratoga,  Herkimer,  Orange,  and  Putnam  Cos.;  at  the  Tilly  Foster 
iron  mine,  Brewster,  Putnam  Co.,  in  crystals  and  massive  accompanied  by  chondrodite,  etc. 
In  N.  J.,  at  Hamburg,  near  Franklin  Furnace  and  elsewhere.  In  Pa.,  at  Goshen,  Chester 
Co.,  and  at  the  French  Creek  mines;  delineations  forming  hexagonal  figures  in  mica  at 
Pennsbury.  Good  lodestones  are  obtained  at  Magnet  Cove,  Ark.  In  Cal.,  in  Sierra  Co., 
abundant,  massive,  and  in  crystals;  in  Plumas  Co.;  and  elsewhere.  In  Wash.,  in  large 
deposits.  In  crystals  from  Millard  Co.,  Utah.  Fine  crystals  from  Fiqrmeza,  Cuba. 

Named  from  the  loc.  Magnesia  bordering  on  Macedonia.  But  Pliny  favors  Nicander's 
derivation  from  Magnes,  who  first  discovered  it,  as  the  fable  runs,  by  finding,  on  taking  his 
herds  to  pasture,  that  the  nails  of  his  shoes  and  the  iron  ferrule  of  his  staff  adhered  to  the 
ground. 

Use.  —  An  important  ore  of  iron. 

FRANKLINITE. 

Isometric.  Habit  octahedral;  edges  often  rounded,  and  crystals  passing 
into  rounded  grains.  Massive,  granular,  coarse  or  fine  to  compact. 

Pseudo-cleavage,  or  parting,  octahedral,  as  in  magnetite.  Fracture  con- 
choidal  to  uneven.  Brittle.  H.  =  5'5-6'5.  G.  =  5-07-5-22.  Luster  metallic, 
sometimes  dull.  Color  iron-black.  Streak  reddish  brown  or  black.  Opaque. 
Slightly  magnetic. 

Comp.  —  (Fe,Zn,Mn)O.(Fe,Mn)2O3,  but  varying  rather  widely  in  the 
relative  quantities  of  the  different  metals  present,  while  conforming  to  the 
general  formula  of  the  spinel  group. 

Pyr.,  etc.—  B.B.  infusible.  With  borax  in  O.F.  gives  a  reddish  amethystine  bead 
(manganese),  and  in  R.F.  this  becomes  bottle-green  (iron).  With  soda  gives  a  bluish 
green  manganate,  and  on  charcoal  a  faint  coating  of  zinc  oxide,  which  is  much  more  marked 
when  a  mixture  with  borax  and  soda  is  used.  Soluble  in  hydrochloric  acid,  sometimes 
with  evolution  of  a  small  amount  of  chlorine. 

Diff.  —  Resembles  magnetite,  but  is  only  slightly  attracted  by  the  magnet,  and  has  a 
dark  brown  streak;  it  also  reacts  for  zinc  on  charcoal  B.B. 

°bs>  T"*1^  (^ermany  occurs  in  cubic  crystals  near  Eibach  in  Nassau;  in  amorphous 
masses  at  Altenberg,  near  Aix-la-Chapelle.  Abundant  at  Mine  Hill,  Franklin  Furnace 
JN.  J.,  with  wulemite  and  zmcite  in  granular  limestone;  also  at  Sterling  Hill,  two  miles 
distant,  associated  with  willemite. 

Use.  —  An  ore  of  zinc. 


*;'      Magnofernte.      MgFe?O4.      In  octahedrons.      H.  =  6-6'5     G.  = 
H4t>54.     Luster    color,  and  streak  as  in  magnetite.     Strongly  magnetic.   Formed 
about  the  fumaroles  of  Vesuvius-,  and  especially  those  of  the  eruption  of  1855;  also  found 
at  iviont  jJor 


OXIDES 


423 


Jacobsite.       (Mn,Mg)O.(Fe,Mn)2O3.     Isometric;    in  distorted  octahedrons.     H.  =  6. 
Color  deep  black.     Magnetic.  _  From  Jakobsberg,  in  Nordmark,  Wermland, 


G.  =  475. 

and  at  Langban,  Sweden. 


Reported  from  Bulgaria. 


CHROMITE. 

Isometric.    In  octahedrons.    Commonly  massive;  fine  granular  to  compact. 

Fracture  uneven.  Brittle.  H.  =  5-5.  G.  =  4-32-4-57.  Luster  sub- 
metallic  to  metallic.  Color  between  iron-black  and  brownish  black,  but 
sometimes  yellowish  red  in  very  thin  sections.  Streak  brown.  Translucent 
to  opaque.  Sometimes  feebly  magnetic. 

Comp.  —  FeCr2O4  or  FeO.Cr2O3  =  Chromium  sesquioxide  68'0,  iron 
protoxide  32-0  =  100. 

The  iron  may  be  replaced  by  magnesium;  also  the  chromium  by  alu- 
minium and  ferric  iron.  The  varieties  containing  but  little  chromium  (up 
to  10  p.  c.)  are  hardly  more  than  varieties  of  spinel  and  are  classed  under 
picotite,  p.  419. 

Pyr.,  etc.  —  B.B.  in  O.F.  infusible;  in  R.F.  slightly  rounded  on  the  edges,  and  becomes 
magnetic.  With  borax  and  salt  of  phosphorus  gives  beads  which,  while  hot,  show  only  a 
reaction  for  iron,  but  on  cooling  become  chrome-greeny  the  green  color  is  heightened  by 
fusion  on  charcoal  with  metallic  tin.  Not  acted  upon  by  acids,  but  decomposed  by  fusion 
with  potassium  or  sodium  bisulphate. 

Diff.  —  Distinguished  from  magnetite  by  feeble  magnetic  properties,  streak  and  by 
yielding  the  reaction  for  chromic  acid  with  the  blowpipe. 

Artif.  —  Chromite  can  be  prepared  artificially  by  fusing  together  chromic,  ferric  and 
boric  oxides. 

Obs.  —  Occurs  in  peridotite  rocks  and  the  serpentines  derived  from  them,  forming 
veins,  or  in  embedded  masses.  It  is  one  of  the  earliest  minerals  to  crystallize  in  a  cooling 
magma  and  its  large  ore  bodies  are  probably  formed  during  the  solidification  of  the  rock 
by  the  process  of  magmatic  differentiation.  It  assists  in  giving  the  variegated  color  to 
verde-antique  marble.  Not  uncommon  in  meteoric  irons,  sometimes  in  nodules  as  in  the 
Coahuila  iron,  less  often  in  crystals  (Lodran). 

Occurs  in  the  Gulsen  mountains,  near  Kraubat  in  Styria;  in  crystals  in  the  islands  of 
Unst  and  Fetlar,  in  Shetland;  in  the  province  of  Trondhjem  in  Norway;  in  the  Department 
du  Var  in  France;  in  Silesia  and  Bohemia;  abundant  in  Asia  Minor;  in  the  Eastern  and 
Western  Ural  Mts.;  in  New  Caledonia,  affording  ore  for  commerce. 

In  Md.  at  Baltimore,  in  the  Bare  Hills,  in  veins  or  masses  in  serpentine;  also  in  Mont- 
gomery Co.,  etc.  In  Pa.,  Chester  Co.,  near  Unionville,  abundant;  at  Wood's  Mine,  near 
Texas,  Lancaster  Co.,  very  abundant.  Massive  and  in  crystals  at  Hoboken,  N.  J.,  in  ser- 
pentine and  dolomite.  In  various  localities  in  N.  C.  In  the  southwestern  part  of  the  town 
of  New  Fane,  etc.,  Vt.  A  magnesian  variety  (mitchellite)  from  Webster,  N.  C.  In  Cal., 
in  Monterey  Co.;  'also  Santa  Clara  Co.,  near  the  New  Almaden  mine. 

Use.  —  An  ore  of  chromium;  used  in  refractory  bricks  for  metallurgical  furnace  linings; 
as  source  of  certain  red  and  yellow  pigments  and  dyes. 

CHROMITITE.  Material  in  minute  octahedral  crystals  occurring  in  sand  at  Zeljin  Mt., 
Servia,  said  to  have  composition,  FeCrO3.  712  ..„ 

CHRYSOBERYL.     Cymophane. 
Orthorhombic.     Axes  a  :  b  :  c  = 
0-4701 


1:1: 

0-5800. 

mm'", 

110 

A 

110  = 

50°  21'. 

ss', 

120 

A 

120  = 

93° 

32'. 

XX', 

101 

A 

101  = 

101° 

57'. 

ii'J 

Oil 

A 

Oil  = 

60° 

14'. 

PP', 

031 

A 

031  = 

120° 

14'. 

00', 

111 

A 

Til  = 

93° 

44'. 

oo'", 

111 

A 

111  = 

40° 

7'. 

nn't 

121 

A 

121  = 

77° 

43'. 

Twins:    tw.  pi.  p(031),  both  contact-  and  penetration-twins;   often  re- 
peated and  forming  pseudo-hexagonal  crystals  with  or  without  re-entrant 


424  DESCRIPTIVE   MINERALOGY 

angles  (Fig.  395,  p.  164) .  Crystals  generally  tabular  1 1  a(100) .  Face  a  striated 
vertically,  in  twins  a  feather-like  striation  (Fig.  713). 

Cleavage:  »"(QH)  quite  distinct;  6(010)  imperfect;  a(100)  more  so.  Frac- 
ture uneven  to  conchoidal.  Brittle.  H.  =  8-5.  G.  =  3'5-3'84.  Luster 
vitreous.  Color  asparagus-green,  grass-green,  emerald-green,  greenish  white, 
and  yellowish  green;  greenish  brown;  yellow;  sometimes  raspberry- or  colum- 
bine-red by  transmitted  light.  Streak  uncolored.  Transparent  to  trans- 
lucent. Sometimes  a  bluish  opalescence  or  chatoyancy,  and  asteriated. 
Pleochroic,  vibrations  ||  Y  (=  b  axis)  orange-yellow,  Z  (=  c  axis)  emerald- 
green,  X  (  =  a  axis)  columbine-red.  Optically  +.  Ax.  pi.  ||  6(010).  Bx.  _L 
c(001).  a  =  1747.  0  =  1748.  7  =  1'757.  2E  =  84°  43'. 

Var.  1.  Ordinary.  —  Color  pale  green,  being  colored  by  iron;  also  yellow  and  trans- 
parent and  then  used  as  a  gem. 

2.  Alexandrite.  —  Color  emerald-green,  but  columbine-red  by  transmitted  light;  valued 
as  a  gem.     G.  =  3 '644,  mean  of  results,     ^upposed  to  be  colored  by  chromium.     Crystals 
often  very  large,  and  in  twins,  like  Fig.  395,  either  six-sided  or  six-rayed. 

3.  Cat's-eye.  —  Color  greenish  and  exhibiting  a  fine  chatoyant  effect;  from  Ceylon. 

Comp.  —  Beryllium  aluminate,  BeAl2O4  or  BeO.Al203  =  Alumina  80'2, 
glucina  19 '8  =  100. 

Pyr.,  etc.  —  B.B.  alone  unaltered;  with  soda,  the  surface  is  merely  rendered  dull. 
With  borax  or  salt  of  phosphorus  fuses  with  great  difficulty.  Ignited  with  cobalt  solu- 
tion, the  powdered  mineral  gives  a  bluish  color.  Not  attacked  by  acids. 

Diff.  —  Distinguished  by  its  extreme  hardness,  greater  than  that  of  topaz;  by  its  in- 
fusibility;  also  characterized  by  its  tabular  crystallization,  in  contrast  with  beryl. 

Obs.  —  In  Minas  Geraes,  Brazil,  in  rolled  pebbles;  from  Ceylon  in  pebbles  and  crystals; 
at  Marschendorf  in  Moravia;  in  the  Ural  Mts.,  85  yersts  from  Ekaterinburg,  in  mica  slate 
with  beryl  and  phenacite,  the  variety  alexandrite;  in  the  Orenburg  district,  southern  Ural 
Mts.,  yellow;  in  the  Mourne  Mts.,  Ireland. 

In  the  United  States  at  Haddam,  Conn.,  in  granite  traversing  gneiss,  with  tourmaline, 
garnet,  beryl;  at  Greenfield,  near  Saratoga,  N.  Y.,  with  tourmaline,  garnet,  and  apatite; 
has  been  found  in  crystals  in  the  rocks  of  New  York  City;  in  Me.  at  Norway,  in  granite 
with  garnet  and  at  Stoneham,  with  fibrolite,  at  Topsham,  Buckfield  and  Greenwood. 

Chrysoberyl  is  from  xpvvos,  golden,  ftrjpvXXos,  beryl.  Cymophane,  from  Kv/j.a,  wave,  and 
<f>aij>a),  appear,  alludes  to  a  peculiar  opalescence  the  crystals  sometimes  exhibit.  Alexandrite 
is  after  the  Czar  of  Russia,  Alexander  I. 

Use.  —  As  a  gem  stone;  see  under  Var.  above. 

Hausmannite.    Mn3O4  or  MnO.  Mn2O3.    In  tetragonal  octahedrons  and  twins  (Fig.  414, 

E.  167);    also  granular  massive,  particles  strongly  coherent.     H.  =  5-5'5.     G.  =  4'856. 
uster  submetallic.     Color  brownish  black.     Streak  chestnut-brown.     Occurs  near  Ilme- 
nau  in  Thuringia,  Germany;  .Ilefeld  in  the  Harz  Mts.,  Germany;    Filipstad,  Langban, 
Nordmark,  in  Sweden;  from  Brazil. 

Coronadite.  (Mn,Pb)Mn3O7.  Massive  with  delicate  fibrous  structure.  H.  =  4. 
G.  =  5'2.  Color  black.  Streak  brownish  black.  Occurs  in  Coronado  vein  of  the  Clifton- 
Morenci  district,  Arizona.  Hollandite  is  a  similar  manganate  of  manganese,  barium 'and 
ferric  iron  from  the  Kaljlidongri  manganese  mine,  Central  India. 

Cesllrolite.  H2PbMn3O8.  In  cellular  masses.  Color,  steel-gray.  H.  =  4'5.  G.  =  5'29. 
From  Sidi-Amer-bers-Salem,  Tunis. 

Minium.  Pb304  or  2PbO.PbO2.  Pulverulent,  as  crystalline  scales.  G.  =  4'6.  Color 
vivid  red,  mixed  with  yellow;  streak  orange-yellow.  Occurs  in  Germany  at  Bleialf  in  the 
Jjjifel;  Badenweiler  in  Baden,  etc. 

Crednerite.  Cu3Mn4O9  or  3CuO.2Mn2O3.  Foliated  crystalline.  H.  =  4'5.  G.  =  4'9- 
5*1.  Luster  metallic.  Color  iron-black  to  steel-gray.  Streak  black,  brownish.  From 
Fnednchroda,  Germany. 

Pseudobrookite.  Probably  Fe4(TiO4)3.  Usually  in  minute  orthorhombic  crystals,  tab- 
ular ||  a(100)  and  often  prismatic  ||  the  macro-axis.  G.  =  4-4-4'98.  Color  dark  brown  to 
black,  btreak  ocher-yellow.  Found  with  hypersthene  (szaboite)  in  cavities  of  the  andesite 
ot  Aranyer  Berg,  Transylvania,  and  elsewhere;  on  recent  lava  (1872)  from  Vesuvius;  at 
Havredal,  Bamle,  Norway,  embedded  in  kjerulfine  (wagnerite)  altered  to  apatite. 


OXIDES  425 

BRAUNITE. 

Tetragonal.  Axis  c  =  0;9850.  Commonly  in  octahedrons,  nearly  iso- 
metric in  angle  (ppf  111  A  111  =  70°  7').  Also  massive. 

Cleavage  :  p(lll)  perfect.  Fracture  uneven  to  subconchoidal.  Brittle. 
H.  =  6-6-5.  G.  =  4-75-4-82.  Luster  submetallic.  Color  and  streak,  dark 
brownish  black  to  steel-gray. 

Comp.  —  3Mn203.MnSiO3  =  Silica  lO'O,  manganese  protoxide  11 '7,  man- 
ganese sesquioxide  78 -3  =  100. 

Pyr.,  etc.  —  B.B.  infusible.  With  borax  and  salt  of  phosphorus  gives  an  amethystine 
bead  in  O.F.,  becoming  colorless  in  R.F.  With  soda  gives  a  bluish  green  bead.  Dissolves 
in  hydrochloric  acid  leaving  a  residue  of  gelatinous  silica.  Marceline  gelatinizes  with  acids. 

Obs.  —  Occurs  in  veins  traversing  porphyry,  at  Oehrenstock,  near  Ilmenau,  Thuringia, 
and  near  Ilefeld  in  the  Harz  Mts.,  Germany;  St.  Marcel  in  Piedmont,  Italy;  at  Elba; 
at  Botnedal,  Upper  Tellemark,  in  Norway;  at  the  manganese  mines  of  Jakobsberg,  also  at 
Langban,  and  at  the  Sjo  mine,  Grythyttan,  Orebro,  Sweden.  Marceline  (heterocline)  from 
St.  Marcel,  Ptedmont,  is  impure  braunite. 

Bixbyite.  Essentially  FeO.MnO2.  In  black  isometric  crystals.  H.  =  6-6'5.  G.  = 
4'945.  Occurs  with  topaz  in  cavities  in  rhyolite;  from  Utah. 


IV.   Dioxides,  RO2. 
Rutile  Group.     Tetragonal 

c  c 

Cassiterite        SnO2          0-6723  Rutile  TiO2      0-6442 

Polianite  MnO2        0'6647  Plattnerite        PbO2     0'6764 

'  The  RUTILE  GROUP  includes  the  dioxides  of  the  elements  tin,  manganese, 
titanium,  and  lead.  These  compounds  crystallize  in  the  tetragonal  system 
with  closely  similar  angles  and  axial  ratio;  furthermore  in  habit  and  method 
of  twinning  there  is  much  similarity  between  the  two  best  known  species 
included  here.  Chemically  these  minerals  are  sometimes  considered  as  salts 
of  their  respective  acids,  as  stannyl  metastannate,  (SnO)SnO3,  for  cassiterite 
and  titanyl  metatitanate,  (TiO)TiO3,  for  rutile. 

With  the  Rutile  Group  is  also  sometimes  included  Zircon.  ZrO2SiO2;  c  =  0'6404. 
In  this  work,  however,  Zircon  is  classed  among  the  silicates,  with  the  allied  species  Thorite, 
ThO2.SiO2,  c  =  0-6402. 

A  tetragonal  form,  approximating  closely  to  that  of  the  species  of  the  Rutile  Group, 
belongs  also  to  a  number  of  other  species,  as  Xenotime,  YPO4;  Sellaite,  MgF2;  Tapiolite, 
Fe(Ta,Nb)2O6. 

It  may  be  added  that  ZrO2,  as  the  species  Baddeleyite,  crystallizes  in  the  monoclinic 
system. 

CASSITERITE.     Tin-stone,  Tin  Ore 
Tetragonal.     Axis  c  =  0-6723. 

ee',   101  A  Oil  =  46°  28'.  ms,    110  A  111  =  46°  27'. 

ee",  101  A  101  =  67°  50'.  zz',     321  A  231  =  20°  53£' 

£«',   111  A  111  =  58°  19'.  zzv«,  321  A  321  =  61°  42'. 

ss",  111  A  111  =  87°    7' 

Twins  common:  tw.  pi.  e(101);  both  contact-  and  penetration-twins  (Fig. 
717);  often  repeated.  Crystals  low  pyramidal;  also  prismatic  and  acutely 
terminated.  Often  in  reniform  shapes,  structure  fibrous  divergent;  also  mas- 
sive, granular  or  impalpable;  in  rolled  grains. 


426 


DESCRIPTIVE   MINERALOGY 


Cleavage:  a(100)  imperfect;   8(111)   more   so;   m(110)   hardly   distinct. 
Fracture  subconchoidal  to  uneven.   Brittle.    H.  =  6-7.    G.  =  6-8-71.    Luster 
adamantine,  and  crystals  usually  splendent.     Color  brown  or  black;   some- 
714  715  716  717 


times  red,  gray,  white,  or  yellow.    Streak  white,  grayish,  brownish.     Nearly 
transparent  to  opaque.     Optically  +  .    Indices:   co  =  1-9966,  e  =  2-0934. 

Var.  —  Ordinary.     Tin-stone.     In  crystals  and  massive. 

Wood-tin.  In  botryoidal  and  reniform  shapes,  concentric  in  structure,  and  radiated 
fibrous  internally,  although  very  compact,  with  the  color  brownish,  of  mixed  shades,  looking 
somewhat  like  dry  wood  in  its  colors.  Toad's-eye  tin  is  the  same,  on  a  smaller  scale.  Stream- 
tin  is  the  ore  in  the  state  of  sand,  as  it  occurs  along  the  beds  of  streams  or  in  gravel. 

Comp.  —  Tin  dioxide,  Sn02  =  Oxygen  21'4,  tin  78'6  =  100.  A  little 
Ta2O5  is  sometimes  present,  also  Fe2O3. 

Pyr.,  etc.  —  B.B.  alone  unaltered.  On  charcoal  with  soda  reduced  to  metallic  tin,  and 
gives  a  white  coating.  With  the  fluxes  sometimes  gives  reactions  for  iron  and  manganese. 
Only  slightly  acted  upon  by  acids. 


Artif .  —  Cassiterite  has  been  artificially  prepared  by  the  action  of  aqueous  vapor  upon 
tin  tetrachloride  in  a  heated  tube  and  by  other  similar  methods  employing  heated  vapors. 

Obs.  —  Cassiterite  has  been  noted  as  an  original  constituent  of  igneous  rocks  but  usu- 
ally it  occurs  in  veins  traversing  granite,  rhyolite,  quartz  porphyry,  pegmatite,  gneiss,  mica 
schist,  chlorite  or  clay  schist;  also  in  finely  reticulated  veins  forming  the  ore-deposits 
called  stockworks,  or  simply  impregnating  the  enclosing  rock.  It  is  most  commonly 
found  in  quartz  veins  traversing  granite,  accompanied  by  minerals  containing  boron  and 
fluorine  which  indicates  a  pneumatolytic  origin.  The  commonly  associated  minerals  are 
quartz,  wolframite,  scheelite;  also  mica,  topaz,  tourmaline,  apatite,  fluorite;  further 
pyrite,  arsenopyrite,  sphalerite;  molybdenite,  native  bismuth,  etc. 

Formerly  very  abundant,  now  less  so,  in  Cornwall,  in  fine  crystals,  and  also  as  wood-tin 
and  stream-tin;  in  Devonshire,  near  Tavistock  and  elsewhere;  in  pseudomorphs  after 
feldspar  at  Wheal  Coates,  near  St.  Agnes,  Cornwall;  in  fine  crystals,  often  twins,  at 
Schlackenwald,  Graupen,  Joachimstal,  Zinnwald,  etc.,  in  Bohemia,  and  at  Ehrenfrieders- 
dorf,  Altenberg,  etc.,  in  Saxony;  at  Limoges,  France,  in  splendid  crystals;  Sweden,  at 
Fmbo;  Finland,  at  Pitkaranta. 

In  the  East  Indies,  on  the  Malay  peninsula  of  Malacca  and  the  neighboring  islands, 
Banca,  and  Bilitong  near  Borneo.  In  New  South  Wales  abundant  over  an  area  of  8500  sq. 
miles,  also  in  Victoria,  Queensland  and  Tasmania.  In  Bolivia  in  veins  containing  silver, 
lead,  and  bismuth;  Mexico,  in  Durango,  Guanajuato,  Zacatecas,  Jalisco. 

In  the  United  States,  in  Me.,  sparingly  at  Paris,  Hebron,  etc.  In  Mass.,  at  Chesterfield 
and  Goshen,  rare.  In  N.  H.,  at  Jackson.  In  Va..  on  Irish  Creek,  Rockbridge  Co.,  with 
wolframite,  etc.  In  N.  C.  and  S.  C.  In  Ala.,  in  Coosa  Co.  In  S.  D.,  near  Harney  Peak 
and  near  Custer  City  in  the  Black  Hills,  where  it  has  been  mined.  In  Wy.,  in  Crook  Co.; 
in  Mon.,  near  Dillon.  In  Cal.,  in  San  Bernardino  Co.,  at  Temescal.  Has  been  mined  in 
the  York  district,  Seward  Peninsula,  Alaska. 

Use.  —  The  most  important  ore  of  tin. 


OXIDES 


427 


Polianite.  Manganese  dioxide,  MnO2.  In  composite  parallel  groupings  of  minute 
crystals;  also  forming  the  outer  shell  of  crystals  having  the  form  of  manganite.  H.  =  6-6'5. 
G.  =  4'992.  Luster  metallic.  Color  light  steel-gray  or  iron-gray.  Streak  black.  From 
Flatten,  Bohemia.  It  is  distinguished  from  pyrolusite  by  its  hardness  and  its  anhydrous 
character.  Like  pyrolusite  it  is  often  a  pseudomorph  after  manganite. 


RUTILE. 

Tetragonal. 
«vu, 
ee't 
ee", 

718 


Axis_c  =  0-64415. 
310  A  310  =*  36°  54'. 
101  A  Oil  =  45°    2'. 
101  A  101  =  65°  34*'. 


ss',  111  A  111  =  56  25|'. 
««",  111  A  111  =  84°  40'. 
it',  313  A  133  =  29°  6'. 


719  720 


721 


Twins:  tw.  pi.  (1)  e(101);  often  geniculated  (Figs.  720, 
721) ;  also  contact-twins  of  very  varied  habit,  sometimes 
sixlings  and  eightlings  (Fig.  399,  p.  164;  Fig.  413,  p.  166). 
(2)  v(301)  rare,  contact-twins  (Fig.  415,  p.  167).  Crys- 
tals commonly  prismatic,  vertically  striated  or  fur- 
rowed; often  slender  acicular.  Occasionally  compact, 
massive. 

Cleavage:  a(100)  and  w(110)  distinct;  s(lll)  in  traces.  Fracture  sub- 
conchoidal  to  uneven.  Brittle.  H.  =  6y6'5.  G.  =  4'18-4'25;  also  to  5'2. 
Luster  metallic-adamantine.  Color  reddish  brown,  passing  into  red;  some- 
times yellowish,  bluish,  violet,  black,  rarely  grass-green;  by  transmitted  light 
deep  red.  Streak  pale  brown.  Transparent  to  opaque.  Optically  +. 
Refractive  indices  high:  co  =  2-6158,  e  =  2-9029.  Birefringence  very  high. 
Sometimes  abnormally  biaxial. 

Comp.  —  Titanium  dioxide,  Ti02  =  Oxygen  40'0,  titanium  60'0  =  100. 
A  little  iron  is  usually  present,  sometimes  up  to  10  p.  c.  While  the  iron  present 
is  often  reported  as  ferric  the  probability  is  that  in  the  unaltered  mineral  it 
existed  in  the  ferrous  state. 

The  formula  for  rutile  may  be  written  as  a  titanyl  metatitanate  (TiO)TiO3  With  this 
the  ferrous  titanate  FeTiO3  may  be  considered  isomorphous  and  so  account  for  the  iron 
frequently  present.  It  has  been  suggested  that  the  tapiolite  molecule,  FeO.Ta2O5  is  also 
isomorphous  and  that  tapiolite  belongs  in  the  same  group  as  rutile  and  cassiterite,  see 
ilmenorutile,  below. 

Var.  —  Ordinary.  Brownish  red  and  other  shades,  not  black.  G.  =  4*  lS-4'25.  Trans- 
parent quartz  (sagenite)  is  sometimes  penetrated  thickly  with  acicular  or  capillary  crystals. 
Dark  smoky  quartz  penetrated  with  the  acicular  rutile  or  "rutilated  quartz,"  is  the  Filches 
d'amour  Fr.  (or  Venus  hair-stone).  Acicular  crystals  often  implanted  in  parallel  position 
on  tabular  crystals  of  hematite;  also  somewhat  similarly  on  magnetite. 

Ferriferous,  (a)  Nigrine  is  black  in  color,  whence  the  name;  contains  up  to  30  p.  c.  of 
ferrous  titanate.  (b)  Ilmenorutile  is  a  black  variety  from  the  Ilmen  Mts.,  Russia;  contain- 
ing iron  in  the  form  of  ferrous  titanate,  niobate  and  tantalate.  G.  =  5'14.  Struverite  is 
the  same  mineral  with  greater  amounts  of  the  niobate  present,  (c)  Iserine  from  Iserweise, 
Bohemia,  formerly  considered  to  be  a  variety  of  ilmenite  is  probably  also  a  ferriferous  rutile. 


428  DESCRIPTIVE   MINERALOGY 

pyr  etc.  —  B.B.  infusible.  With  salt  of  phosphorus  gives  a  colorless  bead,  which  in 
R.F.  assumes  a  violet  color  on  cooling.  Most  varieties  contain  iron,  and  give  a  brownish 
yellow  or  red  bead  in  R.F.,  the  violet  only  appearing  after  treatment  of  the  bead  with 
metallic  tin  on  charcoal.  Insoluble  in  acids;  made  soluble  by  fusion  with  an  alkali  or 
alkaline  carbonate.  The  solution  containing  an  excess  of  acid,  with  the  addition  of  tin- 
foil, gives  a  beautiful  violet  color  when  concentrated. 

Diff.  —  Characterized  by  its  peculiar  sub-adamantine  luster  and  brownish  red  color. 
Differs  from  tourmaline,  vesuvianite,  augite  in  being  entirely  unaltered  when  heated  alone 
B.B.  Specific  gravity  about  4,  of  cassiterite  6'5. 

Micro.  —  In  thin  sections  shows  red-brown  to  yellow  color,  very  high  relief  and  high 
order  of  interference  color. 

Artif .  —  Rutile  has  been  formed  artificially  by  heating  titanic  oxide  with  boric  oxide, 
with  sodium  tungstate,  etc.  Rutile,  octahedrite  and  brookite  have  all  been  formed  by  heat- 
ing potassium  titanate  and  calcium  chloride  in  a  current  of  hydrochloric  acid  gas  and  air. 
RutUe  is  formed  at  the  highest  temperature,  brookite  at  lower  temperatures,  and  octahedrite 
at  the  lowest  of  all. 

Obs.  —  Rutile  occurs  as  an  accessory  mineral  in  granite,  gneiss,  mica  schist,  and  sye- 
nitic  rocks,  and  sometimes  in  granular  limestone  and  dolomite;  common,  as  a  secondary 
product,  in  the  form  of  microlites  in  many  slates.  A  dike  rock  from  Nelson  Co.,  Va.,  con- 
sists essentially  of  rutile  and  apatite.  It  is  generally  found  in  embedded  crystals,  often  in 
masses  of  quartz  or  feldspar,  and  frequently  in  acicular  crystals  penetrating  quartz ;  also 
in  phlqgopite  (which  see),  and  has  been  observed  in  diamond.  It  has  also  been  met  with  in 
hematite  and  limenite,  rarely  in  chromite.  It  is  common  in  grains  or  fragments  in  many 
auriferous  sands. 

Prominent  localities  are:  Arendal  and  Kragero  in  Norway;  Horrsjoberg,  Sweden,  with 
lazulite  and  cyanite;  Saualpe,  Carinthia;  in  the  Ural  Mts.;  in  the  Tyrol,  Austria;  at  St. 
Gothard  and  Binnental,  Switzerland;  at  Yrieux,  near  Limoges  in  France;  at  Ohlapian  in 
Transylvania,  nigrine  in  pebbles;  in  large  crystals  in  Perthshire,  Scotland;  in  Donegal  Co., 
Ireland. 

In  Me.,  at  Warren.  In  Ver.,  at  Waterbury;  also  in  loose  bowlders  in  middle  and 
northern  Vermont,  acicular,  some  specimens  of  great  beauty  in  transparent  quartz.  In 
Mass.,  at  Barre,  in  gneiss;  at  Shelburne,  in  mica  slate,  at  Chester.  In  N.  Y.,  in  Orange  Co., 
Edenville;  Warwick;  east  of  Amity.  In  Pa.,  at  Sudsbury,  Chester  Co.,  and  the  adjoining 
district  in  Lancaster  Co.;  at  Parksburg,  Concord,  West  Bradford,  and  Newlin,  Chester  Co.; 
at  the  Poor  House  quarry,  Chester  Co.  In  N.  J.,  at  Newton,  with  spinel.  In  N.  C.,  at 
Crowder's  Mountain;  at  Stony  Point,  Alexander  Co.,  in  splendent  crystals.  In  Ga.,  in 
Habersham  Co.;  in  Lincoln  Co.,  at  Graves'  Mountain,  with  lazulite  in  large  and  splendent 
crystals.  In  Ark.,  at  Magnet  Cove,  commonly  in  twins,  with  brookite  and  perovskite,  also 
as  paramorphs  after  brqokite. 

Fine  specimens  of  "rutilated  quartz,"  from  Minas  Geraes,  Brazil;  Madagascar; 
Tavetch  and  elsewhere,  Switzerland;  West  Hartford,  Ver.;  Alexander  Co.,  N.  C. 

Use.  —  A  source  of  titanium. 

Plattnerite.  Lead  dioxide,  PbO2.  Rarely  in  prismatic  crystals,  usually  massive. 
H.  =  5-5*5.  G.  =  8'5.  Luster  submetallic.  Color  iron-black.  Streak  chestnut-brown. 
From  Leadhill  and  Wanlockhead,  Scotland.  Also  at  the  "As  You  Like"  mine,  Mullan, 
Cceur  d'Alene  Mts.,  Idaho. 

Baddeleyite.  Zirconium  dioxide,  ZrO2.  In  tabular  monoclinic  crystals.  H.  =  6'5.  £t.  = 
5-5-6-0.  Colorless  to  yellow,  brown  and  black.  Index,  174.  From  Ceylon;  from  Brazil 
near  Caldas,  Minas  Geraes  and  Jacupiranga,  (brazilite)  where  it  is  associated  with  zirkelite, 
(Ca,Fe)0.2(Zr,Ti,Th)O2.  Noted  at  Mte.  Somma,  Vesuvius.  Also  near  Boseman,  Mon. 
Various  minerals  occurring  as  rolled  pebbles  in  the  diamond  sands  of  Brazil  are  known  as 


favas  (beans).  Some  of  them  consist  of  nearly  pure  TiO2  others  of  nearly  pure  ZrO2,  while 
others  are  various  phosphates.  Paredrite  is  a  "fava,"  composed  of  TiO2  with  a  little 
water. 

Uhligite.     Ca(Ti  Zr)05.Al(Ti,Al)06.     Isometric.     Octahedral.     Color  black.     Brown 
and  transparent  on  thin  edges.     Found  in  a  nepheline  syenite  on  the  shore  of  Lake  Magad, 

ri.QQt.     A  TT1OQ 


OCTAHEDRITE.     Anatase. 
Tetragonal.     Axis  c  =  17771. 
Commonly  octahedral  in  habit,  either  acute  (p,  111),  or  obtuse  (v,  117); 


OXIDES 


429 


also  tabular,  c(001)   predominating;    rarely  prismatic  crystals;   frequently 
highly  modified. 


ee',.  101  A  Oil  = 
ee",  101  A  101  = 
ppf,  111  A  111  = 
pp",Ul  A  111  = 
zz',  113  A  113  = 
vv'  117  A  117  = 


76°  5' 
121°  16' 

82°  9' 
136°  36' 

54°  1' 

27°  39' 


722 


723 


Cleavage:  c  (001)  and  p  (111) 
perfect.  Fracture  subconchoidal. 
Brittle.  H.  =  5-5-6.  G.  =  3-82-3-95; 
sometimes  4-11-4-16  after  heating. 
Luster  adamantine  or  metallic-ad- 
amantine. Color  various  shades  of 
brown,  passing  into  indigo-blue,  and 
black;  greenish  yellow  by  transmitted 
light.  Streak  uncolored.  Transparent  to  nearly  opaque.  Optically  — . 
Birefringence  rather  high.  Indices:  o>  =  2-554,  e  =  2-493.  Sometimes  abnor- 
mally biaxial. 

Comp.  —  Titanium  dioxide,  TiO2  =  Oxygen  40'0,  titanium  60*0  =  100. 

Pyr.,  etc.  —  Same  as  for  rutile. 

Artif.  —  See  under  rutile. 

Obs.  —  Most  abundant  at  Bpurg  d'Oisans,  in  Dauphine,  France,  with  feldspar,  axinite, 
and  ilmenite;  near  Hof  in  the  Fichtelgebirge,  Germany;  at  Selva  and  Naderanertal,  Swit- 
zerland; Norway;  the  Ural  Mts.;  in  chlorite  in  Devonshire,  near  Tavistock;  with  brookite 
at  Tremadoc,  in  North  Wales ;  in  Cornwall,  near  Liskeard  and  at  Tintagel  Cliffs ;  in  Brazil 
in  quartz,  and  in  detached  crystals.  In  Switzerland  in  the  Binnental  the  variety  wiserine, 
long  supposed  to  be  xenotime;  also  Cavradi,  Tavetsch;  Rauris,  Salzburg,  in  the  Eastern 
Alps;  also  at  Pfitsch  Joch. 

In  the  United  States,  at  the  Dexter  lime  rock,  Smithfield,  R.  L,  in  dolomite;  from  granite 
pegmatite,  Quincy,  and  from  Somerville,  Mass.;  in  the  washings  at  Brindletown,  Burke 
Co.,  N.  C.,  in  transparent  tabular  crystals;  at  Magnet  Cove,  Ark.;  in  unusual  crystals  from 
Beaver  Creek,  Gunnison  Co.,  Col. 

BROOKITE. 

Orthorhombic.     Axes  a  :  b  :  c  =  0-8416  :  1  :  0-9444. 

mm'",  110  A  lIO  =  80°  10'.  ee',      122  A  122  =  44°  23'. 

zz',       112  A  112  =  53°  48'.  ee'",    122  A  122  =  78°  57'. 

zz"'      112  A  112  =  44°  46'.  me,     110  A  122  =  45°  42'. 


725 


726 


727 


Only  in  crystals,  of  varied  habit. 

Cleavage:  w(110)  indistinct;  c(001)  still  more  so.  Fracture  subcon- 
choidal to  uneven.  Brittle.  H.  =  5-5-6.  G.  =  3-87-4-08.  Luster  metallic- 
adamantine  to  submetallic.  Color  hair-brown,  yellowish;  reddish,  reddish 


430  DESCRIPTIVE   MINERALOGY 

brown  and  translucent;  also  brown  to  iron-black,  opaque.  Streak  uncolored 
to  grayish  or  yellowish,  a  =  2-583.  0  =  2*586.  7  =  2741.  Other  optical 
characters,  see  p.  298. 

Comp.  —  Titanium  dioxide,  TiO2  =  Oxygen  40*0,  titanium  60'0  ==  100. 

Pyr.  —  Same  as  for  rutile. 

Obs.'—  Occurs  at  Bourg  d'Oisans  in  Dauphine,  France;  in  Switzerland  at  St.  Gothard, 
with  albite  and  quartz,  and  Maderanertal;  in  the  Ural  Mts.;  district  of  Zlatoust,  near  Miask, 
and  in  the  gold-washings  in  the  Sanarka  river  and  elsewhere;  at  Fronolen,  near  Tremadoc, 
Wales.  From  Companhia,  Lencoes,  Bahia,  Brazil. 

In  the  United  States  in  thick  black  crystals  (arkansite)  at  Magnet  Cove,  Ozark  Mts., 
Ark.  with  elaeolite,  black  garnet,  schorlomite,  rutile,  etc.;  in  small  crystals  from  the  gold- 
washings  of  N.  C.;  at  the  lead  mine  at  Ellenville,  Ulster  Co.,  N.  Y.,  on  quartz,  with  chal- 
copyrite  and  galena;  at  Paris,  Me.,  Somerville,  Mass. 

Named  after  the  English  mineralogist,  H.  J.  Brooke  (1771-1857). 


PYROLUSITE. 

Orthorhombic,  but  perhaps  only  pseudomorphous.  Commonly  columnar, 
often  divergent;  also  granular  massive,  and  frequently  in  reniform  coats. 

Soft,  often  soiling  the  fingers.  H.  =  2-2-5.  G.  =  473-4-86.  Luster 
metallic.  Color  iron-black,  dark  steel-gray,  sometimes  bluish.  Streak  black 
or  bluish  black,  sometimes  submetallic.  Opaque. 

Comp.  —  Manganese  dioxide,  MnO2,  like  polianite  (p.  427).  Commonly 
contains  a  little  water  (2  p.  c.),  it  having  had  usually  a  pseudomorphous 
origin  (after  manganite). 

It  is  uncertain  whether  pyrolusite  is  an  independent  species,  with  a  crystalline  form  of 
its  own,  or  only  a  secondary  mineral  derived  chiefly  from  the  dehydration  of  manganite; 
also  from  polianite  (Breith.).  Pseudomorphous  crystals  having  distinctly  the  form  of 
manganite  are  common. 

I^r.,  etc.  —  Like  polianite,  but  most  varieties  yield  some  water  in  the  closed  tube. 

Diff.  —  Hardness  less  than  that  of  psilomelane.  Differs  from  iron  ores  in  its  reaction 
for  manganese  B.B.  Easily  distinguished  from  psilomelane  by  its  inferior  hardness,  and 
usually  by  being  crystalline.  Its  streak  is  black;  that  of  manganite  is  more  or  less  brown. 

Obs.  —  Manganese  ore  deposits  in  general  are  secondary  in  origin,  the  manganese 
content  of  the  rocks  having  been  concentrated  in  favorable  places.  They  often  occur  as 
irregular  bodies  in  residual  clays.  Pyrolusite  is  extensively  worked  at  Elgersberg  near 
Ilmenau,  and  other  places  in  Thuringia,  Germany;  at  Vorderehrensdorf  in  Moravia;  at 
Flatten  in  Bohemia,  and  elsewhere;  near  Johanngeorgenstadt,  at  Hirschberg  in  West- 
phalia, Germany;  Matzka,  Transylvania;  in  Australia;  in  India. 

Occurs  in  the  United  States'  with  psilomelane,  abundantly  in  Ver.,  at  Brandon,  etc.; 
at  Plainfield  and  West  Stockbridge,  Mass.;  Augusta  Co.,  Va.;  Pope,  Pulaski,  Montgomery 
Cos.,  Ark.  Negaunee,  Mich.;  Lake  Co.,  N.  M.  In  New  Brunswick,  7  m.  from  Bathurst. 
In  Nova  Scotia,  at  Teny  Cape;  at  Walton,  etc. 

The  name  is  from  -nvp,  fire,  and  \oveiv,  to  wash,  because  used  to  discharge  the  brown 
and  green  (FeO)  tints  of  glass;  and  for  the  same  reason  it  is  whimsically  entitled  by  the 
French  le  savon  de  verriers. 

Use.  —  An  ore  of  manganese;  as  an  oxidizing  agent  in  manufacture  of  chlorine,  bro- 
mine and  oxygen;  as  a  drier  in  paints,  a  decolorizer  in  glass  and  in  electric  batteries,  as  color- 
ing material  in  bricks,  pottery,  glass,  etc. 


B.  HYDROUS  OXIDES. 

ddes  the  DIASPORE  Gi 

3  of  aluminium,  iron  an 

in 
formula  is  properly  written  RO(OH).     The  three  species  here  included  are 


Among  the  hydrous  oxides  the  DIASPORE  GROUP  is  well  characterized. 
Here  belong  the  hydroxides  of  aluminium,  iron  and  manganese.     The  general 


OXIDES 


431 


orthorhombic  in  crystallization  with  related  angles  and  axial  ratios;  this  rela- 
tion is  deviated  from  by  manganite  in  the  prismatic  zone. 

Another  less  prominent  group  is  the  BRUCITE  GROUP,  including  the 
rhombohedral  species  Brucite,  Mg(OH),  and  Pyrochroite,  Mn(OH). 

Gibbsite,  A1(OH)3,  and  Sassolite,  B(OH)3,  are  also  related,  and  further 
Hydrotalcite  and  Pyroaurite. 

.   TTT 

Diaspore  Group. 


p.    RO(OH) 

or  R203.H20. 

a  :b 

Orthorhombic. 

c 

:  c 

a 

A1203.H20 

o- 

9372 

1 

:0 

•6039 

or 

0 

•6443 

Fe2O3.H2O 

0' 

9185 

1 

:0 

•6068 

or 

0 

•6606 

Mn2O3.H2O 

6- 

8441 

1 

:0 

•5448 

or 

0 

•6463 

Diaspore 
Gothite 
Manganite 
DIASPORE. 

Orthorhombic.  Axes:  a  :  b  :  c  =  0-9372  :  1  :  0-6039.  Crystals  prismatic, 
mm'",  110  A  110,  =  86°  17';  usually  thin,  flattened  ||  6(010);  sometimes 
acicular.  Also  foliated  massive  and  in  thin  scales;  sometimes  stalactitic. 

Cleavage:  6(010)  eminent;  A(210)  less  perfect.  Fracture  conchoidal, 
very  brittle.  H.  =  6*5—7.  G.  =  3 "3— 3*5.  Luster  brilliant; 'pearly  on  cleav- 
age-face, elsewhere  vitreous.  Color  whitish,  grayish  white,  greenish  gray, 
hair-brown,  yellowish,  to  colorless.  Pleochroic.  Transparent  to  subtrans- 
lucent.  Optically  +  .  Birefringence  high.  Ax.  pi.  ||  6(010).  Bx.  J_  a(100). 
Dispersion  p  <  v,  feeble.  2  V  =  84°.  a  =  1-702.  0  =  1-722.  7  =  1750. 

Comp.  —  AIO(OH)  or  A1203.H2O  =  Alumina  85'0,  water  15'0  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  usually  decrepitates  strongly,  separating  into  white  pearly 
scales,  and  at  a  high  temperature  yields  water.  Infusible;  ignited  with  cobalt  solution 
gives  a  deep  blue  color.  Not  attacked  by  acids,  but  after  ignition  soluble  in  sulphuric  acid. 

Diff.  —  Distinguished  by  its  hardness  and  pearly  luster;  also  (B.B.)  by  its  decrepitation 
and  yielding  water;  by  the  reaction  for  alumina  with  cobalt  solution.  Resembles  some 
varieties  of  hornblende,  but  is  harder. 

Artif .  —  Diaspore  crystals  have  been  artificially  formed  by  heating  in  a  steel  tube 
aluminium  oxide  in  sodium  hydroxide  to  temperatures  less  than  500°. 

Obs.  —  Commonly  found  with  corundum  or  emery.  Occurs  near  Kossoibrod,  in  the 
Ural  Mts.;  at  Schemnitz,  Hungary;  with  corundum  in  dolomite* at  Campolongo,  Tessin,  in 
Switzerland;  Greiner  in  the  Zillertal,  Austria.  In  the  United  States,  with  corundum  and 
margarite  at  Newlin,  Chester  Co.,  Pa.;  at  the  emery  mines  of  Chester,  Mass.;  in  cavities 
in  massive  corundum  at  the  Culsagee  mine,  near  Franklin,  Macon  Co.,  N.  C.;  with  alunite 
forming  rock  masses  at  Mt.  Robinson,  Rosita  Hills,  Col. 

Named  by  Haiiy  from  dtaaTre'ipeiv,  to  scatter,  alluding  to  the  usual  decrepitation  before  the 
blowpipe. 

GOTHITE.  72? 

Orthorhombic.     Axes  a  :  b  :  c  =  0*9185  :  1_ :  0*6068. 
mm'",  110  A  110  =  85°    8'.  pp',    111  A  111  =  58°  55'. 

ee',       Oil  A  Oil  =  62°  30'.  pp"',  111  A  ill  =  53°  42'. 

In  prisms  vertically  striated,  and  often  flattened  into 
scales  or  tables  ||  6(010).  Also  fibrous;  foliated  or  in  scales; 
massive,  reniform  and  stalactitic,  with  concentric  and  radiated 
structure. 

Cleavage:  6(010)  very  perfect.    Fracture  uneven.    Brittle. 
H.  =  5-5-5.     G.  =  4*28.     Luster  imperfect  adamantine.     Col- 
or yellowish,  reddish,  and  blackish  brown.     Often  blood-red 
by  transmitted  light.     Streak  brownish  yellow  to  ocher-yellow.     a  =  2 -26. 
]8  =  2-39.    7  =  2-4.    Only  weakly  pleochroic. 


432 


DESCRIPTIVE    MINERALOGY 


Var.  —  In  thin  scale-like  or  tabular  crystals,  usually  attached  by  one  edge.  Also  in 
acicular  or  capillary  (not  flexible)  crystals,  or  slender  prisms,  often  radiately  grouped:  the 
Needle-Ironstone.  It  passes  into  a  variety  with  a  velvety  surface;  the  Przibramite  (Sammet- 
blende)  of  Pfibram,  Bohemia,  is  of  this  kind.  Also  columnar,  fibrous,  etc.,  as  above. 

Comp.  —  FeO(OH)  or  Fe203.H2O  =  Oxygen  27'0,  iron  62'9,  water  101 
=  100,  or  Iron  sesquioxide  89*9,  water  10*1  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  gives  off  water  and  is  converted  into  red  iron  sesqui- 
oxide. With  the  fluxes  like  hematite;  most  varieties  give  a  manganese  reaction,  and  some, 
treated  in  the  forceps  in  O.F.,  after  moistening  in  sulphuric  acid,  impart  a  bluish  green 
color  to  the  flame  (phosphoric  acid).  Soluble  in  hydrochloric  acid. 

Diff.  —  Distinguished  from  hematite  by  its  yellow  streak;  from  limonite  by  crystalline 
nature;  it  also  contains  less  water  than  limonite.  . 

Obs.  —  Found  with  the  other  oxides  of  iron,^ especially  hematite  or  limonite.  Occurs 
at  Eiserfeld  near  Siegen,  in  Nassau,  Germany;  Pfibram,  Bohemia;  at  Clifton,  near  Bristol, 
England;  in  Cornwall.  In  the  United  States,  at  the  Jackson  Iron  mine,  Negaunee,  Lake 
Superior;  in  Conn.,  at  Salisbury;  in  Pa.,  near  Easton;  in  the  Pike's  Peak  region  and  at 
Crystal  Peak,  Col.  Named  Gothite  (Goethite)  after  the  poet-philosopher  Goethe  (1749-1832) . 

A  colloidal  form  of  iron  hydroxide  having  the  composition  of  goethite  and  occurring  as 
pseudomorphs  after  pyrite  has  been  called  ehrenwerthite. 

Use.  —  An  ore  of  iron. 

Lepidocrocite.  A  dimorphous  form  of  goethite.  Orthorhombic  but  with  different 
axial  ratio.  Scaly,  fibrous.  G  =  4'09.  £  =  2*20.  Strongly  pleochroic. 


MANGANITE. 
Orthorhombic. 


Axes  a  :  b  :  c  =  0*8441 


729 


730 


1  :  0-5448. 

hh'",  410  A  410  =  23°  50'. 
mm'",  110  A  110  =  80°  20'. 
ee',  205  A  205  =  28°  57'. 
ee',  Oil  A  Oil  =  57°  10'. 
ppf,  111  A  Til  =  59°  5|'. 

Crystals  commonly  prismatic,  the 
faces  deeply  striated  vertically;  often 
grouped  in  bundles.  Twins:  tw.  pi. 
e(011).  Also  columnar;  stalactitic. 

Cleavage:  6(010)  very  perfect;  w(110) 
perfect.  Fracture  uneven.  Brittle. 
H.  =  4.  G.  =  4-2-4-4.  Luster  sub- 
metallic.  Color  dark  steel-gray  to  iron-black.  Streak  reddish  brown, 
sometimes  nearly  black.  Opaque;  in  minute  splinters  sometimes  brown 
by  transmitted  light. 

Comp.  —  MnO(OH)  or  Mn2O3.H20  =  Oxygen   27'3,  manganese  62'4, 
water  10'3  =  100,  or  Manganese  sesquioxide  897,  water  10-3  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  yields  water;  manganese  reactions  with  the  fluxes,  p.  339, 
Obs.  —  Occurs  in  Germany  at  Ilefeld  in  the  Harz  Mts.;  Ilmenau  in  Thuringia;  Lang- 
ban  and  Bolet,  Sweden;  Cornwall,  at  various  places;  also  in  Cumberland,  etc.  In  the 
Lake  Superior  mining  region  at  the  Jackson  mine,  Negaunee;  Devil's  Head,  Douglas  Co., 
Col.  In  Nova  Scotia,  at  Cheverie,  Hants  Co.,  and  Walton.  In  New  Brunswick,  at  Shep- 
ody  mountain,  Albert  Co.,  etc. 

Sphenomanganite  is  a  variety  of  manganite  from  Langban,  Sweden,  showing  sphenoidal 
forms. 

Use.  —  An  ore  of  manganese. 


LIMONITE.    Brown  Hematite. 

Not  crystallized.  Usually  in  stalactitic  and  botryoidal  or  mammillary 
torms,  having  a  fibrous  or  subfibrous  structure;  also  concretionary,  massive- 
and  occasionally  earthy. 


OXIDES  433 

H.  =  5-5*5.  G.  =  3'6-4-0.  Luster  silky,  often  submetallic;  sometimes 
dull  and  earthy.  Color  of  surface  of  fracture  various  shades  of  brown,  com- 
monly dark,  and  none  bright;  sometimes  with  a  nearly  black  varnish-like 
exterior;  when  earthy,  brownish  yellow,  ocher-yellow.  Streak  yellowish 
brown.  Opaque. 

Var.  —  (1)  Compact,  Submetallic  to  silky  in  luster;  often  stalactitic,  botryoidal,  etc. 
(2)  Ocherous  or  earthy,  brownish  yellow  to  ocher-yellow,  often  impure  from  the  presence  of 
clay,  sand,  etc.  (3)  Bog  ore.  The  ore  from  marshy  places,  generally  loose  or  porous  in 
texture,  often  petrifying  leaves,  wood,  nuts,  etc.  (4)  Brown  clay-ironstone,  in  compact 
masses,  often  in  concretionary  nodules. 

Comp.  —  Approximately  2Fe203.3H2O  =  Oxygen  257,  iron  59'8,  water 
14'5  =  100,  or  Iron  sesquioxide  85  '5,  water  14*5  =  100.  The  water  content 
varies  widely  and  it  is  probable  that  limonite  is  essentially  an  amorphous 
form  of  goethite  with  adsorbed  and  capillary  water.  In  the  bog  ores  and 
ochers,  sand,  clay,  phosphates,  oxides  of  manganese,  and  humic  or  other 
acids  of  organic  origin  are  very  common  impurities. 

Pyr.,  etc.  —  Like  gpthite.  Some  varieties  leave  a  siliceous  skeleton  in  the  salt  of  phos- 
phorus bead,  and  a  siliceous  residue  when  dissolved  in  acids. 

Diff  .  —  Distinguished  from  hematite  by  its  yellowish  streak,  inferior  hardness,  and  its 
reaction  for  water.  Does  not  decrepitate  B.B.,  like  turgite.  Not  crystallized  like  gothite 
and  yields  more  water. 

Obs.  —  In  all  cases  a  result  of  the  alteration  of  other  ores,  or  minerals  containing 
iron,  through  exposure  to  moisture,  air,  and  carbonic  or  organic  acids;  derived  largely 
from  the  change  of  pyrite,  magnetite,  siderite,  ferriferous  dolomite,  etc.;  also  various 
species  (as  mica,  pyroxene,  hornblende,  etc.),  which  contain  iron  in  the  ferrous  state  (FeO). 
Waters  containing  iron  in  solution  when  brought  into  marshy  places  deposit  the  metal 
usually  in  the  form  of  limonite.  The  evaporation  of  the  carbonic  acid  in  the  water  which 
held  the  iron  in  solution  is  one  cause  for  the  separation  of  the  iron  oxide.  This  separation 
is  also  aided  by  the  so-called  "iron  bacteria"  which  absorb  the  iron  from  the  water  and 
later  deposit  it  again  as  ferric  hydroxide.  Limonite  consequently  occupies,  as  a  bog  ore, 
marshy  places,  into  which  it  has  been  borne  by  streamlets  from  the  hills  around.  It  is 
also  found  in  deposits  associated  with  iron-bearing  limestones  where  the  original  iron  con- 
tent of  the  rock  has  been  largely  dissolved  and  redeposited  later  in  some  favorable  spot. 
Limonite  forms  the  capping  or  gossan,  iron  hat,  of  many  metallic  veins.  It  is  often  asso- 
ciated with  manganese  ores.  Limonite  is  a  common  ore  in  Bavaria,  the  Harz  Mts.,  Ger- 
many, Luxemburg,  Scotland,  Sweden,  etc. 

Abundant  in  the  United  States.  Extensive  beds  exist  at  Salisbury  and  Kent,  Conn., 
also  in  the  neighboring  towns  of  N.  Y.,  and  in  a  similar  situation  in  Berkshire  Co.,  Mass., 
and  in  Ver.;  in  Pa.,  widely  distributed;  also  in  Tenn.,  Ala.,  Ohio,  etc. 

Named  Limonite  from  Xei/icoi>,  meadow. 

Use.  —  An  ore  of  iron;  as  a  yellow  pigment. 

TURGITE.  Hydrohematite.  Approximately  2Fe2O3.H2O.  Probably  to  be  considered 
as  a  solid  solution  of  goethite  with  hematite  together  with  enclosed  and  adsorbed  water. 
Resembles  limonite  but  has  a  red  streak.  G.  =  4'14-4'6.  Decrepitates  B.B.  From  the 
Turginsk  mine  in  the  Ural  Mts.,  etc.;  also  from  Salisbury,  Conn.  Intermediate  between 
hematite  and  limonite. 

HYDRO  GOETHITE.  3Fe203.4H20.  Orthorhombic,  radiating  fibrous.  H.  =4.  G.  = 
37.  Color  and  streak  brick-red.  With  limonite  at  various  localities  in  Tula,  Russia. 

Xanthosiderite.  Fe2O3.2H2O.  In  fine  needles  or  fibers,  stellate  and  concentric;  also 
as  an  ocher.  Color  golden  yellowish,  brown  to  brownish  red.  Associated  with  manganese 
ores  at  Ilmenau,  Thuringia,  Germany,  etc. 

Esmeraldaite.  Fe203.4H2O.  In  small  pod-shaped  masses  enclosed  in  limonite.  Con- 
choidal  fracture.  H.  =  2'5.  G.  =  2  '58.  Color  coal  black.  Yellow-brown  streak.  From 
Esmeralda  Co., 


BAUXITE.     Beauxite. 

In  round  concretionary  disseminated  grains.  Also  massive,  oolitic;  and 
earthy,  clay-like.  G.  =  2'55.  Color  whitish,  grayish,  to  ocher-yeHow,  brown, 
and  red. 


434  DESCRIPTIVE   MINERALOGY 

Var.  —  1.  In  concretionary  grains,  or  oolitic;  bauxite.  2  Clay-like,  wocheinite;  the 
purer  kind  grayish,  clay-like,  containing  very  little  iron  oxide;  also  red  from  the  iron 
oxide  present. 

Comp.  —  Essentially  A1203.2H2O  =  Alumina  73'9,  water  26'1  =  100; 
some  analyses,  however,  give  A12O3.H2O  like  diaspore. 

Bauxite  is  probably  a  mixture  of  varying  character  but  containing  large  amounts  of 
a  colloidal  form  of  Al2Os.H2O.  This  substance  has  been  called  sporogelite  or  diasporogelite, ' 
cliachite  and  alumogel. 

Iron  sesquioxide  is  usually  present,  sometimes  in  large  amount,  in  part  replacing 
alumina,  in  part  only  an  impurity.  The  name  hematogelite  has  been  suggested  for  this 
colloidal  form  of  ferric  oxide.  Silica,  phosphoric  acid,  carbonic  acid,  lime,  magnesia  are 
common  impurities. 

Obs.  —  Bauxite  is  a  product  of  the  decomposition  of  certain  rocks,  particularly  those 
rich  in  plagioclase  feldspars,  and  has  been  found  under  various  conditions.  The  later ites 
of  India,  etc.,  are  probably  similar  in  origin  and  might  be  considered  as  iron-rich  bauxites. 
Bauxite  is  certainly  not  a  definite  mineral  species  but  consists  of  a  mixture  of  several 
different  materials.  From  Baux  (or  Beaux),  near  Aries,  and  elsewhere  in  France,  dissemi- 
nated in  grains  in  compact  limestone,  and  also  oolitic.  Wocheinite  occurs  in  Carniola, 
Austria,  between  Feistritz  and  Lake  Wochein.  The  purest  bauxite  is  used  for  the  manu- 
facture of  aluminium  (aluminum),  and  is  called  aluminum  ore.  In  the  United  States, 
bauxite  occurs  in  Saline  and  Pulaski  Cos.,  Ark.;  also  in  Cherokee  and  Calhoun  Cos.,  Ala., 
and  in  Floyd,  Barton  and  Walker  Cos.,  Ga. 

Use.  —  As  an  aluminum  ore. 


Brucite  Group.    R(OH)2.     Rhombohedral 
BRUCITE. 

Jlhombohedral.  Axis  c  =  1-5208;  cr  0001  A  1011  =  60°  20i',  rr'  1011 
A  1101  =  97°  37J'. 

Crystals  usually  broad  tabular.  Also  commonly  foliated  massive;  fibrous, 
fibers  separable  and  elastic. 

H.  =  2-5.  G.  =  2-38-2-4.  Cleavage:  c(0001)  eminent.  Folia  separable 
and  flexible,  nearly  as  in  gypsum.  Sectile.  Luster  ||  c  pearly,  elsewhere 
waxy  to  vitreous.  Color  white,  inclining  to  gray,  blue,  or  green.  Transparent 
to  translucent.  Optically  +  .  Indices:  o>r  =  1-559,  er  =  1-5795. 

Comp.  --Magnesium  hydroxide,  Mg(OH)2  or  MgO.H2O  =  Magnesia 
69*0,  water  31*0  =  100.  Iron  and  manganese  protoxide  are  sometimes 
present. 

Var-  —  Ordinary,  occurring  in  plates,  white  to  pale  greenish  in  color;  strong  pearly 
luster  on  the  cleavage  surface.  Nemalite  is  a  fibrous  variety  containing  4  to  5  p.  c.  iron 
protoxide,  with  G.  =  2  "44.  Manganbrucite  contains  manganese;  occurs  granular;  color 
honey-yellow  to  brownish  red.  Ferrobrucite  contains  iron. 

Pyr.,  etc.  —  In  the  closed  tube  gives  off  water,  becoming  opaque  and  friable,  sometimes 
turning  gray  to  brown;  the  manganesian  variety  becomes  dark  brown.  B.B.  infusible, 
glows  with  a  bright  light,  and  the  ignited  mineral  reacts  slightly  alkaline  to  test-paper. 
ignited  with  cobalt  solution  gives  the  pale  pink  color  of  magnesia.  The  pure  mineral  is 
soluble  in  acids  without  effervescence. 

i,  P^vT  D/SitingUiS^  by  -its.  infusibility,  softness,  cleavage,  and  foliated  structure.  Is 
harder  than  talc  and  differs  in  its  solubility  in  acids;  the  magnesia  test  and  optical  char- 
acters separate  it  from  gypsum,  which  is  also  somewhat  softer. 

«l«n  f^'r^-  Arsecon  dary  mm«f  a.1  accompanying  other  magnesian  minerals  in  serpentine, 
also  found  m  limestone.  At  Swmaness  in  Unst,  Shetland  Isles;  at  the  iron  mine  of  Cogne 
Aosta  Italy;  near  Fihpstadt  in  Sweden.  At  Hoboken,  N.  J,  in  serpentine;  at  the  Tilly 
Foster  iron  nime,  Brewster  N.  Y,  well  crystallized;  Richmond  Co  ,  N.  Y.;  at  Wood's 
e  *'  m  ?  5  °r  m-asses'  and  often  crystallizations  several  inches  across, 

hydjomagnesite      From  Crestmore,  Riverside  Co.,  Cal.     Nemalite, 
ur 


the  fibrvHHp  rom     resmore,      verse     o.,     a.     Nemalite, 

the  fibrous  variety,  occurs  at  Hoboken,  N.  J.,  and  at  Xettes  in  the  Vosges  Mts.     Mangos 


OXIDES  435 

brucite  occurs  with  hausmannite  and  other  manganese  minerals  in  the  granular  limestone 
of  Jakobsberg,  Nordmark,  Sweden. 

Named  after  the  early  American  mineralogist,  A.  Bruce  (1777-1818). 

Pyrochroite.  —  Manganese  hydroxide,  Mn(OH)2.  Usually  foliated,  like  brucite.  Lus- 
ter pearly.  Color  white,  but  growing  dark  on  exposure,  to  =  1723.  e  =  1'681.  In 
Sweden  occurs  in  magnetite  at  Pajsberg,  also  at  Nordmark  and  Langban;  in  N.  J.  at 
Franklin  Furnace. 


Backstromite.     Manganese    hydroxide,    Mn(OH)2.     Orthorhombic.     From    Langban, 
Sweden. 


GIBBSITE.     Hydrargillite. 

Monoclinic.  Axes  a  :  b  :  c  =  17089  :  1  :  1-9184;  0  =  85°  29'.  Crystals- 
tabular  |  c(001),  hexagonal  in  aspect.  Occasionally  in  spheroidal  concretions. 
Also  stalactitic,  or  small  mammillary,  incrusting,  with  smooth  surface,  and 
often  a  faint  fibrous  structure  within. 

Cleavage:  c(001)  eminent.  Tough.  H.  =  2-5-3 -5.  G.  =  2-3-2-4. 
Color  white,  grayish,  greenish,  or  reddish  white.  Luster  of  c(001)  pearly;  ot 
other  faces  vitreous;  of  surface  of  stalactites  faint.  Translucent;  sometimes 
transparent  in  crystals.  Indices,  1-535-1-558.  A  strong  argillaceous  odor 
when  breathed  on. 

Comp.  —  Aluminium  hydroxide,  A1(OH)3  or  A1203.3H20  =  Alumina 
65-4,  water  34-6  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  becomes  white  and  opaque,  and  yields  water.  B.B.  in- 
''usible,  whitens,  and  does  not  impart  a  green  color  to  the  flame.  Ignited  with  cobalt 
solution  gives  a  deep  blue  color.  Soluble  in  concentrated  sulphuric  acid. 

Artif .  —  When  solutions  of  sodium  aluminate  are  slowly  decomposed  by  carbon  dioxide 
gibbsite  is  precipitated. 

Obs.  —  The  crystallized  gibbsite  (hydrargillite)  occurs  in  the  Shishimsk  mountains  near 
Zlatoust  in  the  Ural  Mts. ;  also  in  crystals  filling  cavities  in  natrolite  at  Langesundfiord, 
Norway;  Ouro  Preto,  Minas  Geraes,  Brazil.  Occurs  in  nodular  plates  at  Kodikanal,  Palni 
Hills,  Madras,  and  at  Talevadi,  Bombay,  India.  In  the  United  States,  in  stalactitic  form 
at  Richmond,  Mass.,  in  a  bed  of  limonite ;  at  the  Clove  Mine,  Union  Vale,  Dutchess  Co., 
N.  Y.,  on  limonite;  in  Orange  Co.,  N.  Y. 

Named  after  Col.  George  Gibbs. 

Sassolite.  Boric  acid,  B(OH)3.  Crystals  tabular  ||  c(001)  (triclinic).  Usually  small, 
white,  pearly  scales.  G.  =  1'48.  Index,  1*46.  From  the  waters  of  the  Tuscan  lagoons 
of  Monte  Rotondo  and  Castelnuovo,  Italy.  Exists  also  in  other  natural  waters,  as  at 
Clear  Lake,  in  Lake  Co.,  Cal.  Occurs  also  abundantly  in  the  crater  of  Vulcano,  Lipari  isles. 

Hydrotalcite.  Perhaps  Al(OH)3.3Mg(OH)2.3H2O.  Lamellar-massive,  or  foliated,  some- 
what fibroiR.  H.  =2.  G.  =  2 -04-2 '09.  Color  white.  Luster  pearly.  Uniaxial,  -. 
w  =  1'47.  Occurs  at  the  mines  of  Shishimsk,  district  of  Zlatoust,  Ural  Mts.;  at  Snarum, 
Norway,  in  serpentine. 

Pyroaurite.  Perhaps  Fe(OH)3.3Mg(OH)2.3H2O.  Rhombohedral.  Thin  tabular  crys- 
tals. H.  =  2-3.  G.  =  2-07.  Luster  pearly  to  greasy.  Color  yellow  to  yellow-brown. 
Optically  — .  Occurs  at  the  Langban  iron-mine,  Wermland,  Sweden,  in  gold-like  sub- 
metallic  scales  (pyroaurite) .  From  the  Moss  mine,  Norway.  In  thin  seams  of  a  silvery 
white  color  in  serpentine  in  the  island  Haaf-Grunay,  Scotland  (igelstromite). 

Chalcophanite.  Hydrofranklinite.  (Mn,Zn)O.2MnO2.2H2O.  In  druses  of  minute 
tabular  rhombohedral  crystals;  sometimes  octahedral  in  aspect.  Also  in  foliated  aggre- 
gates; stalactitic  and  plumose.  G.  =  3 '907.  Luster  metallic,  brilliant.  Color  oluish 
black  to  iron-black.  Streak  chocolate-brown,  dull.  Occurs  at  Sterling  Hill,  near  Ogdens- 
burg,  Sussex  Co.,  N.  J.  From  Leadville,  Col. 

Hetserolite.  2ZnO.2Mn2O3.lH2O.  In  radiating  botryoidal  masses.  Black.  Brown- 
black  streak.  H.  =5.  G.  =  4 '85.  From  Franklin,  N.  J.,  and  Leadville,  Col.  (Wolf- 
tonite). 


436  DESCRIPTIVE   MINERALOGY 

ALAITE.  V^Oe.H^O.  Rare.  Found  in  dark  bluish  red  moss-like  masses  in  Alai  Mts., 
Turkestan. 

SHANYAVSKWE.  A12O8.4H2O.  Amorphous,  transparent  material  found  in  dolomite, 
near  Moscow,  Russia. 

PSILOMELANE. 

Massive  and  botryoidal;  reniform;  stalactitic.  H.  =  5-6.  G.  =  37-4-7. 
Luster  submetallic,  dull.  Streak  brownish  black,  shining.  Color  iron-black, 
passing  into  dark  steel-gray.  Opaque. 

Comp.  —  A  hydrous  manganese  manganate  in  wjrich  part  of  the  man- 
ganese is  often  replaced  by  barium  or  potassium,  perhaps  conforming  to 
H4Mn06.  The  material  is  generally  very  impure,  and  the  composition  hence 
doubtful. 

Pyr.,  etc.  —  In  the  closed  tube  most  varieties  yield  water,  and  all  lose  oxygen  on  igni- 
tion; with  the  fluxes  reacts  for  manganese.  Soluble  in  hydrochloric  acid,  with  evolution 
of  chlorine. 

Obs.  —  A  common  but  impure  ore  of  manganese;  frequently  in  alternating  layers  with 
pyrolusite.  From  Devonshire  and  Cornwall.  In  Germany  at  Ilefeld  in  the  Harz  Mts., 
at  Ilmenau,  Siegen,  etc.  From  the  Crimea,  Russia;  also  various  localities  in  India. 
Forms  mammillary  masses  at  Brandon,  etc.,  Vt.  In  Independence  Co.,  and  elsewhere  in 
Ark.  With  pyrolusite  at  Douglas,  Hants  Co.,  Nova  Scotia.  Named  from  ^i\6s,  smooth 
or  naked,  and  ne\as,  black. 

Use.  —  An  ore  of  manganese. 

The  following  mineral  substances  here  included  are  mixtures  of  various  oxides,  chiefly 
of  manganese  (MnO2,  also  MnO),  cobalt,  copper,  with  also  iron,  and  from  10  to  20  p.  c. 
water.  These  are  results  of  the  decomposition  of  other  ores  —  partly  of  oxides  and  sul- 
phides, partly  of  manganesian  carbonates,  and  can  hardly  be  regarded  as  representing 
distinct  mineral  species. 

WAD.  In  amorphous  and  reniform  masses,  either  earthy  or  compact;  also  in  crusting 
or  as  stains.  Usually  very  soft,  soiling  the  fingers;  less  often  hard  to  H.  =6.  G.  =  3'0- 
4-26;  often  loosely  aggregated,  and  feeling  very  light  to  the  hand.  Color  dull  black, 
bluish  or  brownish  black. 

BOG  MANGANESE  consists  mainly  of  oxide  of  manganese  and  water,  with  some  oxide  of 
iron,  and  often  silica,  alumina,  baryta. 

ASBOLITE,  or  Earthy  Cobalt,  contains  oxide  of  cobalt,  which  sometimes  amounts  to 
32  p.  c. 

LAMPADITE,  or  Cupreous  Manganese,  is  a  wad  containing  4  to  18  p.  c.  of  oxide  of  copper, 
and  often  oxide  of  cobalt  also. 

SKEMMATITE.  3MnO2.2Fe2O3.6H2q.  Color  black.  Streak  dark  brown.  H.  =  5'5-6. 
Fusible  to  magnetic  globule.  Alteration  product  of  pyroxmangite.  From  Iva,  Anderson 
Co.,  S.  C. 

BELDONGRITE.  6Mn306.Fe2O3.8H20.  Luster  pitchy.  Color  black.  From  Beldongri, 
District  Ndgpur,  India. 

VI.   OXYGEN-SALTS 

The  Sixth  Class  includes  the  salts  of  the  various  oxygen  acids.  These  fall 
into  the  following  seven  sections:  1.  Carbonates;  2.  Silicates  and  Titanates; 
3.  Niobates  and  Tantalates;  4.  Phosphates,  Arsenates,  etc.;  also  the 
Nitrates;  5.  Borates  and  Uranates;  6.  Sulphates,  Chromates  and  Tellurates; 
7.  Tungstates  and  Molybdates. 

1.   CARBONATES 
A.  Anhydrous  Carbonates 

The  Anhydrous  Carbonates  include  two  distinct  isomorphous  groups, 
the  CALCITE  GROUP  and  the  ARAGONITE  GROUP.  The  metallic  elements 


CARBONATES 


437 


present  in  the  former  are  calcium,  magnesium,  iron,  manganese,  zinc  and 
cobalt;  in  the  latter,  they  are  calcium,  barium,  strontium  and  lead. 
The  species  included  are  as  follows: 


1.    Calcite  Group.     RCO3.     Rhombohedral 


Calcite 
Dolomite 

Normal  Dolomite 
Ankerite 
Magnesite 

Breunnerite 
Mesitite 

Pistomesite 
Siderite 

Oligonite 
Rhodochrosite 

Manganosiderite 

Manganocalcite  pt. 
Smithsonite 

Monheimite 
Sphaerocobaltite 


CaC03 

(Ca,Mg)C03 

CaC03.MgC03 

CaC03.(Mg,Fe)C03 

MgC03 

(Mg,Fe)C03 

2MgC03.FeC03 

MgCO3.FeCO3 

FeCO3 

(Fe,Mn)C03 

MnCO3 

(Mn,Fe)C03 

(Mn,Ca)CO3 

ZnCO3 

(Zn,Fe)C03 

CoCO3 


Tri-rhombohedral 


rr'  c 

74°  55'  0-8543 

73°  45'  0-8322 

73°  48'  0-8332 

72°  36'  0-8112 

72°  46'  0  -8141 

72°  42'  0-8129 

73°    0'  0-8184 

73°    0'  0-8184 


72°  20'   0-8063 


This  list  gives  not  only  the  prominent  species  of  this  group,  but  also  some  of  the  isomor- 
phous  intermediate  compounds. 

The  CALCITE  GROUP  is  characterized  by  rhombohedral  crystallization. 
All  the  species  show,  when  distinctly  crystallized,  perfect  rhombohedral 
cleavage,  the  angle  varying  from  75°  (and  105°)  in  calcite  to  73°  (and  107°) 
in  siderite.  This  is  exhibited  in  the  table  above. 

2.   Aragonite  Group.     RC03.     Orthorhombic 


Aragonite 

Bromlite 

Witherite 

Strontianite 

Cerussite 


CaCO3 

(Ca,Ba)CO, 

BaCO3 

SrC03 

PbC03 


mm'" 
63°  48' 

62°  12' 
62°  41' 
62°  46' 


a  :  b  :  c 
0-6224  :  1  :  07206 

0-6032  :  1  :  07302 
0-6090  :  1  :  0*7239 
0-6100  :  1  :  07230 


The  species  of  the  ARAGONITE  GROUP  crystallize  in  the  orthorhombic 
system,  but  the  relation  to  those  of  the  Calcite  Group  is  made  more  close  by 
the  fact  that  the  prismatic  angle  varies  a  few  degrees  only  from  60°  (and  120°) 
and  the  twinned  forms  with  the  fundamental  prism  as  twinning-plane  are 
pseudo-hexagonal  in  character. 


438 


DESCRIPTIVE   MINERALOGY 


1.    Calcite  Group.     RC03.     Rhombohedral 
CALCITE.     Calc  Spar;  Calcareous  Spar. 
Rhombohedral.     Axis  c  =  0*8543. 

731  732  733  734 


735 


cr* 

ce, 

me, 

rr'. 

MM', 


ff', 


0001  A  1011  =  44°  36£'. 
0001  A  0112  =  26°  15'. 

1010  A  0112  =  63°  45'. 

1011  A  1101  =  74°  55'. 
4041  A  4401  =  114°  10'. 
0112  A  1012  =  45°  3' 
0554  A  5054  =  84°  324'. 
0221  A  2021  =  101°  9'. 


w',  2131  A  2311  =  75°  22'. 
wv,  2131  A  3121  =  35°  36'. 
wvi,  2131  A  1231  =  47°  1|'. 
yy't  3251  A  3521  =  70°  59'. 
yyv,  3251  A  5231  =  45°  32'. 
yy*,  3251  A  2351  =  29°  16'. 

v,     2134  A  3124  =  20°  36f  '. 

wv,  3145  A  4135  =  16°     0'. 


*  See  the  stereographic  projection,  Fig.  269,  p.  108. 


CARBONATES  439 

Habit  of  crystals  very  varied,  as  shown  in  the  figures,  from  obtuse  to  acute 
rhombohedral ;  from  thin  tabular  to  long  prismatic;  and  scalenohedral  of 
many  types,  often  highly  modified. 

Twins  (see  Figs.  419-426,  p.  168):   (1)  Tw.  pi.  c(0001),  common,  the  crys- 
tals having  the  same    vertical    axis.      (2)  Tw. 
pi.    6(0112),   very   common,    the  vertical   axes  750 

inclined  127°  29  J'  and  52°  30  J';  often  producing 
twinning  lamellae  as  in  Iceland  Spar,  which  are, 
in  many  cases,  of  secondary  origin  as  in  granular 
limestones  (Fig.  750) ;  this  twinning  may  be 
produced  artificially  (see  p.  188).  (3)  Tw.  pi. 
r(10Tl),  not  common;  the  vertical  axes  inclined 
90°  46'  and  89°  14'.  (4)  Tw.  pi.  /(0221),  rare; 
the  axes  intersect  at  angles  of  53°  46'  and 
126°  14'. 

Also  fibrous,  both  coarse  and  fine;  sometimes 
lamellar;    often  granular;   from  coarse  to  impal-  Section  of  crystalline  limestone 
pable,  and  compact  to  earthy.      Also  stalactitic,  in  polarized  light, 

tuberose,  nodular,  and  other  imitative  forms. 

Cleavage:  r(1011)  highly  perfect.  Parting  ||  e(0112)  due  to  twinning. 
Fracture  conchoidal,  obtained  with  difficulty.  H.  =  3,  but  varying  with 
the  direction  on  the  cleavage  face;  earthy  kinds  softer.  G.  =  2'714,  in  pure 
crystals,  but  varying  somewhat  widely  in  impure  forms,  as  in  those  contain- 
ing iron,  manganese,  etc.  Luster  vitreous  to  sub  vitreous  to  earthy.  Color 
white  or  colorless;  also  various  pale  shades  of  gray,  red,  green,  blue,  violet, 
yellow;  also  brown  and  black  when  impure.  Streak  white  or  grayish. 
Transparent  to  opaque. 

Optically  — .  Birefringence  very  high.  Refractive  indices  for  the  D  line : 
co  =  1-65849,  e  =  1-48625. 

Comp.  —  Calcium  carbonate,  CaC03  =  Carbon  dioxide  44'0,  lime  56*0 
=  100.  Small  quantities  of  magnesium,  iron,  manganese,  zinc,  and  lead  may 
be  present  replacing  the  calcium. 

Var.  —  The  varieties  are  very  numerous,  and  diverse  in  appearance.  They  depend 
mainly  on  the  following  points:  differences  in  crystallization  and  structural  condition, 
presence  of  impurities,  etc.,  the  extremes  being  perfect  crystals  and  earthy  massive  forms; 
also  on  composition  as  affected  by  isomorphous  replacement. 

A.  VARIETIES   BASED   CHIEFLY   UPON  CRYSTALLIZATION    AND   ACCIDENTAL   IMPURITIES 

1.  Ordinary.     In  crystals  and  cleavable  masses,  the  crystals  varying  very  widely  in 
habit  as  already  noted.     Dog-tooth  Spar  is  an  acute  scalenohedral  form;   Nail-head  Spar, 
a  composite  variety  having  the  form  suggested  by  the  name.     The  transparent  variety 
from  Iceland,  used  for  polarizing  prisms,  etc.,  is  called  Iceland  Spar  or  Doubly-refracting 
Spar.     As  regards  color,  crystallized  calcite  varies  from  the  kinds  which  are  perfectly 
clear  and  colorless  through  yellow,  pink,  purple,  blue,  to  brown  and  black.     The  color  is 
usually  pale  except  as  caused  by  impurities.     These  impurities  may  be  pyrite,  native 
copper,  malachite,  sand,  etc.;    they  are  sometimes  arranged  in  symmetrical   form,  as 
depending  upon  the  growth  of  the  crystals  and  hence  produce  many  varieties. 

Fontainebleau  limestone,  from  Fontainebleau  and  Nemours,  France,  contains  a  large 
amount  of  sand,  some  50  to  63  p.  c*  Siliceous  calcite  crystals  come  from  S.  D.,  Wy.,  Cal., 
etc. 

2.  Fibrous  and  lamellar  kinds.    Satin  Spar  is  fine  fibrous,  with  a  silky  luster;  resembles 
fibrous  gypsum,  also  called  satin  spar,  but  is  much  harder  than  gypsum  and  effervesces 
with  acids.     Lublinite  is  a  fibrous  variety,  probably  pseudomorphous  after  some  organic 
material. 


440  DESCRIPTIVE   MINERALOGY 

Argentine  is  a  pearly  lamellar  calcite,  the  lamellae  more  or  less  undulating;  color  white, 
grayish,  yellowish.  Aphrite,  in  its  harder  and  more  sparry  variety,  is  a  foliated  white 
pearly  calcite,  near  argentine;  in  its  softer  kinds  it  approaches  chalk,  though  lighter, 
pearly  in  luster,  silvery  white  or  yellowish  in  color,  soft  and  greasy  to  the  touch,  and  more 
or  less  scaly  in  structure.  Aphrite  has  been  thought  to  be  aragonite  pseudomorphous 
after  gypsum. 

3.   Granular  massive  to  cryptocrystalline  kinds:  Limestone,  Marble,  Chalk. 

Granular  limestone  or  Saccharoidal  limestone,  so  named  because  like  loaf  sugar  in  frac- 
ture, varying  from  coarse  to  very  fine  granular,  and  hence  to  compact  limestone;  colors 
are  various,  as  white,  yellow,  reddish,  green;  usually  they  are  clouded  and  give  a  handsome 
effect  when  the  material  is  polished.  When  such  limestones  are  fit  for  polishing,  or  for 
architectural  or  ornamental  use,  they  are  called  marbles.  Many  varieties  have  special 
names.  Shell-marble  consists  largely  of  fossil  shells;  Lumachelle  or  fire-marble  is  a  dark 
brown  shell-marble,  with  brilliant  fire-like  or  chatoyant  internal  reflections.  Ruin-marble 
is  a  kind  of  a  yellow  to  brown  color,  showing,  when  polished,  figures  bearing  some  resem- 
blance to  fortifications,  temples,  etc.,  in  ruins,  due  to  infiltration  of  iron  oxide,  etc. 

Lithographic  stone  is  a  very  even-grained  compact  limestone,  of  buff  or  drab  color;  as 
that  of  Solenhofen,  Bavaria.  Hydraulic  limestone  is  an  impure  limestone  which  after  igni- 
tion sets,  i.e.,  takes  a  solid  form  under  water,  due  to  the  formation  of  a  silicate.  The 
French  varieties  contain  2  or  3  p.  c.  of  magnesia,  and  10  to  20  of  silica  and  alumina  (or 
clay).  The  varieties  in  the  United  States  contain  20  to  40  p.  c.  of  magnesia,  and  12  to  30 
p.  c.  of  silica  and  alumina.  Hard  compact  limestone  varies  from  nearly  pure  white,  through 
grayish,  drab,  buff,  yellowish,  and  reddish  shades,  to  bluish  gray,  dark  brownish  gray,  and 
black,  and  sometimes  variously  veined.  Many  kinds  make  beautiful  marble  when  pol- 
ished. Red  oxide  of  iron  produces  red  of  different  shades.  Shades  of  green  are  due  to 
iron  protoxide,  chromium  oxide,  iron  silicate. 

Chalk  is  white,  grayish  white,  or  yellowish,  and  soft  enough  to  leave  a  trace  on  a  board. 
It  is  composed  of  the  shells  of  minute  sea  organisms.  Calcareous  marl  is  a  soft  earthy 
deposit,  with  or  without  distinct  fragments  of  shells;  it  generally  contains  much  clay,  and 
graduates  into  a  calcareous  clay. 

Oolite  is  a  granular  limestone,  its  grains  minute  concretions,  looking  somewhat  like  the 
roe  of  fish,  the  name  coming  from  u6i>,  egg.  Pisolite  consists  of  concretions  as  large  often 
as  a  small  pea,  or  larger,  having  usually  a  distinct  concentric  structure. 

Deposited  from  calcareous  springs,  streams,  or  in  caverns,  etc.  (a)  Stalactites  are  cal- 
careous cylinders  or  cones  that  hang  from  the  roofs  of  limestone  caverns,  and  which  are 
formed  from  the  waters  that  drip  through  the  roof;  these  waters  hold  some  calcium 
bicarbonate  in  solution,  and  leave  calcium  carbonate  to  form  the  stalactite  when  evapora- 
tion takes  place.  Stalactites  vary  from  transparent  to  nearly  opaque;  from  a  crystalline 
structure  with  single  cleavage  directions  to  coarse  or  fine  granular  cleavable  and  to  radi- 
ating fibrous;  from  a  white  color  and  colorless  to  yellowish  gray  and  brown.  (6)  Stalag- 
mite is  the  same  material  covering  the  floors  of  caverns,  it  being  made  from  the  waters 
that  drop  from  the  roofs,  or  from  sources  over  the  bottom  or  sides;  cones  of  it  sometimes 
rise  from  the  floor  to  meet  the  stalactites  above.  It  consists  of  layers,  irregularly  curved, 
or  bent.  Stalagmite,  or  a  solid  kind  of  travertine  (see  below)  when  on  a  large  scale,  is  the 
alabaster  stone  of  ancient  writers,  that  is,  the  stone  of  which  ointment  vases,  of  a  certain 
form  called  alabasters,  were  made.  A  locality  near  Thebes,  now  well  known,  was  largely 
explored  by  the  ancients,  and  the  material  has  often  been  hence  called  Egyptian  alabaster. 
It  was  also  formerly  called  onyx  and  onychites  because  of  its  beautiful  banded  structure. 
In  the  arts  it  is  often  now  called  Oriental  alabaster  or  onyx  marble.  Very  beautiful  marble 
of  this  kind  is  obtained  in  Algeria.  Mexican  onyx  is  a  similar  material  obtained  from 
lecah,  Puebla,  Mexico;  also  in  a  beautiful  brecciated  form  from  the  extinct  crater  of  Zem- 
poaltepec  in  southern  Mexico.  Similar  kinds  occur  in  Missouri,  Arizona,  San  Luis  Obispo 
Co.,  California,  (c)  Calc-sinter,  Travertine,  Calc  Tufa.  Travertine  is  of  essentially  the 
same  origin  with  stalagmite,  but  is  distinctively  a  deposit  from  springs  or  rivers,  especially 
where  m  large  deposits,  as  along  the  river  Anio,  at  Tivoli,  near  Rome,  where  the  deposit  is 
icores  ot  feet  in  thickness.  Similar  material  is  being  deposited  at  the  Mammoth  Hot 
Springs,  Yellowstone  Park,  (d)  Agaric  mineral;  Rock-milk  is  a  very  soft  white  material, 
breaking  easily  m  the  fingers,  deposited  sometimes  in  caverns,  or  about  sources  holding 
lime  in  solution,  (e)  Rock-meal  is  white  and  light,  like  cotton,  becoming  a  powder  on 
the  slightest  pressure. 

B.  VARIETIES  BASED  UPON  COMPOSITION 

These  include:  Dolomitic  calcite.  Contains  magnesium  carbonate,  thus  graduating 
toward  true  dolomite.  Also  baricalcite  (which  contains  some  BaCO3);  similarly,  stron- 


CARBONATES  441 

tianocalcite  (SrCO3),  ferrocalcite   (FeCO3),   manganocalcite   (MnCOa)   (see  under  agnolite, 
p.  582),  zincocalcite  (ZnCO3),  plumbocalcite  (PbCOs),  cobal'ocalcite  (CoCO3). 

Pyr.,  etc.  —  B.B.  infusible,  glows,  and  colors  the  flame  reddish  yellow;  after  ignition 
the  assay  reacts  alkaline;  moistened  with  hydrochloric  acid  imparts  the  characteristic 
lime  color  to  the  flame.  In  the  solid  mass  effervesces  when  moistened  with  hydrochloric 
acid,  and  fragments  dissolve  with  brisk  effervescence  even  in  cold  acid.  See  further  under 
aragonite,  p.  447. 

Diff.  —  Distinguishing  characters:  perfect  rhombohedral  cleavage;  softness,  can  be 
scratched  with  a  knife;  effervescence  in  cold  dilute  acid;  infusibility.  Less  hard  and  of 
lower  specific  gravity  than  aragonite  (which  see).  Resembles  in  its  different  varieties  the 
other  rhombohedral  carbonates,  but  is  less  hard,  of  lower  specific  gravity,  and  more 
readily  attacked  by  acid.  Also  resembles  some  varieties  of  barite,  but  has  lower  specific 
gravity;  it  is  less  hard  than  feldspar  and  harder  than  gypsum. 

Micro.  —  Recognized  in  thin  sections  by  its  low  refraction  and  very  high  birefringence, 
the  polarization  colors  in  the  thinnest  sections  attaining  white  of  the  highest  order.  The 
negative  interference  figure,  with  many  closely  crowded  colored  rings,  is  also  character- 
istic. The  rhombohedral  cleavage  is  often  shown  in  the  fine  fracture  lines;  systems  of 
twinned  lamellae  often  conspicuous  (Fig.  750),  especially  in  crystalline  limestone. 

Artif .  —  Crystals  of  calcite  are  formed  when  a  solution  of  calcium  carbonate  in  dilute 
carbonic  acid  is  evaporated  slowly  at  ordinary  temperatures.  Calcite  is  formed  when 
aragonite  is  heated,  the  transformation  being  complete  at  470°. 

Obs.  —  Calcite,  in  its  various  forms,  is  one  of  the  most  widely  distributed  of 
minerals.  Beds  of  sedimentary  limestone,  formed  from  organic  remains,  shells,  crinoids, 
corals,  etc.,  yield  on  metamorphism  crystalline  limestone  or  marble,  and  in  connection 
with  these  crystallized  calcite  and  also  deposits  in  caves  of  stalactites  and  stalagmites  often 
occur.  Common  with  the  zeolites  in  cavities  and  veins  of  igneous  rocks  as  a  result  of 
alteration,  and  similarly  though  less  abundant  with  granite,  syenite,  etc.  A  frequent 
mineral  in  metalliferous  deposits,  with  lead,  copper,  silver,  etc.  Deposited  from  lime- 
bearing  waters  as  calc  sinter,  travertine,  etc.,  especially  in  connection  with  hot  springs  as 
at  the  Mammoth  Hot  Springs  in  the  Yellowstone  region. 

Some  of  the  best  known  localities  for  crystallized  calcite  are  the  following:  Andreas^- 
berg  in  the  Harz  Mts.;  the  mines  of  Freiberg,  Schneeberg,  etc.,  in  Saxony;  Kapnik  in 
Hungary;  Aussig  in  Bohemia;  Bleiberg  in  Carinthia;  Traversella  in  Piedmont,  Italy; 
Elba.  In  England  at  Alston  Moor  and  Egremont  in  Cumberland;  Matlock,  Derbyshire; 
Beer  Alston  in  Devonshire;  at  numerous  points  in  Cornwall;  Weardale  in  Durham; 
Stank  mine,  Lancashire,  In  twin  crystals  of  great  variety  and  beauty  at  Guanajuato, 
Mexico.  The  Iceland  spar  has  been  obtained  from  Iceland  near  Helgustadir  on  the  Eske- 
fiord.  It  occurs  in  a  large  cavity  in  basalt.  The  crystals,  usually  showing  the  fundamental 
rhombohedron,  are  often  coated  with  tufts  of  stilbite. 

In  the  United  States,  crystallized  calcite  occurs  in  N.  Y.,  in  St.  Lawrence  Co.,  especially 
at  the  Rossie  lead  mine;  in  Jefferson  Co.,  near  Oxbow;  dog-tooth  spar,  in  Niagara  Co., 
near  Lockport,  with  pearl  spar,  celestite,  etc.;  in  Lewis  Co.,  at  Leyden  nd  Lowville,  and 
at  the  Martinsburg  lead  mine;  at  Anthony's  Nose  on  the  Hudson,  formerly  groups  of 
large  tabular  crystals;  twins  from  Union  Springs,  Cayuga  Co  In  N.  J.,  at  Bergen,  yel- 
low calcite  with  datolite,  etc.  In  Va.,  at  Wier's  cave,  stalactites  of  great  beauty;  also  in 
the  large  caves  of  Ky.  In  pyramidal  crystals  from  Kelly's  Island,  Lake  Erie.  At  the 
Lake  Superior  Copper  mines,  complex  crystals  often  containing  scales  of  native  copper. 
At  Warsaw,  111.,  in  great  variety  of  form,  lining  geodes  and  implanted  on  quartz  crystals; 
at  Quincy.  In  Mo.,  with  dolomite,  near  St.  Louis;  also  with  sphalerite  at  Joplin  and  other 
points  in  the  zinc  region  in  the  south-western  part  of  the  state,  the  crystals  usually  scaleno- 
hedral  and  of  a  wine-yellow  color.  Wis.,  from  Hazel  Green.  From  the  Bad  Lands, 
S.  p.  In  Nova  Scotia,  at  Partridge  Island,  a  wine-colored  calcite,  and  other  interesting 
varieties. 

Use.  —  In  the  manufacture  of  mortars  and  cements;  as  a  building  and  ornamental 
material;  as  a  flux  in  metallurgical  operations;  Iceland  spar  is  used  to  make  polarizing 
prisms;  chalk  as  a  fertilizer,  in  whitewash,  etc. 

THINOLITE.  A  tufa  deposit  of  calc  um  carbonate  occurring  on  an  enormous  scale  in 
north-western  Nev.;  also  occurs  about  Mono  Lake,  Cal.  It  forms  layers  of  interlaced 
crystals  of  a  pale  yellow  or  light  brown  color  and  often  skeleton  structure  except  when 
covered  by  subsequent  deposit  of  calcium  carbonate. 


442 


DESCRIPTIVE   MINERALOGY 


DOLOMITE.     Pearl  Spar  pt. 
Tri-rhombohedral.     Axis  c  =  0-8322. 

or    0001  A  10T1  =  43°  52'.  MM',  4041  A  4401  =  113°  53'. 

rr\  lOll  A  Ilt)l  =  73°  45'. 

Habit  rhombohedral,  usually  r(10ll)  or  M(4041);  the  presence  of  rhom- 

bohedrons   of    the  second  or  third 

751  752  series  after  the  phenacite  type  very 

characteristic.  The  r  faces  com- 
monly curved  or  made  up  of  sub- 
individuals,  and  thus  passing  into 
saddle-shaped  forms  (Fig.  752). 
Also  granular,  coarse  or  fine, 
resembling  ordinary  marble. 

Cleavage:  r(1011)  perfect. 
Fracture  subconchoidal.  Brittle. 
H.  =  3-5-4.  G.  =  2-8-2-9.  Luster  vitreous,  inclining  to  pearly  in  some  vari- 
eties. Color  white,  reddish,  or  greenish  white;  also  rose-red,  green,  brown, 
gray  and  black.  Transparent  to  translucent.  Optically  — .  w  =  1-68174. 
e  =  1-50256. 

Comp.  —  Carbonate  of  calcium  and  magnesium  (Ca,Mg)CO3;  for  nor- 
mal dolomite  CaMgC2O6  or  CaC03MgCO3  =  Carbon  dioxide  47-9,  lime  30-4, 
magnesia  21'7  =  100,  or  Calcium  carbonate  54-35,  magnesium  carbonate  45*65 
=  100.  Varieties  occur  in  which  the  ratio  of  the  two  carbonates  varies  from 
1:1.  The  carbonates  of  iron  and  manganese  also  frequently  enter  replacing 
the  magnesium  carbonate  and  grading  to  ankerite ;  rarely  cobalt  and  zinc 
carbonates. 

Pyr.t  etc.  —  B.B.  acts  like  calcite.  In  solution  gives  tests  for  magnesium  and  usually 
for  iron.  Fragments  thrown  into  cold  acid,  unlike  calcite,  are  only  very  slowly  acted  upon, 
if  at  all,  while  in  powder  in  warm  acid  the  mineral  is  readily  dissolved  with  effervescence. 
The  ferriferous  dolomites  become  brown  on  exposure. 

Diff.  —  Resembles  calcite  (see  p.  441),  but  generally  to  be  distinguished  in  that  it  does 
not  effervesce  readily  in  the  mass  in  cold  acid. 

Artif.  —  Artificial  dolomite  has  been  formed  in  several  ways.  The  results  of  many  ex- 
periments would  indicate  that  heat  and  pressure  are  favorable  for  its  formation.  Sea 
water  in  contact  with  calcium  carbonate  when  heated  in  a  sealed  tube  produced  dolomite. 
It  has  been  observed  that  such  reactions  take  place  more  readily  with  aragonite  than 
with  calcite,  indicating  the  possibility  of  coral  deposits  (aragonite)  being  transformed 
into  dolomite. 

Micro.  —  Similar  to  calcite  in  thin  sections  except  that  it  more  often  shows  crystal 
outlines  and  less  commonly  polysynthetic  twinning. 

Obs.  —  Massive  dolomite  constitutes  extensive  strata,  called  limestone  strata,  in  various 
regions,  as  in  the  dolomite  region  of  the  southern  Tyrol.  Crystalline  and  compact  varieties 
are  often  associated  with  serpentine  and  other  magnesian  rocks,  and  with  ordinary  lime- 
stones. Dolomite,  as  a  rock,  is  of  secondary  origin,  having  been  transformed  from  ordinary 
limestone  by  the  action  of  solutions  containing  magnesium.  This  change,  called  dolomiti- 
zaiion,  may  take  place  in  various  ways.  The  more  favorable  conditions  would  involve 
heat,  pressure,  high  magnesium  content  of  waters  and  long  periods  of  time.  Consequently 
the  older  and  more  deeply  buried  in  the  earth's  crust  the  greater  is  the  probability  of  a  lime- 
stone being  converted  into  dolomite.  Dolomite  is  also  commonly  a  vein  mineral,  frequently 
occurring  with  various  metallic  ores.  Some  prominent  localities  are:  Leogang  in  Salzburg, 
Austria;  Schemnitz  and  Kapnik  in  Hungary;  Freiberg  in  Saxony,  Germany.  In  Switzer- 
land, at  Bex,  in  crystals;  also  in  the  Binnental;  Traversella  in  Piedmont  and  Campolongo, 
Italy.  In  unusual  dark  colored  crystals  from  Teruel,  Spain. 

In  the  United  States,  in  Ver.,  at  Roxbury.  In  N.  J.,  at  Hoboken.  In  N.  Y.  at  Lock- 
port,  Niagara  Falls,  etc.;  at  the  Tilly  Foster  iron  mine,  Brewster,  Putnam  Co.,  with  mag- 
netite, chondrodite.  In  Pa.  at  Phoenixville.  In  saddle-shaped  crystals  with  the  sphalerite 


CARBONATES  443 

of  Joplin,  Mo.  In  N.  C.  at  Stony  Point,  Alexander  Co.  In  fine  crystals  from  Alamosa, 
Alaska. 

Named  after  Dolomieu  (1750-1801),  who  announced  some  of  the  marked  characteristics 
of  the  rock  in  1791  —  its  not  effervescing  with  acids,  while  burning  like  limestone,  and 
solubility  after  heating  in  acids. 

Use.  —  As  a  building  and  ornamental  stone;  for  the  manufacture  of  certain  cements; 
for  the  production  of  magnesia  used  in  the  preparation  of  refractory  linings  in  metallurgical 
furnaces . 

Ankerite.  CaCO3.(Mg,Fe,Mn)CO3,_or  for  normal  ankerite  2CaCO3.MgCO3.FeCO3. 
In  rhombohedral  crys  als;  rr'  1011  A  1101  =73°  48'  also  crystalline  massive,  granular, 
compact.  G.  =  2  -95-31.  Color  white,  gray,  reddish.  Occurs  with  siderite  at  the  Styrian 
mines.  From  Traversella,  Italy.  With  the  hematite  of  northern  New  York/ 

MAGNESITE. 

Rhombohedral  Axis:  c  =  0-8112.  rr'  1011  A  TlOl  =  72°  36'.  Crystals 
rare,  usually  rhombohedral,  also  prismatic.  Commonly  massive;  granular 
cleavable  to  very  compact;  earthy. 

Cleavage:  r(1011)  perfect.  Fracture  flat  conchoidal.  Brittle.  H.  =  3-5- 
4-5.  G.  =  3-0-3-12,  cryst.  Luster  vitreous;  fibrous  varieties  sometimes 
silky.  Color  white,  yellowish,  or  grayish  white,  brown.  Transparent  to 
opaque.  Optically  — .  co  =  1*717.  c  =  1*515. 

Comp.  —  Magnesium  carbonate,  MgC03  =  Carbon  dioxide  52'4,  mag- 
nesia 47-6  =  100.  Iron  carbonate  is  often  present. 

Breunnerite  contains  several  p.  c.  of  FeO;  G.  =  3-3 '2;  white,  yellowish,  brownish, 
rarely  black  and  bituminous;  often  becoming  brown  on  exposure,  and  hence  called  Brown 
Spar. 

Pyr.,  etc.  —  B.B.  resembles  calcite  and  dolomite,  and  like  the  latter  is  but  slightly  acted 
upon  by  cold  acids;  in  powder  is  readily  dissolved  with  effervescence  in  warm  hydro- 
chloric acid.  In  solution  gives  strong  test  for  magnesium  with  little  or  no  calcium. 

Obs.  —  Found  as  a  secondary  mineral  formed  by  the  alteration  of  various  magnesian 
minerals;  in  talcose  schist,  serpentine  and  other  magnesian  rocks,  also  gypsum;  as  veins 
in  serpentine,  or  mixed  with  it  so  as  to  form  a  variety  of  verd-antique  marble.  Occurs 
at  Hrubschiitz  in  Moravia;  at  Kraubat  and  Maria-ZeU,  Styria;  Greiner  in  the  Zillertal, 
Tyrol,  Austria;  Snarum,  Norway. 

In  the  United  States,  in  Mass.,  at  Bolton;  at  Roxbury,  veining  serpentine;  in  Md.,  at- 
Barehills,  near  Baltimore;  in  Pa.,  in  crystals,  at  West  Goshen,  Chester  Co.,  near  Texas, 
Lancaster  Co.;  in  Cal.  it  is  mined  in  Tulare,  Kern,  Santa  Clara,  Sonoma  Cos.  and  else- 
where. A  white  saccharqidal  magnesite  resembling  statuary  marble  has  been  found  as 
loose  blocks  on  an  island  in  the  St.  Lawrence  River,  near  the  Thousand  Island  Park.  In 
small  prismatic  crystals  from  Orangedale,  Nova  Scotia. 

Use.  —  In  the  preparation  of  magnesite  brick  for  the  linings  of  metallurgical  furnaces; 
in  the  manufacture  of  various  chemical  compounds,  as  epsom  salts,  magnesia,  etc. 

Intermediate  between  magnesite  and  siderite  are: 

MESITITE.  2MgCO3.FeCO3.  rr'  lOll  A  TlOl  =  72°  46'.  G.  =  3-35-3-36.  Usually 
in  flat  rhombohedrons  (e,  0112)  with  rounded  faces.  Traversella,  Piedmont,  Italy. 

PISTOMESITE.  MgCOs.FeCOs  =  Magnesium  carbonate  42'0,  iron  carbonate  58'0  =  100. 
rr'  1011  A  TlOl  =  72°  42'.  G.  =  3 '42.  Thurnberg,  Salzburg,  Austria;  also  Traversella, 
Italy. 

SIDERITE.     Chalybite,  Spathic  Iron. 

Rhombohedral.     Axis  c  =  0-8184. 

•cr,  0001  A  lOTl  =  43°  23'.  rr',  1011  A  1101  =  73°  0'. 
cM,  0001  A  4041  =  75°  11'.  MM',  4041  A  4401  =  113°  42'. 
cs,  0001  A  0551  =  78°  3'.  ss',  0551  A  5051  =  115°  50'. 
cd,  0001  A  0881  =  82°  28'.  dd',  0881  A  8081  =  118°  18£'. 

Crystals  commonly  rhombohedral  r  (1011)  or  e(0112)  the  faces,  often 
curved  and  built  up  of  sub-individuals  like  dolomite.  Often  cleavable  massive 


444  DESCRIPTIVE  MINERALOGY 

to  coarse  or  fine  granular.  Also  in  botryoidal  and  globular  forms,  subfibrous 
within,  occasionally  silky  fibrous;  compact  and  earthy. 

Cleavage:  r(1011)  perfect.  Fracture  uneven  or  subconchoidal.  Brittle. 
H.  =  3'5-4.  G.  =  3-83-3-88.  Luster  vitreous,  inclining  to  pearly.  Color 
ash-gray,  yellowish  gray,  greenish  gray,  also  brown  and  brownish  red,  rarely 
green;  and  sometimes  white.  Streak  white.  Translucent  to  subtranslucent. 
Optically  -.  «  =  1'873.  €  =  1-633. 

Comp.  —  Iron  protocarbonate,  FeC03  =  Carbon  dioxide  37-9,  iron  pro- 
toxide 62-1  =  100  (Fe  =  48'2  p.  c.).  Manganese  may  be  present  (as  in 
oligonite,  manganospherite) ,  also  magnesium  and  calcium. 

Pyr.,  etc.  —  In  the  closed  tube  decrepitates,  gives  off  CO2,  blackens  and  becomes  mag- 
netic. B.B.  blackens  and  fuses  at  4 '5-5.  With  the  fluxes  reacts  for  iron,  and  with  soda 
and  niter  on  platinum  foil  generally  gives  a  manganese  reaction.  Only  slowly  acted  upon 
by  cold  acid,  but  dissolves  with  brisk  effervescence  in  hot  hydrochloric  acid.  Exposure  to 
the  atmosphere  darkens  its  color,  rendering  it  often  of  a  blackish  brown  or  brownish  red 
color. 

Diff.  —  Characterized  by  rhombohedral  form  and  cleavage.  Specific  gravity  higher 
than  that  of  calcite,  dolomite  and  ankerite.  Resembles  some  sphalerite  but  lacks  the 
resinous  luster,  differs  in  cleavage  angle  and  yields  COa  (not  H^S)  with  hydrochloric  acid. 

Obs.  — ,Siderite  may  form  as  "  bog  ore  "  by  the  action,  out  of  contact  with  the  air,  of 
organic  matter  in  a  bicarbonate  solution.  It  may  also  be  formed  by  the  action  of  ferrous 
solutions  upon  limestones.  It  frequently  occurs  also  as  a  vein  mineral.  It  occurs  in  many 
of  the  rock  strata,  in  gneiss,  mica  slate,  clay  slate,  and  as  clay  iron-stone  in  connection  with 
the  Coal  formation  and  many  other  stratified  deposits.  It  is  often  associated  with  metallic 
ores.  At  Freiberg,  Saxony,  it  occurs  in  silver  mines.  In  Cornwall  it  accompanies  tin.  It 
is  also  found  accompanying  copper  and  iron  pyrites,  galena,  chalcocite,  tetrahedrite.  Occa- 
sionally it  is  to  be  met  with  in  trap  rocks  as  spherosiderite  in  globular  concretions.  Exten- 
sive deposits  occur  in  the  Eastern  Alps,  in  Styria  and  Carinthia  at  Tavetsch,  Switzerland. 
At  Harzgerode  and  elsewhere  in  the  Harz  Mts.,  it  occurs  in  fine  crystals  in  gray-wacke; 
also  in  Cornwall  of  varied  habit  at  many  localities;  at  Alston-Moor,  and  Tavistock,  Devon- 
shire. In  large  rhombohedrons  from  Allevard,  France.  Fine  cleavage  masses  occur  with 
cryolite  in  Greenland. 

In  the  United  States,  in  Ver.,  at  Plymouth.  In  Mass.,  at  Sterling.  In  Conn.,  at  Rox- 
bury,  an  extensive  vein  in  quartz,  traversing  gneiss.  In  N.  Y.,  a  series  of  deposits  occur  in 
Columbia  Co.;  at  the  Rbssie  iron  mines,  St.  Lawrence  Co.  In  N.  C.,  at  Fentress  and  Har- 
lem mines.  The  argillaceous  carbonate,  in  nodules  and  beds  (clay  ironstone),  is  abundant 
in  the  coal  regions  of  Pa.,  Ohio,  and  many  parts  of  the  country.  In  a  clay-bed  under  the 
Tertiary  along  the  west  side  of  Chesapeake  Bay  for  50  m. 

Use.  —  An  ore  of  iron. 

RHODOCHROSITE.     Dialogite. 

Rhombohedral.  Axis  c  =  0-8184,  rr'  1011  A  TlOl  =_73°  0'.  Distinct 
crystals  not  common;  usually  the  rhombohedron  r(1011);  also  e(0112), 
with  rounded  striated  faces.  Cleavable,  massive  to  granular-massive  and 
compact.  Also  globular  and  botryoidal,  with  columnar  structure,  sometimes 
indistinct;  incrusting. 

Cleavage:  r(10Tl)  perfect.  Fracture  uneven.  Brittle.  H.  =  3-5-4-5. 
G.  =  3-45-3*60  and  higher.  Luster  vitreous,  inclining  to  pearly.  Color 
shades  of  rose-red;  yellowish  gray,  fawn-colored,  dark  red,  brown.  Streak 
white.  Translucent  to  subtranslucent.  Optically  -.  co  =  1-820.  e  =  1*600. 

Comp.  —  Manganese  protocarbonate,  MnCO3  =  Carbon  dioxide  38'3, 
manganese  protoxide  61-7  =  100.  Iron  carbonate  is  usually  present  even  up 
to  40  p.  c  ,  as  in  manganosiderite;  sometimes  the  carbonate  of  calcium,  as  in 
manganocalcite,  also  magnesium,  zinc,  and  rarely  cobalt. 


green  manganate. 


CARBONATES  445 

effervescence  in  warm  hydrochloric  acid.  On  exposure  to  the  air  changes  to  brown,  and 
some  bright  rose-red  varieties  become  paler. 

Diff.  —  Characterized  by  its  pink  color,  rhombohedral  form  and  cleavage,  effervescence 
in  acids. 

Obs.  —  Occurs  commonly  in  veins  along  with  ores  of  silver,  lead  and  copper,  and  with 
other  ores  of  manganese.  Found  at  Schemnitz  and  Kapnik  in  Hungary ;  Nagyag  in  Tran- 
sylvania; ponite  is  a  ferriferous  variety  from  Roumania;  in  Germany  at  Freiberg  in  Sax- 
ony; at  Diez  near  Oberneisen  in  Nassau;  at  Daaden,  Rheinprovinz ;  in  Belgium  at 
Moet-Fontaine  in  the  Ardennes.  A  variety  containing  45  per  cent  of  zinc  carbonate  from 
Rosseto,  Elba,  has  been  called  zincorodochrosite.  In  the  United  States  at  Branchville, 
Conn.;  in  N.  J.,  with  franklinite  at  Mine  Hill,  Franklin  Furnace.  In  Col.,  at  the  John 
Reed  mine,  Alicante,  Lake  Co.,  in  beautiful  clear  rhombohedrons ;  also  at  the  Oulay  mine, 
near  Lake  City  and  Alma,  Park  Co.;  in  Chaff ee,  Gilpin  and  Ouray  Cos.  In  Mon.,  at  Butte 
City.  Abundant  at  the  silver  mines  of  Austin,  Nev.  At  Placentia  Bay,  Newfoundland. 

Named  rhodochrosite  from  podov,  a  rose,  and  xpoxris,  color;  and  dialogite,  from  5ux\oyrj, 
doubt. 

Use.  —  A  minor  ore  of  manganese. 

SMITHSONITE.     Calamine  pt.     Dry-bone  ore  Miners. 

Rhombohedral.  Axis  c  =  0-8063.  rrf  lOll  A  IlOl  =  72°  20'.  Rarely 
well  crystallized;  faces  r(1011)  generally  curved  and  rough.  Usually  reni- 
form,  botryoidal,  or  stalactitic,  and  in  crystalline  incrustations;  also  granular, 
and  sometimes  impalpable,  occasionally  earthy  and  friable. 

Cleavable:  r(1011)  perfect.  Fracture  uneven  to  imperfectly  conchoidal. 
Brittle.  H.  =  5.  •  G.  =  4*30-4 '45.  Luster  vitreous,  inclining  to  pearly. 
Streak  white.  Color  white,  often  grayish,  greenish,  brownish  white,  some- 
times green,  blue  and  brown.  Subtransparent  to  translucent.  Optically  — . 
co  =  1-818.  e  -  1-618. 

Comp.  —  Zinc  carbonate,  ZnCO3  =  Carbon  dioxide  35-2,  zinc  protoxide 
64-8  =  100.  Iron  carbonate  is  often  present  (as  in  monheimite) ',  also  manga- 
nese and  cobalt  carbonates;  further  calcium  and  magnesium  carbonates  in 
traces;  rarely  cadmium  and  indium. 

Pyr.,  etc.  —  In  the  closed  tube  loses  carbon  dioxide,  and,  if  pure,  is  yellow  while  hot 
and  white  on  cooling.  B.B.  infusible,  giving  characteristic  zinc  flame;  moistened  with  co- 
balt solution  and  heated  in  O.F.  gives  a  green  color  on  cooling.  With  soda  on  charcoal 
coats  the  coal  with  the  oxide,  which  is  yellow  while  hot  and  white  on  cooling;  this  coating, 
moistened  with  cobalt  solution,  gives  a  green  color  after  heating  in  O.F.  Soluble  in 
hydrochloric  acid  with  effervescence. 

Diff.  —  Distinguished  from  calamine,  which  it  often  closely  resembles,  by  its  efferves- 
cence in  acids. 

Obs.  —  Found  both  in  veins  and  beds,  especially  in  company  with  galena  and  sphalerite; 
also  with  copper  and  iron  ores.  It  usually  occurs  in  calcareous  rocks,  and  is  generally  asso- 
ciated with  calamine,  and  sometimes  with  limonite.  It  frequently  replaces  limestone,  pseu- 
domorphs  after  calcite  crystals  being  often  observed.  Commonly  a  secondary  mineral  and 
is  often  produced  by  the  action  of  carbonated  waters  upon  zinc  sulphide.  Often  is  in  a 
porous,  honey-comb-like  material,  known  commonly  as  "dry-bone"  ore. 

Found  at  Nerchinsk  in  Siberia;  at  Dognaczka  in  Hungary;  Bleiberg  and  Raibel  in 
Carinthia;  Wiesloch  in  Baden  and  at  AJtenberg,  Germany.  Moresnet  in  Belgium  and 
Altenberg.  In  the  province  of  Santander,  Spain,  at  Puente  Viesgo.  In  England,  at 
Roughten  Gill,  Alston  Moor,  near  Matlock,  in  the  Mendip  Hills,  and  elsewhere;  in  Ireland, 
at  Donegal.  At  Laurion,  Greece,  varieties  of  many  colors;  from  Sardinia.  From  Broken 
Hill,  New  South  Wales. 

In  the  United  States,  in  Pa.,  at  Lancaster  abundant,  the  variety  called  "dry-bone";  at 
the  Ueberroth  mine,  near  Bethlehem,  in  scalenohedrons.  In  Wis.,  at  Mineral  Point, 
Shullsburg,  etc.,  pseudomorphs  after  sphalerite  and  calcite.  In  la.,  at  Swing's  diggings, 
N.  W.  of  Dubuque,  etc.  In  south-western  Mo.,  associated  with  sphalerite  and  calamine. 
In  Ark.,  at  Calamine,  Lawrence  Co.;  in  Marion  Co.  A  pink  cobaltiferous  variety  occurs 
at  Boleo,  Lower  California.  In  N.  M.  from  Socorro  Co.  and  in  translucent  green  botryoidal 
masses  from  Kelly.  In  Tooele  Co.,  Utah. 


446 


DESCRIPTIVE   MINERALOGY 


Named  after  James  Smithson  (1754-1829),  who  founded  the  Smithsonian  Institution  in 
Washington.  The  name  calamine  is  frequently  used  in  England,  cf.  calamme,  p.  539. 

Use.  —  An  ore  of  zinc. 

Sphserocobaltite.  Cobalt  protocarbonate,  CoCO3.  Rhombohedral  In  small  spheri- 
cal masSs  with  crystalline  surface,  rarely  in  crystals.  G.  =  4 '02-4-13.  Color  rose-red. 
From  Schneeberg,  Saxony.  From  Boleo,  Lower  California. 


2.   Aragonite  Group.     RC03.     Orthorhombic 

For  list  of  species,  see  p.  437. 

ARAGONITE. 

Orthorhombic.     Axes  a  :  b  :  c  =  0'62244  : 1  :  072056. 
mm"',  110  A  110  =  63°  48'. 
kk'       Oil  A  Oil  =  71°  33'. 
pp'       111  A  111  =  86°  24£'. 
pp"',    111  A  111  =  50°  27'. 

Crystals  often  acicular,  and  characterized  by  the  presence  of  acute  domes 
or  pyramids.    Twins:  tw.  pi.  ra(110)  commonly  repeated,  producing  pseudo- 


763  ' 


754 


755 


756 


757 


\ 


m 


\ 


hexagonal  forms  (see  Figs.  755-757) .  Also  globular,  renif orm,  and  coralloidal 
shapes;  sometimes  columnar,  straight  or  divergent;  alsostalactitic;  incrusting. 

Cleavage:  6(010)  distinct;  also  ra(110);  fc(Oll)  imperfect.  Fracture 
subconchoidal.  Brittle.  H.  =  3'5^.  G.  =  2*93-2-95.  Luster  vitreous, 
inclining  to  resinous  on  surfaces  of  fracture.  Color  white;  also  gray,  yel- 
low, green  and  violet;  streak  uncolored.  Transparent  to  translucent.  Op- 
tically -.  Ax.  pi.  ||  a(100).  Bx  J_  c(001).  Dispersion  p  >  v  small.  2  E 
=  30°  54'.  a  =  1-531.  0  =  1-682.  7  =  1-686. 

Comp.  —  Calcium  carbonate,  CaCO3  =  Carbon  dioxide  44'0,  lime  56*0 
=  100.  Some  varieties  contain  a  little  strontium,  others  lead,  and  rarely  zinc. 

Aragonite  changes  to  calcite  at  470°. 

Var.  —  Ordinary,  (a)  Crystallized  in  simple  or  compound  crystals,  the  latter  much  the 
most  common;  often  in  radiating  groups  of  acicular  crystals.  Columnar;  also  fine  fibrous 
with  silky  luster,  (c)  Massive. 

Stalactitic  or  stalagmitic:  Either  compact  or  fibrous  in  structure,  as  with  calcite;  Spru- 
delstein  is  stalactitic  from  Carlsbad,  Bohemia.  Coralloidal:  In  groupings  of  delicate  inter- 
lacing and  coalescing  stems,  of  a  snow-white  color,  and  looking  a  little  like  coral;  often  called 
Flosferri.  Tarnowitzite  is  a  kind  containing  lead  carbonate  (4  to  8  p.  c.),  from  Tarnowitz 
in  Silesia;  with  G.  =  2 '99.  Zeyringite  is  a  calcareous  sinter,  probably  aragonite,  colored 
greenish  white  or  sky-blue  with  nickel,  from  Zeyring,  Styria.  Nicholsonite  is  aragonite 
containing  zinc  from  Leadville,  Col.,  and  the  Tintic  District,  Utah. 


CARBONATES  447 

Pyr.,  etc.  —  B.B.  whitens  and  falls  to  pieces,  and  sometimes,  when  containing  strontia, 
imparts  a  more  intensely  red  color  to  the  flame  than  lime;  otherwise  reacts  like  calcite. 
When  immersed  in  cobalt  nitrate  solution  powder  turns  lilac  and  the  color  persists  on  boiling 
while  calcite  under  like  conditions  remains  uncolored  or  becomes  blue  on  long  boiling.  It 
is  stated  that  these  tests  are  not  always  strictjy  reliable. 

DM.  —  Distinguished  from  calcite  by  higher  specific  gravity  and  absence  of  rhombo- 
hedral  cleavage;  from  the  zeolites  (e.g.,  natrolite),  etc.,  by  effervescence  in  acid.  Stron- 
tianite  and  witherite  are  fusible,  higher  in  specific  gravity  and  yield  distinctive  flames  B.B. 
The  resinous  luster  on  fracture  surfaces  is  to  be  noted. 

Artif .  —  Aragonite  will  form  when  solutions  of  calcium  carbonate  are  evaporated  at 
temperatures  from  80°  to  100°;  it  will  form  at  lower  temperatures  if  the  solution  contains 
some  sulphate  or  small  amounts  of  the  carbonates  of  strontium  or  lead. 

Obs.  —  The  most  common  repositories  of  aragonite  are  beds  of  gypsum;  also  beds  of 
iron  ore,  as  the  Styrian  mines,  where  it  occurs  in  coralloidal  forms,  and  is  denominated  flos- 
ferri,  "flower  of  iron"',  in  cavities  in  basalt  and  lavas ;  often  associated  with  copper  and  iron 
pyrites,  galena,  and  malachite.  It  constitutes  the  pearly  layer  of  shells  and  the  skeleton 
material  of  corals. 

First  discovered  in  Aragon,  Spain  (whence  its  name),  at  Molina  and  Valencia,  in  six- 
sided  prisms,  with  gypsum,  similarly  at  Dax,  France.  Prominent  localities  are  Bilin, 
Bohemia;  Racanbunto,  Silesia;  Leogang  in  Salzburg,  Austria;  Herrengrund,  Hungary; 
with  sulphur  in  Sicily  in  fine  prisms;  also  at  Alston  Moor  and  elsewhere,  England,  fine 
frequently  replaced  by  native  copper  from  Coro-Coro,  Bolivia. 


In  fibrous  crusts  at  Hoboken,  N.  J.;  at  Edenville  and  Rossie,  N.  Y.;  Wood's  Mine, 
Lancaster  Co.,  Pa.;  Warsaw,  111.,  lining  geodes;  Mine-la-Motte,  Mo.,  in  crystals.  Flos- 
ferri  in  the  Organ  Mts.,  N.  M.;  from  Bisbee,  Ariz. 

Ktypeite  is  calcium  carbonate  in  the  form  of  pisolites  from  Carlsbad,  Bohemia,  and 
Hammam-Meskoutine,  Algeria.  G.  =  2'58-270.  Decrepitates  when  heated  and  changes 
to  calcite. 

WITHERITE. 

Orthorhombic.  Axes  a  :  b  :  c  =  0-6032  :  1  :  07302.  Crystals  always  re- 
peated twins,  simulating  hexagonal  pyramids.  Also  massive,  columnar  or 
granular. 

Cleavage:  6(010)distinct;  m(110)  imperfect.  Fracture  uneven.  Brittle. 
H.  =  3—3*75.  G.  =  4'27-4'35.  Luster  vitreous,  inclining  to  resinous  on  sur- 
faces of  fracture.  Color  white,  yellowish,  grayish.  Streak  white.  Subtrans- 
parent  to  translucent.  Optically  -.  a  =  1'529.  0  =  1-676.  7  =  1-677. 

Comp.  —  Barium  carbonate,  BaCO3  =  Carbon  dioxide  22*3,  baryta  77 -7 
=  100. 

Pyr.,  etc.  —  B.B.  fuses  at  2  to  a  bead,  coloring  the  flame  yellowish  green;  after  fusion 
reacts  alkaline.  B.B.  on  charcoal  with  soda  fuses  easily,  and  is  absorbed  by  the  coal.  Solu- 
ble in  dilute  hydrochloric  acid;  this  solution,  even  when  very  much  diluted,  gives  with  sul- 
phuric acid  a  white  precipitate  which  is  insoluble  in  acids. 

Diff.  —  Distinguished  by  its  high  specific  gravity;  effervescence  in  acid;  green  colora- 
tion of  the  flame  B.B.  Barite  is  insoluble  in  hydrochloric  acid. 

Obs.  —  Occurs  at  Alston  Moor  in  Cumberland,  with  galena;  at  Fallowfield  near  Hex- 
ham  in  Northumberland;  Tarnowitz  in  Silesia.  Leogang  in  Salzburg,  Austria.  Near 
Lexington,  Ky.,  with  barite.  In  a  silver-bearing  vein  near  Rabbit  Mt.,  Thunder  Bay,  Lake 
Superior.  From  Tsubaki  mine,  Prov.  Ugo,  Japan. 

Use.  —  A  minor  source  of  barium  compounds. 

Bromlite.  (Ba,Ca)CO3.  In  pseudohexagonal  pyramids  (Figs.  611,  612,  p.  299).  In- 
dices, 1*525-1 '670.  Bromley  Hill,  near  Alston,  Cumberland,  England. 

STRONTIANITE. 

Orthorhombic.     Axes  a  :  b  :  c  =  0-6090  :  1  :  07239. 

Crystals  often  acicular  or  acute  spear-shaped,  like  aragonite.  Twins:  tw. 
pi.  m(110)  common.  Also  columnar,  fibrous  and  granular. 

Cleavage:  ra(110)  nearly  perfect;  6(010)  in  traces.  Fracture  uneven. 
Brittle.  H.  =  3-5-4.  G.  =  3-680-3-714.  Luster  vitreous;  inclining  to 


448 


DESCRIPTIVE   MINERALOGY 


resinous  on  faces  of  fracture.  Color  pale  asparagus-green,  apple-green;  also 
white,  gray,  yellow,  and  yellowish  brown.  Streak  white.  Transparent  to 
translucent.  Optically  -.  Ax.  pi.  ||  Z>(&10).  Bx  _L  c(001).  Dispersion 
p  <  v  small.  2Er  =  12°  17'.  a  =  t'52f6.  (3  =  T667.  y  =  T667. 

Comp.  —  Strontium  carbonate,  SrCOs  =  Carbon  diozide  29*9,  strontia 
70-1  =  100.     A  little  calcium  is  sometimes  present. 

Pyr.,  etc.  —  B.B.  swells  up,  throws  out  minute  sprouts,  fuses  only  on  the  thin  edges,  and 
colors  the  flame  strontia-red;  the  assay  reacts  alkaline  after  ignition.  Moistened  with 
hydrochloric  acid  and  treated  either  B.B.  or  in  the  naked  lamp  gives  an  intense  red  color. 
Soluble  in  hydrochloric  acid;  the  mediumly  dilute  solution  when  treated  with  sulphuric 
acid  gives  a  white  precipitate. 

Diff.  —  Differs  from  related  minerals,  not  carbonates,  in  effervescing  with  acids;  has  a 
higher  specific  gravity  than  aragonite  and  lower  than  witherite;  colors  the  flame  red  B.B. 

Obs.  —  Occurs  at  Strontian  in  Argyllshire  and  in  Yorkshire,  England;  Claustal  in  the 
Harz  Mts.,  Germany;  Braunsdorf,  near  Freiberg,  Saxony;  Leogang  in  Salzburg,  Austria; 
near  Brixlegg,  Tyrol,  Austria  (calciostrontianite) ;  in  Westphalia,  Germany  in  fine  crystals 
near  Hamm,  and  at  the  Wilhelmine  mine  near  Altahlen. 

In  the  United  States,  occurs  in  N.  Y.  at  Schoharie,  at  Muscalonge  Lake,  Chaumont 
Bay  and  Theresa,  in  Jefferson  Co.;  Mifflin  Co.,  Pa. 

Use.  —  A  minor  source  of  strontium  compounds. 

CERUSSITE.    White  Lead  Ore. 


Orthorhombic. 
758 


Axes  a  :  6  :  c  =  0-60997  :  1  :  072300. 

mm'",  110  A  110  =  62°  46'. 

759  760  J*',      oil  A  Oil  =  71°  44'. 

ii',        021  A  021  =  110°  40'. 
cp,       001  A  111  =  54°  14'. 
pp'j      111  A  111  =  87°  42'. 
pp'",    111  A  111  =  49°  59£'. 

Simple  crystals  often 
tabular  ||  6(010),  pris- 
matic ||  caxis;  also  pyr- 
amidal. Twins:  tw.  pi. 
m(110)  very  common, 
contact-  and  penetration- 
twins,  often  repeated 
yielding  six-rayed  stellate  groups.  Crystals  grouped  in  clusters,  and 
aggregates.  Rarely  fibrous,  often  granular  massive  and  compact-  earthv 
Sometimes  stalactitic. 

Cleavage:    m(110)   and  {(021)   distinct;    6(010)   and  z(012)   in  traces. 
Fracture  conchoidal.     Very  brittle.    H.  =  3-3-5.    G.  =  6-46-6-574.    Luster 
adamantine,  inclining  to  vitreous,  resinous,  or  pearly;  sometimes  submetallic. 
Color  white   gray,  grayish  black,  sometimes  tinged  blue  or  green  (copper); 
streak  uncolored.     Transparent  to  subtranslucent.     Optically-.    Ax.  nil 
6(010).     Bx  _L  c(001).     Dispersion  p  >  v  large.     2  V  =  8°  14'.     a  =  1-804 
p  =  2*076.    7  =  2-078. 

Q  rF°miPnVT~ Lead   carbonate>  pbC03  =  Carbon  dioxide  16-5,  lead   oxide 

oo.o  =  1UU- 


at 


- 


£ecrepitates,  loses  carbon  dioxide,  turns  first  yellow,  and 

n  yellow  on  coolin^     B'B'  on  cha™al 
d'     Soluble  in  dilute  nitric  acid  with 

Aiding 


CAEBONATES  449 

Artif .  —  Cerussite  has  been  produced  artificially  by  the  slow  diffusion  of  a  carbonate 
solution  into  a  lead  solution  through  a  porous  membrane;  by  the  action  of  a  carbonate 
solution  upon  a  lead  plate. 

Obs.  —  A  secondary  mineral  occurring  in  connection  with  other  lead  minerals,  and  is 
formed  from  galena,  which,  as  it  passes  to  a  sulphate,  may  be  changed  to  carbonate  by 
means  of  solutions  of  calcium  bicarbonate.  It  is  tound  in  Germany  at  Johanngeorgenstadt 
in  beautiful  crystals;  Friedrichssegen,  Nassau;  Badenweiler,  Baden;  at  Claustal  in  the 
Harz  Mts.  Other  important  localities  are  Monte  Poni,  Sardinia;  at  Bleiberg  in  Carinthia; 
at  Mies  and  Pfibram,  Bohemia;  in  England,  in  Cornwall;  at  East  Tamar  mine,  Devonshire; 
near  Matlock  and  Wirksworth,  Derbyshire;  at  Leadhill  and  Wanlockhead,  Scotland. 
Fine  crystals  from  Broken  Hill,  New  South  Wales. 

Found  in  Pa.,  at  Phenixyille.  In  Va.,  at  Austin's  mines,  Wythe  Co.  In  N.  C.,  in  King's 
mine.  In  lead  mines  of  Wis.  but  rarely  in  crystals;  at  Hazelgreen,  crystals  coating  galena. 
In  Col.,  at  Leadyille,  and  elsewhere.  In  Ariz.,  at  the  Flux  mine,  Pima  Co.,  in  large  crys- 
talline masses;  in  crystals  at  the  Red  Cloud  mine,  Yuma  Co.  In  Utah  from  Flagstaff 
mine;  in  Idaho  at  Wardner  and  Kingston. 

Use.  —  An  ore  of  lead. 

BARYTOCALCITE. 

Monoclinic.  Axes  a  :  b  :  c  =  07717  :  1  :  0-6254;  /3  =  73°  52'.  In  crys- 
tals; also  massive. 

Cleavage:  ra(  110)  perfect;  c(001)  less  so.  Fracture  uneven  to  subcon- 
choidal.  Brittle.  H.  =  4.  G.  =  3 -64-3 '66.  Luster  vitreous,  inclining  to 
resinous.  Color  white,  grayish,  greenish  or  yellowish.  Streak  white.  Trans- 
parent to  translucent.  Optically  -.  a  =  1-525.  0  =  1'684.  7  =  1-686. 

Comp.  —  Carbonate  of  barium  and  calcium,  BaCO3.CaCO3  =  Carbon 
dioxide  29'6,  baryta  51 '5,  lime  18'9  =  100. 

Pyr.,  etc.  —  B.B.  colors  the  flame  yellowish  green,  and  at  a  high  temperature  fuses  on 
the  thin  edges  and  assumes  a  pale  green  color;  the  assay  reacts  alkaline  after  ignition. 
Soluble  in  dilute  hydrochloric  acid  with  effervescence.  Dilute  solution  gives  an  abundant 
precipitate,  BaSO4,  with  a  few  drops  of  sulphuric  acid. 

Obs.  —  Occurs  at  Alston  Moor  in  Cumberland,  England,  in  limestone  with  barite  and 
fluorite. 

ROSASITE.  2CuO.3CuC03.5ZnC03?.  Mammillary  fibrous  of  a  bright  green  to  sky- 
blue  color.  From  Rosas  mine  at  Sulcis,  Sardinia. 

Bismutospharite.  Bi2(CO3)3.2Bi2O3.  In  spherical  forms  with  radiated  structure. 
G.  =  7 '42.  Color  yellow  to  gray  or  blackish  brown.  From  Schneeberg,  Saxony.  Also 
sparingly  at  Willimantic  and  Portland,  Conn.,  as  a  result  of  the  alteration  of  bismuthinite. 
From  the  Stewart  mine,  Pala,  San  Diego  Co.,  Cal. 

Rutherfordine.  Uranyl  carbonate,  UO2CO3.  A  yellow  ocher  resulting  from  alteration 
of  uraninite.  G.  =  4*8.  From  Uruguru  Mts.,  German  East  Africa. 

Parisite.  A  fluocarbonate  of  the  cerium  metals,  [(Ce,La,Di)F]2Ca(C03)2.  Rhombo- 
hedral.  Crystals  small  and  slender.  Habit  pyramidal  or  prismatic.  Crystals  horizontally 
grooved  due  to  oscillatory  combination  of  faces.  H.  =  4'5.  G.  =  4*358.  Color  brownish 
yellow.  Optically  +  .  co  =  1*676.  e  =  1757.  From  the  emerald  mines,  Muso,  Colom- 
bia; Ravalli,  Mon.;  Quincy,  Mass.;  Montorfano,  Italy;  Narsarsuk,  Greenland  (syn- 
chisite) . 

Cordylite  is  a  parisite  containing  barium  from  Narsarsuk,  South  Greenland.  Other 
material  from  Narsarsuk  thought  to  be  a  new  species  and  named  synchisite  is  parisite. 

Bastnasite.  Hamartite.  A  fluocarbonate  of  the  cerium  metals  (RF)COs.  H.  =  4 '5- 
G.  =  4 '948.  Color  wax-yellow  to  reddish  brown.  Uniaxial,  +.  Strong  birefringence. 
cc  =  1715.  From  the  Bastnas  mine,  Riddarhyttan,  Sweden.  Also  in  parallel  growth  with 
tysonite  in  the  granite  of  the  Pike's  Peak  region  in  Colorado.  Found  to  the  east  of  Ambo- 
sitra,  Madagascar. 

Ancylite.  4Ce(OH)CO3.3SrCO3.3H2O.  Orthorhombic.  In  small  pyramids  with  curved 
faces  and  edges.  H.  =4'5.  G.  =  3 '9.  Color  light  yellow,  orange,  brown,  gray.  Infu- 
sible. From  Narsarsuk,  Greenland.  WeibyeUe  is  a  related  mineral. 

Ambatoarinite.  A  carbonate  of  strontium  and  the  rare  earths.  Orthorhombic?  In 
crystals  with  parallel  axes,  forming  skeleton-like  groups.  Index,  >  1'66.  From  Arnba- 
toarina,  near  Ambositra,  Madagascar. 


450  DESCRIPTIVE   MINERALOGY 

PHOSGENITE. 

Tetragonal.     Axis  c  =  1-0876.     Crystals   prismatic;    sometimes  tabular 

°  Cleavage:  m(110),  a(100)  distinct;  also  c(001).  Rather  sectile.  H.  = 
275-3.  G.  =  6-0-6-3.  Luster  adamantine.  Color  white,  gray,  and  yellow. 
Streak  white.  Transparent  to  translucent.  Optically  +.  w  =  2-114.  e  = 

Comp.— Chlorocarbonate  of  lead,  (PbCl)2CO3  or  PbCO3.PbCl2  =  Lead 
carbonate  49'0,  lead  chloride  51*0  =  100. 

Pyr.,  etc.  —  B.B.  melts  readily  to  a  yellow  globule,  which  on  cooling  becomes  white 
and  crystalline.  On  charcoal  in  R.F.  gives  metallic  lead,  with  a  white  coating  of  lead 
chloride.  Dissolves  with  effervescence  in  dilute  nitric  acid  and  solution  reacts  for  chlorine 
with  silver  nitrate. 

Obs.  —  At  Cromford  near  Matlock  in  Derbyshire;  at  Gibbas,  Monte  Pom  and  Monte- 
vecchio  in  Sardinia.  From  Broken  Hill,  New  South  Wales;  Dundas,  Tasmania. 

Northupite.  MgCO3.Na2CO3.NaCl.  In  isometric  octahedrons.  H.  =  3'5-4.  G.  = 
2'38.  White  to  yellow  or  gray,  n  =  T514.  From  Borax  Lake,  San  Bernardino  Co.,  Cal. 

Tychite.  2MgCO3.2Na2CO3.Na2SO4.  Isometric.  Octahedral  habit.  H.  =  3'5.  G. 
=  2'5.  n  =  l;51.  Very  rare.  From  Borax  Lake,  San  Bernardino  Co.,  Cal.,  associated 
with  northupite. 

B.     ACID,  BASIC,  AND  HYDROUS  CARBONATES 

Teschemacherite.  Acid  ammonium  carbonate,  HNH4CO3.  Orthorhombic.  In  yel- 
lowish to 'white  crystals.  G.  =  1'45.  Indices,  1'423-1'536.  From  guano  deposits  of 
Africa,  Patagonia,  the  Chincha  Islands. 


MALACHITE. 
Monoclinic.     Axes  a  :  b  :  c  =  0-8809  :  1  :  0-4012;  $  =  61°  50'. 

Crystals  rarely  distinct,  usually  slender,  acicular  prisms  (mm"'  110  A  110 
=  75°  40'),  grouped  in  tufts  and  rosettes.  Twins:  tw.  pi.  a(100)  common. 
Commonly  massive  or  incrusting,  with  surface  botryoidal,  or  stalactitic,  and 
structure  divergent;  often  delicately  compact  fibrous,  and  banded  in  color; 
frequently  granular  or  earthy. 

Cleavage:  c(001)  perfect;  6(010)  less  so.  Fracture  subconchoidal,  un- 
even. Brittle.  H.  =  3-5-4.  G.  =  3-9-4-03.  Luster  of  crystals  admantine, 
inclining  to  vitreous;  of  fibrous  varieties  more  or  less  silky;  often  dull  and 
earthy.  Color  bright  green.  Streak  paler  green.  Translucent  to  sub- 
translucent  to  opaque.  Optically  — .  /3  =  1'88. 

Comp.  —  Basic  cupric  carbonate,  CuC03.Cu(OH)2  =  Carbon  dioxide 
19-9,  cupric  oxide  71-9,  water  8'2  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  blackens  and  yields  water.  B.B.  fuses  at  2,  coloring  the 
flame  emerald-green;  on  charcoal  is  reduced  to  metallic  copper;  with  the  fluxes  reacts  like 
cuprite.  Soluble  in  acids  with  effervescence. 

Diff.  —  Characterized  by  green  color  and -copper  reactions  B.B.;  differs  from  other 
copper  ores  of  a  green  color  in  its  effervescence  with  acids. 

Artif.  —  Malachite  has  been  formed  artificially  by  heating  precipitated  copper  carbon- 
ate with  a  solution  of  ammonium  carbonate  for  several  days. 

Obs.  —  Common  with  other  ores  of  copper  and  as  a  product  of  their  alteration ;  thus 
as  a  pseudomorph  after  cuprite  and  azurite.  Occurs  abundantly  in  the  Ural  Mts.;  at 
Chessy  in  France;  in  Cornwall  and  in  Cumberland,  England;  in  Germany  at  Rheinbreit- 
bach;  Dillenburg,  Nassau;  Betzdorf  near  Siegen.  At  the  copper  mines  of  Nizhni  Tagilsk, 
Russia;  with  the  copper  ores  of  Cuba;  Chile;  at  the  Cobar  mines  and  elsewhere  in  New 
bouth  Wales;  South  Australia;  Rhodesia.  In  crystals  from  Katanga,  Congo,  and  Min- 
douh,  French  Congo. 


CARBONATES 


451 


Occurs  in  N.  J.,  at  Schuyler's  mines,  and  at  New  Brunswick.  In  Pa.,  at  Cornwall, 
Lebanon  Co.;  at  the  Perkiomen  and  Phenixville  lead-mines.  In  Wis.,  at  the  copper  mines, 
of  Mineral  Point,  and  elsewhere.  Abundantly  in  fine  masses  and  acicular  crystals,  with 
calcite  at  the  Copper  Queen  mine,  Bisbee,  Cochise  Co.,  Ariz.;  also  in  Graham  Co.,  at 
Morenci  (6  m.  from  Clifton),  in  stalactitic  forms  of  malachite  and  azurite  in  concentric 
bands.  At  the  Santa  Rita  mines,  Grant  Co.,  and  elsewhere  in  N.  M.  Tintic  district, 
Utah.  In  pseudomorphs  from  Good  Springs,  Nev.  Named  from  naXaxi),  mallows,  in 
allusion  to  the  green  color. 

Use.  —  An  ore  of  copper;  at  times  as  an  ornamental  stone. 

AZURITE. 
Monoclinic.     Axes  a  :  b  :  c  =  0-8501  :  1  :  0-8805;  0  =  87°  36'. 

761  762  763 


mm'",  110  A  110  =  80°  41'. 
ac,  100  A  001  =  87°  36'. 
ca,  001  A  101  =  44°  46'. 
II',  023  A  023  =  60°  47'. 


ppf,  021  A  021  =  120°  47'. 
cm,  001  A  110  =  88°  10'. 
cd,  001  A  243  =  54°  29'. 
hhf,  221  A  221  =  73°  56'. 


Crystals  varied  in  habit  and  highly  modified.  Also  massive,  and  present- 
ing imitative  shapes,  having  a  columnar  composition;  also  dull  and  earthy. 

Cleavage:  p(021)  perfect  but  interrupted;  a(100)  less  perfect;  ra(HO)  in 
traces.  Fracture  conchoidal.  Brittle.  H.  =  3-5-4.  G.  =  3-77-3-83.  Lus- 
ter vitreous,  almost  adamantine.  Color  various  shades  of  azure-blue,  passing 
into  Berlin-blue.  Streak  blue,  lighter  than  the  color.  Transparent  to  sub- 
translucent,  a  =  1730.  0-=  1-758.  7  =  1-838. 

Comp.  —  Basic  cupric  carbonate,  2CuCO3.Cu(OH)2  =  Carbon  dioxide 
25-6,  cupric  oxide  69-2,  water  5 -2  =  100. 

Pyr.,  etc.  —  Same  as  in  malachite. 

Diff.  —  Characterized  by  its  blue  color;  effervescence  in  nitric  acid;  copper  reactions 
B.B. 

Artif .  — Azurite  has  been  formed  by  allowing  a  solution  of  copper  nitrate  to  lie  in  con- 
tact with  fragments  of  calcite  for  several  years. 

Obs.  —  Occurs  in  splendid  crystallizations  in  France  at  Chessy,  near  Lyons,  whence  it 
derived  the  name  Chessy  Copper  or  chessylite.  Also  in  fine  crystals  in  Siberia;  Moldawa  in 
the  Banat,  Hungary;  at  Wheal  Buller,  near  Redruth  in  Cornwall;  in  Devonshire  and  Derby- 
shire, England;  at  Broken  Hill  and  elsewhere  in  New  South  Wales;  South  Australia. 

Occurs  in  Pa.,  at  Phenixville,  in  crystals.  In  N.  J.,  near  New  Brunswick.  In  Wis., 
near  Mineral  Point.  In  Ariz.,  at  the  Longfellow  and  other  mines  in  Graham  Co.;  with 
malachite  in  beautiful  crystals  at  the  Copper  Queen  mine,  Bisbee;  at  Morenci.  In  Grant 
Co.,  N.  M.  At  the  Mammoth  mine  in  the  Tintic  district  and  in  Tooele  Co.,  Utah.  In 
Cal.,  Calaveras  Co.,  at  Hughes's  mine,  in  crystals. 

Use.  —  An  ore  of  copper. 

Aurichalcite.  A  basic  carbonate  of  zinc  and  copper,  2(Zn,Cu)CO3,.3(Zn,Cu)(OH)2. 
Orthorhombic?  In  drusy  incrustations.  G.  =  3'54-3'64.  Luster  pearly.  Color  pale 
green  to  sky-blue.  Indices,  1  '634^1  '682.  From  the  Altai  Mts.,  Mongolia;  Chessy,  near 
Lyons,  France;  Rezbdnya,  Hungary;  Ondarroa,  Vizcaya,  Spain;  Chihuahua,  Mexico.  In 
the  United  States,  at  Lancaster,  Pa.;  Salida,  Col.;  the  Santa  Caterina  Mts.,  Ariz.;  Beaver 
Co.,  Utah;  Kelly,  N.  M. 

Hydrozincite.  A  basic  zinc  carbonate,  perhaps  ZnCO3.2Zn(pH)2.  Massive,  fibrous, 
earthy  or  compact,  as  incrustations.  G.  =  3'58-3'8.  Color  white,  grayish  or  yellowish. 


452 


DESCRIPTIVE   MINERALOGY 


Index,  1-695.  Occurs  at  mines  of  zinc,  as  a  result  of  alteration.  In  great  quantities  at  the 
Dolores  mine,  Santander,  Spain.  From  Chihuahua,  Mexico;  Bleyberg,  Belgium;  Mal- 
fidano,  Sardinia.  In  the  United  States  at  Friedensville,  Pa.;  at  Linden,  in  Wis.;  Granby, 
Mo. 

OTAVITE.  A  basic  cadmium  carbonate  of  uncertain  composition.  In  crusts  showing  min- 
ute rhombohedral  crystals.  Color  white  to  reddish.  From  the  Otavi  district,  German 
Southwest  Africa. 

Hydrocerussite.  A  basic  lead  carbonate,  probably  2PbCO3.Pb(pH)2.  In  thin  color- 
less hexagonal  plates.  Index,  2 '07.  Occurs  as  a  coating  on  native  lead,  at  Langban, 
Sweden;  with  galena  at  Wanlockhead,  Scotland. 

Dundasite.  A  basic  carbonate  of  lead  and  aluminium,  Pb(AlO)2(CO3)2.4H2O.  In 
small  spherical  aggregates  of  radiating  acicular  crystals.  Color  white.  From  Dundas  and 
Mt.  Read,  Tasmania,  and  from  near  Trefriw,  Carnarvonshire,  Wales;  Wensley,  Derbyshire; 
near  Maam,  County  Gal  way,  Ireland. 

Dawsonite.  A  basic  carbonate  of  aluminium  and  sodium,  Na3Al(CO3)3.2Al(OH)3. 
Orthorhombic.  In  thin  incrustations  of  white  radiating  bladed  crystals.  Perfect  cleavage, 
ra(110).  G.  =  2-40.  Indices,  1-466-1-596.  Found  on  a  feldspathic  dike  near  McGill 
College,  Montreal.  From  the  province  of  Siena,  Pian  Castagnaio,  Tuscany,  Italy 


Thermonatrite.  Hydrous  sodium  carbonate,  Na2CO3.H2O.  G.  =  l'S-1'6.  Occurs  m 
various  lakes,  and  as  an  efflorescence  over  the  soil  in  many  dry  regions. 

Nesquehonite.  Hydrous  magnesium  carbonate,  MgCO3.3H2O.  In  radiating  groups 
of  prismatic  crystals.  G.  =••  1 '83-1-85.  Colorless  to  white.  Biaxial,  — .  Indices,  1-495- 
1'526.  From  a  coal  mine  at  Nesquehoning,  Schuylkill  Co.,  Pa.  See  lansfordite,  p.  453. 

Natron.  Hydrous  sodium  carbonate,  Na2CO3.10H2O.  Occurring  in  nature  only  in 
solution,  as  in  the  soda  lakes  of  Egypt,  and  elsewhere,  or  mixed  with  the  other  sodium 
carbonates. 

Pirssonite.  CaCO3.Na2CO3.2H2O.  In  prismatic  crystals,  orthorhombic-hemimorphic. 
H.  =3.  G.  =  2'35.  Colorless  to  white.  Optically  +.  Indices,  I'504-r575.  Borax 
Lake,  San  Bernardino,  Cal. 

GAY-LUSSITE. 

Monoclinic.     Axes  a  :  b  :  c  =  1  -4897  :  1 


764 


765 


:  1-4442;  0  =  _78°  27'. 
mm'",  110  A  UO  =  111°  10'. 
ee',       Oil  A  Oil  =  109°  30'. 
me,       110  A  Oil  =    42°  21'. 
rrf,        112  A  112  =    69°  29'. 


Crystals  often  elongated  ||  a  axis;  also 
flattened  wedge-shaped.  Cleavage: 
m  (110)  perfect;  c  (001)  rather  difficult. 
Fracture  conchoidal.  Very  brittle. 
H.  =  2-3.  G.  =  1-93-1-95.  Luster 
vitreous.  Color  white,  yellowish  white. 
Streak  uncolored  to  grayish.  Translu- 
cent. Optically  — .  a  =  1*444  6  = 
T517.,  7  =  1-518. 
Comp.  — Hydrous  carbonate  of  calcium  and  sodium,  CaCO3.Na2CO3. 

Calcium  carbonate  33-8,  sodium  carbonate  35-8,  water  30-4  =  100. 
Pyr.,  etc.  —  Heated  in  a  closed  tube  decrepitates  and  becomes  opaque.     B.B.  fuses 

•  briskyeffervesoene  ^^'l  ""Vu^  the  flame  inten^ly  yellow.     Dissolve!  in  acids  with  a 
brisk  effervescence;  partly  soluble  in  water,  and  reddens  turmeric  paper. 

the  botton"  of  r^ll  aVLa?Un^  ™a^Merida>  in  Venezuela,  in  crystals  disseminated  at 
Lake  or  So£  iM  '  'SV1  &  ^  °f  day'  covermg  trona.  Also  abundant  in  Little  Salt 
tion  of  the  t«tPr  'Fn  th%Carsfm  Desert  near  Ragtown,  Nev,  deposited  upon  the  evapora- 
cms  1850)  Sweetwater  VaUey'  Wv'  Named  after  Gay  Lussac,  the  French 


CARBONATES  453 

Lanthanite.  La2(CO3)3.9H2O.  In  thin  tabular  orthorhombic  crystals;  also  granular, 
earthy.  G.  =  2 '605.  Color  grayish  white,  pink,  yellowish.  Optically  — .  Found  coat- 
ing cerite  at  Bastnas,  Sweden;  with  zinc  ores  of  the  Saucon  valley,  Lehigh  Co.,  Pa.;  at  the 
Sandford  iron-ore  bed,  Moriah,  N.  Y. 

TRONA.'    Urao. 

Monoclinic.     Axes  a  :  b  :  c  =  2-8460: 1:  2-9700;  0  =  77°  23'. 
ca,     001  A  100  =  77°  23'. 

co,     001  A  Til  =  75°  53^.  766 

oo",  111  A  111  =  47°  35|'. 

Often  fibrous  or  columnar  massive.  .         . 

Cleavage:  a  (100)  perfect;  o  (111) ;  c  (001)  in  traces.     \ 
Fracture   uneven  to   subconchoidal.       H.  =  2*5-3.      \ 
G.  =  2-11-2-14.    Luster  vitreous,  glistening.     Color 

gray    or    yellowish    white.      Translucent.       Taste    alkaline.     Optically—. 
Index,  1-507. 

Comp.  —  Na2CO3.HNaCO3.2H2O  or  3Na2O.4CO3.5H20  =  Carbon  diox- 
ide 38-9,  soda  41-2,  water  19-9  =  100. 

Chatard  established  the  above  composition  for  urao,  and  showed  that  trona,  sometimes 
called  "  sesquicarbonate  of  soda,"  is  an  impure  form  of  the  same  compound. 

Pyr.,  etc.  —  In  the  closed  tube  yields  water  and  carbon  dioxide.  B.B.  imparts  an 
intensely  yellow  color  to  the  flame.  Soluble  in  water,  and  effervesces  with  acids.  Reacts 
alkaline  with  moistened  test-paper. 

Obs.  —  Found  in  the  province  of  Fezzan,  Africa,  forming  thin  superficial  crusts;  Na- 
troun  lakes,  Egypt;  from  Vesuvius;  at  the  bottom  of  a  lake  at  Lagunilla,  Venezuela. 
Efflorescences  of  trona  occur  near  the  Sweetwater  river,  Rocky  Mountains.  An  extensive 
bed  in  Churchill  Co.,  Nev.  In  fine  crystals  at  Borax  lake,  San  Bernardino  Co.,  Cal.,  with 
hanksite,  glauberite,  thenardite,  etc. 

Hydromagnesite.  Basic  magnesium  carbonate,  3MgCO3.Mg(OH)2.3H2O.  Crystals 
small,  tufted.  Also  amorphous;  as  chalky  crusts.  Color  and  streak  white.  Index,  1 '530. 
Often  occurs  with  serpentine;  thus  at  Hrubschiitz,  in  Moravia;  at  Kraubat,  Styria,  etc. 
Also  similarly  near  Texas,  Pa.;  Hoboken,  N.  J.  Material  closely  similar  from  saline  crusts 
on  lava  at  Alpharoessa,  Santorin  Island,  has  been  called  giorgiosite. 

Hydrogiobertite.  MgCO3.Mg(OH)2.2H2O.  In  light  gray  spherical  forms.  From  the 
neighborhood  of  Pollena,  Italy.  Deposited  from  Phillips  Springs,  Napa  Co.,  Cal. 

Artinite.  MgCO3.Mg(OH)2.3H2O.  Orthorhombic.  Radiating  fibrous.  H.  =  2'0. 
G.  =  2-0.  White,  ft  =  1'54.  From  Val  Laterna  and  Emarede,  Val  Aosta,  Piedmont, 
Italy. 

Lansfordite.  3MgCO3.Mg(OH)2.21H2O.  Biaxial  -.  Indices,  1'42-1-503.  Occurs  as 
small  stalactites  in  the  anthracite  mine  at  Nesquehoning  near  Lansford,  Schuylkill  Co., 
Pa.;  changed  on  exposure  to  nesquehonite. 

Brugnatellite.  MgCO3.5Mg(OH)2.Fe(OH)3.4H2O.  Micaceous/ lamellar.  Perfect  cleav- 
age. Color  flesh-pink,  co  =  T53.  Found  in  an  old  asbestos  mine  at  Torre  Santa 
Maria,  Val  Malenco,  Lombardy,  Italy. 

GAJITE.  A  basic  hydrous  calcium,  magnesium  carbonate.  Rhombqhedral  cleavage. 
Granular  structure.  H.  =  3'5.  G.  =  2'62.  Color,  white.  Strong  birefringence.  Found 
near  Plesce,  in  the  district  Gorskikotar,  Croatia. 

Stichtite.  2MgCO3.5Mg(OH)2.2Cr(OH)3.  Micaceous.  In  scales.  G.=  2'16.  Color 
lilac.  Optically  uniaxial  or  feebly  biaxial.  Optically  — .  Index,  1'54.  An  alteration 
product  of  serpentine  from  Dundas,  Tasmania. 

Zaratite.  Emerald  Nickel.  NiCO3.2Ni(OH)2.4H2O.  Inmammillary  incrustations;  also 
massive,  compact.  Color  emerald-green.  Occurs  on  chromite  at  Texas,  Lancaster  Co., 
Pa.;  at  Swinaness,  Unst,  Shetland;  Igdlokunguak,  Greenland. 

Remingtonite.  A  hydrous  cobalt  carbonate.  A  rose-colored  incrustation,  soft  and 
earthy.  From  a  copper  mine  near  Finksburg,  Carroll  Co.,  Md.;  Boleo,  Lower  California. 


454  DESCRIPTIVE   MINERALOGY 

Tengerite.  A  supposed  yttrium  carbonate.  In  white  pulverulent  coatings.  On  gado- 
linite  at  Ytterby,  Sweden.  A  similar  mineral  is  associated  with  the  gadolinite  of  Llano 
Co.,  Tex. 

Bismutite.  A  basic  bismuth  carbonate,  perhaps  Bi2O3.CO2.H2O.  Incrusting,  or  earthy 
and  pulverulent;  amorphous.  G.  =  6'86-6'9  Breith.;  7 '67  Rg.  Color  white,-  green,  yel- 
low and  gray.  Index,  2'25.  Occurs  in  Germany,  at  Schneeberg  and  Johanngeorgenstadt, 
with  native  bismuth,  and  at  Joachimstal,  Bohemia.  In  the  United  States,  in  S.  C.,  at 
Brewer's  mine;  hi  Gaston  Co.,  N.  C. 

Uranothallite.  2CaCO3.U(CO3)2.10H2O.  In  scaly  or  granular  crystalline  aggregates. 
Color  siskin-green.  Occurs  on  uraninite  at  Joachimstal,  Bohemia. 

Liebigite.  A  hydrous  carbonate  of  uranium  and  calcium.  In  mammillary  concretions, 
or  thin  coatings.  Color  apple-green.  Occurs  on  uraninite  near  Adrianople,  Turkey;  also 
Johanngeorgenstadt,  Germany,  and  Joachimstal,  Bohemia. 

Voglite.  A  hydrous  carbonate  of  uranium,  calcium  and  copper.  In  aggregations  of 
crystalline  scales.  Color  emerald-green  to  bright  grass-green.  From  the  Elias  mine,  near 
Joachimstal,  on  uraninite,  Bohemia. 


Oxygen  Salts 
2.   SILICATES 

The  Silicates  are  in  part  strictly  anhydrous,  in  part  hydrous,  as  the  zeolites 
and  the  amorphous  clays,  etc.  -Furthermore,  a  large  number  of  the  silicates 
yield  more  or  less  water  upon  ignition,  and  in  many  cases  it  is  known  that  they 
are,  therefore,  to  be  regarded  as  basic  (or  acid)  silicates.  The  line,  however, 
between  the  strictly  anhydrous  and  hydrous  silicates  cannot  be  sharply  drawn, 
since  with  many  species  which  yield  water  upon  ignition  the  part  played  by 
the  elements  forming  the  water  is  as  yet  uncertain.  Furthermore,  in  the  cases 
of  several  groups,  the  strict  arrangement  must  be  deviated  from,  since  the 
relation  of  the  species  is  best  exhibited  by  introducing  the  related  hydrous 
species  immediately  after  the  others. 

This  chapter  closes  with  a  section  including  the  Titanates,  Silico-titanates, 
Titano-niobates,  etc.,  which  connect  the  Silicates  with  the  Niobates  and 
Tantalates.  Some  Titanates  have  already  been  included  among  the  Oxides. 


Section  A.  Chiefly  Anhydrous  Silicates 

I.  Disilicates,  Polysilicates 

II.  Metasilicates 

III.  Orthosilicates 

IV.  Subsilicates 

The  DISILICATES,  RSi205,  are  salts  of  disilicic  acid,  H2Si2O5,  and  have  an 
oxygen  ratio  of  silicon  to  bases  of  4  :  1,  as  seen  when  the  formula  is  written 
after  the  dualistic  method,  RO.2Si02. 

The  POLYSILICATES,  R2Si308,  are  salts  of  polysilicic  acid,  H4Si3O8,  and 
have  an  oxygen  ratio  of  3  :  1,  as  seen  in  2R0.3Si02. 

The  METASILICATES,  RSiO3,  are  salts  of  metasilicic  acid,  H2SiO3,  and  have 
an  oxygen  ratio  of  2  :  1.  They  have  hence  been  called  bisilicates. 

The  ORTHOSILICATES,  R2Si04,  are  salts  of  orthosilicic  acid,  H4Si04,  and 
have  an  oxygen  ratio  of  1  :  1.  They  have  hence  been  called  unisilicates.  The 
majority  of  the  silicates  fall  into  one  of  the  last  two  groups. 


SILICATES  455 

Furthermore,  there  are  a  number  of  species  characterized  by  an  oxygen 
ratio  of  less  than  1:1,  e.g.,  3  :  4,  2  :  3,  etc.  These  basic  species  are  grouped 
as  SUBSILICATES.  Their  true  position  is  often  in  doubt;  in  most  cases  they 
are  probably  to  be  regarded  as  basic  salts  belonging  to  one  of  the  other  groups. 

The  above  classification  cannot,  however,  be  carried  through  strictly,  since 
there  are  many  species  which  do  not  exactly  conform  to  any  one  of  the  groups 
named,  and  often  the  true  interpretation  of  the  composition  is  doubtful. 
Furthermore,  within  the  limits  of  a  single  group  of  species,  connected  closely 
in  all  essential  characters,  there  may  be  a  wide  variation  in  the  proportion  of 
the  acidic  element.  Thus  the  triclinic  feldspars,  placed  among  the  polysili- 
cates,  range  from  the  true  polysilicate,  NaAlSisOg,  to  the  orthosilicate, 
CaAl2Si2O8,  with  many  intermediate  compounds,  regarded  as  isomorphous 
mixtures  of  these  extremes.  Similarly  of  the  scapolite  group,  which,  how- 
ever, is  included  among  the  orthosilicates,  since  the  majority  of  the  compounds 
observed  approximate  to  that  type.  The  micas  form  another  example. 

I.   Disilicates,  RSi205.    Polysilicates,  R2Si308 
PETALITE. 

Monoclinic.  Crystals  rare  (castorite).  Usually  massive,  foliated  cleavable 
(petalite) . 

Cleavage:  c  (001)  perfect;  o  (201)  easy;  z  (905)  difficult  and  imperfect. 
Fracture  imperfectly  conchoidal.  Brittle.  H.  =  6-6-5.  G.  =  2-39-2*46. 
Luster  vitreous,  on  c  (001)  pearly.  Colorless j  white,  gray,  occasionally  reddish 
or  greenish  white.  Streak  uncolored.  Transparent  to  translucent,  a  = 
1-504.  ft  =  1-510.  y  =  1-516. 

Comp.  —  LiAl(Si2O5)2  or  Li2O.Al2O3.8SiO2  =  Silica  78'4,  alumina  167, 
lithia,  4-9  =  100. 

Pyr.,  etc.  —  Gently  heated  emits  a  blue  phosphorescent  light.  B.B.  fuses  quietly  at 
4  and  gives  the  reaction  for  lithia.  With  borax  it  forms  a  clear,  colorless  glass.  Not  acted 
on  by  acids. 

Obs.  —  Petalite  occurs  at  the  iron  mine  of  Uto,  Sweden,  with  lepidolite,  tourmaline, 
spodumene,  and  quartz;  on  Elba  (castorite).  In  the  United  States,  at  Bplton,  Mass.,  with 
scapolite;  at  Peru,  Me.,  with  spodumene  in  albite.  The  name  petalite  is  from  TreraXov,  a 
leaf,  alluding  to  the  cleavage. 

Milarite.  HKCa2Al2(Si2O5)6.  In  hexagonal  prisms.  H.  =  5'5-6.  G.  =  2'55-2'59. 
Colorless  to  pale  green,  glassy.  From  Val  Giuf,  Grisons,  Switzerland. 

Eudidymite.  HNaBeSisOs.  Monoclinic.  In  white,  glassy,  twinned  crystals,  tabular  in 
habit.  H.  =6.  G.  =  2 '553.  Optically  +.  Indices,  1  '545-1  '551.  Occurs  very  spar- 
ingly in  elaeolite-syenite  on  the  island  Ovre-Aro,  in  the  Langesundfiord,  Norway;  from  Nar- 
sarsuk,  Greenland. 

Epididymite.  Same  composition  as  eudidymite.  Orthorhombic.  Tabular  ||  c  (001). 
Cleavage,  6(010)  and  c(001),  perfect.  H.  =  5 '5.  G.  =  3  "55.  Optically  -.  Indices, 
1-565-1-569.  Narsarsuk,  Greenland. 

RIVAITE.  (Ca,Na2)Si2O5.  Monoclinic?  In  fibrous  aggregates.  H.  =5.  G.  =  2*55. 
Color,  pale  lavender  to  dark  blue.  Fibers  show  parallel  extinction  with  positive  elongation. 
Easily  fusible.  Insoluble  in  hydrochloric  acid.  Found  in  loose  nodules  on  Vesuvius. 


456 


DESCRIPTIVE   MINERALOGY 


Orthoclase 

Soda-Orthoclase 

Hyalophane 
Celsian 


Microcline 

Soda-microcline 
Anorthoclase 


Feldspar  Group 

a.  Monoclinic  Section 

a 

KAlSi3O8  0-6585 

{ (K,Na)  AlSi3O8 
\(Na,K)AlSi3O8 
(K2,Ba)Al2Si4Oi2        0*6584 
BaAl2Si208  0-657 

j8.  Triclinie  Section 
KAlSi3O8 

(K,Na)AlSi3O8 
(Na,K)AlSi3O8 


:  0'5554 


0'5512 
0'554 


116°    3' 


115°  35' 
115°    2' 


Albite-anorthite  Series.     Plagioclase  Feldspars 

Albite          NaAlSi308  0' 6335  :'l:  0*5577      94°*  3'     116°  29'  88°    9' 

Oligoclasej  0'6321: 1:0'5524      93°    4'     116°  23'  90°    5' 

Andesine     (  n£faf!?J?9v8  ^  0'6357 : 1 : 0'5521      93°  23'     116°  29'  89°  59' 


Labra- 

dorite     J 
Anorthite     CaAl2Si208 


0-6377:1:0-5547 
0-6347:1:0-5501 


93°  31'  116°  3'  89°54J' 
93°  13'  115°  55'  91°  12' 


The  general  characters  of  the  species  belonging  in  the  FELDSPAR  GROUP 
are  as  follows : 

1,  Crystallization  in  the  monoclinic  or  triclinie  systems,  the  crystals  of  the 
different  species  resembling  each  other  closely  in  angle,  in  general  habit,  and 
in  methods  of  twinning.     The  prismatic  angle  in  all  cases  differs  but  a  few 
degrees  from  60°  and  120°. 

2,  Cleavage  in  two  similar  directions  parallel  to  the  base  c  (001)  and  clino- 
pinacoid  (or  brachypinacoid)  6  (010),  inclined  at  an  angle  of  90°  or  nearly  90°. 
3,  Hardness  between  6  and  6'5.     4,  Specific  Gravity  varying  between  2"5  and 
2'9,  and  mostly  between  2-55  and  275.     5,  Color  white  or  pale  shades  of 
yellow,  red  or  green,  less  commonly  dark.     6,  In  composition  silicates  of  alu- 
minium with  either  potassium,  sodium,  or  calcium,  and  rarely  barium,  while 
magnesium  and  iron  are  always  absent.     Furthermore,  besides  the  several 
distinct  species  there  are  many  intermediate  compounds  having  a  certain 
independence  of  character  and  yet  connected  with  each  other  by  insensible 
gradations;  all  the  members  of  the  series  showing  a  close  relationship  not  only 
in  composition  but  also  in  crystalline  form  and  optical  characters. 

The  species  of  the  Feldspar  Group  are  classified,  first  as  regards  form,  and 
second  with  reference  to  composition.  The  monoclinic  species  include  (see 
above) :  ORTHOCLASE,  potassium  feldspar,  and  SODA-ORTHOCLASE,  potassium- 
sodium  feldspar;  also  HYALOPHANE  and  CELSIAN,  barium  feldspars. 

The  triclinie  species  include :  MICROCLINE  and  ANORTHOCLASE,  potassium- 
sodium  feldspars;  ALBITE,  sodium  feldspar;  ANORTHITE,  calcium  feldspar. 

Also  intermediate  between  albite  and  anorthite  the  isomorphous  sub- 
species, sodium-calcium  or  calcium-sodium  feldspars:  OLIGOCLASE,  ANDESINE, 
LABRADORITE. 


SILICATES 

a.  Monoclinic  Section 
ORTHOCLASE. 

Monoclinic.     Axes  a  :  b  :  c  =  0*6585  :  1  :  0-5554; 

767  768  769 


457 


63°  57'. 


770 


m 


mm'",  110  A  110  =  61°  13'. 
zz',   130  A  130  =  58°  48'. 
ex,   001  A  101  =  50°  16|'. 
cy,   001  A  201  =  80°  18'. 


m 


cn,    001  A  021  =  44° 
nn',  021  A  021  =  89°  53 
cm,  001  A  110  =  67°  47 
co,    001  A  Til  =  55°  14 


Twins:  tw.  pi.  (1)  a  (100),  or  tw.  axis  c,  the  common  Carlsbad  twins, 
either  of  irregular  penetratipm  (Fig.  772)  or  contact  type;  the  latter  usually 
with  b  (010)  as  composition-face,  often  then  (Fig.  773)  with  c  (001)  and 
x  (101)  nearly  in  a  plane,  but  to  be  distinguished  by  luster,  cleavage,  etc. 
(2)  n  (021),  the  Baveno  ..twins  forming  nearly  square  prisms  (Fig.  774),  since 
cn  =  44°  SGJ'^and  hence  cc  =  89°  53';  often  repeated  as  fourlings  (Fig.  447, 
p.  171), /also  in*square  prisms,  elongated  ||  a  axis.  (3)  c  (001),  the  Manebach 

773 


771 


772 


774 


776 


twins  (Fig.  775),  usually  contact-twins  with  c  as  comp.-face.  Also  other  rarer 
laws. 

Crystals  often  prismatic  ||  c  axis;  sometimes  orthorhombic  in  aspect  (Fig. 
770)  since  c  (001)  and  x  (101)  are  inclined  at  nearly  equal  angles  to  the  vertical 
axis  ;  also  elongated  ||  a  axis  (Fig.  771)  with  b  (010)  and  c  (001)  nearly  equally 
developed;  also  thin  tabular  ||  6  (010):  rarely  tabular  ||  a  (100),  a  face  not 
often  observed.  Often  massive,  coarsely  cleavable  to  granular;  sometimes 
lamellar.  Also  compact  crypto-crystalline,  and  flint-like  or  jasper-like. 

Cleavage:  c  (001)  perfect;  6  (010)  somewhat  less  so;  prismatic  m  (110) 
imperfect,  but  usually  more  distinct  parallel  to  one  prismatic  face  than  to  the 
other.  Parting  sometimes  distinct  parallel  to  a  (100),  also  to  a  hemi-ortho- 
dome,  inclined  a  few  degrees  to  the  orthopinacoid;  this  may  produce  a  satin- 
like  luster  or  schiller  (p.  251),  the  latter  also  often  present  when  the  parting 


458 


DESCRIPTIVE    MINERALOGY 


is  not  distinct.  Fracture  conchoidal  to  uneven.  Brittle.  H.  =6.  G.  = 
2'57.  Luster  vitreous;  on  c  (001)  often  pearly.  Colorless,  white,  pale  yellow 
and  flesh-red  common,  gray;  rarely  green.  Streak  uncolored. 

Optically  negative  in  all  cases  (Fig.  776).     Ax.  pi.  usually  J_  b  (010), 
sometimes  1 1  6,  also  changing  from  the  former  to  the  latter  on  increase  of  tem- 

,*m<-,\        ?i  .7.  »__•_    T->__         A     .  £!r»o    i  -i  r     ID,,  A 


perature  (see  p 
776 


297).  For  adularia  Bxa.r  Ac  axis  =  -  69°  11',  Bxa.w  A 
c  axis  =  —69°  37'.  Hence  Bxa  and  the.extinction- 
direction  (Fig.  776)  inclined  a  few  degrees  only 
to  a  axis,  or  the  edge  b/c;  thus +3°  to +7° 
usually,  or  up  to  +10°  or  +12°  in  varieties  rich 
in  Na20.  Dispersion  p  >v\  also  horizontal, 
strongly  marked,  or  inclined,  according  to  position 
of  ax.  pi.  Axial  angles  variable.  Birefringence 
low,  7  -  a  =  0-007  -  0-005.  For  adularia 
ay  =  1-5190,  fty  =  1-5237,  yy  =  1'5260. 
/.  2Vy  =  69°  43',  2Ey=  121°  6'. 

Comp.  —  A  silicate  of  aluminium  and  potas- 
sium, KAlSi308  or  K2O.Al2O3.6SiO2  =  Silica 
647,  alumina  18-4,  potash  16'9  =  100.  Sodium 
is  often  also  present,  replacing  part  of  the  potassium,  and  sometimes  exceeds  it 
in  amount;  these  varieties  are  embraced  under  the  name  soda-orthoclase 
(the  name  barbierite  has  been  proposed  for  this  material  whose  existence,  as  a 
distinct  though  rare  mineral,  seems  to  have  been  proven). 

Var.  —  The  prominent  varieties  depend  upon  crystalline  habit  and  method  of  occur- 
rence more  than  upon  difference  of  composition. 

1.  Adularia.     The  pure  or  nearly  pure  potassium  silicate.     Usually  in  crystals,  like 
Fig.  770  inhabit;  often  with  vicinal  planes;  Baveno  twins  common.     G.  =  2 '565.     Trans- 
parent or  nearly  so.     Often  with  a  pearly  opalescent  reflection  or  schiller  or  a  delicate  play 
of  colors;  some  moonstone  is  here  included,  but  the  remainder  belongs  to  albite  or  other  of 
the  triclinic  feldspars.     The  original  adularia  (Adular)  is  from  the  St.  Gothard  region  in 
Switzerland.     Valencianite,  from  the  silver  mine  of  Valencia,  Mexico,  is  adularia. 

2.  Sanidine  or  glassy  feldspar.     Occurs   in   crystals,   often  transparent   and   glassy, 
embedded  in  rhyolite,  trachyte  (as  of  the  Siebengebirge,  Germany),  phonolite,  etc.     Habit 
often  tabular  ||  6  (010)  (hence  named  from  (ravls,  a  tablet,  or  board) ;  also  in  square  prisms 
(6,  c) ;  Carlsbad  twins  common.     Most  varieties  contain  sodium  as  a  prominent  constituent, 
and  hence  belong  to  the  soda-orthoclase.     Natronsanidine  is  a  sanidine-like  soda-ortho- 
clase from  a  soda  liparite  from  Mitrowitza,  Servia. 

Rhyacolite.     Occurs  in  glassy  crystals  at  Monte  Somma,  Vesuvius;   named  from  pva£, 
stream  (lava  stream). 

3.  Isothose  is  said  to  be  a  variety  having  a  different  optical  orientation  than  normal 
orthoclase. 

4.  Ordinary.     In  crystals,  Carlsbad  and  other  twins  common;  also  massive  or  cleavable, 
varying  in  color  from  white  to  pale  yellow,  red  or  green,  translucent;  sometimes  avent urine. 
Here  belongs  the  common  feldspar  of  granitoid  rocks  or  granite  veins.     Usually  contains  a 
greater  or  less  percentage  of  soda  (soda-orthoclase).     Compact  cryptocrystalline  orthoclase 
makes  up  the  mass  of  much  felsite,  but  to  a  greater  or  less  degree  admixed  with  quartz;  of 
various  colors,  from  white  and  brown  to  deep  red.     Much  of  what  has  been  called  ortho- 
clase, or  common  potash  feldspar,  has  proved  to  belong  to  the  related  triclinic  species, 
microcline.     Cf.  p.  461  on  the  relations  of  the  two  species.     Chesterlite  and  Amazon  stone 
are  microcline;  also  most  aventurine  orthoclase.     Loxoclase  contains  sodium  in  considerable 
amount  (7 '6  Na2O);   from  Hammond,  St.  Lawrence  Co.,  N.  Y.     Murchisonite  is  a  flesh- 
red  feldspar  similar  to  perthite  (p.  460),  with  gold-yellow  reflections  in  a  direction  _|_  b  (010) 
and  nearly  parallel  to  701  or  801  (p.  457) ;  from  Dawlish  and  Exeter,  England. 

The  spherulities  noted  in  some  volcanic  rocks,  as  in  the  rhyolite  of  Obsidian  Cliff  in  the 
Yellowstone  Park,  are  believed  to  consist  essentially  of  orthoclase  needles  with  quartz. 


SILICATES  459 

(from  Iddings;  much  magnified) 


777 


778 


Pyr.,  etc.  —  B.B.  fuses  at  5;  varieties  containing  much  soda  are  more  fusible.  Loxo- 
clase  fuses  at  4.  Not  acted  upon  by  acids.  Mixed  with  powdered  gypsum  and  heated 
B.  B.  gives  violet  potassium  flame  visible  through  blue  glass. 

Diff .  —  Characterized  by  its  crystalline  form  and  the  two  cleavages  at  right  angles  to 
each  other;  harder  than  barite  and  calcite;  not  attacked  by  acids;  difficultly  fusible.  Mas- 
sive corundum  is  much  harder  and  has  a  higher  specific  gravity. 

Micro.  —  Distinguished  in  rock  sections  by  its  low  refraction  (low  relief)  and  low'inter- 
f erence-colors,  which  last  scarcely  rise  to  white  of  the  first  order  —  hence  lower  than  those 
of  quartz;  also  by  its  biaxial  character  in  convergent  light  and  by  the  distinct  cleavages. 
It  is  colorless  in  ordinary  light  and  may  be  limpid,  but  is  frequently  turbid  and  brownish 
from  the  presence  of  very  minute  scales  of  kaolin  due  to  alteration  from  weathering;  this 
change  is  especially  common  in  the  older  granular  rocks,  as  granite  and  gneiss. 

Artif.  —  Orthoclase  has  not  been  produced  artificially  by  the  methods  of  dry  fusion. 
It  can,  however,  be  crystallized  from  a  dry  melt  when  certain  other  substances,  like  tungstic 
acid,  alkaline  phosphates,  etc.,  are  added.  The  function  of  these  additions  in  the  reactions 
is  not  clear.  Orthoclase  is  more  easily  formed  by  hydrochemical  methods.  It  has  been 
produced  by  heating  gelatinous  silica,  alumina,  caustic  potash  and  water  in  a  sealed  tube. 
Orthoclase  has  also  been  formed  by  heating  potassium  silicate  and  water  together  with 
muscovite. 

Obs.  —  Orthoclase  in  its  several  varieties  belongs  especially  to  the  crystalline  rocks, 
occurring  as  an  essential  constituent  of  granite,  gneiss,  syenite,  also  porphyry,  further  (var., 
sanidine)  trachyte,  phonolite,  etc.  In  the  massive  granitoid  rocks  it  is  seldom  in  distinct, 
well-formed,  separable  crystals,  except  in  veins  and  cavities;  such  crystals  are  more  com- 
mon, however,  in  volcanic  rocks  like  trachyte. 

Adularia  occurs  in  the  crystalline  rocks  of  the  central  and  eastern  Alps,  associated  with 
smoky  quartz  and  albite,  also  titanite,  apatite,  etc.;  the  crystals  are  often  coated  with 
chlorite;  also  ^n  Elba.  Fine  crystals  of  orthoclase,  often  twins,  are  obtained  from  Baveno, 
Lago  Maggiore,  Italy;  the  Fleimstal,  Tyrol,  Austria,  a  red  variety;  Bodenmais,  Carlsbad, 
and  Elbogen  in  Bohemia;  Striegau,  etc.,  in  Silesia.  Also  Arendal  in  Norway,  and  near 
Shaitansk  in  the  Ural  Mts.;  Land's  End  and  St.  Agnes  in  Cornwall;  the  Mourne  Mts., 
Ireland,  with  beryl  and  topaz.  From  Tamagama  Yama,  Japan,  with  topaz  and  smoky 
quartz.  Moonstone  is  brought  from  Ceylon.  Crystals  of  gem  quality  from  Itrongahy, 
Madagascar  Valencianite  from  Guanajuato,  Mexico.  Crystals  from  Eganville,  Ontario. 

In  the  United  States,  orthoclase  is  common  in  the  crystalline  rocks  of  New  England,  also 
of  States  south,  further  Colorado,  California,  etc.  Thus  at  the  Paris  tourmaline  locality, 
Me.  In  N.  H.,  at  Acworth.  In  Mass.,  at  South  Royalston  and  Barre.  In  Conn.,  at 
Haddam  and  Middletown,  in  large  coarse  crystals.  In  N.  Y.,  in  St.  Lawrence  Co.,  at 
Rossie;  at  Hammond  (loxoclase)',  in  Lewis  Co.,  in  white  limestone  near  Natural  Bridge;  at 
Amity  and  Edenville.  In  Pa.,  in  crystals  at  Leiperville,  Mineral  Hill,  Delaware  Co.;  sun- 
stone  in  Kennett  Township.  In  N.  C.,  at  Washington  Mine,  Davidson  Co.  In  Col.,  at  the 
summit  of  Mt.  Antero,  Chaffee  Co.,  in  fine  crystals,  often  twins;  at  Gunnison;  Black 


460 


DESCRIPTIVE   MINERALOGY 


Hawk;  Kokomp,  Summit  Co.,  Robinson,  also  at  other  points.  Also  similarly  in  Nev.  and 
Cal.  Large  twin  crystals  from  Barringer  Hill,  Llano  Co.,  Texas. 

Alter.  —  Orthoclase  is  frequently  altered,  especially  through  the  action  of  carbonated  or 
alkaline  waters;  the  final  result  is  often  the  removal  of  the  potash  and  the  formation  of 
kaolin.  Steatite,  talc,  chlorite,  leucite,  mica,  laumontite,  occur  as  pseudomorphs  after 
orthoclase;  and  cassiterite  and  calcite  often  replace  these  feldspars  by  some  process  of  solu- 
tion and  substitution. 

Use.  —  In  the  manufacture  of  porcelain,  both  in  the  body  of  the  ware  and  in  the  glaze 
on  its  surface. 

PERTHITE.  As  first  described,  a  flesh-red  aventurine  feldspar  from  Perth,  Ontario, 
Canada,  called  a  soda-orthoclase,  but  shown  by  Gerhard  to  consist  of  interlaminated  ortho- 
clase and  albite.  Many  similar  occurrences  have  since  been  noted,  as  also  those  in  which 
microcline  and  albite  are  similarly  interlaminated,  the  latter  called  microcline-perthite,  or 
microcline-albite-perthite;  this  is  true  in  part  of  the  original  perthite.  When  the  structure 
is  discernible  only  with  the  help  of  the  microscope  it  is  called  microperthite.  Brogger  has 
investigated  not  only  the  microperthites  of  Norway,  but  also  other  feldspars  characterized 
by  a  marked  schiller;  he  assumes  the  existence  of  an  extremely  fine  interlamination  of  albite 
and  orthoclase  ||  801,  not  discernible  by  the  microscope  (cryptoperthite),  and  connected 
with  secondary  planes  of  parting  ||  100  or  ||  801,  which  is  probably  to  be  explained  as  due  to 
incipient  alteration. 

Hyalophane.  (K2,Ba)Al2(SiO3)4  or  K2O.BaO.2Al2O3.8SiO2.  Silica  51 '6,  alumina  21'9, 
baryta  16*4,  potash  101  =  100.  In  crystals,  like  adularia  in  habit  (Fig.  770,  p.  457);  also 
massive.  Cleavage:  c  (001)  perfect;  b  (010)  somewhat  less  so.  H.  =  6-6*5.  G.  =2*805. 
Optically  -.  a.  =  1*542.  ft  =  1*545.  7  =  1-547.  Occurs  in  a  granular  dolomite  in  the 
Binnental,  Switzerland;  also  at  the  manganese  mine  of  Jakobsberg,  Sweden.  Some  other 
feldspars  containing  7  to  15  p.  c.  BaO  have  been  described. 

Celsian.  BaAl2Si2Og,  similar  in  composition  to  anorthite,  but  containing  barium  in- 
stead of  calcium.  Monoclinic.  In  crystals  showing  a  number  of  forms;  twinned  according 
to  Carlsbad,  Manebach  and  Baveno  laws.  Usually  cleavable  massive.  H.  =  6-6*5. 
G.  =  3'37.  Extinction  on  6  (010)  =  28°  3'.  Colorless.  Optically  +  .  a  =  1*584.  ft  = 
1*589.  7  =  1*594.  From  Jakobsberg,  Sweden.  Name  baryta-orthoclase  given  to  mixtures 
of  celsian  and  orthoclase.  Paracelsian  from  Candoglia,  Piedmont,  Italy,  is  the  same  species. 


ft.   Triclinic  Section 


MICROCLINE. 


779 


Triclinic.     Near  orthoclase  in  angles  and  habit,  but  the  angle  be  (010  A 

001)  =  about  89°  30'.  Twins:  like 
orthoclase,  also  polysynthetic  twinning 
according  to  the  albite  and  pericline  laws 
(p.  464),  common,  producing  two  series  of 
fine  lamellae  nearly  at  right  angles  to  each 
other,  hence  the  characteristic  grating- 
structure  of  a  basal  section  in  polarized 
light  (Fig.  779).  Also  massive  cleavable 
to  granular  compact. 

Cleavage:  c(001)  perfect;  6(010)  some- 
what less  so;  M  (1TO)  sometimes  distinct; 
m  (110)  also  sometimes  distinct,  but  less 
easy.  Fracture  uneven.  Brittle.  H.  =  6-6'5.  G  =  2'54-2*57  Luster 
vitreous,  on  c  (001)  sometimes  pearly.  Color  white  to  pale  cream-yellow 
also  red,  green  Transparent  to  translucent.  Optically  -.  Ax.  pi.  nearly 
perpendicular  (82°-83°)  to  6  (010).  Bx0  inclined  15°  26'  to  a  normal  to  6 
°  *'  Bx°-  Extinction-angle  on  c  (001),  +15° 

.     «=  1-522. 


SILICATES  461 

The  essential  identity  of  orthoclase  and  microcline  has  been  urged  by  Mallard  and 
Michel-Levy  on  the  ground  that  the  properties  of  the  former  would  belong  to  an  aggregate 
of  submicroscopic  twinning  lamellae  of  the  latter,  according  to  the  albite  and  pericline  laws. 

Comp.  — Like  orthoclase,  KAlSi3O8  or  K2O.Al2O3.6Sip2  =  Silica  647, 
alumina  18 -4,  potash  16*9  =  100.  Sodium  is  usually  present  in  small  amount: 
sometimes  prominent,  as  in  soda-microcline. 

Pyr.  — •  As  for  orthoclase. 

Diff.  —  Resembles  orthoclase  but  distinguished  by  optical  characters  (e.g.,  the  grating 
structure  in  polarized  light,  Fig.  779);  also  often  shows  fine  twinning-striations  on  a  basal 
surface  (albite  law). 

Micro.  —  In  thin  sections  like  orthoclase  but  usually  to  be  distinguished  by  the  grating- 
like  structure  in  polarized  light  due  to  triclinic  twinning. 

Obs.  —  Occurs  under  the  same  conditions  as  much  common  orthoclase.  The  beautiful 
amazonstone  from  the  Ural  Mts.,  also  that  occurring  in  fine  groups  of  large  crystals  of  deep 
color  in  the  granite  of  Pike's  Peak,  Col.,  is  microcline.  Crystals  from  Ivigtut,  Greenland. 
From  Antsongombato  and  Antoboko  (amazonstone),  Madagascar.  Chesterlite  from  Poor- 
house  quarry,  Chester  Co.,  Pa.,  and  the  aventurine  feldspar  of  Mineral  Hill,  Pa.,  belong  here. 
A  pure  variety  occurs  at  Magnet  Cove,  Ark.  Ordinary  microcline  is  common  at  many  points. 

Use.  —  Same  as  for  orthoclase;  sometimes  as  an  ornamental  material  (amazonstone). 

Anorthoclase.  Soda-microcline.  A  triclinic  feldspar  with  a  cleavage-angle,  be,  010  A  001, 
varying  but  little  from  90°.  Form  like  that  of  the  ordinary  feldspars.  Twinning  as 
with  orthoclase;  also  polysynthetic  according  to  the  albite  and  pericline  laws;  but  in  many 
cases  the  twinning  laminae  very  narrow  and  hence  not  distinct.  Rhombic  section  (see  p. 
462)  inclined  on  6  (010)  4°  to  6°  to  edge  b/c.  G.  =  2 '57-2 "60.  Cleavage,  hardness,  luster, 
and  color  as  with  other  members  of  the  group.  Optically  — ._  Extinction-angle  on  c  (001) 
+5°  45'  to  +2°;  on  b  (010)  6°  to  9.8°.  Bxa  nearly  _L  y  (201).  Dispersion  p  >  v;  hor- 
izontal distinct,  a  =  1'523.  /3  =  1'529.  7  =  1'531.  Axial  angle  variable  with  tem- 
perature, becoming  in  part  monoclinic  in  optical  symmetry  between  86°  and  264°  C.,  but 
again  triclinic  on  cooling;  this  is  true  of  those  containing  little  calcium. 

Chiefly  a  soda-potash,  feldspar  NaAlSisOs  and  KAlSi3p8,  the  sodium  silicate  usually  in 
larger  proportion  (2  :  1,  3  :  1,  etc.),  as  if  consisting  of  albite  and  orthoclase  molecules.  Cal- 
cium (CaAl2Si2p8)  is  also  present  in  relatively  very  small  amount. 

These  triclinic  soda-potash  feldspars  are  chiefly  known  from  the  andesitic  lavas  of 
Pantelleria.  Most  of  these  feldspars  come  from  a  rock,  called  pantellerite.  Also  prominent 
from  the  augite-syenite  of  southern  Norway  and  from  the  "  Rhomben-porphyr  "  near  Chris- 
tiania.  Here  is  referred  also  a  feldspar  in  crystals,  tabular  j|  c  (001),  and  twinned  according 
to  the  Manebach  and  less  often  Baveno  laws  occurring  in  the  lithophyses  of  the  rhyolite  of 
Obsidian  Cliff.  Yellowstone  Park.  It  shows  the  blue  opalescence  in  a  direction  parallel 
with  a  steep  orthodome  (cf.  p.  457). 

Albite-Anorthite  Series.     Plagioclase  Feldspars  * 
Between  the  isomorphous  species 

ALBITE  NaAlSisOg  Ab 

ANORTHITE  CaAl2Si208  An 

there  are  a  number  of  intermediate  subspecies,  regarded,  as  urged  by  Tscher- 
mak,  as  isomorphous  mixtures  of  these  molecules,  and  defined  according  to  the 
ratio  in  which  they  enter;  their  composition  is  expressed  in  general  by  the 
formula  AbnAnm.  They  are: 

OLIGOCLASE  Ab6Ani    to    Ab3Ani 

ANDESINE  Ab3Ani    to 

LABRADORITE  AbiAni    to 

and  Bytownite  AbiAn3    to     AbiAn6 

From  albite  through  the  successive  intermediate  compounds  to  anorthite 
with  the  progressive  change  in  composition  (also  specific  gravity,  melting 

*  The  triclinic  feldspars  of  this  series,  in  which  the  two  cleavages  6  (010)  and  c  (001)  are 
oblique  to  each  other,  are  often  called  in  general  plagioclase  (from  Tr\ayios,  oblique). 


462 


DESCRIPTIVE  MINERALOGY 


points,  etc.),  there  is  also  a  corresponding  change  in  crystallographic  form,  and 
in  certain  fundamental  optical  properties. 

Crystalline  Form.     The  axial  ratios  and  angles  given  on  p.  456  show  that 

these    triclinic     feldspars 

780  781  approach  orthoclase  close- 

ly in  form,  the  most  ob- 
vious difference  being  in 
the  cleavage-angle  6c010 
A  001,  which  is  90°  in 
orthoclase,  86°  24'  in  albite, 
and  85°  50'  in  anorthite. 
There  is  also  a  change  in 
the  axial  angle  7,  which  is 
88°  in  albite,  about  90°  in 
oligoclase  and  andesine, 
and  91°  in  anorthite.  This 
transition  appears  still 
more  strikingly  in  the 
position  of  the  "  rhombic 
section,"  by  which  the 
twins  according  to  the  pericline  law  are  united  as  explained  below. 

Twinning.  The  plagioclase  feldspars  are  often  twinned  in  accordance 
with  the  Carlsbad,  Baveno,  and  Manebach  laws  common  with  orthoclase 
(p.  457).  Twinning  is  also  almost  universal  according  to  the  albite  law 
—  twinning  plane  the  brachypinacoid;  this  is  usually  polysynthetic,  i.e., 
repeated  in  the  form  of  thin  lamellae,  giving  rise  to  fine  striations  on  the  basal 
cleavage  surface  (Figs.  780,  781).  Twinning  is  also  common  according  to  the 
pericline  law  —  twinning  axis  the  macrodiagonal  axis  6;  when  polysynthetic 
this  gives  another  series  of  fine  striations  seen  on  the  brachypinacoid. 

The  composition-plane  in  this  pericline  twinning  is  a  plane  passing  through  the  crystal  in 
such  a  direction  that  its  intersections  with  the  prismatic  faces  and  the  brachypinacoid  make 
equal  plane  angles  with  each  other.  The  position  of  this  rhombic  section  and  the  consequent 
direction  of  the  striations  on  the  brachypinacoid  change  rapidly  with  a  small  variation  in 
the  angle  7.  In  general  it  may  be  said  to  be  approximately  parallel  to  the  base,  but  in 
albite  it  is  inclined  backward  (+,  Figs.  782  and  784)  and  in  anorthite  to  the  front  (— ,  Fig. 
783) ;  for  the  intermediate  species  its  position  varies  progressively  with  the  composition. 
782  783  784 


Plagioclase  with  twinning  lamellae.  Fig.  780  section  ||  c 
(001)  showing  vibration-directions  (cf.  Fig.  784),  ordin- 
ary light;  Fig.  781  section  in  polarized  light. 


Fig.  782,  Rhombic  section  in  albite.     783,  Same  in  anorthite.     784,  Typical  form  showing 
+  and  —  extinction-directions  on  c  (001)  and  6  (010). 

Thus  for  the  angle  between  the  trace  of  this  plane  on  the  brachypinacoid  and  the  edge 
6/c,  we  have  for  Albite  +22°  to  +20°;  for  Oligoclase  +9°  to  +3£°;  for  Andesine  +1° 
to  -2°;  for  Labradorite  -9°  to  -10°;  for  Anorthite  -15°  to  -17°. 


SILICATES 


463 


785 


the 

togeth 

of  microline. 

Optical  Characters.  There 
is  also  a  progressive  change 
in  the  position  of  the  ether- 
axes  and  the  optic  axial 
plane  in  passing  from 
albite  to  anorthite.  This 
is  most  simply  exhibited  by 
the  position  of  the  planes 
of  light- vibration,  as  observed 
in  sections  parallel  to  the 
two  cleavages,  basal  c  and 
brachy-pinacoidal  6,  in  other 
words  the  extinction-angle 
formed  on  each  face  with  the 
edge  b/c  (cf.  Fig.  784).  _ 

The  approximate  position 
of    the    ether-axes    for    the 
different   feldspars  is  shown 
in  Fig.  785  (after  Iddings). 
The  axis  Z  does  not  vary  very  Projection  of  the  optical  directions  X,  Y  and  Z  upon 
much     from     the     zone     bc\      b    (010).     1,    Albite;    2,   Oligoclase;    3,    Andesine; 
010   A   001,  but  the  axis   X      4»  Labradorite;  5,  Anorthite.     (After  Iddings.) 
varies  widely,  and  hence  the  axial  plane  has  an  entirely  different  position 
in  albite  from  what  it  has  in  anorthite.     Furthermore  albite  is  optically  pos- 


786 


Albife 


or*. 


Andesine 


Anorthite 


+20 


-10 


-20 


-30 


-40 


Ab  100          90  80  70*  60  50  40  30  20  0 

An   0  10  20  30  40  50  60  70  80  90          100 

Extinction  Angles  on  (001)  and  (010)  in  the  Lime-soda  feldspars.     (After  Iddings.) 


464 


DESCRIPTIVE  MINERALOGY 


itive,  that  is  Z  —  Bx,  while  anorthite  is  negative  or  X  =  Bx;    for  certain 
andesines  the  axial  angle  is  sensibly  90°. 

Fig.  786  (after  Iddings)  shows  the  variation  in  the  extinction  angles  on 
the  cleavage  faces,  c  (001)  and  b  (010),  for  the  different  mixtures  of  the  albite 
and  anorthite  molecule. 

Micro.  —  In  rock  sections  the  plagioclase  feldspars  are  distinguished  by  their  lack  of 
color,  low  refractive  relief,  and  low  interference-colors,  which  in  good  sections  are  mainly 
dark  gray  and  scarcely  rise  into  white  of  the  first  order;  also  by  their  biaxial  character  in 
converging  light.  In  the  majority  of  cases  they  are  easily  told  by  the  parallel  bands  or  fine 
lamellae  which  pass  through  them  due  to  the  multiple  twinning  according  to  the  albite 
law;  one  set  of  bands  or  twin  lamellae  exhibits  in  general  a  different  interference-color 
from  the  other  (cf.  Figs.  780,  781).  They  are  thus  distinguished  not  only  from  quartz  and 
orthoclase,  with  which  they  are  often  associated,  but  from  all  the  common  rock-making 
minerals.  To  distinguish  the  different  species  and  sub-species  from  one  another,  as  albite 
from  laboradorite  or  andesine,  is  more  difficult.  In  sections  having  a  definite  orientation 
(||  c  (001)  and  ||  6  (010)  )  this  can  generally  be  done  by  determining  the  extinction  angles  (cf . 
p.  462  and  Fig.  784).  In  general  in  rock  sections  special  methods  are  required;  these  are 
discussed  in  the  various  texts  devoted  to  this  subject. 


ALBITE. 
Triclinic. 
=  88°  9'. 


Axed  a  :  b  :  c  =  0*6335  :  1  :  0-5577;  a  =  94°  3',  (3  =  116°  29', 


787 


788 


be,  010  A  001  =  86°  24'. 
mM,  110  A  110  =  59°  14'. 
bm,  010  A  110  =  60°  26'. 
cm,  001  A  110  =  65°  17'. 
cM,  001  A  110  =  69°  10'. 
ex,  001  A  101  =  52°  16'. 

Twins  as  with  orthoclase; 
also  very  common,  the  tw.  pi. 
b  (010),  albite  law  (p.  462), 
usually  contact-twins,  and 
polysynthetic,  consisting  of 
thin  lamellae  and  with  con- 
sequent fine  striations  on 
c(001)  (Fig.  790);  tw.  axis  b  axis,  peridine  law,  contact-twins  whose  compos- 
ition-face is  the  rhombic  section  (Figs.  782  and  792);  often  polysynthetic 
and  showing  fine  striations  which  on  6  (010) 
are  inclined  backward  +22°  to  the  edge  b/c. 

Crystals  often  tabular  ||  b  (010);  also 
elongated  ||  6  axis  as  in  the  variety  pericline. 
Also  massive,  either  lamellar  or  granular;  the 
laminae  often  curved,  sometimes  divergent; 
granular  varieties  occasionally  quite  fine  to 
impalpable. 

Cleavage:  c(001)  perfect;  6(010)  somewhat 
less  so;  m  (110)  imperfect.  Fracture  uneven 
to  conchoidal.  Brittle.  H.  =  6-6*5.  G.  = 
2-62-2-65.  Luster  vitreous;  on  a  cleavage 
surface  often  pearly.  Color  white;  also  occa- 
sionally bluish,  gray,  reddish,  greenish,  and 
green;  sometimes  having  a  bluish  opalescence 

or    play    of    colors    on    c  (001).     Streak  uncolored.     Transparent  to  sub- 
translucent. 


SILICATES  465 

Optically-!-.     Extinction-angle  with   edge  b/c  =4-4°  30'  to  2°  on  c, 
and  =   +20°  to  15°  on  b  (Fig.  782).     Dispersion  for  Bxa,  p  <  v;  also  in- 
clined, horizontal;    for  Bx0,  ^91  ^92 
p    >  v,    inclined,    crossed. 
a=l-531.    J3  =  l'£ 
1-540.     2V=  77°. 
fringence  weak,    y  —  a  = 
0-009. 

Comp.  —  A  silicate  of 

aluminium     and     sodium,  Pericline 

NaAlSi3O8  or  NaaO.Al20». 
6SiO2  =  Silica  687,  alumina  19'5,  soda  11 -8  =100.  Calcium  is  usually 
present  in  small  amount,  as  anorthite  (CaAl2Si2O8),  and  as  this  in- 
creases it  graduates  through  oligoclase-albite  to  oligoclase  (cf.  p.  466).  Potas- 
sium may  also  be  present,  and  it  is  then  connected  with  anorthoclase  and 
microcline. 

Var.  —  Ordinary.  In  crystals  and  massive.  The  crystals  often  tabular  ||  b  (010).  The 
massive  forms  are  usually  nearly  pure  white,  and  often  show  wavy  or  curved  laminae.  Per- 
isterite  is  a  whitish  adularia-like  albite,  slightly  iridescent,  named  from  Trepto-repa,  pigeon. 
Aventurine  and  moonstone  varieties  also  occur.  Pericline  from  the  chloritic  schists  of  the 
Alps  is  in  rather  large  opaque  white  crystals,  with  characteristic  elongation  in  the  direction 
of  the  6  axis,  as  shown  in  Figs.  791  and  792,  and  commonly  twinned  with  this  as  the  twinning 
axis  (pericline  law). 

Pyr.,  etc.  —  B.B.  fuses  at  4  to  a  colorless  or  white  glass,  imparting  an  intense  yellow  to 
the  flame.  Not  acted  upon  by  acids. 

Diff.  —  Resembles  barite  in  some  forms,  but  is  harder  and  of  lower  specific  gravity; 
does  not  effervesce  with  acid  (like  calcite).  Distinguished  optically  and  by  the  common 
twinning  striations  on  c  (001)  from  orthoclase;  from  the  other  tri clinic  feldspars  partially 
by  specific  gravity  and  better  by  optical  means  (see  p.  463). 

Artif.  —  Albite  acts,  in  regard  to  its  artificial  formation,  like  orthoclase,  which  see. 

Obs.  —  Albite  is  a  constituent  of  many  igneous  rocks,  especially  those  of  alkaline  type, 
as  granite,  elaeolite-syenite,  diorite,  etc.;  also  in  the  corresponding  feldspathic  lavas.  In 
perthite  (p.  460)  it  is  interlaminated  with  orthoclase  or  microcline,  and  similar  aggrega- 
tions, often  on  a  microscopic  scale,  are  common  in  many  rocks.  Albite  is  common  also 
in  gneiss,  and  sometimes  in  the  crystalline  schists.  Veins  of  albitic  granite  are  often 
repositories  of  the  rarer  minerals  and  of  fine  crystallizations  of  gems,  including  beryl,  tour- 
maline, allanite,  columbite,  etc.  It  is  found  in  disseminated  crystals  in  granular  limestone. 

Some  of  the  most  prominent  European  localities  are  in  cavities  and  veins  in  the  granite 
or  granitoid  rocks  of  the  Swiss  and  Austrian  Alps,  associated  with  adularia,  smoky  quartz, 
chlorite,  titanite,  apatite,  and  many  rarer  species :  it  is  often  implanted  in  parallel  position 
upon  the  orthoclase.  Thus  in  the  Alps  the  St.  Gothard  region;  Roc  Tourne  near  Modane, 
Savoie;  on  Mt.  Skopi  (pericline);  Tavetschtal;  in  Austria  at  Schmirnand  Greiner,  Tyrol; 
also  Pfitsch,  Rauris,  the  Zillertal,  Krimml,  Schneeberg  in  Passeir,  Tyrol,  in  simple  crystals. 
Also  in  DaupLine,  France,  in  similar  association;  Elba.  Also  Hirschberg  in  Silesia;  Penig 
in  Saxony;  with  topaz  at  Mursinka  in  the  Ural  Mts.  and  near  Miask  in  the  Ilmen  Mts.; 
Cornwall,  England;  Mourne  Mts.  in  Ireland.  Fine  crystals  from  Greenland. 

In  the  United  States,  in  Me.,  at  Paris,  with  red  and  blue  tourmalines,  also  at  Topsham. 
In  Mass.,  at  Chesterfield,  in  lamellar  masses  (cleavelandite) ,  slightly  bluish,  also  fine  granu- 
lar. In  N.  H.,  at  Acworth  and  Alstead.  In  Conn.,  at  Haddam;  at  the  Middletown  feld- 
spar quarries,  at  Branchville,  in  fine  crystals  and  massive.  In  N.  Y.,  at  Moriah,  Essex 
Co.,  of  a  greenish  color;  at  Diana,  Lewis  Co.,  and  Macomb,  St.  Laurence  Co.  In  Pa.,  at 
Union ville,  Chester  Co.  In  Va.,  at  the  mica  mines  near  Amelia  Court-House  in  splendid 
crystallizations.  In  Col.,  in  the  Pike's  Peak  region  with  smoky  quartz  and  amazonstone. 

The  name  albite  is  derived  from  albus,  white,  in  allusion  to  its  common  color. 

Use.  —  Same  as  orthoclase  but  not  so  commonly  employed;  some  varieties  which 
show  an  opalescent  play  of  colors  when  polished  form  the  ornamental  material  known  as 
moonstone. 


466  DESCRIPTIVE    MINERALOGY 

Oligoclase. 

Triclinic.  Axes,  see  p.  456.  be,  010  A  001  =  86°  32'.  Twins  observed 
according  to  the  Carlsbad,  albite,  and  pericline  laws.  Crystals  not  common. 
Usually  massive,  cleavable  to  compact. 

Cleavage:  c  (001)  perfect;  6  (010)  somewhat  less  so.  Fracture  conchoidal 
to  uneven.  Brittle.  H.  =  6-6 -5.  G.  =  2 1-65-2 '67.  Luster  vitreous  to  some- 
what pearly  or  waxy.  Color  usually  whitish,  with  a  faint  tinge  of  grayish 
green,  grayish  white,  reddish  white,  greenish,  reddish;  sometimes  aventurine. 
Transparent,  subtranslucent.  Optical  characters,  see  p.  463. 

Comp.  —  Intermediate  between  albite  and  anorthite  and  corresponding 
to  Ab6Ani  to  Ab2Ani,  but  chiefly  to  Ab3Ani,  p.  461. 

Var.  —  1.  Ordinary.  In  crystals  or  more  commonly  massive,  cleavable.  The  varieties 
containing  soda  up  to  10  p.  c.  are  called  oligoclase-albite.  2.  Aventurine  oligoclase,  or  sun- 
stone,  is  of  a  grayish  white  to  reddish  gray  color,  usually  the  latter,  with  internal  yellowish 
or  reddish  fire-like  reflections  proceeding  from  disseminated  crystals  of  probably  either 
hematite  or  gothite. 

Pyr.,  etc.  —  B.B.  fuses  at  3-5  to  a  clear  or  enamel-like  glass.  Not  materially  acted 
upon  by  acids. 

Diff.  —  See  orthoclase  (p.  459)  and  albite  (p.  465);  also  pp.  456,  463. 

Obs.  —  Occurs  in  porphyry,  granite,  syenite,  and  also  in  different  effusive  rocks,  as 
andesite.  It  is  sometimes  associated  with  orthoclase  in  granite  or  other  granite-like  rock. 
Among  its  localities  are  Danviks-Zoll  near  Stockholm,  Sweden;  Pargas  in  Finland;  Shai- 
tansk,  Ural  Mts.;  in  syenite  of  the  Vosges  Mts.,  France;  at  Albula  in  Orisons,  Switzerland; 
Marienbad,  Bohemia;  in  France  at  Chalanches  in  Allemont,  and  Bourg  d'Oisans,  Dauphine; 
as  sunstone  at  Tvedestrand,  Norway;  at  Hittero,  Norway;  Lake  Baikal,  Siberia. 

In  the  United  States,  at  Fine  and  Macomb,  St.  Lawrence  Co.,  N.  Y.,  in  good  crystals; 
at  Danbury,  Conn.,  with  orthoclase  and  danburite;  Haddam,  Conn.;  at  the  emery  mine, 
Chester,  Mass.,  granular;  at  Unionville,  Pa.,  with  euphyllite  and  corundum;  Mineral  Hill, 
Delaware  Co.,  Pa.;  at  Bakersville,  N.  C.,  in  clear  glassy  masses,  showing  cleavage  but  no 
twinning.  Named  in  1826  by  Breithaupt  from  0X1705,  little,  and  /cXao-is,  fracture. 

Andesine. 

Triclinic.  Axes,  see  p.  456.  be,  010  A  001  =  86°  14'.  Twins  as  with 
albite.  Crystals  rare.  Usually  massive,  cleavable  or  granular. 

Cleavage:  c  (001)  perfect;  b  (010)  less  so;  also  M  (110)  sometimes 
observed.  H.  =  5-6.  G.  =  2'68-2'69.  Color  white,  gray,  greenish,  yellow- 
ish, flesh-red.  Luster  subvitreous  to  pearly.  Optical  characters,  see  p.  463. 

Comp.  —  Intermediate  between  albite  and  anorthite,  corresponding  to 
Ab  :  An  in  the  ratio  of  3  :  2,  4  :  3  to  1  :  1,  see  p.  461. 


_  r.,  etc.  —  Fuses  in  thin  splinters  before  the  blowpipe.  Imperfectly  soluble  in  acids: 
Obs.  —  Observed  in  many  granular  and  volcanic  rocks;  thus  occurs  in  the  Andes,  at 
Marmato,  Colombia,  as  an  ingredient  of  the  rock  called  andesite;  in  the  porphyry  of 
1  JLsterel,  Dept.  du  Var,  France;  in  the  syenite  of  Alsace  in  the  Vosges  Mts.;  at  Vapnefiord, 
Iceland;  Bodenmais,  Bavaria;  Frankenstein,  Silesia.  Sanford,  Me.,  with  vesuvianite 
Common  in  the  igneous  rocks  of  the  Rocky  Mts.  Crystals  from  Sardinia  and  Greenland. 

Labradorite.    Labrador  Feldspar. 

Triclinic.  Axes,  see  p.  456.  Cleavage  angle  be  010  A  001  =  86°  4'. 
Forms  and  twinning  similar  to  the  other  plagioclase  species.  Crystals  often 
very  thin  tabular  1 1  b  (010) ;  and  rhombic  in  outline  bounded  by  cy  or  ex  (Fig. 
455,  p.  172).  Also  massive,  cleavable  or  granular;  sometimes  crvptocrvstal- 
hne  or  hornstone-like. 

Cleavage:  c  (001)  perfect;  b  (010)  less  so;  M  (110)  sometimes  distinct. 
*T  ~~  5~b<  G<  =  270-272.  Duster  on  c  pearly,  passing  into  vitreous;  else- 
where vitreous  or  subresinous.  Color  gray,  brown,  or  greenish;  sometimes 


SILICATES 


467 


colorless  and  glassy;  rarely  porcelain- white;  usually  a  beautiful  change  of 
colors  in  cleavable  varieties,  especially  ||  6  (010).  Streak  uncolored.  Trans- 
lucent to  subtranslucent.  Optical  characters,  see  p.  463. 

Play  of  colors  a  common  character,  but  sometimes  wanting  as  in  some  colorless  crys- 
tals. Blue  and  green  are  the  predominant  colors;  but  yellow,  fire-red,  and  pearl-gray  also 
occur.  Vogelsang  regards  the  common  blue  color  of  labradorite  as  an  interference-phenom- 
enon due  to  its  lamellar  structure,  while  the  golden  or  reddish  schiller,  with  the  other  colors, 
is  due  to  the  presence  of  black  acicular  microlites  and  yellowish  red  microscopic  lamellae,  or 
to  the  combined  effect  of  these  with  the  blue  reflections.  Schrauf  has  examined  the  inclu- 
sions, their  position,  etc.,  and  given  the  names  microplakite  and  microphyllite  to  two  groups 
of  them.  (See  references  on  p.  181.) 

Comp.  —  Intermediate  between  albite  and  anorthite  and  corresponding 
chiefly  to  Ab  :  An  in  a  ratio  of  from  1  :  1  to  1  :  3,  p.  461. 

The  feldspars  which  lie  between  labradorite  proper  and  anorthite  have  been  embraced 
by  Tschermak  under  the  name  bytownite.  The  original  bytownite  of  Thomson  was  a 
greenish  white  feldspathic  mineral  found  in  a  boulder  near  Bytown  (now  Ottawa)  in  Onta- 
rio, Canada. 

Pyr.,  etc.  —  B.B.  fuses  at  3  to  a  colorless  glass.  Decomposed  with  difficulty  by  hydro- 
chloric acid,  generally  leaving  a  portion  of  undecomposed  mineral. 

Diff.  —  The  beautiful  play  of  colors  is  a  common  but  not  universal  character.  Other- 
wise distinguished  as  are  the  other  feldspars  (pp.  459,  465). 

Obs.  —  Labradorite  is  an  essential  constituent  of  various  igneous  rocks,  especially  of 
the  basic  kinds,  and  usually  associated  with  some  member  of  the  pyroxene  or  amphibole 
groups.  Thus  with  hypersthene  in  norite,  with  diallage  in  gabbro,  with  some  form  of 
pyroxene  in  diabase,  basalt,  dolerite,  also  andesite,  tephrite,  etc.  Labradorite  also  occurs 
in  other  kinds  of  lava,  and  is  sometimes  found  in  them  in  glassy  crystals,  as  in  those  of  Etna, 
Vesuvius,  at  Kilauea,  Hawaiian  Islands. 

The  labradoritic  massive  rocks  are  most  common  among  the  formations  of  the  Archaean 
era.  Such  are  part  of  those  of  British  America,  northern  New  York,  Pennsylvania,  Arkan- 
sas; those  of  Greenland,  Norway,  Finland,  Sweden,  and  probably  of  the  Vosges  Mts. 

On  the  coast  of  Labrador,  labradorite  is  associated  with  hornblende,  hypersthene,  and 
magnetite.  It  is  met  with  in  many  places  in  Quebec.  Occurs  abundantly  through  the  cen- 
tral Adirondack  region  in  northern  N.  Y.;  in  the  Wichita  Mts.,  Ark. 

Labradorite  was  first  brought  from  the  Isle  of  Paul,  on  the  coast  of  Labrador,  by  Mr. 
Wolfe,  a  Moravian  missionary,  about  the  year  1770. 

Use.  —  The  varieties  showing  a  play  of  colors  are  used  as  ornamental  material. 

MASKELYNITE.     In  colorless  isotropic  grains  in  meteorites;  composition  near  labradorite. 

ANORTHITE.     Indianite. 

Triclinic.     Axes  a  :  b  :  c  =  0-6347 
7  =  91°  12'. 

be,  010  A  001  =  85°  50'. 
mM,  110  A  110  =  59°  29'. 
bm,  010  A  110  =  58°  4'. 
cm,  001  A  110  =  65°  53'. 
cM,  001  A  110  =  69°  20'. 
cy,  001  A  201  =  81°  14'. 

Twins  as  with  albite  (p.  462 
and  p.  464).  Crystals  usually 
prismatic  ||  c  axis  (Fig.  793,  also 
Fig.  364,  p.  146),  less  often  elon- 
gated 1 1  b  axis,  like  pericline  (Fig. 
794).  Also  massive,  cleavable, 
with  granular  or  coarse  lamellar 
structure. 

Cleavage:  c  (001)  perfect;  b  (010)  somewhat  less  so.     Fracture  conchoidal 


1  :  0-5501;  a  =  93°  13',  ft  =  115°  55|', 


793 


794 


468  DESCRIPTIVE   MINERALOGY 

to  uneven.  Brittle.  H.  =  6-6'5.  G.  =  2-74-276.  Color  white,  grayish, 
reddish.  Streak  uncolored.  Transparent  to  translucent. 

Optically  -.  Ax.  pi.  nearly  _L  e  (021),  and  its  trace  inclined  60°  to  the 
edge  c/e  from  left  above  behind  to  right  in  front  below.  Extinction-angles 
on  c  (001),  -34°  to  -42°  with  edge  6/c;  on  b  (010),  -35°  to  -43°  (Fig. 
784,  p.  462).  Dispersion  p  <  v,  also  inclined.  2  V  =  78°.  a  =  1'576. 
j8  =  1*584.  7  =  1*588.  Birefringence  stronger  than  with  albite. 

Comp.  —  A  silicate  of  aluminium  and  calcium,  CaAl2Si2O8  or  CaO.Al203. 
2SiO2  =  Silica  43'2,  alumina  367,  lime  20-1  =  100.  Soda  (as  NaAlSi3O8)  is 
usually  present  in  small  amount,  and  as  it  increases  there  is  a  gradual  transi- 
tion through  bytownite  to  labradorite. 

Var.  —  Anorthite  was  described  from  the  glassy  crystals  of  Mte.  Somma,  Vesuvius;  and 
christianite  and  biotine  are  the  same  mineral.  Thiorsauite  is  the  same  from  Iceland.  In- 
dianite  is  a  white,  grayish,  or  reddish  granular  anorthite  from  India,  where  it  occurs  as  the 
gangue  of  corundum,  first  described  in  1802  by  Count  Bournon.  Cyclopite  occurs  in  small, 
transparent,  and  glassy  crystals,  tabular  ||-  b  (010),  coating  cavities  in  the  dolerite  of  the 
Cyclopean  Islands  and  near  Trezza  on  Etna.  Amphodelite,  lepolite,  latrobite  also  belong  to 
anorthite. 

Pyr.,  etc.  —  B.B.  fuses  at  5  to  a  colorless  glass.  Anorthite  from  Mte.  Somma,  and 
indianite  from  the  Carnatic,  India,  are  decomposed  by  hydrochloric  acid,  with  separation.of 
gelatinous  silica. 

Artif.  —  Anorthite  is  the  easiest  of  the  feldspars  to  be  formed  artificially.  Unlike  the 
alkalic  feldspars  it  can  be  easily  formed  in  a  dry  fusion  of  its  constituents.  This  method 
becomes  progressively  more  difficult  as  the  albite  molecule  is  added  to  the  composition. 
Anorthite  is  frequently  observed  in  slags  and  is  easily  produced  in  artificial  magmas.  It 
further  is  often  produced  when  more  complex  silicates  are  broken  down  by  fusion. 

Obs.  —  Occurs  in  some  diorites;  occasionally  in  connection  with  gabbro  and  serpentine 
rocks;  in  some  cases  along  with  corundum;  in  many  volcanic  rocks,  andesites,  basalts,  etc.; 
as  a  constituent  of  some  meteorites  ( Juvenas,  Stannern) . 

Anorthite  (christianite  and  biotine)  occurs  at  Mount  Vesuvius  in  isolated  blocks  among 
the  old  lavas  in  the  ravines  of  Monte  Somma;  in  the  Albani  Mts.;  on  the  Pesmeda  Alp, 
Monzoni,  Tyrol,  as  a  contact  mineral;  Aranyer  Berg,  Transylvania,  in  andesite;  in  Ice- 
land; near  Bogoslovsk  in  the  Ural  Mts.  In  the  Cyclopean  Islands  (cyclopite).  In  the  lava 
of  the  island  of  Miyake,  Japan. 

In  crystals  from  Franklin,  N.  J.;  from  Phippsburg,  Me. 

Anorthite  was  named  in  1823  by  Rose  from  avopdos,  oblique,  the  crystallization  being 
triclinic. 

Anemousite.  A  feldspar  having  the  composition,  Na2O.2CaO.3Al2O3.9SiO2.  This  does 
not  agree  with  any  possible  member  of  the  albite-anorthite  series.  This  is  explained  by 
assuming  the  presence  in  small  amount  of  a  sodium-anorthite  molecule,  Na2O.Al2O3.2SiO2, 
to  which  the  name  carnegieite  has  been  given.  Cleavage  angle  =  85°  59'.  G.  =  2 '68. 
a  =  1-555.  j8  =  1-559.  7  =  1'563.  2  V  =  82°  48'.  Found  as  loose  crystals  on  Mte. 
Rosso,  Island  of  Linosa.  Name  derived  from  the  ancient  Greek  name  of  the  island.  Car- 
negieite is  named  in  honor  of  Andrew  Carnegie. 


;H.   Metasilicates.     RSiO3 

Salts  of  Metasilicic  Acid,  H^SiOs;  characterized  by  an  oxygen  ratio  of  2  :  1 
for  silicon  to  bases.  The  Division  closes  with  a  number  of  species,  in  part  of 
somewhat  doubtful  composition,  forming  a  transition  to  the  Orthosilicates. 

The  metasilicates  include  two  prominent  and  well-characterized  groups, 
viz.,  the  Pyroxene  Group  and  the  Amphibole  Group.  There  are  also  others 
less  important. 


SILICATES 


469 


Leucite  Group.     Isometric 

In  several  respects  leucite  is  allied  to  the  species  of  the  FELDSPAR  GROUP,  which  imme- 
diately precede. 

Leucite  KAl(SiO3)2  Isometric  at  500° 

Pseudo-isometric  at  ordinary  temperatures. 
Pollucite  H2Cs4Al4(Si03)9  Isometric 

LEUCITE.     Amphigene. 

Isometric  at  500°  C.;  pseudo-isometric  under  ordinary  conditions  (see  p. 
302).  Commonly  in  crystals  varying  in  angle  but 
little  from  the  tetragonal  trisoctahedron  n  (211), 
sometimes  with  a  (100),  and  d  (110)  as  subordinate 
forms.  Faces  often  showing  fine  striations  due  to 
twinning  (Fig.  795).  Also  in  disseminated  grains; 
rarely  massive  granular. 

Cleavage:  d  (110)  very  imperfect.  Fracture 
conchoidal.  Brittle.  H.  =  5'5-6.  G.  =  2-45-2-50. 
Luster  vitreous.  Color  white,  ash-gray  or  smoke- 
gray.  Streak  uncolored.  Translucent  to  opaque. 
Usually  shows  very  feeble  double  refraction:  co  = 
1-508,6  =  1-509  (p.  302). 

Comp.  —  KAl(Si03)2  or  K2O.Al2O3.4Si02  =  Silica  55*0,  alumina   23'5. 
potash  21'5  =  100. 

Soda  is  present  only  in  small  quantities,  unless  as  introduced  by  alteration;  traces  of 
lithium,  also  of  rubidium  and  caesium,  have  been  detected.  Leucite  and  analcite  are  closely 
related  chemically  as  is  shown  by  the  fact  that  the  two  species  can  be  converted  into  each 
other  when  heated  with  sodium  or  potassium  chlorides  or  carbonates. 

Pyr.,  etc.  —  B.B.  infusible;  with  cobalt  solution  gives  a  blue  color  (aluminium).  De- 
composed by  hydrochloric  acid  without  gelatinization. 

Diff .  —  Characterized  by  its  trapezohedral  form,  absence  of  color,  and  inf usibility.  It 
is  softer  than  garnet  and  harder  than  analcite;  the  latter  yields  water  and  fuses. 

Micro.  —  Recognized  in  thin  sections  by  its  extremely  low  refraction,  isotropic  charac- 
ter, and  the  symmetrical  arrangement  of  inclusions  (Fig.  796;  also  Fig.  485,  p.  180).  Larger 

796 


Leucite  crystals  from  the  leucitite  of  the  Bearpaw  Mts.,  Montana  (Pirsson).     These  show 
the  progressive  growth  from  skeleton  forms  to  complete  crystals  with  glass  inclusions . 

crystals  are  commonly  not  wholly  isotropic  and,  further,  show  complicated  systems  of 
twinning-lines  (Fig.  795);  the  birefringence  is,  however,  very  low,  and  the  colors  scarcely 
rise  above  dark  gray;  they  are  best  seen  by  introduction  of  the  quartz  or  gypsum  plate 
yielding  red  of  the  first  order.  The  smaller  leucites,  which  lack  this  twinning  or  the  inclu- 
sions, are  only  to  be  distinguished  from  sodalite  or  analcite  by  chemical  tests. 

Artif .  —  Leucite  is  easily  prepared  artificially  by  simply  fusing  together  its  constitu- 
ents in  proper  proportion  and  allowing  the  melt  to  crystallize  slowly.  The  addition  of 
potassium  vanadate  produces  larger  crystals.  Leucite  has  been  formed  when  microcline 
and  biotite  were  fused  together  and  also  when  muscovite  was  fused  alone. 

Obs.  —  Leucite  occurs  only  in  igneous  rocks,  and  especially  in  recent  lavas,  as  one  of 
the  products  of  crystallization  of  magmas  rich  in  potash  and  low  in  silica  (for  which  reason 
this  species  rather  than  orthoclase  is  formed) .  The  larger  embedded  crystals  are  commonly 
anisotropic  and  show  twinning  lamellae;  the  smaller  ones,  forming  the  groundmass,  are 
isotropic  and  without  twinning.  Found  in  leucitites  and  leucite-basalts,  leucitophyres, 
leucite-phonolites  and  leucite-tephrites;  also  in  certain  rocks  occurring  in  dikes.  Very  rare 


470  DESCRIPTIVE    MINERALOGY 

in  intruded  igneous  rocks,  only  one  or  two  instances  being  known;  but  its  former  presence 
under  such  conditions  is  indicated  by  pseudomorphs,  often  of  large  size  (pseudoleucite) 
consisting  of  neph  elite  and  orthoclase,  also  of  anal  cite. 

The  prominent  localities  are,  first  of  all,  Vesuvius  and  Mte.  Somma,  where  it  is  thickly 
disseminated  through  the  lava  in  grains,  and  in  large  perfect  crystals;  also  in  ejected 
masses;  also  near  Rome,  at  Capo  di  Bove,  Rocca  Monfina,  etc.  Further  in  leucite-tephrite 
at  Proceno  near  Lake  Bolsena  in  central  Italy;  in  Germany  about  the  Laacher  See  and  at 
several  points  in  the  Eifel;  at  Riedennear  Andernach;  at  Meichesin  the  Vogelsgebirge;  in 
the  Kaiserstuhlgebirge;  Wiesental,  Bohemia.  Occurs  in  Brazil,  at  Pinhalzinho.  From  the 
Cerro  de  las  Virgines,  Lower  California.  In  the  United  States  it  is  present  in  a  rock  in 
the  Green  River  Basin  at  the  Leucite  Hills,  Wy. ;  also  in  the  Absaroka  range,  in  north- 
western Wy.;  in  the  Highwood  and  Bearpaw  Mts.,  Mon.  (in  part  pseudoleucite).  On  the 
shores  of  Vancouver  Island,  where  magnificent  groups  of  crystals  have  been  found  as  drift 
boulders. 

Pseudoleucite  (see  above)  occurs  in  the  phonolite  (tinguaite)  of  the  Serra  de  Tingua, 
Brazil;  at  Magnet  Cove,  Ark.;  near  Hamburg,  N.J.;  Mon.;  also  in  the  Cariboo  District, 
British  Columbia. 

Named  from  Xewcos,  white,  in  allusion  to  its  color. 

Pollucite.  Essentially  H2O.2Cs2O.2Al2O3.9SiO2.  Isometric;  often  in  cubes;  also  mas- 
sive. H.  =  6'5.  G.  =  2-901.  Colorless,  n  =  1-525.  Occurs  very  sparingly  in  the  island 
of  Elba,  with  petalite  (castorite);  also  at  Hebron  and  Rumford,  Me. 


Ussingite.  HNa2Al(Si03)3.  Triclinic.  Three  cleavages.  G.  =  2-5.  H.  =  6-7.  Color 
reddish  violet.  Indices,  1-50-1 '55.  Easily  fusible.  Soluble  in  hydrochloric  acid.  Found 
in  rolled  masses  from  pegmatite  at  Kangerdluarsuk,  Greenland. 

Pyroxene  Group 

Orthorhombic,  Monoclinic,  Triclinic 

Composition  for  the  most  part  that  of  a  metasilicate,  RSiO3,  with  R  = 
Ca,Mg,Fe  chiefly,  also  Mn,Zn.  Further  RSiO3  with  R(Fe,Al)2SiO6,  less  often 

containing  alkalies  (Na,K),  and  then  RSiO3  with  RAl(Si03)2.     Rarely  includ- 
ing zirconium  and  titanium,  also  fluorine. 

«.  Orthorhombic  Section 

_,  a  :  b  :  c  or  b  :  a  *  c 

Enstatite  MgSi03  0'9702  :  1  :  0'5710         1'0307  •  1  •  0'5885 

Bronzite  (Mg,Fe)Si03 

Hypersthene          (Fe,Mg)SiO3        0'9713  :  1  :  0'5704         T0319  :  1  :  0'5872 

ut  the  similarity  of  the  form  to  the 


0.  Monoclinic  Section 

Pyroxene  .1-0921  1 1  ':  0-5893     74°  10' 

I.    NON-ALUMINOUS  VARIETIES: 

1.  DIOPSIDE  {CaMg(Si03)2 

Ayr  ,      r,  .   iCa(Mg,Fe)(Si03)2 

Malacohte,  Sahte,  Diallage,  etc. 

2.  HEDENBERGITE  CaFe(SiO3)2 

Manganhedenbergite    Ca(Fe,Mn)  (SiO3)2 

3.  SCHEFFERITE  (Ca,Mg)  (Fe,Mn)(SiO3)2 

Jeffersomte  (Ca,Mg)  (Fe,Mn,Zn)  (Si03)2 


SILICATES  471 

II.  ALUMINOUS  VARIETIES.- 

4    AUGITE  {Ca(Mg,Fe)(Si03)2 

(with  (Mg,Fe)(Al,Fe)2Si06 

Leucaugite,  Fassaite,  ^Egirite-augite. 


AcmiteU^Sgiritel         NaFe(SiO3)2  1'0996 :  1  : 0'6012  73°  11' 

Spodumene  LiAl(SiO3)2  1*1238  :  1  :  0'6355  69°  40' 

Jadeite  NaAl(Si03)2  1*103    :  1  : 0'613  72°  44|' 

a  :  b  :  c  /8 

WoUastonite  CaSiO3  1'0531  :  1  : 0'9676  84°  30' 

Pectolite  HNaCa«(SiOi)s  1'1140  :  1  :  0'9864  84°  40' 

7-   Triclinic  Section 

Rhodonite       MnSiO3  1-0729  :'  1 ':  0-6213     103°  18'     108°  44'     81°  39' 

also  (Mn,Ca)Si03 
(Mn,Fe)SiO3 
(Mn,Zn,Fe,Ca)Si03 
Babingtonite  (Ca,Fe,Mn)SiO3.Fe2(Si03;3 

1-0691  :  1  :  0-6308     104°  21|'  108°  31'     83°  34' 

The  rare  species  Rosenbuschite,  Layenite,  Wohlerite  also  belong  under  the  monoclinic 
section  and  Hiortdahlite  under  the  triclinic  section  of  this  group. 

The  PYROXENE  GROUP  embraces  a  number  of  species  which,  while  falling 
in  different  systems  —  orthorhombic,  monoclinic,  and  triclinic  —  are  yet 
closely  related  in  form.  Thus  all  have  a  fundamental  prism  with  an  angle  of 
93°  and  87°,  parallel  to  which  there  is  more  or  less  distinct  cleavage.  Further, 
the  angles  in  other  prominent  zones  show  a  considerable  degree  of  similarity. 

In  composition  the  metasilicates  of  calcium,  magnesium,  and  ferrous  iron  are 

ii        m  i 

most  prominent,  while  compounds  of  the  form  R(Al,Fe)2SiOe,  RAl(Si03)2  are 
also  important. 

The  species  of  the  pyroxene  group  are  closely  related  in  composition  to  the 
corresponding  species  of  the  amphibole  group,  which  also  embraces  members 
in  the  orthorhombic,  monoclinic,  and  triclinic  systems.  In  a  number  of  cases 
the  same  chemical  compound  appears  in  each  group;  furthermore,  a  change 
by  paramorphism  of  pyroxene  to  amphibole  is  often  observed.  In  form  also 
the  two  groups  are  related,  as  shown  in  the  axial  ratio;  also  in  the  parallel 
growth  of  crystals  of  monoclinic  amphibole  upon  or  about  those  of  pyroxene 
(Fig.  461,  p.  173).  The  axial  ratios  for  the  typical  monoclinic  species  are: 

Pyroxene  a  :    b  :c  =  1'0921  :  1  :  0'5893  /3  =  74°  10' 

Amphibole  a  :  ±6  :  c  =  M022  :  1  :  0-5875  /?  =  73°  58' 

See  further  on  p.  486. 

The  optical  relations  of  the  prominent  members  of  the  Pyroxene  Group, 
especially  as  regards  the  connection  between  the  position  of  the  ether-axes  and 
the  crystallographic  axes  are  exemplified  in  the  following  figures  (Cross). 
A  corresponding  exhibition  of  the  prominent  amphiboles  is  given  under  that 
group,  Fig.  826,  p.  486, 


472 


DESCRIPTIVE   MINERALOGY 
797 


I,  Enstatite,  etc. 


II,  Spodumene.     Ill,  Diopside,  etc.     IV,  Hedenbergite,  Augite. 
V,  Augite.     VI,  Acmite. 


798 


a.   Orthorhombic  Section 
ENSTATITE. 

Orthorhombic.     Axes  a  :  b  :  c  =  0'9702  :  1  :  0'5710. 

mm'",  110  A  110  =  88°  16'.  rr',    223  A  223  =  40°  16^. 

qqf,       023  A  023  =  241°  41'.  XT'",  223  A  223  =  39°    H'. 

Twins  rare:  tw.  pi.  h  (014)  as  twinning  lamellae;  also  tw.  pi.  (101)  as -stel- 
late twins  cros'sing  at  angles  of  nearly  60°,  sometimes  six-rayed.  Distinct 
crystals  rare,  habit  prismatic.  Usually  massive,  fibrous,  or  lamellar. 

Cleavage:  m  (110)  rather  easy.  Parting  ||  6  (010);  also  a  (100).  Frac- 
ture uneven.  Brittle.  H.  =  5*5.  G.  =  31-3-3. 
Luster,  a  little  pearly  on  cleavage-surfaces  to  vitreous; 
often  metalloidal  in  the  bronzite  variety.  Color 
grayish,  yellowish  or  greenish  white,  to  olive-green 
and  brown.  Streak  uncolored,  grayish.  Translucent 
to  nearly  opaque.  Pleochroism  weak,  more  marked  in 
varieties  relatively  rich  in  iron.  Optically  +.  Ax. 
pi.  1 1  b  (010) .  Bxa  J_  c  (001) .  Dispersion  p  <  v  weak. 
Axial  angle  large  and  variable,  increasing  with  the 
amount  of  iron,  usually  about  90°  for  FeO  =  10  p.  c. 
j8  =  1-669;  7  -  a  =  0'009. 
Comp.  —  MgSiO3  or  MgO.SiO2  =  Silica  60,  magnesia  40  =  100.  Also 
(Mg,Fe)SiO3  with  Mg  :  Fe 
=  8  :  1,  6  :  1,  3  :  1,  etc. 

Var.  —  1.  With  little  or  no 
iron;  Enstatite.  Color  white, 
yellowish,  grayish,  or  green- 
ish white;  luster  vitreous  to 
pearly;  G.  =  3'10-3'13. 
Chladnite  (Shepardite  of  Rose), 
which  makes  up  90  p.  c.  of  the 
Bishopville  meteorite,  belongs 
here  and  is  the  purest  kind. 
Victorite,  occurring  in  the  Deesa 
meteoric  iron  in  rosettes  of 
acicular  crystals,  is  similar. 

2.  Ferriferous;  Bronzite.  Col- 
or grayish  green  to  olive-green 
and  brown.     Luster  on  cleav-        ,-,          .,     .-„ 
age-surface  often  adamantine-        ^nstatite  (Bronzite)  Hypersthene 

pearly  to  submetallic  or  bronze-like;   this,  however,  is  usually  of  secondary  origin  and  is 


Bamle 


799 


800 


001 


100 


001 


100 

x^-H— *K h- 


t 


SILICATES 


473 


not  essential.  With  the  increase  9f  iron  (above  12  to  14  p.  c.)  bronzite  passes  to  hyper- 
sthene,  the  optic  axial  angle  changing  so  that  in  the  latter  X  =  Bxa  _L  «  (100).  This  is 
illustrated  by  Figs.  799,  800. 

Pyr.,  etc.  —  B.B.  almost  infusible,  being  only  slightly  rounded  on  the  thin  edges; 
F.  =  6.  Insoluble  in  hydrochloric  acid. 

Artif .  —  Enstatite  is  formed  from  a  melt  having  the  proper  composition  at  temperatures 
slightly  under  1100°.  At  higher  temperatures  the  monoclinic  pyroxenes  appear.  Enstatite 
has  also  been  formed  by  fusing  olivine  with  silica.  When  serpentine  is  melted  it  breaks 
down  into  enstatite  and  olivine. 

Micro.  —  In  thin  sections  is  colorless  or  light  yellow  or  green;  marked  relief;  prominent 
cleavage  with  parallel  extinction;  little  pleochroism  but  becoming  stronger  with  increase  of 
iron;  inclusions  common  lying  parallel  to  brachypinacoid,  producing  characteristic  schiller 
of  mineral. 

Obs.  —  Enstatite  (including  bronzite)  is  a  common  constituent  of  peridotites  and  the 
serpentines  derived  from  them;  it  also  occurs  in  crystalline  schists.  It  is  often  associated 
in  parallel  growth  with  a  monoclinic  pyroxene,  e.g.,  diallage.  A  common  mineral  in  mete- 
oric stones  often  occurring  in  chondrules  with  eccentric  radiated  structure. 

Occurs  near  Aloystal  in  Moravia,  in  serpentine;  at  Kupferberg  in  Bavaria;  at  Baste  in 
the  Harz  Mts.,  Germany  (protobastite) ;  in  the  so-called  olivine  bombs  of  the  Dreiser  Weiher 
in  the  Eifel,  Germany;  in  immense  crystals,  in  part  altered,  at  the  apatite  deposits  of 
Kjorrestad  near  Bamle,  Norway;  in  the  peridotite  associated  with  the  diamond  deposits  of 
South  Africa. 

In. the  United  States,  in  N.  Y.  at  the  Tilly  Foster  magnetite  mine,  Brewster,  Putnam  Co., 
with  chondrodite  and  at  Edwards;  Texas,  Pa.;  bronzite  from  Webster,  N.  C.;  Bare  Hills, 
Baltimore,  Md. 

Named  from  evaaTT-rjs,  an  opponent,  because  so  refractory.  The  name  bronzite  has 
priority,  but  a  bronze  luster  is  not  essential,  and  is  far  from  universal. 


HYPERSTHENE. 

Orthorhombic. 


Axes  a  :  b  :  c  =  0-9713  :  1  :  0-5704. 


mm 
hh', 


110  A  110  =  88°  20'. 
014  A  014  =  16°  14'. 


oo'",  111  A  111  =  52' 
uu'"t  232  A  232  =  72< 


23'. 
50'. 


Crystals  rare,  habit  prismatic,  often  tabular  ||  a  (100),  less  often  ||  b  (010). 
Usually  foliated  massive ;  sometimes  in  embedded  spherical  forms. 

Cleavage:  b  (010)  perfect;  m  (110)  and  a  (100)  distinct  but  interrupted. 
Fracture  uneven.  Brittle.  H.  =  5-6.  G.  =  3 '40-3 '50.  Luster  somewhat 
pearly  on  a  Cleavage-surface,  and  sometimes  metalloidal.  Color  dark  brown- 
ish green,  grayish  black,  greenish  black,  pinchbeck-brown.  Streak  grayish, 


801 


802 


803 


Figs.  801,  Amblystegite,  Laacher  See.     802,  Malnas.     803,  Section  ||  6  (010)  showing  inclu- 
sions; the  exterior  transformed  to  actinolite;  from  Lacroix. 

brownish  gray.  Translucent  to  nearly  opaque.  Pleochroism  often  strong, 
especially  in  the  kinds  with  high  iron  percentage;  thus  1 1  X  or  a  axis  brownish 
red,  Y  or  b  axis  reddish  yellow,  Z  or  c  axis  green.  Optically  — .  Ax.  pi.  || 
b  (010).  Bxa  J_  a  (100).  Dispersion  p  >  v.  Axial  angle  rather  large  and 


474  DESCRIPTIVE   MINERALOGY 

variable,  diminishing  with  increase  of  iron,  cf .  enstatite,  p.  472,  and  Figs.  799, 
800,  p.  472.     0  =  1702;  y  -  a  =  0-013. 

Hypersthene  often  encloses  minute  tabular  scales,  usually  of  a  brown  color,  arranged 
mostly  parallel  to  the  basal  plane  (Fig.  803),  also  less  frequently  vertical  or  inclined  30°  to 
c  axis;  they  may  be  brookite  (gothite,  hematite),  but  their  true  nature  is  doubtful.  They 
are  the  cause  of  the  peculiar  metalloidal  luster  or  schiller,  and  are  often  of  secondary  origin, 
being  developed  along  the  so-called  " solution-planes"  (p.  189)'. 

Comp.  —  (Fe,Mg)SiO3  with  Fe  :  Mg  =  1  :  3(FeO  =  167  p.  c.),  1  .  2 
(FeO  =  217  p.  c.)  to  nearly  1  :  l(FeO  =  31 '0  p.  c.).  Alumina  is  sometimes 
present  (up  to  10  p.  c.)  and  the  composition  then  approximates  to  the  alu- 
minous pyroxenes. 

Of  the  orthorhombic  magnesium-iron  metasilicates,  those  with  FeO  >  12  to  15p.  c.  are 
usually  to  be  classed  with  hypersthene,  which  is  further  characterized  by  being  optically 
negative  and  having  dispersion  p  >  v. 

•Pyr.,  etc.  —  B.B.  fuses  to  a  black  enamel,  and  on  charcoal  yields  a  magnetic  mass; 
fuses  more  easily  with  increasing  amount  of  iron.  Partially  decomposed  by  hydro- 
chloric acid. 

Micro.  —  In  thin  sections  similar,  to  enstatite  except  shows  distinct  reddish  or  greenish 
color  with  stronger  pleochroism  and  is  optically  — . 

Artif .  —  Similar  to  enstatite,  which  see. 

Obs.  —  Hypersthene,  associated  with  a  triclinic  feldspar  (labradorite),  is  common  in 
certain  granular  eruptive  rocks,  as  norite,  hyperite,  gabbro,  also  in  some  andesites  (hyper- 
sthene-andesite) ,  a  rock  shown  to  occur  rather  extensively  in  widely  separated  regions. 

It  occurs  at  Isle  St.  Paul,  Labrador;  in  Greenland;  at  Farsund  and  elsewhere  in  Nor- 
way; Elfdalen  in  Sweden;  Penig  in  Saxony;  Ronsberg  in  Bohemia;  the  Tyrol;  Neurode 
in  Silesia;  Bodenmais,  Bavaria.  Amblystegite  is  from  the  Laacher  See,  Germany.  Sza- 
boite  occurs  with  pseudobrookite  and  tridymite,  in  cavities  in  the  andesite  of  the  Aranyer 
Berg,  Transylvania,  and  elsewhere. 

Occurs  in  the  norites  of  the  Cortlandt  region  on  the  Hudson  river,  N.'  Y.;  also  common 
with  labradorite  in  the  Adirondack  Archa3an  region  of  northern  N.  Y.  and  northward  in 
Canada.-  In  the  hypersthene-andesites  of  Mt  Shasta,  Cal.;  Buffalo  Peaks,  Col.,  and 
other  points. 

Hypersthene  is  named  from  virep  and  <r0ei>os,  very  strong,  or  tough. 

BASTITE,  or  SCHILLER  SPAR.  An  altered  enstatite  (or  brqnzite)  having  approximately 
the  composition  of  serpentine.  It  occurs  in  foliated  form  in  certain  granular  eruptive 
rocks  and  is  characterized  by  a  bronze-like  metalioidal  'luster  or  schiller  on  the  chief 
cleavage-face  6  (010),  which  "schillerization"  (p.  251)  is  of  secondary  origin.  H.  =  3'5-4. 
G.  =  2 '5-2 '7.  Color  leek-green  to  olive-  and  pistachio-green,  and  pinchbeck-brown. 
Pleochroism  not  marked.  Optically  -.  Double  refraction  weak.  Ax.  pi.  ||  a  (010) 
(hence  normal  to  that  of  enstatite).  Bxa  ±  b  (010).  Dispersion  p  >  v.  The  original 
bastite  was  from  Baste  near  Harzburg  in  the  Harz  Mts.,  Germany;  also  from  Todtmoos 
in  the  Schwarzwald,  Germany. 

PECKHAMITE,  2(Mg,Fe)SiO3.(Mg,Fe)SiO4.  Occurs  in  rounded  nodules  hi  the  meteorite 
of  Estherville,  Emmet  Co.,  Iowa,  May  10,  1879.  G.  =  3 '23.  Color  light  greenish  yellow. 

)8.  Monoclinic  Section 
PYROXENE. 

Monoclinic.     Axes_a  :  b  :  c  =  1-0921  :  1  :  0-5893;  J3  =  74°  10'. 

mm'",  110  A  110  =  92°  50'.  '  &>,    001  A  221  =  49°  54'. 
co,        001  A  100  =  74°  10'.  en,  001  A  110  =  79°  9£'. 

cp,       001  A  101  =  31°  20'.  a,    001  A  Til  =  42°  2'. 

ee',       Oil  A  Oil  =  59°  6'.  uu',  111  A  ill  =  48°  29'/ 

•     22',       021  A  021  =  97°  11'.  SSf,   111  A  TTl  =  59°  11'. 

cu,        001  A  111  =  33°  49*'.  oo',  221  A  221  =  84°  11'. 

Twins:  tw.  pi.  (1)  a  (100),  contact-twins,  common  (Fig.  810),  sometimes 
polysynthetic.  (2)  c  (001),  as  twinning  lamellae  producing  striations  on  the 
vertical  faces  and  pseudocleavage  or  parting  ||  c  (Fig.  811);  very  common, 


SILICATES 


475 


often  secondary.     (3)  y  (101)  cruciform-twins,  not  common  (Fig.  451,  p.  171). 
(4)  W  (122)  the  vertical  axes  crossing  at  angles  of  nearly  60°;  sometimes  re- 
peated as  a  six-rayed  star  (Fig.  450,  p.  171).     Crystals  usually  prismatic  in 
804  805  806  807  808 


813 


100 

habit,  often  short  and  thick,  and  either  a  square  prism  (a  (100),  6  (010)  prom- 
inent), or  nearly  square  (93°,  87°)  with  m  (110)  predominating;  sometimes  a 
nearly  symmetrical  8-sided  prism  with  a,  6,  m  (Fig.  811).  Often  coarsely 
lamellar,  ||  c  (001)  or  a  (100).  Also  granular,  coarse  or  fine;  rarely  fibrous 
or  columnar. 

Cleavage:  m  (110)  sometimes  rather  perfect,  but  interrupted,  often  only 
observed  in  thin  sections  J_  caxis  (Fig.  812). 
Parting  ||  c  (001),  due  to  twinning,  often 
prominent,  especially  in  large  crystals  and 
lamellar  masses  (Fig.  811);  also  ||  a  (100) 
less  distinct  and  not  so  common.  Fracture 
uneven  to  conchoidal.  Brittle.  H.  =  5-6. 
G.  =  3*2-3*6,  varying  with  the  compo- 
sition. Luster  vitreous  inclining  to  res- 
inous; often  dull;  sometimes  pearly  || 
c(001)  in  kinds  showing  parting.  Color 
usually  green  of  various  dull  shades,  varying 
from  nearly  colorless,  white,  or  grayish 
white  to  brown  and  black;  rarely  bright 
green,  as  in  kinds  containing  chromium; 
also  blue.  Streak  white  to  gray  and  grayish 
green.  Transparent  to  opaque.  Pleo- 
chroism  usually  weak,  even  in  dark-colored 
varieties;  sometimes  marked,  especially  in  violet-brown  kinds  containing 
titanium.  (Violaite  is  name  given  to  a  highly  pleochroic  variety  from  the 
Caucasus  Mts.) 


X 


476  DESCRIPTIVE   MINERALOGY 

v,« 

Optically  +.  Birefringence  strong,  (7  —  a)  =  0'02  —  0'03.  Ax.  pi.  || 
b  (010).  Bxa  or  Z  A  c  axis  =^4-36°  in  diopside,  to  -j-52°  in  augite  (which 
see),  or  Z  A  c  (001)  =  20°  to  gg°,  the  angle  in  general  increasing  with  amount 
of  iron.  For  diopside  2  V  =  59-°.  a  =  1-673.  0  =  1-680.  7  =  1702. 

Comp.  —  For  the  most  g^rt  a  normal  metasilicate,  RSiO3,  chiefly  of 
calcium  and  magnesium,  also  iron,  less  often  manganese  and  zinc.  The 
alkali  metals  potassium  anc^  sodium  present  rarely,  except  in  very  small 
amount.  Also  in  certain  varieties  containing  the  trivalent  metals  aluminium, 
ferric  iron,  and  manganese.  These  last  varieties  may  be  most  simply  con- 
sidered as  molecular  compounds  of  Ca(Mg,Fe)Si2O6  and  (Mg,Fe)(Al,Fe)2Si06, 
as  suggested  by  Tschermak.  Chromium  is  sometimes  present  in  small 
amount;  also  titanium  "replacing  silicon. 

The  name  Pyroxene  is  from  iryp,  fire  and  £evps,  stranger,  and  records  Haiiy's  idea  that 
the  mineral  was,  as  he  expresses  it,  "a  stranger  in  the  domain  of  fire,"  whereas,  in  fact,  it 
is,  next  to  the  feldspars,  tjje  most  Tmiversal  constituent  of  igneous  rocks. 

The  varieties  are  numerous  and  depend  upon  variations  in  composition  chiefly;  the 
more  prominent  of  the  varieties  p*>perly  rank  as  sub-species . 

Artif.  —  The  monoclinic  pyroxene,  MgSiOs,  can  be  crystallized  from  a  melt  having  the 
theoretical  composition  at  temperatures  about  1500°  or  at  a  lower  temperature  from  solu- 
tion in  molten  calcium  or  magnesium  vanadate.     It  is  the  most  stable  form  of  MgSiO?. 
It  has  no  true  melting  point  but  af  about  1550°  breaks  down  into  forsterite  and  silica. 
• 

I.   Containing  little  or  no  Aluminium 

1.  DIOPSIDE.     Malacolite,  Alalite.     Calcium-magnesium  pyroxene.     For- 
mula CaM"g(Si03)2  =  Silica  55-6,  lime  25-9,  magnesia  18-5  =  100.     Color 
white,  yellowish,  grayish  white  to  pale  green,  and  finally  to  dark  green  and 
nearly  black;  sometimes  transparent  and  colorless,  also  rarely  a  fine  blue.     In 
prismatic  crystals,  often  slender;  also  granular  and  columnar  to  lamellar  mas- 
sive.    G.  =  3-2-3-38.     Bxa  A  c  axis  =  +  36°  and  upwards.     7  -  a  =  0-03. 
Iron  is  present  usually  in  small  amount  as  noted  below,  and  the  amount 
increases  as  it  graduates  toward  true  hedenbergite. 

The  following  belong  here:  Chrome-diopside,  contains  chromium  (1  to  2'8  p.  c.  C^Oa), 
often  a  bright  green. 

Malacolite,  as  originally  described,  was  a  pale-colored  translucent  variety  from  Sala, 
Sweden. 

Alalite  occurs  in  broad  right-angled  prisms,  colorless  to  faint  greenish  or  clear  green, 
from  the  Mussa  Alp  in  the  Ala  valley,  Piedmont,  Italy. 

Traversellite,  from  Trayersella,  Piedmont,  Italy,  is  similar. 

Violan  is  a  fine  blue  diopside  from  St.  Marcel,  Piedmont,  Italy;  occurring  in  prismatic 
crystals  and  massive. 

Canaanite  is  a  grayish-white  or  bluish-white  pyroxene  rock  occurring  with  dolomite  at 
Canaan,  Conn. 

Lavrovite  is  a  pyroxene,  colored  green  by  vanadium,  from  the  neighborhood  of  Lake 
Baikal,  in  eastern  Siberia. 

Diopside  is  named  from  6is,  twice  or  double,  and  o^is,  appearance.  Malacolite  is  from 
na\otKos,  soft,  because  softer  than  feldspar,  with  which  it  was  associated. 

2.  HEDENBERGITE.     Calcium-iron    pyroxene.     Formula    CaFe(Si03)2  = 
Silica  48'4,  iron  protoxide  29'4,  lime  22'2  =  100.     Color  black.     In  crystals, 
and  also  lamellar  massive.     G.  =  3-5-3-58.     Bxa  A  c  axis  =  +  48°.     Man- 
ganese is  present  in  manganhedenbergite  to  6 -5  p.  c.     Color  grayish  green. 
G.  =  3'55. 

Between  the  two  extremes,  diopside  and  hedenbergite,  there  are  numerous  transitions 
jonformmg  to  the  formula  Ca(Mg,Fe)Si2O6.     As  the  amount  of  iron  increases  the  color 
langes  irom  light  to  dark  green  to  nearly  black,  the  specific  gravity  increases  from  3 -2  to 
3-6,  and  the  angle  Bxa  A    c  axis  also  from  36°  to  48°. 


SILICATES  477 

The  following  are  varieties,  coming  under  these  two  sub-species,  based  in  part  upon 
structure,  in  part  on  peculiarities  of  composition. 

Salite  (Sahlite),  color  grayish  green  to  deep  green  and  black;  sometimes  grayish  and 
yellowish  white;  in  crystals;  also  lamellar  (parting  ||  c  (001)),  and  granular  massive;  from 
Sala  in  Sweden.  Baikalite,  a  dark  dingy  green  variety,  in  crystals,  with  parting  j|  c  (001), 
from  Lake  Baikal,  in  Siberia. 

Coccolite  is  a  granular  variety,  embedded  in  calcite,  also  forming  loosely  coherent  to 
compact  aggregates;  color  varying  from  white  to  pale  green  to  dark  green,  and  then  con- 
taining considerable  iron;  the  latter  the  original  coccolite.  Named  from  KOKKOS,  a  grain. 

DIALLAGE.  A  lamellar  or  thin-foliated  pyroxene,  characterized  by  a  fine  lamellar 
structure  and  parting  ||  a  (100),  with  also  parting  |j  6  (010),  and  less  often  ||  c  (001).  Also  a 
fibrous  structure  ||  c  axis.  Twinning  ||  a  (100),  often  poly  synthetic ;  interlamination  with 
an  orthorhombic  pyroxene  common.  Color  grayish  green  to  bright  grass-green,  and  deep 
green;  also  brown.  Luster  of  surface  a  (100)  often  pearly,  sometimes  metalloidal  or 
exhibiting  schiller  and  resembling  bronzite,  from  the  presence  of  microscopic  inclusions  of 
secondary  origin.  Bxa  A  c  axis  =  +39  to  40°;  0  =  1-681;  y  -  a  =  0;024.  H.  =  4; 
G.  =  3'2-3'35.  In  composition  near  diopside,  but  often  containing  alumina  and  some- 
times in  considerable  amount,  then  properly  to  be  classed  with  the  augites.  Often  changed 
to  amphibole,  see  smaragdite,  and  uralite,  p.  490.  Named  from  dta^Xayrj,  difference, 
in  allusion  to  the  dissimilar  planes  of  fracture.  This  is  the  characteristic  pyroxene  of 
gabbro,  and  other  related  rocks. 

Omphacite.  The  granular  to  foliated  pyroxenic  constituent  of  the  garnet-rock  called 
eclogite,  often  interlaminated  with  amphibole  (smaragdite);  color  grass-green.  Contains 
some  A^Os. 

3.  SCHEFFERITE.     A  manganese    pyroxene,   sometimes   also   containing 
much  iron.     Color  brown  to  black. 

In  crystals,  sometimes  tabular  ||  c  (00_1),  also  with  p  (101)  prominent,  more  often  elongated 
in  the  direction  of  the  zone  b  (010)  :  p  (101),  rarely  prismatic,  ||  c  axis.  Twins,  with  a  (100) 
as  tw.  pi.  very  common.  Also  crystalline,  massive.  Cleavage  prismatic,  very  distinct. 
Color  yellowish  brown  to  reddish  brown;  also  black  (iron-schefferite} .^Optically  +. 
Bxa  or  Z  A  c  axis  =  44°  25£'.  The  iron-schefferite  from.Pajsberg,  Sweden,  is  black  in 
color  and  has  Z  A  c  axis  =  +  49°  to  59°  for  different  zones  in  the  same  crystal.  The 
brown  iron-schefferite  (urbanite)  from  Langban,  Sweden,  has  Z  A  c  axis  =  69°  3'.  It 
resembles  garnet  in  appearance. 

Jeffersonite  is  a  manganese-zinc  pyroxene  from  Franklin  Furnace,  N.  J.  (but  the  zinc 
may  be  due  to  impurity).  In  large,  coarse  crystals  with  edges  rounded  and  faces  uneven. 
Color  greenish  black,  on  the  exposed  surface  chocolate-brown. 

Blanfordite.  A  pyroxene  containing  some  sodium,  manganese  and  iron.  Strongly  pleo- 
chroic  (rose-pink  to  sky-blue).  Found  with  manganese  ores  in  the  Central  Provinces, 
India. 

Clinoenstatite  has  been  suggested  as  the  name  for  the  monoclinic  magnesium  pyroxene. 

II.   Aluminous 

4.  AUGITE.     Aluminous  pyroxene.     Composition  chiefly  CaMgSi2Oe  with 
(Mg,Fe)(Al,Fe)2SiO6,  and  occasionally  also  containing  alkalies  and  then  gradu- 
ating toward  acmite.     Titanium  is  also  sometimes  present.     Here  belong: 

a.  LEUC AUGITE.     Color  white  or  grayish.     Contains  alumina,  with  lime  and  magnesia, 
and  little  or  no  iron.     Looks  like  diopside.     H.  =  6'5;  G.  =  3*19.     Named  from  Xeu/cos, 
white. 

b.  FASSAITE.     Includes  the  pale  to  dark,  sometimes  deep-green  crystals,  or  pistachio- 
green  and  then  resembling  epidote.     The  aluminous  kinds  of  diallage  also  belong  here. 
Named  from  the  locality  in  the  Fassatal,  Tyrol.     Pyrgom  is  from  irvpyu/jia,  a  tower. 

c.  AUGITE.     Includes  the  greenish  or  brownish  black  and  black  kinds,  occurring  mostly 
in  eruptive  rocks.     It  is  usually  in  short  prismatic  crystals,  thick  and  stout,  or  tabular  || 
a  (100);    often  twins  (Figs.  809,  810).     Ferric  iron  is  here  present,  in  a  relatively  large 
amount,  and  the  angle  Bxa  A  c  axis  becomes  +50°  to  52°.     0  =  1717;   y  —  a  '=  0'022. 
TiO2  is  present  in  some  kinds,  which  are  then  pleochroic.     Named  from  avyij,  luster. 

d.  ALKALI- AUGITE.     Here  belong  varieties  of  augite  characterized  by  the  presence  of 
alkalies,  especially  soda;    they  approximate  in  composition  and  optically  to  acmite  and 
ajgirite  (Bxa  A  c  axis  =  60°,  Fig.  814),  and  are  sometimes  called  aegirite-augite  (cf.  Fig.  818, 


478 


DESCRIPTIVE   MINERALOGY 


814 


p.  480).   -Known  chiefly  from  rocks  rich  in  alkalies,  as  elseolite-syenite,  phonolite,  leu- 

Pyr.  etc.  —  Varying  widely,  owing  to  the  wide  variations  in  composition  in  the  differ- 
ent varieties,  and  often  by  insensible  gradations. 
Fusibility,  3*75  in  diopside;  3 '5  in  salite,  baikalite, 
and  omphacite;  3  in  jeffersonite  and  augite;  2 '5  in 
hedenbergite.  Varieties  rich  in  iron  afford  a  mag- 
netic globule  when  fused  on  charcoal,  and  in  general 
the  fusibility  varies  with  the  amount  of  iron.  Many 
varieties  give  with  the  fluxes  reactions  for  man- 
ganese. Most  varieties  are  unacted  upon  by  acids. 

Diff.  —  Characterized  by  monoclinic  crystallization 
and  the  prismatic  angle  of  87°  and  93°,  hence  yield- 
ing nearly  square  prisms;  these  may  be  mistaken  for 
scapolite  if  terminal  faces  are  wanting  or  indistinct 
(but  scapolite  fuses  easily  B.  B.  with  intumescence). 
The  oblique  parting  (||  c  (001),  Fig.  811)  often 
distinctive,  also  the  common  dull  green  to  gray  and 
brown  colors.  Amphibole  differs  in  prismatic  angle 
(55^°  and  124|°)  and  cleavage,  and  in  having  com- 
mon columnar  to  fibrous  varieties,  which  are  rare 
with  pyroxene.  (See  also  p.  486.) 

Micro.  —  The  common  rock-forming  pyroxenes 
are  distinguished  in  thin  sections  by  their  high  relief;  usually  greenish  to  olive  tones  of 
color;  distinct  system  of  interrupted  cleavage-cracks  crossing  one  another  at  nearly  right 
angles  in  sections  _L  c  axis  (Fig.  812);  high  interference-colors;  general  lack  of  pleo- 
chroism;  large  extinction-angle,  35°  to  50°  and  higher,  for  sections  ||  b  (010).  The  last- 
named  sections  are  easily  recognized  by  showing  the  highest  interference  colors;  yielding 
no  optical  figures  in  convergent  light  and  having  parallel  cleavage-cracks,  the  latter  in 
the  direction  of  the  vertical  axis.  See  also  segirite,  p.  480. 

A  zonal  banding  is  common,  the  successive  laminae  sometimes  differing  in  extinction- 
angle  and  pleochroism;  also  thje  hour-glass  structure  occasionally  distinct 
(Fig.  815,  from  Lacroix). 

Obs.  —  Pyroxene  is  a  very  common  mineral  in  igneous  rocks,  being  the 
most  important  of  the  ferromagnesian  minerals.  Some  rocks  consist  almost 
entirely  of  pyroxene.  It  most  commonly  occurs  in  volcanic  rocks  but  is 
found  also,  but  less  abundantly,  in  connection  with  granitic  rocks.  It  is 
a  common  mineral  in  crystalline  limestone  and  dolomite,  in  serpentine  and 
metamorphic  schists;  sometimes  forms  large  beds  or  veins,  especially  in 
Archaean  rocks.  It  occurs  also  in  meteorites.  The  pyroxene  of  limestone 
is  mostly  white  and  light  green  or  gray  in  color,  falling  under  diopside 
(malacoh'te,  salite,  coccolite);  that  of  most  other  metamorphic  rocks  is 
sometimes  white  or  colorless,  but  usually  green  of  different  shades,  from 
pale  green  to  greenish  black,  and  occasionally  black;  that  of  serpentine  is 
sometimes  in  fine  crystals,  but  often  of  the  foliated  green  kind  called 
diallage;  that  of  eruptive  rocks  is  usually  the  black  to  greenish  black  augite. 

In  limestone  the  associations  are  often  amphibole,  scapolite,  vesuvianite,  garnet,  ortho- 
clase, titanite,  apatite,  phlogopite,  and  sometimes  brown  tourmaline,  chlorite,  talc,  zircon, 
spinel,  rutile,  etc.;  and  in  other  metamorphic  rocks  mostly  the  same.  In  eruptive  rocks  it 
may  be  in  distinct  embedded  crystals,  or  in  grains  without  external  crystalline  form;  it 
often  occurs  with  similarly  disseminated  chrysolite  (olivine),  crystals  of  orthoclase  (sani- 
dine),  labradorite,  leucite,  etc.;  also  with  a  rhombic  pyroxene,  amphibole,  etc. 

Pyroxene,  as  an  essential  rock-making  mineral,  is  especially  common  in  basic  eruptive 
rocks.  Thus,  as  augite,  with  a  triclinic  feldspar  (usually  labradorite),  magnetite,  often 
chrysolite,  in  basalt,  basaltic  lavas  and  diabase;  in  andesite;  also  in  trachyte;  in  peridotite 
and  pikrite;  with  nephelite  in  phonolite.  Further  with  elseolite,  orthoclase,  etc.,  in 
elaeohte-syenite  and  augite-syenite;  also  as  diallage  in  gabbro;  in  many  peridotites  and  the 
serpentines  formed  from  them;  as  diopside  (malacolite)  in  crystalline  schists.  In  limburg- 
ite,  augitite  and  pyroxenite,  pyroxene  is  present  as  the  prominent  constituent,  while  feld- 
spar is  absent;  it  may  also  form  rock  masses  alone  nearly  free  from  associated  minerals. 

Diopside  (alalite,  mussite)  occurs  in  fine  crystals  on  the  Mussa  Alp  in  the  Ala  valley  in 
Piedmont,  Italy,  associated  with  garnets  (hessonite)  and  talc  in  veins  traversing  serpentine; 
in  fine  crystals  at  Traversella,  Piedmont;  at  Zermatt  in  Switzerland;  Schwarzenstein  in  the 
Zillertal,  Ober-Sulzbachtal,  and  elsewhere  in  Tyrol  and  in  the  Salzburg  Alps;  Reichenstein, 


SILICATES  479 

Silesia,  Germany;  Ober-Sulzbachtal  and  elsewhere  in  Tyrol  and  in  the  Salzburg  Alps; 
Reichenstein  Lake;  Rezbanya,  Hungary;  Achmatoysk  in  the  Ural  Mts.,  with  almandite, 
clinochlore;  Lake  Baikal  (baikalite)  in  eastern  Siberia;  Pargas  in  Finland;  at  Nordmark, 
Sweden. 

Hedenbergite  is  from  Tunaberg  and  Nordmark,  Sweden;  Arendal,  Norway.  •  Mangan- 
hedenbergite  from  Vester  Silfberg,  Sweden;  schefferite  from  Langban,  Sweden. 

Augite  (including  fassaite)  occurs  on  the  Pesmeda  Alp,  Mt.  Monzoni,  and  elsewhere  in  the 
Fassatal,  Tyrol,  as  a  contact  formation;  at  Carlsbad  and  Teplitz,  Bohemia;  Traversella, 
Piedmont,  Italy;  the  Laacher  See,  Eifel  and  Sasbach  in  the  Kaiserstuhl,  Germany;  in 
Italy  at  Vesuvius,  white  rare,  green,  brown,  yellow  to  black,  Frascati,  Etna;  the  Azores  and 
Cape  Verde  Islands;  the  Hawaiian  Islands,  and  many  other  regions  of  volcanic  rocks. 

In  North  America,  occurs  in  Me.,  at  Raymond  and  Rumford,  diopside,  salite,  etc.  In 
Vt.,  at  Thetford,  black  augite,  with  chrysolite,  in  bowlders  of  basalt.  In  Conn.,  at  Canaan, 
white  crystals,  often  externally  changed  to  tremolite,  in  dolomite;  also  the  pyroxenic  rock 
called  canaanite.  In  N.  Y.,  at  Warwick,  fine  crystals;  in  Westchester  Co.,  white,  at  the 
Sing  Sing  quarries;  in  Orange  Co.,  in  Monroe,  at  Two  Ponds,  crystals,  often  large,  in  lime- 
stone; near  Greenwood  furnace,  and  also  near  Edenville;  in  Lewis  Co.,  at  Diana,  white 
and  black  crystals;  in  St.  Lawrence  Co.,  at  Fine,  in  large  crystals;  at  De  Kalb,  fine  diopside; 
also  at  Gouverneur,  Rossie,  Russell,  Pitcairn;  at  Moriah,  coccolite,  in  limestone.  In  N.  J., 
Franklin  Furnace,  Sussex  Co.,  good  crystals,  also  jeffersonite.  In  Pa.,  near  Attleboro, 
crystals,  and  granular;  in  Pennsbury,  at  Burnett's  quarry,  diopside;  at  the  French  Creek 
mines,  Chester  Co.,  chiefly  altered  to  fibrous  amphibole.  In  Tenn.,  at  the  Ducktown  mines. 

In  Canada,  at  Calumet  Island,  grayish  green  crystals  in  limestone;  in  Bathurst,  color- 
less or  white  crystals;  at  Grenville,  dark  green  crystals,  and  granular;  Burgess,  Lanark 
Co.;  Renfrew  Co.,  with  apatite,  titanite,  etc.;  crystals  from  Adams  Lake,  Ontario;  Orford, 
Sherbrooke  Co.,  white  crystals,  also  of  a  chrome-green  color  with  chrome  garnet;  at  Hull 
and  Wakefield,  white  crystals  with  nearly  colorless  garnets,  honey-yellow  vesuvianite,  etc. 
At  many  other  points  in  the  Archaean  of  Quebec  and  Ontario,  especially  in  connection  with 
the  apatite  deposits. 

Pyroxene  undergoes  alteration  in  different  ways.  A  change  of  molecular  constitution 
without  essential  change  of  composition,  i.e.,  by  paramorphism  (using  the  word  rather 
broadly),  may  result  in  the  formation  of  some  variety  of  amphibole.  Thus,  the  white 
pyroxene  crystals  of  Canaan,  Conn.,  are  often  changed  on  the  exterior  to  tremolite;  sim- 
ilarly with  other  varieties  at  many  localities.  See  uralite,  p.  490.  Also  changed  to  steatite, 
serpentine,  etc. 

PIGEONITE,  is  the  name  given  to  a  pyroxene  with  small  and  variable  axial  angle  from 
Pigeon  Point,  Minn. 


ACMITE. 

Monoclinic.     Axes:  a  :  b  :  c  =  1-0996  :  1  :  0-6012;  0  =  73°  11'. 

Twins:  tw.  pi.  a  (100)  very  common;  crystals  often  polysynthetic,  with 
enclosed  twinning  lamellae.  Crystals  long  prismatic,  vertically  striated  or 
channeled;  acute  terminations  very  characteristic. 

The  above  applies  to  ordinary  acmite.  For  cegirite,  crystals  prismatic,  bluntly  termi- 
nated; twins  not  common;  also  in  groups  or  tufts  of  slender  acicular  to  capillary  crystals, 
and  in  fibrous  forms. 

Cleavage:  m  (110)  distinct;  6  (010)  less  so.  Fracture  uneven.  Brittle. 
H.  =  6-6*5.  G.  =  3-50-3-55.  Luster  vitreous,  inclining  to  resinous.  Streak 
pale  yellowish  gray.  Color  brownish  or  reddish  brown,  green;  in  the  fracture 
blackish  green.  Subtransparent  to  opaque.  Optically  —  .  Ax.  pi.  ||  b  (010). 
Bxa  or  X  A  c  axis  =  +2|°  acmite,  to  6°  segirite.  a  =  1-763.  0  =  1799, 
7  =  1-813. 

Var.  —  Includes  acmite  in  sharp-pointed  crystals  (Fig.  816)  often  twins.  Bxa  A  c  axis 
=  5|°-6°.  Also  cegirite  (Fig.  817)'  in  crystals  bluntly  terminated,  twins  rare,  Bxa  A  c  axis 
=  2£°-3*°. 

Crystals  of  acmite  often  show  a  marked  zonal  structure,  green  within  and  brown  on  the 
exterior,  particularly  ||  a  (100),  b  (010),  p  (101),  s  (111).  The  brown  portion  (acmite)  is 
feebly  pleochroic,  the  green  (agirite)  strongly  pleochroic.  Both  have  absorption  X  >  Y 
>  Z,  but  the  former  has  X  light  brown  with  tinge  of  green,  Y  greenish  yellow  with  tinge  of 


480 


DESCRIPTIVE   MINERALOGY 


Acmite 


^Egirite 


brown,  Z  brownish  yellow;  the  latter  has  X  deep  grass-green,  Y  lighter  grass-green,  Z  yel- 
lowish brown  to  yellowish. 

With  some  authors  (vom  Rath,  etc.)  s  =  (Oil)  and  X  A  c  axis  =  -  2°  to  —  6°,  as  in 
Fig.  819.     Fig.  818  shows  the  optical  orientation  according  to  Brogger. 

Ill 

Comp.  —  Essentially  NaFe(SiO3)2  or  Na2O.Fe2O3.4Si02  = 
Silica  52'0,  iron  sesquioxide  34'6,  soda  13'4  =  100.     Ferrous 
iron  is  also  present. 

Pyr..  etc.  —  B.B.  fuses  at  2  to  a  lustrous  black  mag- 
netic globule,  coloring  the  flame  deep  yellow;  with  the 
fluxes  reacts  for  iron  and  sometimes  manganese.  Slightly 
acted  upon  by  acids. 

Micro.  —  ^Egirite  is  characterized  in  thin  sections  by 
its  grass-green  color;  strong  pleochroism  in  tones  of  green 
and  yellow;  the  small  extinction-angle  in  sections  ||  &(010). 
Distinguished  from  common  green  hornblende,  with  which 
it  might  be  confounded,  by  the  fact  that  in  such  sections 
the  direction  of  extinction  lying  near  the  cleavage  is  neg- 
ative (X),  while  the  same  direction  in  hornblende  is  pos- 
itive (Z). 

Artif .  —  Acmite  can  be  produced  artificially  by  fusing 
together  its  constituent  oxides  but   usually   under  such 
conditions  only  a  glass  containing  crystals  of  magnetite  is  formed. 

Obs.  —  The  original  acmite  occurs  in  a  pegmatite  vein;  at  Rundemyr, 
east  of  the  little  lake  called  Rokebergskjern,  in  the  parish  of  Eker,  near 
Kongsberg,  Norway.  It  is  in  slender  crystals,  sometimes  a  foot  long, 
embedded  in  feldspar  and  quartz. 

jEgirite  occurs  especially  in  igneous  rocks  rich  in  soda  and  containing  iron,  commonly  in 
rocks  containing  leucite  or.  nephelite;  thus  in  aegirite-granite,  nephelite-syenite,  and  some 
varieties  of  phonolite;  often  in  such  cases  iron-ore  grains  are  wanting  in  the  rock,  their 
place  being  taken  by  aegirite  crystals. 
In  the  sub-variety  of  phonolite 
called  tinguaite,  the  rock  has  often 
a  deep  greenish  color  due  to  the 
abundance  of  minute  crystals  of 
aegirite.  Large  crystals  are  found 
in  the  pegmatite  facies  of  nephelite- 
syenites  as  in  West  Greenland, 
Southern  Norway,  the  peninsula 
Kola  in  Russian  Lapland,  Ditro  in 
Transylvania. 

Prominent  American  occurrences     „ 
are  the  following:     Magnet  Cove,    ' 
Ark.  (large    crystals);    Salem  and 
Quincy,  Mass.;    Libertyville,  N.  J. 
(dike);     Trans    Pecos    district    in 
Texas;   Black  Hills,  S.  D.;  Cripple 
Creek,  Col.;  Bearpaw  Mts.,  Judith 
Mts.  and  the  Crazy  Mts.  in  Mon.; 
also  vanadium-bearing  aegirites  from 
Libby,  Mon.,  also  at  Montreal,  Canada. 

Acmite  is  named  from  &KM,  point,  in  allusion  to  the  pointed  extremities  of  the  crystals; 
Mginte  is  from  ^Egir,  the  Icelandic  god  of  the  sea. 

SPODUMENE.     Triphane. 

Monoclinic.    Axes  a  :  b  :  c  =  1-1238  :  1  :  0*6355;  0  =  69°  40'. 

Twins:  tw.  pi.  a  (100).     Crystals  prismatic  (mm'"  110  A  HO  =  93°  0'), 
often  flattened  ||  a  (100);  the  vertical  planes  striated  and  furrowed;'  crystals  , 
sometimes  very  lar,ge.     Also  massive,  cleavable. 

Cleavage  m  (110)  perfect.     A  lamellar  structure  ||  a  (100)  sometimes  very 


818 


SILICATES 


481 


820 


Norwich,  Mass         Hiduenite 


prominent,  a  crystal  then  separating  into  thin  plates.  Fracture  uneven 
to  subconchoidal.  Brittle.  H.  =  6'5-7.  G.  =  3-13-3-20.  Luster  vitreous, 
on  cleavage  surfaces  somewhat  pearly.  Color  greenish  white,  grayish  white, 
yellowish  green,  emerald-green,  yellow,  ame- 
thystine purple.  Streak  white.  Transparent 
to  translucent.  Pleochroism  strong  in  deep 
green  varieties.  Optically  +  .  Ax.  pi.  || 
b  (010).  Bxa  A  c  axis  =  +  26°.  Dispersion 
p  >  v,  horizontal.  2  V  =  58°.  a  =  1-651. 
j8  =  1-669.  7  =  1-677. 

Hiddenite  has  a  yellow-green  to  emerald-green  color; 
the  latter  variety  is  used  as  a  gem.  In  small  (£  to  2 
inches  long)  slender  prismatic  crystals,  faces  often 
etched. 

Kunzite  is  a  clear  lilac-colored  variety  found  near 
Pala,  San  Diego  Co.,  California,  and  also  at  Vanakarata, 
Madagascar .  The  unaltered  material  from  Branch ville, 
Conn.,  shows  the  same  color.  Used  as  a  gem  stone. 

Comp.  —  LiAl(SiO8)2  or  Li2O.Al2O3.4SiO2  = 
Silica  64-5,  alumina  27-4,  lithia  8*4  =  100.  Generally  contains  a  little 
sodium;  the  variety  hiddenite  also  chromium,  to  which  the  color  may 
be  due. 

Pyr.,  etc.  —  B.B.  becomes  white  and  opaque,  swells  up,  imparts  a  purple-red  color 
(lithia)  to  the  flame  (sometimes  obscured  by  sodium),  and  fuses  at  3 '5  to  a  clear  or  white 
glass.  Not  acted  upon  by  acids.  Kunzite  shows  strong  phosphorescence  with  an  orange- 
pink  color  when  excited  by  an  oscillating  electric  discharge,  by  ultra  violet  rays,  X-rays,  or 
radium  emanations. 

Diff.  —  Characterized  by  its  perfect  parting  ||  a  (100)  (in  some  varieties)  as  well  as 
by  prismatic  cleavage;  has  a  higher  specific  gravity  and  more  pearly  luster  than  feldspar 
or  scapolite.  Gives  a  red  flame  B.B.  Less  fusible  than  amblygonite. 

Alter.  —  Spodumene  undergoes  very  commonly  alteration.  First  by  the  action  of  solu- 
tions containing  soda  it  is  changed  to  a  mixture  of  eucryptite,  LiAlSiO4,  and  albite,  NaAl 
SisOg.  Later  through  the  influence  of  potash  salts  the  eucryptite  is  changed  to  muscovite. 
This  resulting  mixture  of  albite  and  muscovite  is  known  as  cymatolite,  having  a  wavy 
fibrous  structure  and  silky  luster .  These  alteration  products  are  well  shown  in  the  specimens 
from  Branch  ville,  Conn. 

Artif .  —  An  artificial  spodumene  has  been  obtained  together  with  other  silicates  by 
fusing  together  lithium  carbonate,  alumina  and  silica.  This  spodumene  differs,  however, 
from  the  natural  mineral  in  its  optical  properties  and  has  been  called  ^-spodumene.  The 
natural  mineral,  or  spodumene,  is  transformed  into  the  /3  modification  on  heating  to  1000°. 

Obs.  —  Spodumene  occurs  in  pegmatite  veins,  sometimes  in  crystals  of  very  great  size. 
Crystals  from  the  Etta  tin  mine,  S.  D.,  with  faces  up  to  40  feet  in  length  have  been  reported. 
Occurs  on  the  island  of  Uto,  Sweden;  at  Killiney  Bay,  Ireland;  in  small  transparent  crystals 
of  a  pale  yellow  in  Brazil,  province  of  Minas  Geraes.  Variously  colored  spodumene  from 
Madagascar. 

In  the  United  States,  in  granite  at  Goshen,  Mass.;  also  at  Chesterfield,  Chester,  Hunt- 
ington  (formerly  Norwich),  and  Sterling,  Mass.;  at  Windham,  Me.,  with  garnet  and  stau- 
rolite  and  at  Peru,  with  beryl,  triphylite,  petalite.  In  Conn.,  at  Branchville,  the  crystals 
often  of  immense  size;  near  Stony  Point,  Alexander  Co.,  N.  C.  (hiddenite)',  in  S.  D.  at  the 
Etta  tin  mine  in  Pennington  Co.  Kunzite  from  Pala,  Cal. 

The  name  spodumene  is  from  awodios,  ash-colored.  Hiddenite  is  named  for  W.  E. 
Hidden  and  Kunzite  for  Dr.  G.  F.  Kunz. 

Use.  —  The  colored  transparent  varieties  are  used  as  gem  stones;  see  above. 

JADEITE. 

Monoclinic.  Axes,  see  p.  471.  Cleavage  and  optical  characters  like 
pyroxene.  Usually  massive,  with  crystalline  structure,  sometimes  granular, 
also  obscurely  columnar,  fibrous  foliated  to  closely  compact. 


482  DESCRIPTIVE   MINERALOGY 

Cleavage:  prismatic,  at  angles  of  about  93°  and  87°;  also  ||  a  (100)  diffi- 
cult. Fracture  splintery.  Extremely  tough.  H.  =  6'5-7.  G.  =  3-33-3-35. 
Luster  subvitreous,  pearly  on  surfaces  of  cleavage.  Color  apple-green  to 
nearly  emerald-green,  bluish  green,  leek-green,  greenish  white,  and  nearly 
white;  sometimes  white  with  spots  of  bright  green.  Optically  +  .  Bxa  A 
c  axis  =  30°  to  40°.  2  V  =  72°.  0=1-654.  Streak  uncolored.  Trans- 
lucent to  subtranslucent. 

Comp.  —  Essentially  a  metasilicate  of  sodium  and  aluminium  corre- 
sponding to  spodumene,  NaAl(SiO3)2  or  Na2O.Al2O3.4SiO2  =  Silica  59*4, 
alumina  25 -2,  soda  15 -4  =  100. 

Chloromelanite  is  a  dark  green  to  nearly  black  kind  of  jadeite  (hence  the  name),  contain- 
ing iron  sesquioxide  and  not  conforming  exactly  to  the  above  formula. 

Pyr.,  etc.  —  B.B.  fuses  readily  to  a  transparent  blebby  glass.  Not  attacked  by  acids 
after  fusion,  and  thus  differing  from  saussurite. 

Obs.  —  Occurs  chiefly  in  eastern  Asia,  thus  in  the  Mogoung  district  in  Upper  Burma, 
in  a  valley  25  miles  southwest  of  Meinkhoom,  in  rolled  masses  in  a  reddish  clay;  in  Yung- 
chang,  province  of  Yunnan,  southern  China;  in  Thibet.  Much  uncertainty  prevails,  how- 
ever, as  to  the  exact  localities,  since  jadeite  and  nephrite  have  usually  been  confused  with 
each  other.  May  occur  also  on  the  American  continent,  in  Mexico  and  South  America ; 
perhaps  also  in  Europe. 

Jadeite  has  long  been  highly  prized  in  the  East,  especially  in  China,  where  it  is  worked 
into  ornaments  and  utensils  of  great  variety  and  beauty.  It  is  also  found  with  the  relics  of 
early  man,  thus  in  the  remains  of  the  lake-dwellers  of  Switzerland,  at  various  points  in 
France,  in  Mexico,  Greece,  Egypt,  and  Asia  Minor. 

A  pyroxene,  resembling  jadeite  in  structure  and  consisting  of  the  molecules  of  jadeite, 
diopside,  and  acmite  in  nearly  equal  proportions,  occurs  at  the  manganese  mines  of  St. 
Marcel,  Italy. 

Use.  —  As  the  material  jade,  is  used  as  an  ornamental  stone.     See  below. 

JADE  is  a  general  term  used  to  include  various  mineral  substances  of  tough,  compact 
texture  and  nearly  white  to  dark  green  color  used  by  early  man  for  utensils  and  ornaments, 
and  still  highly  valued  in  the  East,  especially  in  China.  It  includes  properly  two  species 
only;  nephrite,  a  variety  of  amphibole  (p.  489),  either  tremolite  or  actinolite,  with  G.  = 
2 '95-3-0.  and  jadeite,  of  the  pyroxene  group  and  in  composition  a  soda-spodumene,  with 
G.  =  3-3-3-35;  easily  fusible. 

The  jade  of  China  belongs  to  both  species,  so  also  that  of  the  Swiss  lake-habitations  and 
of  Mexico.  Of  the  two,  however,  the  former,  nephrite,  is  the  more  common  and  makes  the 
jade  (ax  stone  or  Punamu  stone)  of  the  Maoris  of  New  Zealand;  also  found  in  Alaska. 

The  name  jade  is  also  sometimes  loosely  used  to  embrace  other  minerals  of  more  or  less 
similar  characters,  and  which  have  been  or  might  be  similarly  used  —  thus  sillimanite,  pec- 
tolite,  serpentine;  also  vesuvianite,  garnet.  Bowenite  is  a  jade-like  variety  of  serpentine. 
The  "jade  tenace"  of  de  Saussure  is  now  called  saussurite. 

WOLLASTONITE.     Tabular  Spar 

Monoclinic.     Axes  a  :  b  :  c  =  1-0531  :  1  :  0*9676;  0  =  84°  30'. 

822  mm"',  110  A  110  =  92°  42'. 

hhf",  540  A  540  =  79°  58'. 
gg't  Oil  A  Oil  =  87°  51'. 
co,  001  A  101  =  40°  3'. 
cr,  001  A  301  =  74°  59'. 
ct,  001  A  101  =  45°  5'. 
Diana,  N.  Y. 

Twins:    tw.    pi.   a  (100).      Crystals    commonly 

tabular  ||  a  (100)  or  c  (001);    also  short  prismatic.     Usually  cleavable  mas- 
sive to  fibrous,  fibers  parallel  or  reticulated;  also  compact. 

Cleavage:  a  (100)  perfect;  also  c  (001);  t  (101)  less  so.  Fracture  uneven, 
brittle.  H.  =  4-5-5.  G.  =  2-8-2-9.  Luster  vitreous,  on  cleavage  surfaces 
pearly.  Color  white,  inclining  to  gray,  yellow,  red,  or  brown.  Streak  white, 
bubtransparent  to  translucent.  Optically  -.  Bxa  A  c  axis  =  +  32°.  Dis- 


SILICATES  483 

persion  p  >  v,  inclined  distinct.     Ax.  pi.  ||  b  (010).     2E  =  70°;  a  =  T621. 
ft  =  1-633.     7  =  1*635. 

Comp.  • —  Calcium  metasilicate,  CaSi03  or  CaO.SiO2  =  Silica  51*7,  lime 
48-3,  =  100. 

When  wollastonite  is  heated  above  1190°  C.  it  develops  a  basal  cleavage,  becomes  pseudo- 
hexagonal,  optically  positive,  nearly  uniaxial  but  probably  monoclinic.  This  material  has 
been  called  pseudowollastonite. 

Pyr.,  etc.  —  B.B.  fuses  quietly  to  a  white,  almost  glassy  globule.  With  hydrochloric 
acid  decomposed  with  separation  of  silica;  most  varieties  effervesce  slightly  from  the  pres- 
ence of  calcite.  Often  phosphoresces. 

Micro.  —  In  thin  sections  wollastonite  is  colorless  with  a  moderate  relief  and  medium 
birefringence.  The  plane  of  the  optic  axes  is  usually  normal  to  the  elongation  of  the 
crystals. 

Artif .  —  Wollastonite  may  be  obtained  artificially  by  heating  a  glass  of  the  composition 
CaSiOs  to  between  800°  and  1000°.  At  higher  temperatures  the  pseudowollastonite  modi- 
fication is  obtained. 

Obs.  —  Wollastonite  is  found  especially  in  granular  limestone,  and  in  regions  of  granite, 
as  a  contact  formation;  it  is  very  rare  in  eruptive  rocks.  It  is  often  associated  with  a  lime 
garnet,  diopside,  etc. 

Occurs  in  Hungary  in  the  copper  mines  of  Cziklowa  in  the  Banat;  at  Pargas  in  Finland; 
at  Harzburg  in  the  Harz  Mts.,  Germany;  at  Auerbach,  Hesse,  Germany,  in  granular  lime- 
stone; at  Vesuvius,  rarely  in  fine  crystals;  on  the  islands  of  Elba  and  Santorin. 

In  the  United  States,  in  N.  Y.,  at  Willsborough ;  Diana,  Lewis  Co.;  Bonaparte  Lake, 
Lewis  Co.  In  Pa.,  Bucks  Co.,  3m.  west  of  Attleboro;  in  Cal.,  at  Crestmore.  In  Canada, 
at  Grenville;  at  St.  Jerome  and  Morin,  Quebec,  with  apatite. 

Named  after  the  English  chemist,  W.  H.  Wollaston  (1766-1828). 

Alamosite.  Lead  metasilicate,  PbSiOs.  Closely  related  to  wollastonite  in  crystal 
forms.  Monoclinic.  In  radiating  fibrous  aggregates.  Cleavage  ||  6  (010).  G.  =  6'5. 
H.  =  4'5.  Colorless  or  white.  Refractive  index  about  T96.  Found  near  Alamos,  Sonora, 
Mexico. 

PECTOLITE. 

Moneclinic.     Axes  a  :  b  :  c  =  1-1140  :  1  :  0-9864;  ft  =  84°  40'. 

Commonly  in  close  aggregations  of  acicular  crystals;  elongated  ||  b  axis, 
but  rarely  terminated.  Fibrous  massive,  radiated  to  stellate. 

Cleavage:  a  (100)  and  c  (001)  perfect.  Fracture  uneven.  Brittle.  H.  =  5. 
G.  =  2 '68-2 -78.  Luster  of  the  surface  of  fracture  silky  or  subvitreous. 
Color  whitish  or  grayish.  Subtranslucent  to  opaque.  Optically  +.  Ax.  pi. 
and  Bxa  _L  b  (010);  Bx0  nearly  _L  a  (100).  2  V  =  60°.  ft  =  1-61. 

Comp.  —  HNaCa2(SiO3)3  or  H2O.Na2O.4CaO.6Si02  =  Silica  54-2,  lime 
33-8,  soda  9 -3,  water  27  =  100. 

Pectolite  is  sometimes  classed  with  the  hydrous  species  allied  to  the  zeolites. 

Pyr.,  etc.  -  In  the  closed  tube  yields  water.  B.B.  fuses  at  2  to  a  white  enamel.  De- 
composed in  part  by  hydrochloric  acid  with  separation  of  silica  as  a  jelly.  Often  gives  out 
light  when  broken  in  the  dark. 

Obs.  —  A  secondary  mineral,  occurring  like  the  zeolites  mostly  in  basic  eruptive  rocks, 
in  cavities  or  seams;  occasionally  in  metamorphic  rocks.  Found  in  Scotland  near  Edin- 
burgh; at  Kilsyth,  Corstorphine  Hill  (walkerite);  Island  Skye.  Also  at  Mt.  Baldo  and  Mt. 
Monzoni  in  the  Tyrol;  at  Niederkirchen,  Bavaria  (osmelite). 

Occurs  also  at  Bergen  Hill,  Paterson  and  Great  Notch,  N.  J.;  Lehigh  Co.,  Pa.;  compact 
at  Isle  Royale,  Lake  Superior;  at  Magnet  Cove,  Ark.,  in  elseqlite-syenite  (manganpectolite 
with  4  p.  c.  MnO);  compact,  massive  in  Alaska,  where  used,  like  jade,  for  implements. 

Schizolite.  Like  manganpectolite,  HNa(Ca,Mn)2(SiOs)3,  but  triclinic.  In  prismatic 
crystals.  Two  cleavages.  H.  =  5-5 '5.  G.  =  3'0-3'1.  Color  light  red  to  brown.  From 
the  nepheline  syenite  of  Julianehaab,  southern  Greenland. 

Rosenbuschite.  Near  pectolite,  but  contains  zirconium.  Index,  1-65.  From  Norway. 
In  nephelite-syenite-porphyry,  Red  Hill,  Moultonboro,  N.  H. 


484  DESCRIPTIVE   MINERALOGY 

Wohlerite.  A  zirconium-silicate  and  niobate  of  Ca,  Na,  etc.  In  prismatic,  tabular 
crystals,  yellow  to  brown.  Indices,  1700-1 726.  Occurs  in  elseolite-syenite^  on  several 
islands  of  the  Langesund  fiord,  near  Brevik,  in  Norway.  In  syenite  from  Red  Hill,  N.  H. 

Lavenite.  A  complex  zirconuim-silieate  of  Mn,  Ca,  etc.,  containing  also  F,  Ti,  Ta.  etc. 
In  yellow  to  brown  prismatic  crystals.  Index,  1750.  Found  on  the  island  Laven  in  the 
.Langesund  fiord,  southern  Norway;  also  elsewhere  in  eheolite-syemte. 

7.  Triclinic  Section 
RHODONITE. 

Triclinic.  Axes  a  :  b  :  c  =  1*07285  :  1  :  0-6213;  a  =  103°  18';  ]8  =  108° 
44'-  y  =  81°  39'. 

Crystals  usually  large  and  rough  with  rounded  edges.  Commonly  tabular 
1|  c  (001);  sometimes  resembling  pyroxene  in  habit.  Commonly  massive, 
cleavable  to  compact;  also  in_  embedded  grains. 

Cleavage:  m  (110),  M  (110)  perfect;  c  (001)  less  perfect.  Fracture  con- 
choidal  to  uneven;  very  tough  when  compact.  H.  =  5-5-6-5.  G.  =  3-4- 
3-68.  Luster  vitreous;  on  cleavage  surfaces  somewhat  pearly.  Color  light 
brownish  red,  flesh-red,  rose-pink;  sometimes  greenish  or  yellowish,  when 
impure;  often  black  outside  from  exposure.  Streak  white.  Transparent  to 
translucent.  Optically  — .  .0  =  173. 

Comp.  —  Manganese  metasilicate,  MnSiOa  or  MnO.SiO2  =  Silica  45-9, 
manganese  protoxide  54-1  =  100.  Iron,  calcium  (in  bustamite),  and  occasion- 
ally zinc  (in  'fowlerite)  replace  part  of  the  manganese. 

823  824  825 


Franklin  Furnace,  N.  J. 

db,    100  A  010  =  94°  26'.  mM,  110  A  110  =  92°  28|'. 

ac,    100  A  001  =  72°  36*'.  en,     001  A  221  =  73°  52'. 

be,    010  A  001  =  78°  42i'.  ck,      001  A  221  =  62°  23'. 

am,  100  A  110  =  48°  33'.  kn,     221  A  221  =  86°    5'. 

Pyr.,  etc.  —  B.B.  blackens  and  fuses  with  slight  intumescence  at  2'5;  with  the  fluxes 
gives  reactions  for  manganese;  fowlerite  gives  with  soda  on  charcoal  a  reaction  for  zinc. 
Slightly  acted  upon  by  acids.  The  calciferous  varieties  often  effervesce  from  mechanical 
admixture  of  calcium  carbonate.  In  powder,  partly  dissolves  in  hydrochloric  acid,  and 
the  insoluble  part  becomes  of  a  white  color.  Darkens  on  exposure  to  the  air,  and  some- 
times becomes  nearly  black. 

Diff. —  Characterized  by  its  pink  color;  distinct  cleavages;  hardness;  fusibility  and 
manganese  reactions  B.B. 

Obs.  —  Occurs  in  Sweden  at  Langban,  Wermland;  in  iron-ore  beds,  in  broad  cleavage- 
plates,  and  also  granular  massive,  and  at  the  Pajsberg  iron  mines  near  Filipstad  (paisbergite) 
sometimes  in  small  brilliant  crystals;  in  the  district  of  Ekaterinburg  in  the  Ural  Mts.,  mas- 
sive like  marble,  whence  it  is  obtained  for  ornamental  purposes;  with  tetrahedrite  at  Kap- 
nik  and  Rezbanya,  Hungary;  St.  Marcel,  Piedmont,  Italy;  Mexico  (bustamite,  containing 
CaO).  In  crystals  from  Broken  Hill,  New  South  Wales. 

Occurs  in  Cummington,  Mass.;   on  Osgood's  farm,  Blue  Hill  Bay,  Me.;  fowlerite  (con- 


SILICATES  485 

taining  ZnO)  at  Mine  Hill,  Franklin  Furnace,  and  Sterling  Hill,  near  Ogdensburgh,  N.  J., 
usually  embedded  in  calcite  and  sometimes  in  fine  crystals. 

Named  from  podov,  a  rose,  in  allusion  to  the  color. 

Rhodonite  is  often  altered  chiefly  by  oxidation  of  the  MnO  (as  in  marceline,  dyssnite); 
also  by  hydration  (stratopeite,  neotocite,  etc.);  further  by  introduction  of  CO2  (allagite, 
photidte,  etc.). 

Use.  —  Rhodonite  at  times  is  used  as  an  ornamental  stone. 

Pyroxmangite.  A  triclinic,  manganese-iron  pyroxene.  In  cleavage  masses.  Indices, 
175-1 -76.  H.  =  5-5-6.  G.  =  3'8.  Color,  amber  to  dark  brown.  Easily  fusible  to  black 
magnetic  globule.  Alters  to  skemmatite.  Found  near  Iva,  Anderson  Co.,  South  Carolina. 

Babingtonite.  (Ca,Fe,Mn)SiO3  with  Fe2(SiO3)a.  In  small  black  triclinic  crystals,  near 
rhodonite  in  angle  (axes  on  p.  471).  H.  =  5'5-6.  G.  =  3'35-3'37.  Index,  172.  From 
Arendal,  Norway;  at  Herbornseelbach,  Nassau,  Germany;  at  Baveno,  Italy.  From  Somer- 
ville  and  Athol,  Mass.;  in  the  zeolite  deposits  of  Passaic  Co.,  N.  J. 

Hiortdahlite.  Essentially  (Na2,Ca)  (Si,Zr)Oa,  with  also  fluorine.  In  pale  yellow  tab- 
ular crystals  (triclinic).  Index,  1'695.  Occurs  sparingly  on  an  island  in  the  Langesund 
fiord,  southern  Norway. 

Sobralite.  A  triclinic  pyroxene.  Optically  +  .  Colorless.  From  eulysite  rock  at 
Sodermanland,  Sweden. 

3.   Amphibole  Group 

Orthorhombic,  Monoclinic,  Triclinic 

Composition  for  the  most  part  that  of  a  metasilicate,  RSi03,  with  R  = 
Ca,Mg,Fe  chiefly,  also  Mn,Na2,K2,H2.  Further  often  containing  aluminium 

and  ferric  iron,  in  part  with  alkalies  as  NaAl(Si03)2  or  NaFe(SiO3)2;  perhaps 

ii  in 
also  containing  RR2SiOe. 

a.  Orthorhombic  Section 

a  :b 

Anthophyllite  (Mg,Fe)SiO3  0-5138  :  1 

GEDRITE  (Mg,Fe)Si03  with  (Mg,Fe)Al2Si06 

0.  Monoclinic  Section 

a  :  b  :  c  /3 

Amphibole  .     0-5511  :  1  : 0-2938        73°  58' 

I.    NONALUMINOUS  VARIETIES. 

1.  TREMOLITE  CaMg3(SiO3)4 

2.  ACTINOLITE  Ca(Mg,Fe)3(SiO3)4 

Nephrite,  Asbestus,  Smaragdite,  etc. 
Cummingtonite         (Fe,Mg)SiO3 
Dannemorite  (Fe,Mn,Mg)SiO3 

Grtinerite  FeSiO3 

3.  RICHTERITE  (K2,Na2Mg,Ca,Mn)4(SiO3)4 


II.  ALUMINOUS  VARIETIES- 

4.   HORNBLENDE 
Edenite 
Pargasite  and 
Common  Hornblende 


Chiefly  Ca(Mg,Fe)3(SiO3)4  with 
Na2Al2(SiO3)4  and  (Mg,Fe)2(Al,Fe)4Si2Oi2 


486 


DESCRIPTIVE   MINERALOGY 


Glaucophane 

Riebeckite 
Crocidolite 
Arfvedsonite 


NaAl(Si03)2.(Fe,Mg)Si03 

a  :  b  :  c  /3 

2NaFe(SiO3)2.FeSiO3    0'5475  :  1  :  0'2925  =  76°  10' 
NaFe(Si03)2.FeSi03 
Na8(Ca,Mg)3(Fe,Mn)14(Al,Fe)2Si21045 

0-5509  :  1  :  0*2378  =  73°  2' 


7.  Triclinic  Section 
^Enigmatite. 

The  only  species  included  under  the  triclinic  section  is  the  rare  and  im- 
perfectly known  aenigmatite  (cossyrite). 

The  AMPHIBOLE  GROUP  embraces  a  number  of  species  which,  while  falling 
in  different  systems,  are  yet  closely  related  in  form  —  as  shown  in  the  common 
prismatic  cleavage  of  54°  to  56°  -—  also  in  optical  characters  and  chemical  com- 
position. As  already  noted  (see  p.  471),  the  species  of  this  group  form  chem- 
ically a  series  parallel  to  that  of  the  closely  allied  Pyroxene  Group,  and  between 
them  there  is  a  close  relationship  in  crystalline  form  and  other  characters. 
The  Amphibole  Group,  however,  is  less  fully  developed,  including  fewer 
species,  and  those  known  show  less  variety  in  form. 

The  chief  distinctions  between  pyroxene  and  amphibole  proper  are  the  following: 

Prismatic  angle  with  pyroxene  87°  and  93°;  with  amphibole  56°  and  124°;  the  prismatic 
cleavage  being  much  more  distinct  in  the  latter. 

With  pyroxene,  crystals  usually  short  prismatic  and  often  complex,  structure  of  massive 
kinds  mostly  lamellar  or  granular;  with  amphibole,  crystals  chiefly  long  prismatic  and 
simple,  columnar  and  fibrous  massive  kinds  the  rule. 

The  specific  gravity  of  most  of  the  pyroxene  varieties  is  higher  than  of  the  like  varieties 
of  amphibole.  In  composition  of  corresponding  kinds,  magnesium  is  present  in  larger 
amount  in  amphibole  (Ca  :  Mg  =  1  :  1  in  diopside,  =  1  :  3  in  tremolite) ;  alkalies  more 
frequently  play  a  prominent  part  in  amphibole. 

The  optical  relations  of  the  prominent  members  of  the  group,  as  regards 
the  position  of  the  ether-axes,  is  exhibited  by  the  following  figures  (Cross) ; 
compare  Fig.  797,  p.  472,  for  a  similar  representation  for  the  corresponding 
members  of  the  pyroxene  group. 


I.   Anthophyllite. 


II.   Glaucophane.         III.   Tremolite,  etc.         IV.   Hornblende. 
V.   Arfvedsonite.        VI.   Riebeckite. 


a.   Orthorhombic  Section 
ANTHOPHYLLITE. 

Orthorhombic.  Axial  ratio  a  :  b  =  0*5137  :  1.  Crystals  rare,  habit  pris- 
matic (mm"'  110  A  110  =  54°  23).  Commonly  lamellar,  or  fibrous  massive; 
fibres  often  very  slender;  in  aggregations  of  prisms. 


SILICATES 


487 


Cleavage:  prismatic,  perfect;  b  (010)  less  so;  a  (100)  sometimes  distinct. 
H.  =  5 -5-6.  G.  =  3 1-3 -2.  Luster  vitreous,  somewhat  pearly  on  the 
cleavage  face.  Color  brownish  gray,  yellowish  brown,  clove-brown,  brownish 
green,  emerald-green,  sometimes  metalloidal.  Streak  uncolored  or  grayish. 
Transparent  to  subtranslucent.  Sometimes  pleochroic  Usually  optically 
+  ;  also  +  for  red,  —  for  yellow,  green.  Ax.  pi.  always  ||  b  (010).  Bxa 
usually  J_  c  (001) ;  also  _L  c  (001)  for  red,  J_  a  (100)  for  yellow,  green.  2  V  = 
84°.  a  =  1-633.  0  =  1'642.  7  =  1-657. 

Comp.  —  (Mg,Fe)SiO3,  corresponding  to  enstatite-bronzite-hypersthene 
in  the  pyroxene  group.  Aluminium  is  sometimes  present  in  considerable 
amount.  There  is  the  same  relation  in  optical  character  between  anthophyl- 
lite  (+)  and  gedrite  (  — )  as  between  enstatite  and  hypersthene  (cf.  Figs.  799 
803,  p.  472). 

Var.  —  ANTHOPHYLLITE,  Mg  :  Fe  =  4  :  1,  3  :  1,  etc.  For  3  :  1,  the  percentage  compo- 
sition is:  Silica  55*6,  iron  protoxide  16'6,  magnesia  27 '8  =  100.  Anthophyllite  sometimes 
occurs  in  forms  resembling  asbestus. 

Aluminous,  GEDRITE.  Iron  is  present  in  larger  amount,  and  also  aluminium;  it  hence 
corresponds  nearly  to  a  hypersthene,  some  varieties  of  which  are  highly  aluminous. 

Ferroanthophyllite  is  a  name  given  to  an  iron  anthophyllite  from  Idaho  and  elsewhere. 

Hydrous  anthophyllites  have  been  repeatedly  described,  but  in  most  cases  they  have  been 
shown  to  be  hydrated  monoclinic  amphiboles. 

Pyr.,  etc.  —  B.B.  fuses  with  difficulty  to  a  black  magnetic  enamel;  with  the  fluxes  gives 
reactions  for  iron;  unacted  upon  by  acids. 

Micro.  —  In  sections  colorless,  non-pleochroic.    Parallel  extinction.     Commonly  fibrous. 

Artif .  —  Anthophyllite  is  formed  artificially  when  magnesium  metasilicate  is  heated 
considerably  above  its  melting  point  and  then  quickly  cooled. 

Obs.  —  Anthophyllite  occurs  in  mica  schist  near  Kongsberg  in  Norway:  at  Hermann- 
schlag,  Moravia.  In  the  United  States,  at  the  Jenks  corundum  mine,  Franklin,  Macon  Co., 
N.  C.;  from  Rockport,  Mass.  A  colorless  or  pale  red  variety  from  Edwards,  N.  Y.,  has 
been  called  valleite.  The  original  gedrite  is  from  the  valley  of  Heas,  near  Gedres,  France. 
Named  from  anthophyllum,  clove,  in  allusion  to  the  clove-brown  color. 


13.  Monoclinic  Section 


AMPHIBOLE. 

Monoclinic. 


mm 

ca, 

cp, 


Hornblende. 

Axes  a  :  b  :  c  =  0*5511 

110  A  110  =  55°  49'. 
001  A  100  =  73°  58'. 
001  A  101  =  31°  0'. 


:  0-2938;  0  =  73°  58'. 
rr',  Oil  A  Oil  =  31°  32'. 
ii,    031  A  031  =  80°  32'. 
pr,   101  A  Oil  =  34°  25'. 

Twins:    (1)  tw.  pi.  a  (100),  common  as  contact-twins;   rarely  polysyn- 
827  829  830  831 


• 


thetic.     (2)  c  (001),  as  tw.  lamellae,  occasionally  producing  a  parting  analogous 
to  that  more  common  with  pyroxene  (Fig.  461,  p.  173).     Crystals  commonly 


488 


DESCRIPTIVE   MINERALOGY 


prismatic;  usually  terminated  by  the  low  clinodome,  r  (Oil),  sometimes  by 
r  and  p  (101)  equally  developed  and  then  suggesting  rhombohedral  forms  (as 
of  tourmaline).  Also  columnar  or  fibrous,  coarse  or  fine,  fibres  often  like  flax; 
rarely  lamellar;  also  granular  massive,  coarse  or  fine,  and  usually  strongly 
coherent,  but  sometimes  friable. 

Cleavage:  m  (110)  highly  perfect;  a  (100),  b  (010)  sometimes  distinct. 
Fracture  subconchoidal,  uneven.  Brittle.  H.  =  5-6.  G.  =  2-9-3-4,  vary- 
ing with  the  composition.  Luster  vitreous  to  pearly  on  cleavage  faces ;  fibrous 
varieties  often  silky.  Color  between  black  and  white,  through  various  shades 
of  green,  inclining  to  blackish  green;  also  dark  brown;  rarely  yellow,  pink, 
rose-red.  Streak  uncolored,  or  paler  than  color.  Sometimes  nearly  trans- 
parent; usually  subtranslucent  to  opaque. 

Pleochroism  strongly  marked  in  all  the  deeply  colored  varieties,  as  described 
beyond.  Absorption  usually  Z  >  Y  >  X.  Optically  — ,  rarely  -f  .  Ax.  pi. 
||  b  (010).  Extinction-angle  on  b  (010),  or  Z  A  c  axis  =  +  15°  to  18°  in  most 
cases,  but  varying  from  about  1°  up  to  37°;  hence  also  Bxa  A  c  axis  =  —  75° 
to  —  72°,  etc.  See  Fig.  832.  Dispersion  p  <  v.  Axial  angles  variable;  see 
beyond. 

Optical  characters,  particularly  indices  of  refraction,  birefringence  and  extinction  angles 
vary  with  change  in  composition,  particularly  with  the  total  amount  of  iron  present.  In 
general  the  indices  and  extinction  angles  increase  with  increase  of  iron  content  while  the 
birefringence  decreases. 

Comp.  —  In  'part  a  normal  metasilicate  of  calcium  and  magnesium, 
RSi03,  usually  with  iron,  also  manganese,  and  thus  in  general  analogous  to  the 
pyroxenes.  The  alkali  metals,  sodium  and  potassium,  also  present,  and  more 
commonly  so  than  with  pyroxene.  In  part  also  aluminous,  corresponding  to 
the  aluminous  pyroxenes.  Titanium  sometimes  is  present  and  also  rarely 
fluorine  in  small  amount. 

The  aluminium  is  in  part  present  as  NaAl(SiO3)2,  but  many  amphiboles  containing 
aluminium  or  ferric  iron  are  more  basic  than  a  normal  metasilicate;  they  may  sometimes  be 

n         m 

explained  as  containing  R(Al,Fe)2SiO6,  but  the  exact  nature  of  the  compound  is  often 
doubtful.  The  amphibole  formulas  are  in  many  cases  double  the  corresponding  ones  for 


832 


833 


pyroxene     Thus,  for  most  tremolite  and  actinolite,  Ca  :  Mg(Fe)  =  1 
kte  is  CaMgaSuOw,  while  diopside  is  CaMgSi206,  etc. 


3,  and  hence  tremo- 


SILICATES  489 

Rammelsberg  has  shown  that  the  composition  of  most  aluminous  amphiboles  may  be 
expressed  in  the  general  form  mRSiO3.nAl2O3;  while  Scharizer,  modifying  this  view,  pro- 
poses to  regard  the  amphiboles  as  molecular  compounds  of  Ca(Mg,Fe)3Si4Oi2  (actinolite), 

i    ii    in 

and  the  orthosilicate  (R2,R)3R2Si3Oi2,  for  which  he  uses  Breithaupt's  name  syntagmatite, 
originally  given  to  the  Vesuvian  hornblende. 

Penfield  concludes  that  (1)  amphibole  is  a  metasilicate,  (2)  that  fluorine  and  hydroxyl 
are  isomorphous  with  the  protoxides  and  (3)  that  the  presence  of  sesquioxides  is  explained 
by  their  introduction  into  the  molecule  in  the  form  of  various  bivalent  radicals. 

The  crystallographic  position  here  adopted  is  that  suggested  by  Tschermak,  which  best 
exhibits  the  relation  between  amphibole  and_pyroxeme.  Some  authors  retain  the  former 
position,  according  to  which  p  =  (001),  r  =  (111),  etc.  Fig.  833  shows  the  corresponding 
optical  orientation. 

I.    Containing  little  or  no  Aluminium 

1.  TEEMOLITE.     Grammatite,     nephrite    in    part.     Calcium-magnesium 
amphibole.     Formula  CaMg3(SiO4)3  =  Silica  577,  magnesia  28*9,  lime  13'4  = 
100.     Ferrous  iron,  replacing  the  magnesium,  present  only  sparingly,  up  to 
3  p.  c.     Colors  white  to  dark  gray.     In  distinct  crystals,  either  long-bladed  or 
short  and  stout..     In  aggregates  long  and  thin  columnar,  or  fibrous;  also  com- 
pact granular  massive  (nephrite,  below).     G.  =  2'9-3'l.     Sometimes  trans- 
parent and  colorless.     Optically  — .     Extinction-angle  on  b  (010),  or  Z  A 
c  axis  =  +16°  to  18°,  hence  Bxa  A  c  axis  =  -  74°  to  -  72°.     2V  =  80°  to 
88°.     a  =  1-609.     (3  =  1-623.     7  =  1'635. 

Tremolite  was  named  by  Pini  from  the  Tremola  valley  on  the  south  side  of  the  St. 
Gothard. 

Winchite  is  the  name  given  to  a  blue  amphibole  near  tremolite  from  the  manganese  mines 
of  Central  India. 

2.  ACTINOLITE.    Calcium-magnesium-iron  amphibole.   Formula  Ca(Mg,Fe)3 
(Si03)4.     Color  bright  green  and  grayish  green.     In  crystals,  either  shortx- 
or  long-bladed,   as  in  tremolite;    columnar  or  fibrous;    granular  massive. 
G.  =  3-3 '2.     Sometimes   transparent.     The    variety   in    long   bright-green 
crystals  is  called  glassy  actinolite;  the  crystals  break  easily  across  the  prism. 
The  fibrous  and  radiated  kinds  are  often  called  asbestiform  actinolite  and 
radiated  actinolite.     Actinolite  owes  its  green  color  to  the  ferrous  iron  present. 

Pleochroism  distinct,  increasing  as  the  amount  of  iron  increases,  and  hence 
the  color  becomes  darker;  Z  emerald-green,  Y  yellow-green,  X  greenish  yellow. 
Absorption  Z  >  Y  >  X,  Zillertal.  Optically  — .  Extinction-angle  on  b  (010), 
Z  A  c  axis  =  +  15°  and  Bxa  A  c  axis  =  -  75°.  2V  =  78°;  p  <  v,  a  = 
1-611.  (3  =  1-627.  7  =  1-636. 

Named  atfinolite  from  a/cris,  a  ray,  and  XZ0os,  stone,  a  translation  of  the  German 
Strahlslein  or  radiated  stone.  Name  changed  to  actinote  by  Haiiy,  without  reason. 

NEPHRITE.  Jade  in  part.  A  tough,  compact,  fine-grained  tremolite  (or  actinolite). 
breaking  with  a  splintery  fracture  and  glistening  luster.  H.  =  (M5'5.  G.  =  2'96-3'l. 
Named  from  a  supposed  efficacy  in  diseases  of  the  kidney,  from  »>e</>p6s,  kidney.  It  varies 
in  color  from  white  (tremolite)  to  dark  green  (actinolite),  in  the  latter,  iron  protoxide  being 
present  up  to  6  or  7  p.  c.  The  latter  kind  sometimes  encloses  distinct  prismatic  crystals  of 
actinolite.  A  derivation  from  an  original  pyroxenic  mineral  has  been  suggested  in  some 
cases.  Nephrite  or  jade  was  brought  in  the  form  of  carved  ornaments  from  Mexico  or  Peru 
soon  after  the  discovery  of  America.  A  similar  stone  comes  from  Eastern  Asia,  New  Zea- 
land and  Alaska.  See  jadeite,  p.  481;  jade,  p.  482. 

Szechenyiite  is  an  amphibole  occurring  with  jadeite  from  Central  Asia. 

ASBESTUS.  Asbestos.  Tremolite,  actinolite,  and  other  varieties  of  amphibole,  except- 
ing those  containing  much  alumina,  pass  into  fibrous  varieties,  the  fibers  of  which  are  some- 
times very  long,  fijie,  flexible,  and  easily  separable  by  the  fingers,  and  look  like  flax.  These 
kinds  are  called  asbestus  (from  the  Greek  for  incombustible) .  The  colors  vary  from  white  to 


490  DESCRIPTIVE   MINEEALOGY 

green  and  wood-brown.  The  name  amianthus  is  applied  usually  to  the  finer  and  more  silky 
kinds.  Much  that  is  popularly  called  asbestus  is  chrysotile,  or  fibrous  serpentine,  containing 
12  to  14  p.  c.  of  water.  Byssolite  is  a  stiff  fibrous  variety. 

Mountain  leather  is  in  thin  flexible  sheets,  made  of  interlaced  fibers;  and  mountain  cork 
the  same  in  thicker  pieces;  both  are  so  light  as  to  ftoat  on  water,  and  they  are  often  hydrous, 
color  white  to  gray  or  yellowish.  Mountain  wood  is  compact  fibrous,  and  gray  to  brown  in 
color,  looking  a  little  like  dry  wood. 

SMARAGDITE.  A  thin-foliated  variety  of  amphibole,  near  actinolite  in  composition  but 
carrying  some  alumina.  It  has  a  light  grass-green  color,  resembling  much  common  green 
diallage.  In  many  cases  derived  from  pyroxene  (diallage)  by  uralitization,  see  below.  It 
retains  much  of  the  structure  of  the  diallage  and  also  often  encloses  remnants  of  the  original 
mineral.  It  forms,  along  with  whitish  or  greenish  saussurite,  a  rock  called  saussurite- 
gabbro,  the  euphotide  of  the  Alps.  The  original  mineral  is  from  Corsica,  and  the  rock  is 
the  verde  di  Corsica  duro  of  the  arts. 

URALITE.  Pyroxene  altered  to  amphibole.  The  crystals,  when  distinct,  retain  the 
form  of  the  original  mineral,  but  have  the  cleavage  of  amphibole.  The  change  usually 
commences  on  the  surface,  transforming  the  outer  layer  into  an  aggregation  of  slender 
amphibole  prisms,  parallel  in  position  to  each  other  and  to  the  parent  pyroxene  (cf .  Fig. 
803,  p.  473).  When  the  change  is  complete  the  entire  crystal  is  made  up  of  a  bundle  of 
amphibole  needles  or  fibers.  The  color  varies  from  white  (tremolite)  to  pale  or  deep  green, 
the  latter  the  more  common.  In  composition  uralite  appears  to  conform  nearly  to  actinolite, 
as  also  in  optical  characters.  The  most  prominent  change  in  composition  in  passing  from 
the  original  pyroxene  is  that  corresponding  to  the  difference  existing  between  the  two  species 
in  general,  that  is,  an  increase  in  the  magnesium  and  decrease  in  calcium.  The  change, 
therefore,  is  not  strictly  a  case  of  paramorphism,  although  usually  so  designated.  Uralite 
was  originally  described  by  Rose  in  a  rock  from  the  Ural  Mts.  It  has  since  been  observed 
from  many  localities.  The  microscopic  study  of  rocks  has  shown  the  process  of  "uralitiza- 
tion" to  be  very  common,  and  some  authors' regard  many  hornblendic  rocks  and  schists  to 
represent  altered  pyroxenic  rocks  on  a  large  scale. 

CUMMINGTONITE.  Amphibole-Anthophyllite.  Iron-Magnesium  Amphibole.  Here  be- 
long certain  varieties  of  amphibole  resembling  anthophyllite  and  essentially  identical  with 
it  in  composition,  but  optically  monoclinic.  From  Kongsberg,  Norway;  Greenland.  The 
original  cummingtonite  is  gray  to  brown  in  color;  usually  fibrous  or  fibre-lamellar,  often 
radiated.  G.  =  3'l-3'32;  from  Cummington,  Mass. 

DANNEMORITE.  Iron-Manganese  Amphibole.  Color  yellowish  brown  to  greenish  gray. 
Columnar  or  fibrous,  like  tremolite  and  asbestus.  Contains  iron  and  manganese.  From 
Sweden.  Juddite  is  a  manganese  amphibole  found  at  Kacharwahi,  India. 

GRUNERITE.  Iron- Amphibole.  Asbestiform  or  lamellar-fibrous.  Luster  silky;  color 
brown;  G.  =  3713.  Formula  FeSiO3. 

3.  RICHTERITE.    Sodium-Magnesium-Manganese  Amphibole.    (K2,Na2,M2;, 
Ca,Mn)4(Si03)4. 

In  elongated  crystals,  seldom  terminated.  G.  =  3 '09.  Color  brown,  yellow,  rose-red. 
Transparent  to^ranslucent.  Z  A  c  axis  =  +  17°-20°;  /3  =  1-63;  7  -  a  =  0'024.  From 
Pajsberg  and  Langban,  Sweden.  Characterized  by  the  presence  of  manganese  and  alkalies 
in  relatively  large  amount. 

Imerinite  is  a  soda-amphibole,  related  to  soda-richterite  from  the  province  Imerina, 
Madagascar. 

Breislakite  occurs  in  wool-like  forms  at  Vesuvius  and  Capo  di  Bove,  Italy.  Color  dark 
brown  to  black,  pleochroism  strongly  marked.  Inferred  to  belong  near  richterite. 

II.  Aluminous. 

4.  ALUMINOUS  AMPHIBOLE.     Hornblende.     Contains  alumina  or  ferric 
iron,  and  usually  both,  with  ferrous  iron  (sometimes  manganese),  magnesium, 
calcium,  and  alkalies.     The  kinds  here  included  range  from  the  light-colored 
edemte  containing  but  little  iron,  through  the  light  to  dark  green  pargasite, 
to  the  dark-colored  or  black  hornblende,  the  color  growing  darker  with  increase 
in  amount  of  iron.     Extinction-angle  variable,  from  0°  to  37°,  see  below. 
Pleochroism  strong.     Absorption  usually  Z  <  Y  <  X. 

EDENTTE.     Aluminous  Magnesium-Calcium  Amphibole.     Color  white  to  gray  and  pale 


SILICATES  491 

green,  and  also  colorless;  G.  =  3'0-3'059.  Resembles  anthophyllite  and  tremolite. 
Named  from  the  locality  at  Edenville,  N.  Y.  To  this  variety  belong  various  pale-colored 
amphiboles,  having  less  than  5  p.  c.  of  iron  oxides. 

Koksharovite  is  a  variety  from  the  neighborhood  of  Lake  Baikal,  Siberia,  named  after  the 
Russian  mineralogist,  von  Koksharov. 

Soretite  is  an  aluminous  amphibole  from  the  anorthite-diorite  rocks  of  Koswinsky  in  the 
northern  Ural  Mts. 

COMMON  HORNBLENDE,  PARGASITE.  Colors  bright  or  dark  green,  and  bluish  green  to 
grayish  black  and  black.  G.  =  3'05-3'47.  Pargasite  is  usually  made  to  include  green  and 
bluish  green  kinds,  occurring  in  stout  lustrous  crystals,  or  granular;  and  Common  horn- 
blende the  greenish  black  and  black  kinds,  whether  in  stout  crystals  or  long-bladed,  colum- 
nar, fibrous,  or  massive  granular.  But  no  line  can  be  drawn  between  them.  The  extinction- 
angle  on  6  (010),  or  Z  A  c  axis  =  +  15°  to  25°  chiefly.  Absorption  Z  >  Y  >  X. 

Pargasite  occurs  at  Pargas,  Finland,  in  bluish  green  and  grayish  black  crystals.  Z  A  c 
axis  =  +  18°;  0  =  1'64;  y  -  a  =  0'019;  2V  =  59°.  Pleochroism:  Z  greenish  blue;  Y 
emerald-green;  X  greenish  yellow. 

The  dark  brown  to  black  hornblendes  from  basaltic  and  other  igneous  rocks  vary  some- 
what widely  in  optical  characters.  The  angle  Z  A  c  axis  =  0°  to  +  10°  chiefly;  0  =  1725; 
y  —  a  =  0'072  (maximum).  Pleochroism:  Z  brown,  Y  yellow,  X  yellow-green,  but 
variable. 

Speziaite,  from  Traversella,  Italy,  is  an  iron  amphibole  with  strong  pleochroism;  X  = 
green,  Y  =  yellow-brown,  Z  =  azure-blue,  Z  A  c  axis  =  23°. 

The  Kataforite  of  Norway  (Brogger)  has  Z  A  c  axis  =  30°  to  60°;  absorption  Y  >  Z  >  X; 
pleochroism:  Z  yellow,  Z  violet,  X  yellow-brown;  it  approximates  toward  arfvedsonite 
(p.  494). 

Kupfferite,  from  a  graphite  mine  in  the  Tunkinsk  Mts.,  near  Lake  Baikal,  Siberia,  is  a 
deep  green  amphibole  (aluminous)  formerly  referred  to  anthophyllite. 

Syntagmatite  is  the  black  hornblende  of  Vesuvius. 

Bergamaskite  is  an  iron-amphibole  containing  almost  no  magnesia.  From  Monte  Altino, 
Province  of  Bergamo,  Italy. 

Kaersutite  is  a  titaniferpus  amphibole  from  Kaersut,  Umanaks  fiord,  North  Greenland. 

Hastingsite  is  an  amphibole  low  in  silica  and  high  in  iron  and  soda,  from  the  nephelite- 
syenite  of  Dungannon,  Hastings  Co.,  Ontario. 

Philipstadite  from  Philipstad,  Sweden,  is  an  iron-magnesium  amphibole  showing  unusual 
pleochroism. 

Pyr.  —  Essentially  the  same  as  for  the  corresponding  varieties  of  pyroxene,  see  p.  478. 

Diff.  —  Distinguished  from  pyroxene  (and  tourmaline)  by  its  distinct  prismatic  cleav- 
age, yielding  angles  of  56°  and  124°.  Fibrous  and  columnar  forms  are  much  more  common 
than  with  pyroxene,  lamellar  and  foliated  forms  rare 
(see  also  pp.  478,  486).  Crystals  often  long,  slender, 
or  bladed.  Differs  from  the  fibrous  zeolites  in  not 
gelatinizing  with  acids.  Epidote  has  a  peculiar  green 
color,  is  more  fusible,  and  shows  a  different  cleavage. 

Micro.  —  In  rock  sections  amphibole  generally 
shows  distinct  colors,  green,  sometimes  olive  or  brown, 
and  is  strongly  pleochroic.  Also  recognized  by  its 
high  relief;  generally  rather  high  interference-colors; 
by  the  very  perfect  system  of  cleavage-cracks  crossing 
at  angles  of  56°  and  124°  in  sections  _L  c  axis  (Fig. 
834).  In  sections  ||  b  (010)  (recognized  by  yielding  no  axial  figure  in  convergent  light,  by 
showing  the  highest  interference-colors,  and  by  having  parallel  cleavage-cracks,  ||  c  axis), 
the  extinction-direction  for  common  hornblendes  makes  a  small  angle  (12°-15°)  with  the 
cleavage-cracks  (i.e.,  with  c  axis);  further,  this  direction  is  positive  Z  (different  from  com- 
mon pyroxene  and  aegirite,  cf.  Figs.  813  and  818). 

Artif .  —  Experiments  on  the  artificial  production  of  the  amphiboles  have  shown  that 
in  general  they  are  unstable  at  high  temperatures  and  that  their  formation  in  igneous  rocks 
is  due  either  to  the  rapid  cooling  of  the  magma,  to  the  presence  of  water  or  to  some  unusual 
conditions  of  pressure,  etc.  In  general  when  the  amphiboles  are  fused  they  are  transformed 
into  the  corresponding  pyroxenes. 

Obs.  —  Amphibole  occurs  only  sparingly  in  volcanic  rocks  but  is  found  in  many  crys- 
talline limestones,  and  granitic  and  schistose  rocks.  Tremolite,  the  magnesia-lime  vari- 
ety, is  especially  common  in  limestones,  particularly  magnesian  or  dolomitic;  actinolite  (also 
nephrite),  the  magnesia-lime-iron  variety,  in  the  crystal  line  schists,  in  steatitic  rocks  and 
with  serpentine;  and  dark  green  and  black  hornblende,  occurs  in  both  igneous  and  meta- 


492  DESCRIPTIVE   MINERALOGY 

morphic  rocks.  It  is  found  in  granites,  syenites,  diorites  and  some  varieties  of  peridotite,  in 
gneisses  and  the  hornblende  schists. 

Hornblende-rock,  or  amphibolite,  consists  of  massive  hornblende  ot  a  dark  greenish  black 
or  black  color,  and  has  a  granular  texture.  Occasionally  the  green  hornblende,  or  actino- 
lite,  occurs  in  rock-masses,  as  at  St.  Francis,  in  Canada.  Hornblende-schist  has  the  same 
composition  as  amphibolite,  but  is  schistose  or  slaty  in  structure.  It  often  contains  a  little 
feldspar.  In  some  varieties  of  it  the  hornblende  is  in  part  in  minute  needles.  Granite  and 
syenite  often  contain  hornblende,  and  with  diorite  it  is  a  common  constituent.  This  is 
also  true  of  the  corresponding  forms  of  gneiss.  In  these  cases  it  is  usually  present  in  small, 
irregular  masses,  often  fibrous  in  structure;  also  as  rough  bladed  crystals. 

Prominent  foreign  localities  of  amphibole  are  the  following:  Tremolite  (grammatite) 
in  dolomite  at  Campolongo,  Switzerland;  also  at  Orawitza,  Rezbanya,  Hungary;  Gulsjo, 
Wermland,  Sweden.  Actinolite  in  the  crystalline  schists  of  the  Central  and  Eastern  Alps, 
especially  at  Greiner  in  the  Zillertal,  Tyrol;  at  Zoblitz  in  Saxony;  Arendal,  Norway. 
Asbestus  at  Sterzing,  Zillertal,  and  elsewhere  in  Tyrol;  in  Savoie,  France;  also  in  the  island 
of  Corsica.  Pargasite  at  Pargas,  Finland;  Saualpe  in  Carinthia.  Hornblende  at  Arendal, 
Kongsberg  and  Kargero,  Norway;  in  Sweden  and  Finland;  at  Vesuvius;  Aussig  and  Tep- 
litz,  Bohemia;  etc.  Nephrite,  which  in  the  form  of  "  jade"  ornaments  and  utensils  is  widely 
distributed  among  the  relics  of  early  man  (see  jade,  p.  482),  is  obtained  at  various  points  in 
Central  Asia.  The  most  important  source  is  that  in  the  Karakash  valley  in  the  Kuen  Lun 
Mts.,  on  the  southern  borders  of  Turkestan;  also  other  localities  in  Central  Asia.  In  New 
Zealand.  Nephrite  has  been  found  in  Europe  as  a  rolled  mass  at  Schwemmsal  near  Leipzig; 
in  Swiss  Lake  habitations  and  similarly  elsewhere. 

In  the  United  States,  in  Me.,  black  crystals- occur  at  Thomaston;  pargasite  at  Phipps- 
burg.  In  Ver.,  actinolite  in  the  steatite  quarries  of  Windham  and  New  Fane.  In  Mass., 
tremolite  at  Lee;  black  crystals  at  Chester;  asbestus  at  Pelham;  cummingtonite  at  Cum- 
mington.  In  Conn.,  in  large  flattened  white  crystals  and  in  bladed  and  fibrous  forms 
(tremolite)  in  dolomite,  at  Canaan.  In  N.  Y.,  Warwick,  Orange  Co.;  near  Eden ville;  near 
Amity;  at  the  Stirling  mines,  Orange  Co.;  in  short  green  crystals  at  Gouverneur,  St. 
Lawrence  Co.;  with  pyroxene  at  Russell;  a  black  variety  at  Pierrepont;  at  Macomb;  Pit- 
cairn;  tremolite  at  Fine;  in  Rossie,  2  miles  north  of  Oxbow;  in  large  white  crystals  at 
Diana,  Lewis  Co.;  asbestus  near  Greenwood  Furnace.  Hudsonite  from  Cornwall,  N.  Y., 
formerly  classed  as  a  pyroxene  has  been  shown  to  be  an  amphibole.  In  N.  J.,  tremolite  or 
gray  amphibole  in  good  crystals  at  Bryam,  and  other  varieties  of  the  species  at  Franklin  and 
Newton,  radiated  actinolite.  In  Pa.,  actinolite  at  Mineral  Hill,  in  Delaware  Co. ;  at  Union- 
vllle;  at  Kennett,  Chester  Co.  In  Md.,  actinolite  and  asbestus  at  the  Bare  Hills  in  serpen- 
tine; asbestus  is  mined  at  Pylesville,  Harford  Co.  In  Va.,  actinolite  at  Willis's  Mt.,  in 
Buckingham  Co.;  asbestus  at  Barnet's  Mills,  Fauquier  Co.  Nephrite  occurs  in  Alaska. 

In  Canada,  tremolite  is  abundant  in  the  Laurentian  limestones,  at  Calumet  Falls,  Litch- 
field,  Pontiac  Co.,  Quebec;  also  at  Blythfield,  Renfrew  Co.,  and  Dalhousie,  Lanark  Co. 
Black  hornblende  at  various  localities  in  Quebec  and  Ontario  with  pyroxene,  apatite, 
titanite,  etc.,  as  in  Renfrew  Co.  Asbestus  and  mountain  cork  at  Buckingham,  Ottawa  Co., 
Quebec;  a  bed  of  actinolite  at  St.  Francis,  Beauce  Co.,  Quebec;  nephrite  has  been  found 
in  British  Columbia  and  Northwest  Territory. 

GLAUCOPHANE. 

Mpnoclinic;  near  amphibole  in  form.  Crystals  prismatic  in  habit,  usually 
indistinct ;  commonly  massive,  fibrous,  or  columnar  to  granular. 

Cleavage:  m  (110)  perfect.  Fracture  conchoidal  to  uneven.  Brittle. 
£L  =  6-6-5.  G.  =  3-103-3-113.  Luster  vitreous  to  pearly.  Color  azure-blue, 
lavender-blue,  bluish  black,  grayish.  Streak  grayish  blue.  Translucent. 
Plepchroism  strongly  marked :  Z  sky-blue  to  ultramarine-blue,  Y  reddish  or 
bluish  violet,  X  yellowish  green  to  colorless.  Absorption  Z  >  Y  >  X.  Opti- 
cally + .  Ax.  pi.  1 1  6  (010) .  Z  A  c  axis  =  4°  to  6°,  rarely  higher  values.  2V  = 
45°.  a  =  1-621.  18  =  1-638.  T  =  1-638. 

Comp.  —  Essentially  NaAl(SiO»)s.(Fe,Mg)SiQ,.  If  Mg  :  Fe  =  2  :  1,  the 
formula  requires:  Silica  57'6,  alumina  16'3,  iron  protoxide  77,  magnesia  8-5, 
soda  9-9  =  100. 

Obs.  — Occurs  as  the  hornblendic  constituent  of  certain  crystalline  schists,   called 
icophane-schuts,  or  glaucophanite;  also  more  or  less  prominent  in  mica  schists,  am- 


SILICATES  493 

phibolites,  gneiss,  eclogites,  etc.  It  is  often  associated  with  mica,  garnet,  diallage  and 
omphacite,  epidote  and  zoisite,  etc.  First  described  from  the  island  of  Syra,  one  of  the 
Cyclades;  since  shown  to  be  rather  widely  distributed,  as  on  the  southern  slope  of  the  Alps 
(gastaldite) ,  Corsica,  Japan,  etc.  Rhodusite  is  a  fibrous  variety  from  the  Island  Rhodus 
and  Asskys  river,  Minassinsk,  Siberia.  Holmquistite  is  a  lithium-bearing  variety  from  the 
Island  of  Uto. 

In  the  United  States,  glaucophane  schists  have  been  described  from  the  Coast  Ranges 
of  California,  as  at  Sulphur  Bank,  Lake  Co. 

Glaucophane  is  named  from  yXavKos,  bluish  green,  and  ^atj/eo-tfm,  to  appear. 

Crossite.  An  amphibole  intermediate  in  composition  between  glaucophane  and 
riebeckite,  being  optically  more  nearly  related  to  the  latter.  Occurs  in  lath  shaped  crystals. 
Color  blue.  Strongly  pleochroic.  Found  in  the  crystalline  schists  of  the  Coast  Ranges  of 
California. 

RIEBECKITE. 

Monoclinic.  Axes  a  :  b  :  c  =  0;5475  :  1  :  0-2925;  0  =  76°  10'.  In  em- 
bedded prismatic  crystals,  longitudinally  striated.  Cleavage :  prismatic  (56°) 
perfect.  Luster  vitreous.  Color  black.  Pleochroism  very  strongly  marked : 
Z  green,  Y  ( =  b  axis)  deep  blue,  X  (nearly  1 1  c  axis)  dark  blue.  Optically  — . 
Extinction-angle  small,  X  A  c  axis  =  4°-5°  (=b?).  Axial  angle  large.  0  = 

1-687. 

in 

Comp.  —  Essentially  2NaFe(Si03)2.FeSiO3  =  Silica  50-5,  iron  sesqui- 
oxide  26-9,  iron  protoxide  12-1,  soda  10*5  =  100.  It  corresponds  closely  to 
acmite  (segirite)  among  the  pyroxenes. 

Obs.  —  Originally  described  from  the  granite  and  syenite  of  the  island  of  Socotra  in  the 
Indian  Ocean,  120  m.  N.  E.  of  Cape  Guardafui.  the  eastern  extremity  of  Africa;  occurs  in 
groups  of  prismatic  crystals,  often  radiating  and  closely  resembling  tourmaline;  also  in 
granophyre  blocks  found  at  Ailsa  Crag  and  at  other  points  in  Scotland  and  Ireland.  A  simi- 
lar amphihqle  occurs  at  Mynydd  Mawr,  Carnarvonshire,  Wales.  Also  another  in  granu- 
lite  in  Corsica.  Found  at  Narsarsuk.  Greenland.  From  pegmatite  at  Quincy,  Mass.  A 
so-called  arfvedsonite  from  St.  Peter's  Dome,  Pike's  Peak  region,  Col.,  occurring  with  astro- 
phyllite  and  zircon,  is  shown  by  Lacroix  to  be  near  riebeckite.  Extinction-angle  on  6, 
X  A  c  axis  =  3°  to  4°.  A  soda  amphibole,  related  to  riebeckite,  from  Bababudan  Hills, 
Mysore,  India,  has  been  named  bababudanite. 

CROCIDOLITE.     Blue  Asbestus. 

Fibrous,  asbestus-like ;  fibers  long  but  delicate,  and  easily  separable.  Also 
massive  or  earthy.  Cleavage:  prismatic,  56°.  H.  =  4.  G.  =  3-20-3-30. 
Luster  silky;  dull.  Color  and  streak  lavender-blue  or  leek-green.  Opaque. 
Fibers  somewhat  elastic.  Pleochroism:  Z  green,  Y  violet,  X  blue.  Optically 
+  .  Extinction-angle  on  b  (010)  inclined  18°  to  20°  with  c  axis.  2E  =  95° 

approx.     7  —  a  =  0'025. 

in 

Comp.  —  NaFe(SiO3)2.FeSiO3  (nearly)  =  Silica  49-6,  iron  sesquioxide 
22-0,  iron  protoxide  19'8,  soda  8'6  =  100. 

Magnesium  and  calcium  replace  part  of  the  ferrous  iron,  and  hydrogen  part  of  the 
sodium. 

Pyr.,  etc.  —  B.B.  fuses  easily  with  intumescence  to  a  black  magnetic  glass,  coloring  the 
flame  yellow  (soda).  With  the  fluxes  gives  reactions  for  iron.  Unacted  upon  by  acids. 

Obs.  —  Occurs  in  South  Africa,  in  Griqualand-West,  north  of  the  Orange  river,  in  a 
range  of  quartzose  schists  called  the  Asbestos  Mountains.  In  a  micaceous  porphyry  near 
Framont,  in  the  Vosges  Mts.  At  Golling  in  Salzburg,  Austria.  In  the  United  States,  at 
Beacon  Pole  Hill,  near  Cumberland,  R.  I.  Emerald  Mine,  Buckingham,  and  Perkin's  Mill, 
Templeton,  Ottawa  Co.,  Ontario,  Canada. 

Abriachanite  is  an  earthy  amorphous  form  occurring  in  the  Abriachan  district,  near 
Loch  Ness,  Scotland.  Crocidolite  is  named  from  KOOK'IS,  woof,  in  allusion  to  its  fibrous 
structure. 


494  DESCRIPTIVE   MINERALOGY 

The  South  African  mineral  is  largely  altered  by  both  oxidation  of  the  iron  and  infiltra- 
tion of  silica,  resulting  in  a  compact  siliceous  stone  of  delicate  fibrous  structure,  chatoyant 
luster,  and  bright  yellow  to  brown  color,  popularly  called  tiger-eye  (also  cat's-eye).  Many 
varieties  occur  forming  transitions  from  the  original  blue  mineral  to  the  final  product;  also 
varieties  depending  upon  the  extent  to  which  the  original  mineral  has  penetrated  the  quartz. 

ARFVEDSONITE. 

Monoclinic.     Axes  a  :  b  :  c  =  0-5569  :  1  :  0*2978;  0  =  73°  2'. 

Crystals  long  prisms,  often  tabular  ||  b  (010),  but  seldom  distinctly  termi- 
nated; angles  near  those  of  amphibole;  also  in  prismatic  aggregates.  Twins: 
tw.  pi.  a  (100). 

Cleavage:  prismatic,  perfect;  b  (010)  less  perfect.  Fracture  uneven. 
Brittle.  H.  =  6.  G.  =  3 -44-3 -45  Luster  vitreous.  Color  pure  black;  in 
thin  scales  deep  green.  Streak  deep  bluish  gray.  Opaque  except  in  thin 
splinters.  Pleochroism  strongly  marked:  Z  deep  greenish  blue,  Y  lavender, 
X  pale  greenish  yellow.  Absorption  Z  >  Y  >  X;  sections  ||  a  (100)  are  deep 
greenish  blue,  ||  b  (010)  olive-green.  Optically  -  .  Axial  angle,  large,  a  = 
1'687.  0  =  1707.  7  =  1708.  Extinction-angle  on  b  (010),  with  c  axis  =  14°. 

Comp.  —  A  slightly  basic  metasilicate  of  sodium,  calcium,  and  ferrous 
iron  chiefly. 

The  supposed  arfvedsonite  from  Greenland  has  been  shown  to  be  segirite;  that  from 
Pike's  Peak,  Col.,  has  been  referred  to  riebeckite. 

Pyr.,  etc.  —  B.B.  fuses  at  2  with  intumescence  to  a  black  magnetic  globule;  colors  the 
flame"  yellow  (soda) ;  with  the  fluxes  gives  reactions  for  iron  and  manganese.  Not  acted 
upon  by  acids. 

Micro.  —  In  thin  sections  shows  brown-  or  gray-green  or  gray- violet  colors;  strongly 
pleochroic  in  blue  and  green  tints;  negative  elongation? 

Obs.  —  Arfvedsonite  and  amphiboles  of  similar  character,  containing  much  iron  and 
soda,  are  constituents  of  certain  igneous  rocks  which  are  rich  in  alkalies,  as  nephelite-syenite, 
certain  porphyries,  etc.  Large  and  distinct  crystals  are  found  only  in  the  pegmatite  veins 
in  such  rocks,  as  at  Kangerdluarsuk,  Narsarsuk,  Greenland,  where  the  associated  minerals 
are  sodalite,  eudialyte,  feldspar,  etc.  Arfvedsonite  occurs  also  in  the  nephelite-syenites  and 
related  rocks  of  the  Christiania  region  in  southern  Norway;  on  the  Kola  peninsula  in 
Russian  Lapland;  Dungannon  township,  Ontario;  Trans  Pecos  district,  Texas.  The  re- 
lated brownish  pleochroic  amphiboles  (cf.  barkevikite)  occur  in  similar  rocks  at  Montreal, 
Canada;  Red  Hill,  N.  H.;  Salem,  Mass.;  Magnet  Cove,  Ark.;  Black  Hills,  S.  D.;  Square 
Butte,  Mon.  St.  Peter's  Dome,  Col.,  etc. 

Osannite  from  an  amphibole-gneiss  at  Cevadaes,  Portugal,  and  Tschernichewite  from  a 
magnetite  bearing  quartzite  in  the  northern  Ural  Mts.,  are  near  arfvedsonite. 

BARKEVIKITE.  An  amphibole  near  arfvedsonite  but  more  basic.  In  prismatic  crys- 
tals. Cleavage:  prismatic  (55°  44f')-  G.  =  3*428.  Color  deep  velvet-black.  Pleochro- 
ism marked,  colors  brownish.  Extinction-angle  with  c  axis  on  b  (010)  =  12|°.  Occurs  at 
the  wohlerite  locality  near  Barkevik,  on  the  Langesund  fiord,  and  elsewhere  in  southern 
Norway.  In  large  crystals  at  Lugar,  Ayrshire,  Scotland. 


JEnigmatite.  Cossyrite.  Essentially  a  titano-silicate  of  ferrous  iron  and  sodium,  but 
containing  also  aluminium  and  ferric  iron.  In  prismatic  triclinic  crystals.  Cleavage: 
prismatic,  distinct  (66°).  G.  =  3 74-3 "80.  Color  black,  ^nigmatite  is  from  the  sodalite- 
syemte  of  Tunugdliarfik  and  Kangerdluarsuk,  Greenland.  Cossyrite  occurs  in  minute 
crystals  embedded  in  the  liparite  lavas  of  the  island  Pantellaria  (ancient  name  Cossyra) ; 
also  widespread  in  the  rocks  of  East  Africa.  Rhonite  is  like  senigmatite  but  contains  much 
less  ferrous  oxide  and  alkalies  with  increase  in  alumina,  ferric  oxide,  etc.  From  basaltic 
rocks  in  the  Rhon  district  and  elsewhere  in  Germany  and  Bohemia.  ' 

WEINBERGERITE.  Perhaps  NaAlSiO4.3FeSiO3.  Orthorhombic.  In  spherical  aggregates 
of  radiating  fibers.  Black  color.  From  a  meteoric  iron  at  Codai  Canal,  Palni  Hills, 
Madras,  India. 


SILICATES 


495 


BERYL. 

Hexagonal.     Axis  c  =  0*4989. 

Crystals  usually  long  prismatic,  often  striated  vertically,  rarely  trans- 
versely; distinct  terminations  exceptional.  Occasionally  in  large  masses, 
coarse  columnar  or  granular  to  compact. 

Cleavage:  c  (0001),  imperfect  and  indistinct.  Fracture  conchoidal  to 
uneven.  Brittle.  H.  =  7*5-8.  G.  =  2-63-2-80;  usually  2-69-2-70.  Lus- 
ter vitreous,  sometimes  resinous.  Colors  emerald-green,  pale  green,  passing 
into  light  blue,  yellow  and  white;  also  pale  rose-red.  Streak  white.  Trans- 
parent to  subtranslucent.  Dichroism  more  or  less  distinct.  Optically  — . 
Birefringence  low.  Often  abnormally  biaxial,  co  =  1-5820,  e  =  1-5765, 
aquamarine. 

835  836  837 


V 
m 

m. 

~y  —  *N 

m 

\ 

m 

>^-& 

rn 

x- 

t 

56 
31 

'*'• 

cs,  0001  A  1121  = 
pp',  1011  A  0111  = 

44°  56' 

28°54i 

f 

m 


cp,  0001  A  1011  =  29 

co,  0001  A  1122  =  26°  31'. 

Var.  —  1.  Emerald.  Color  bright  emerald-green,  due  to  the  presence  of  a  little  chro- 
mium; highly  prized  as  a  gem  when  clear  and  free  from  flaws. 

2.  Ordinary;  Beryl.  Generally  in  hexagonal  prisms,  often  coarse  and  large;  green  the 
common  color.  The  principal  kinds  are  :  (a)  colorless;  (6)  bluish  green,  called  aquamarine; 
(c)  apple-green;  (d)  greenish  yellow  to  iron-yellow  and  honey-yellow;  sometimes  a  clear 
bright  yellow  as  in  the  golden  beryl  (a  yellow  gem  variety  from  Southwest  Africa  has  been 
called  heliodor) ;  (e)  pale  yellowish  green;  (/)  clear  sapphire  blue;  (g)  pale  sky-blue;  (h) 
pale  violet  or  reddish;  (i)  rose  colored  called  morganite  or  vorobyevite;  (j)  opaque 
brownish  yellow,  of  waxy  or  greasy  luster.  The  oriental  emerald  of  jewelry  is  emerald-coi- 
lored  sapphire. 

Comp.  —  Be3Al2(SiO3)6  or  3BeO.Al203.6SiO2  =  Silica  67-0,  alumina  19-0, 
glucina  14-0  =  100. 

Alkalies  (NagO,  Li2O,  Cs2O)  are  sometimes  present  replacing  the  beryllium,  from  0'25 
to  5  p.  c.;  also  chemically  combined  water,  including  which  the  formula  becomes  H2Be6Al4 
Si12O37. 

Pyr.,  etc. —  B.B.  alone,  unchanged  or,  if  clear,  becomes  milky  white  and  clouded;  at 
a  high  temp'erature  the  edges  are  rounded,  and  ultimately  a  vesicular  scoria  is  formed. 
Fusibility  =  5 '5,  but  somewhat  lower  for  beryls  rich  in  alkalies.  Glass  with  borax,  clear 
and  colorless  for  beryl,  a  fine  green  for  emerald.  Unacted  upon  by  acids. 

Diff.  —  Characterized  by  its  green  or  greenish  blue  color,  glassy  luster  and  hexagonal 
form;  rarely  massive,  then  easily  mistaken  for  quartz.  Distinguished  from  apatite  by  its 
hardness,  not  being  scratched  by  a  knife,  also  harder  than  green  tourmaline;  from  chryso- 
beryl  by.  its  form;  from  euclase  and  topaz  by  its  imperfect  cleavage. 

Artif .  —  Crystals  of  beryl  have  been  produced  artificially  by  fusing  a  mixture  of  silica, 
alumina  and  glucina  with  boric  oxide  as  a  flux. 

Obs.  —  Beryl  is  a  common  accessory  mineral  in  granite  veins,  especially  in  those  of  a 
pegmatitic  character.  Emeralds  occur  in  clay  slate,  in  isolated  crystals  or  in  nests,  near 
Muso,  etc.,  75  m.  N.N.E.  of  Bogota,  Colombia.  Emeralds  of  less  beauty,  but  larger,  occur 
in  Siberia,  on  the  river  Tokovoya,  N.  of  Ekaterinburg,  embedded  in  mica  schist.  Emeralds 
of  large  size,  though  not  of  uniform  color  or  free  from  flaws,  have  been  obtained  in  Alex- 
ander Co.,  N.  C. 


496  DESCRIPTIVE   MINERALOGY 

Transparent  beryls  are  found  in  Siberia,  India  and  Brazil.  In  Siberia  they  occur  at 
Mursinka  and  Shaitanka,  near  Ekaterinburg;  near  Miask  with  topaz;  in  the  mountains  of 
Adun-Chalon  with  topaz,  in  E.  Siberia.  A  clear  aquamarine  crystal  weighing  110'5  kg. 
was  found  at  Marambaya,  Minas  Geraes,  Brazil.  Beautiful  crystals  also  occur  at  Elba; 
the  tin  mines  of  Ehrenfriedersdorf  in  Saxony,  and  Schlackenwald  in  Bohemia.  Other  local- 
ities are  the  Mourne  Mts.,  Ireland;  yellowish  green  at  Rubislaw,  near  Aberdeen,  Scotland 
(davidsonite);  Limoges  in  France;  Finbo  and  Broddbo  in  Sweden;  Tamela  in  Finland; 
Pfitsch-Joch,  Tyrol;  Bodenmais  and  Rabenstein  in  Bavaria;  in  New  South  Wales.  Pink, 
alkali-rich  beryls  are  found  in  Madagascar. 

In  the  United  States,  beryls  of  gigantic  dimensions  have  been  found  in  N.  H.,  at  Acworth 
and  Grafton,  and  in  Mass.,  at  Royalston.  In  Me.,  at  Albany;  Norway;  Bethel;  at 
Hebron,  a  ca3sium  beryl  (Cs2O,  3*60  p.  c.),  associated  with  pollucite;  in  Paris,  with  black 
tourmaline;  at  Topsham,  pale  green  or  yellowish;  at  Stowe  and  Stoneham.  In  Mass.,  at 
Barre;  at  Goshen  (goshenite),  and  at  Chesterfield.  In  Conn.,  at  Haddam,  and  at  the  Mid- 
dletown  and  Portland  feldspar  quarries;  at  New  Milford,  of  a  clear  golden  yellow  to  dark 
amber  color;  Branchville.  In  Pa.,  at  Leiperville  and  Chester;  at  Mineral  Hill.  In  ya., 
at  Amelia  Court  House,  sometimes  white.  In  N.  C.,  in  Alexander  Co.,  near  Stony  Point, 
fine  emeralds;  in  Mitchell  Co.;  Morganton,  Burke  Co.,  and  elsewhere.  In  Ala.,  Cposa 
Co.,  of  a  light  yellow  color.  In  Col.,  near  the  summit  of  Mt.  Antero,  beautiful  aquamarines. 
In  S.  D.,  in  the  Black  Hills  in  large  crystals.  Rose-pink  crystals,  often  showing  prominent 
pyramid  faces,  from  San  Diego  Co.,  Cal.,  also  colorless  and  aquamarine. 

Use.  —  The  transparent  mineral  is  used  as  a  gem  stone;  see  above  under  Varieties. 

Eudialyte.  Essentially  a  metasilicate  of  Zr,Fe(Mn),Ca,Na,  etc.  In  red  to  brown 
tabular  or  rhombohedral  crystals;  also  massive.  H.  =  5-5'5.  G.  =  2'9-3'0.  Optically 
-J-.  o>  =  1'606.  6  =  1'611.  From  Kangerdluarsuk,  West  Greenland,  etc.,  with  arfved- 
sonite  and  sodalite;  at  Lujaor  on  the  Kola  peninsula,  Russian  Lapland,  in  elseolite-syenite, 
there  forming  a  main  constituent  of  the  rock-mass.  Eucolite,  from  islands  of  the  Langesund 
fiord  in  Norway,  is  similar  (but  optically  — ).  Eudialyte  and  eucolite  also  occur  at  Magnet 
Cove,  in  Ark.,  of  a  rich  crimson  to  peach-blossom  red  color,  in  feldspar,  with  elseolite  and 
aegirite. 

Elpidite.  Na2O.ZrO2.6SiO2.3H2O.  —  Massive,  fibrous.  H.  =  7.  G.  =  2'54.  Color 
white  to  brick-red.  Biaxial,  +.  Indices  =  1 '560-1 '574.  Southern  Greenland. 

ASTROLITE.  (Na,K)2Fe(Al,Fe)2(SiO3)5.H2O?.  In  globular  forms  with  radiating 
structure.  H.  =  3'5.  G.  =  2'8.  Color  green.  Fusible,  3'5.  Found  in  a  diabase  tuff 
near  Neumark,  Germany. 


The  following  are  rare  species  of  complex  composition,  all  from  the  Lange- 
sund fiord  region  of  southern  Norway. 

Catapleiite.  H4(Na2)Ca)ZrSi3pii.  In  thin  tabular  hexagonal  prisms.  H.  =  6.  G.  = 
2-8.  Color  light  yellow  to  yellowish  brown.  Biaxial,  +.  Indices,  1 '591-1 '627.  Natron- 
catapleiite,  or  soda-catapleiite,  contains  only  sodium;  color  blue  to  gray  and  white;  on  heat- 
ing the  blue  color  disappears. 

Cappelenite.  A  boro-silicate  of  yttrium  and  barium.  In  greenish  brown  hexagonal 
crystals. 

Melanocerite.  A  fluo-silicate  of  the  cerium  and  yttrium  metals  and  calcium  chiefly 
(also  B,  Ta,  etc.).  In  brown  to  black  tabular  rhombohedral  crystals. 

Caryocerite.     Near  melanocerite,  containing  ThO2. 

Steenstrupine  (from  Greenland)  is  allied  to  the  two  last-named  species.  Rhombohe- 
H.  =4.  G.  =  3'4.  Color  dark  brown  to  nearly  black.  Optically  — . 

Tritomite.  A  fluo-silicate  of  thorium,  the  cerium  and  yttrium  metals  and  calcium, 
with  boron.  In  dark  brown  crystals  of  acute  triangular  pyramidal  form. 

The  following  are  also  from  the  same  region : 

Leucophanite.  Na(BeF)Ca(SiO3)2.  In  glassy  greenish  tabular  crystals  (orthorhombic- 
sphenoidal).  H.  =4.  G.  =  2'96.  Optically  -.  Indices,  1'571-1'598. 

Meliphanite.     A  fluo-silicate  of  beryllium,  calcium,  and  sodium  near  leucophanite.     In 
low  square  pyramids  (tetragonal).     Color  yellow.     H.  =  5-5'5.     G.  =  3*01.     Optically  - 
Indices,  1 '593-1 '612. 


SILICATES 


497 


Custerite.  Ca2(OH,F)SiO3.  Monoclinic.  In  fine  granular  masses.  Cleavages  par- 
allel to  base  and  prism,  all  making  nearly  90°  with  each  other.  Twinning  plane  c  (001), 
showing  in  twin  lamellae.  H.  =5.  G.  =  2 -91.  Color  greenish  gray.  Transparent. 
Optically  +.  Bxa  nearly  perpendicular  toe  (001).  Indices,  1 '58-1 '60.  Difficultly  fusible. 
Decomposed  by  hydrochloric  acid.  Found  in  limestone  contact  zone  at  the  Empire  mine, 
Custer  Co.,  Idaho. 

Didymolite.  2CaO.3Al2O3.9SiO2.  Monoclinic.  In  small  twinned  crystals.  H.  =  4-5. 
G.  =  271.  Color  dark  gray.  Opaque.  Index  1 '5.  Difficultly  fusible.  Insoluble.  Found 
as  contact  mineral  in  limestone  from  Tatarka  River,  Yenisei  District,  Siberia. 


IOLITE.     Cordierite.     Dichroite. 

Orthorhombic.     Axes  a  :  b  :  c  =  0-5871  :  1  :  0;5585. 
Twins:  tw.  pi.  m  (110),  also  d  (130),  both  yielding  pseudo-hexagonal  forms. 
prismatic    (mm 


Habit   short 

60°  50')  (Fig.  838).     As  embedded 

grains;    also  massive,  compact. 

Cleavage:  b  (010)  distinct; 
a(100)  and  c(001)  indistinct.  Crys- 
tals often  show  a  lamellar  structure 
||  c  (001),  especially  when  slightly 
altered.  Fracture  subconchoidal. 
Brittle.  H.  =  7-7  '5.  G.  =  2-60- 
2*66.  Luster  vitreous.  Color  va- 
rious shades  of  blue,  light  or  dark, 
smoky  blue.  Transparent  to  trans- 
lucent. Pleochroism  strongly 
marked  except  in  thin  sections. 
Axial  colors  variable.  Thus: 
Bodenmais  Z  (=  b  axis)  dark  Berlin-blue. 
yellowish  white. 


839 


Y  ( =  a  axis)  light  Berlin-blue.     X  ( =  c  axis) 


Absorption  Z  >  Y  >  X.  Pleochroic  halos  common,  often  bright  yellow; 
best  seen  in  sections  ||  c  axis.  Exhibits  idiophanous  figures.  Optically  — . 
Ax.  pi.  ||  a  (100).  Bx.  J_  c  (001).  Dispersion  feeble,  p  <  v.  2V  =  70°  23' 
(also  40°  to  84°).  Indices  variable,  from  1'534  to  1-599. 

Comp.  —  H2(Mg,Fe)4Al8Siio037or  H2O.4(Mg,Fe)O.4Al2O3.10SiO2. 

If  Mg  :  Fe  =  7  :  2,  the  percentage  composition  is:  Silica  49*4,  alumina 
33'6,  iron  protoxide  5*3,  magnesia  10-2,  water  1-5  =  100.  Ferrous  iron  re- 
places part  of  the  magnesium.  Calcium  is  also  present  in  small  amount. 

Pyr.,  etc.  —  B.B.  loses  transparency  and  fuses  at  5-5'5.  Only  partially  decomposed  by 
acids.  Decomposed  on  fusion  with  alkaline  carbonates. 

Diff.  —  Characterized  by  its  vitreous  luster,  color  and  pleochroism;  fusible  on  the  edges 
unlike  quartz;  less  hard  than  sapphire. 

Micro.  —  Recognized  in  thin  sections  by  lack  of  color;  low  refraction  and  low  inter- 
ference-colors; it  is  very  similar  to  quartz,  but  distinguished  by  its  biaxial  character;  in 
volcanic  rocks  commonly  shows  distinct  crystal  outlines  and  a  twinning  of  three  individuals 
like  aragonite.  In  the  gneisses,  etc.,  it  is  in  formless  grains,  but  the  common  occurrence  of 
inclusions,  especially  of  sillimanite  needles,  the  pleochroic  halos  of  a  yellow  color  around  small 
inclusions,  particularly  zircons,  and  the  constant  tendency  to  alteration  to  micaceous  pinite 
seen  along  cleavages,  help  to  distinguish  it. 

Obs.  —  Occurs  in  granite,  gneiss  (cordierite-gneiss) ,  hornblendic,  chloritic  and  talcose 
schist,  and  allied  rocks,  with  quartz,  orthoclase  or  albite,  tourmaline,  hornblende,  andalu- 
site,  sillimanite,  garnet,  and  sometimes  beryl.  Less  commonly  in  or  connected  with  igne- 
ous rocks,  thus  formed  directly  from  the  magma,  as  in  andesite,  etc.;  also  in  ejected  masses 


498  DESCRIPTIVE   MINERALOGY 

(in  fragments  of  older  rocks) ;  further  formed  as  a  contact-mineral  in  connection  with  erup- 
tive dikes,  as  in  slates  adjoining  granite. 

Occurs  at  Bodenmais,  Bavaria,  in  granite,  with  pyrrhotite,  etc.;  Orijarvi,  in  Finland 
(steinheilite)-;  Tunaberg,  in  Sweden;  from  Switzerland;  in  colorless  crystals  from  Brazil; 
Ceylon  affords  a  transparent  variety,  the  saphir  d'eau  of  jewelers;  from  Ibity,  Madagascar; 
from  Greenland. 

In  the  United  States,  at  Haddam,  Conn.,  associated  with  tourmaline  in  a  granitic  vein  in 
gneiss.  In  large  altered  crystals  from  Litchfield,  Conn.  AtBrimfield,  Mass.;  at  Richmond 
N.  H. 

Named  I  elite  from  'lov,  violet,  and  X10os,  stone;  Dichroite  (from  dixpoos,  two-colored), 
from  its  dichroism;  Cordierite,  after  Cordier,  the  French  geologist  (1777-1861). 

Alteration.  The  alteration  of  iolite  takes  place  so  readily  by  ordinary  exposure,  that 
the  mineral  is  most  commonly  found  in  an  altered  state,  or  enclosed  in  the  altered  iolite. 
This  change  may  be  a  simple  hydration;  or  a  removal  of  part  of  the  protoxide  bases  by  car- 
bon dioxide;  or  the  introduction  of  oxide  of  iron;  or  of  alkalies,  forming  pinite  and  mica. 
The  first  step  in  the  change  consists  in  a  division  of  the  prisms  of  iolite  into  plates  parallel 
to  the  base,  and  a  pearly  foliation  of  the  surfaces  of  these  plates;  with  a  change  of  color  to 
grayish  green  and  greenish  gray,  and  sometimes  brownish  gray.  As  the  alteration  proceeds, 
the  foliation  becomes  more  complete;  afterward  it  may  be  lost.  The  mineral  in  this  altered 
condition  has  many  names :  as  hydrous  iolite  ( including  bonsdorffite  and  auralite)  from  Abo, 
Finland;  fahlunite  from  Falun,  Sweden,  also  pyrargillite  from  Helsingfors;  esmarkite  and 
praseolite  from  near  Brevik,  Norway,  also  raumite  from  Raumo,  Finland,  and  peplolite  from 
Ramsberg-,  Sweden;  chlorophyllite  from  Unity,  Me.;  aspasiolite  and  polychroilite  from 
Kragero.  There  are  further  alkaline  kinds,  as  pinite,  cataspilite,  gigantolite,  iberite,  belong- 
ing to  the  Mica  Group. 

Use.  —  Iolite  is  sometimes  used  as  a  gem. 


Jurupaite.      H2(Ca,Mg)2Si2O7.      Monoclinic?      Radiating  fibrous.      White.       H   =  4 
G.  =  275.     n  =  1-57.     Crestmore,  Cal. 


The  following  are  rare  lead,  zinc,  and  barium  silicates: 

Barysilite.  Pb3Si2O7.  Rhombohedral.  In  embedded  masses  with  curved  lamellar 
structure.  Cleavage:  basal.  H.  =  3.  G.  =  611-6-55.  Color  white;  tarnishing  on 
exposure.  From  the  Harstig  mine,  Pajsberg,  and  Langban,  Sweden. 

Molybdophyllite.  (Pb,Mg)SiO4.H2O.  Hexagonal.  In  irregular  foliated  masses  with 
perfect  basal  cleavage.  H.  =  3-4.  G.  =  47.  Colorless  to  pale  green,  co  =  1-81 
Difficultly  fusible.  From  Langban,  Sweden. 

Ganomalite.  Pb4(PbOH)2Ca4(Si2O7)3.  In  prismatic  crystals  (tetragonal);  also  mas- 
sive granular.  H  =3  G.  =574.  Colorless  to  gray.  Indices,  1'83-1'93.  From 
Langban,  Sweden;  also  Jakobsberg. 

Nasonite.  Closely  related  to  ganomalite.  Pb4(PbCl)2Ca4(Si2O7)3.  Probably  tetragonal. 
Massive,  granular  cleavable.  H.  =4.  G.  =  5'4.  White.  Fusible.  From  Franklin^N.  J. 

Margarosanite.    Pb(Ca,Mn)2(SiO3)3.     Triclinic.     Slender  prismatic  crystals  and  cleav- 

able granular.     Three  cleavages,  one  perfect.     Colorless  and  transparent  with  pearly  lus- 

=  2-5-3.   G.  =  3-99.    Easily  fusible.    From  Franklin,  N.  J.,  and  Langban,  Sweden. 

Hardystonite.  CasZnSisOr.  Tetragonal.  In  granular  masses.  Three  cleavages. 
H.  =  3-4.  G.  =  3'4.  Color  white.  From  Franklin,  N.  J. 

Hydotekite.  Approximately  (Pb,Ba,Ca)B2(SiO3)i2.  Massive;  coarsely  crystalline. 
U.  =  5  -5-5.  G.  =  3-81.  Color  white  to  pearly  gray.  From  Langban,  Sweden. 


. 

Barylite.  Ba^SiAt  In  groups  of  colorless  prismatic  orthorhombic  crystals. 
•  '  I  ;  n-  '  r  ?'  LustTer  greasy-  Optically  +.  ft  =  1-685.  Occurs  with  hedyphane 
in  crystalline  limestone  at  Langban,  Sweden. 


ii  in 


Taramellite.      Ba4FeFe4Si10O31.      Orthorhombic?      Fibrous.      Color    reddish    brown. 
Candoglia  Italy  K^t  ^^  "**  tO  ^^     F°Und  ln  lime- 


Roeblingite.  ,H2CaSiO4).2(CaPbSO4).     In  dense,  white,  compact,  crystalline 
n.  —  6.    u.  =  6  433.     From  Franklin  Furnace  N.  J. 


masses. 


SILICATES  499 


III.   Orthosilicates.     R2SiO4 

Salts  of  Orthosilicic  Acid,  H4SiO4;  characterized  by  an  oxygen  ratio  of 
1  :  1  for  silicon  to  bases. 

The  following  list  includes  the  more  prominent  groups  among  the  Ortho- 
silicates. 

A  number  of  basic  orthosilicates  are  here  included,  which  yield  water  upon  ignition; 
also  others  which  are  more  or  less  basic  than  a  normal  orthosilicate,  but  which  are  of 
necessity  introduced  here  in  the  classification,  because  of  their  relationship  to  other  normal 
salts.  The  MICA  GROUP  is  so  closely  related  to  many  Hydrous  Silicates  that  (with  also 
Talc,  Kaolinite,  and  some  others)  it  is  described  later  with  them. 

Nephelite  Group.     Hexagonal.  Scapolite       Group.     Tetragonal- 
Soda  lite  Group.     Isometric.  pyramidal. 

Helvite     Group.     Isometric-tetrahe-  Zircon  Group.     Tetragonal. 

draL  Danburite  Group.      Orthorhom- 
Garnet  Group.     Isometric.  bic. 

Chrysolite  Group.       Orthorhombic.  Datolite  Group.     Monoclinic. 

Phenacite   Group.       Tri-rhombohe-  Epidote  Group.     Monoclinic. 

dral. 


Nephelite  Group.     Hexagonal 

i 
Typical  formula  RAlSiO4 

Nephelite  K^NaeA^C^  c  =  0-8389 

Soda-nephelite  (artif.)    NaAlSi04 
Eucryptite  LiAlSiO4  Kaliophilite  KAlSi04 


Cancrinite  H6Na6Ca(NaC03)2Al8(SiO4)9  2c  =  0'8448 

Microsommite  (Na,K)ioCa4Ali2Sii2052SCl4  2c  =  0'8367 


The  species  of  the  NEPHELITE  GROUP  are  hexagonal  in  crystallization  and 

i 

have  in  part  the  typical  orthosilicate  formula  RAlSi04.  From  this  formula 
nephelite  itself  deviates  somewhat,  though  an  artificial  soda-nephelite, 
NaAlSiO4,  conforms  to  it.  The  species  Cancrinite  and  Microsommite  are 
related  in  form  and  also  in  composition,  though  in  the  latter  respect  some- 
what complex.  They  serve  to  connect  this  group  with  the  sodalite  group 
following. 

NEPHELITE.     Nepheline.     Elseolite. 

Hexagonal-hemimorphic  (p.  101).     Axis  c  =  0-83893. 

In  thick  six-  or  twelve-sided  prisms  with  plane  or  modified  summits. 
Also  massive  compact,  and  in  embedded  grains;  structure  sometimes  thin 
columnar. 

Cleavage:  m  (110)  distinct;  c  (001)  imperfect.  Fracture  subconchoidal. 
Brittle.  H.  =  5'5-6.  G.  =  2-55-2-65.  Luster  vitreous  to  greasy;  a  little 
opalescent  in  some  varieties.  Colorless,  white,  or  yellowish;  also,  when  mas- 
sive, dark  green,  greenish  or  bluish  gray,  brownish  red  and  brick-red.  Trans- 
parent to  opaque.  Optically  —  .  Indices:  o>  =  1-542,  e  =  1-538. 

Var.  —  1.    Nephelite.    Glassy.  —  Usually  in  small  glassy  crystals  or  grains,  transparent 
with  vitreous  luster,  first  found  on  Mte.  Somma,  Vesuvius.     Characteristic  particularly  of 


500  DESCRIPTIVE   MINERALOGY 

younger  eruptive  rocks  and  lavas.  2.  Elceolite.  —  In  large  coarse  crystals,  or  more  com- 
monly massive,  with  a  greasy  luster,  and  reddish,  greenish,  brownish  or  gray  in  color. 
Usually  clouded  by  minute  inclusions.  Characteristic  of  granular  crystalline  rocks,  syenite, 
etc. 

Comp.  —  NaAlSiO4.  This  is  the  composition  of  the  artificial  mineral. 
Natural  nephelite  always  contains  silica  in  varying  excess  and  also  small 
amounts  of  potash.  The  composition  usually  approximates  to  NaeK^AlgSigCV 
Synthetic  experiments,  yielding  crystals  like  nephelite  with  the  composition  NaAlSiO4, 
lead  to  the  conclusion  that  a  natural  soda-nephelite  would  be  an  orthosilicate  with  this 
formula,  while  the  higher  silica  in  the  potash  varieties  may  be  explained  by  the  presence, 
in  molecular  combination,  of  KAlSiO4  and  NaAlSi3O8  (albite  in  hexagonal  modification). 
The  variation  in  composition  may  be  more  simply  explained  by  considering  normal  nephe- 
lite, NaAlSiO4,  to  take  up  in  solid  solution  silica  or  other  silicate  molecules.  The  other 
species  of  the  group  are  normal  orthosilicates,  viz.,  eucryptite  LiAlSiO4.  and  kaliophilite, 


Pyr.?  etc.  —  B.B.  fuses  quietly  at  3 '5  to  a  colorless  glass,  coloring  the  flame  yellow. 
Gelatinizes  with  acids. 

Diff.  —  Distinguished  by  its  gelatinizing  with  acids  from  scapolite  and  feldspar,  as 
also  from  apatite,  from  which  it  differs  too  in  its  greater  hardness.  Massive  varieties  have 
a  characteristic  greasy  luster. 

Micro.  —  Recognized  in  thin  sections  by  its  low  refraction;  very  low  interference- 
colors,  which  scarcely  rise  to  gray;  parallel  extinction  when  in  crystals;  faint  negative 
uniaxial  cross  yielded  by  basal  sections  in  converging  light.  The  negative  character  is  best 
told  by  aid  of  the  gypsum  plate  (see  p.  266).  Micro-chemical  tests  serve  to  distinguish  non- 
characteristic  particles  from  similar  ones  of  alkali  feldspar;  the  section  is  treated  with  dilute 
acid,  and  the  resultant  gelatinous  silica,  which  coats  the  nephelite  particles,  stained  with 
cosine  or  other  dye. 

Artif.  —  Nephelite  is  easily  prepared  artificially  by  fusing  its  constituents  together  in 
the  proper  proportions. 

Obs.  —  Nephelite  is  rather  widely  distributed  (as  shown  by  the  microscopic  study  of 
rocks)  in  igneous  rocks  as  the  product  of  crystallization  of  a  magma  rich  in  soda  and  at  the 
same  time  low  in  silica  (which  last  prevents  the  soda  from  being  used  up  in  the  formation 
of  albite).  It  is  thus  an  essential  component  of  the  nephelite-syenites  and  phonolites  where 
it  is  associated  with  alkali  feldspars  chiefly.  It  is  also  a  constituent  of  more  basic  augitic 
rocks  such  as  nephelinite,  nephelite-basalts,  nephelite-tephrites,  theralite,  etc.,  most  of 
which  are  volcanic  in  origin.  The  variety  elceolite  is  associated  with  the  granular  plutonic 
rocks,  while  the  name  nephelite  was  originally  used  for  the  fresh  glassy  crystals  of  the 
modern  lavas;  the  terms  have  in  this  sense  the  same  relative  significance  as  orthoclase  and 
sanidine.  Modern  usage,  however,  tends  to  drop  the  name  elceolite. 

The  original  nephelite  occurs  in  crystals  in  the  older  lavas  of  Mte.  Somma,  Vesuvius,  with 
mica,  vesuvianite,  etc.;  at  Capo  di  Bove,  near  Rome;  in  the  basalt  of  Katzenbuckel,  near 
Heidelberg,  Germany;  Aussig  in  Bohemia;  Lobau  in  Saxony.  Occurs  also  in  massive  forms 


foyaite);  Ditro,  Hungary _  (in  the  rock  ditroite) ;  Pousac,  France;  Brazil;  South  Africa. 

Elaeolite  occurs  massive  and  crystallized  at  Litchfield,  Me.,  with  cancrinite;  Salem, 
Mass.;  Red  Hill,  N.  H.;  in  the  Ozark  Bits.,  near  Magnet  Cove,  Ark.;  elseolite-syenite 
is  also  found  near  Beemersville,  northern  N.  J.;  near  Montreal,  Canada;  at  Dungannon 
township,  Ontario,  in  enormous  crystals.  Nephelite  rocks  also  occur  at  various  points,  as 
the  Transpecos  district,  Texas;  Pilot  Butte,  Texas;  also  in  western  North  America,  as  in 
Col.  at  Cripple  Creek;  in  Mon.,  in  the  Crazy  Mts.,  the  Highwood,  Bearpaw  and  Judith 
|Cts.;  Black  Hills  in  S.  D.;  Ice  River,  British  Columbia. 

Named  nephelite  from  i/e^eXrj,  a  cloud,  in  allusion  to  its  becoming  cloudy  when  immersed 
in  strong  acid;  elceolite  is  from  eXaiov,  oil,  in  allusion  to  its  greasy  luster. 

Gieseckite  is  a  pseudomorph  after  nephelite.  It  occurs  in  Greenland  in  six-sided  green- 
ish gray  prisms  of  greasy  luster;  also  at  Diana  in  Lewis  Co.,  N.  Y.  Dysyntribite  from 
Diana  is  similar  to  gieseckite,  as  is  also  liebenerite,  from  the  valley  of  Fleims,  in  Tyrol, 
Austria.  See  further  FINITE  under  the  MICA  GROUP. 

Eucryptite.  LiAlSi04.  In  symmetrically  arranged  crystals  (hexagonal),  embedded, 
in  albite  and  derived  from  the  alteration  of  spodumene  at  Branchville,  Conn,  (see  Fig.  488, 
p.  181).  G.  =  2-667.  Colorless  or  white. 


SILICATES  501 

Kaliophilite.  KAlSiO4.  Phacellite.  Phacelite.  Facellite.  In  bundles  of  slender 
acicular  crystals  (hexagonal),  also  in  fine  threads,  cobweb-like.  H.  =6.  G.  =  2*493- 
2'602.  Colorless.  Occurs  in  ejected  masses  at  Mte.  Somma,  Vesuvius. 

CANCRINITE. 

_Hexagonal.  Axis  c  =  04224;  and  mp  1010  A  1011  =  64°,  ppf  1011  A 
0111  =  25°  58'.  Rarely  in  prismatic  crystals  with  a  low  terminal  pyramid. 
Usually  massive. 

Cleavage:  prismatic,  m  (1010)  perfect;  a  (1120)  less  so.  H.  =  5-6. 
G.  =  2 -42-2 -5.  Color  white,  gray,  yellow,  green,  blue,  reddish.  Streak 
uncolored.  Luster  subvitreous,  of  a  little  pearly  or  greasy.  Transparent  to 
translucent.  Optically  -.  co  =  1-524.  e  =  1-496. 

Comp.  —  H6Na6Ca(NaC03)2Al8(SiO4)9  or  3H2O.4Na2O.CaO.4Al2O3. 
9Si02.2C02  =  Silica  387,  carbon  dioxide  6-3,  alumina  29-3,  lime  4-0,  soda 
17-8,  water  3-9  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  gives  water.  B.B.  loses  color,  and  fuses  (F.  =  2)  with 
intumescence  to  a  white  blebby  glass,  the  very  easy  fusibility  distinguishing  it  readily  from 
nephelite.  Effervesces  with  hydrochloric  acid,  and  forms  a  jelly  on  heating,  but  not 
before. 

Micro.  —  Recognized  in  thin  sections  by  its  low  refraction;  quite  high  interference- 
colors  and  negative  uniaxial  character.  Its  common  association  with  nephelite,  socialite, 
etc.,  are  valuable  characteristics.  Evolution  of  CO2  with  acid  distinguishes  it  from  all  other 
minerals  except  the  carbonates,  which  show  much  higher  interference-colors. 

Artif .  —  Cancrinite  has  been  prepared  artificially  by  heating  under  pressure  a  mixture 
of  sodium  silicate,  alumina  and  sodium  carbonate;  also  by  the  treatment  of  nephelite  and 
labradorite  by  sodium  carbonate  at  high  temperatures. 

Obs.  —  Cancrinite  occurs  only  in  igneous  rocks  of  the  nephelite-syenite  and  related 
rock  groups.  It  is  in  part  believed  to  be  original,  i.e.,  formed  directly  from  the  molten  mag- 
ma; in  part  held  to  be  secondary  and  formed  at  the  expense  of  nephelite  by  infiltrating 
waters  holding  calcium  carbonate  in  solution.  Prominent  localities  are  Miask  in  the  Ilmen 
Mte.,  Russia,  in  coarse-grained  nephelite-syenite;  similarly  at  Barkevik  and  other  localities 
on  the  Langesund  fiord  in  southern  Norway;  in  the  parish  of  Knolajarvi  in  northern  Finland 
(where,  associated  with  orthoclase,  segirite  and  nephelite,  it  composes  a  mass  of  cancrinite- 
syenite);  at  Ditro,  Transylvania,  etc.;  in  nephelite-syenite  of  Sarna  and  Alno  in  Sweden, 
and  in  Brazil;  also  in  small  amount  as  an  occasional  accessory  component  of  many  phono- 
litic  rocks  at  various  localities. 

In  the  United  States  at  Litchfield  and  West  Gardiner,  Me.,  with  ela3olite  and  blue  soda- 
lite.  Named  after  Count  Cancrin,  Russian  Minister  of  Finance. 

SULPHATIC  CANCRINITE  with  nearly  one-half  the  CO2  replaced  by  SO3  is  found  in  an 
altered  rock  on  Beaver  Creek,  Gunnison  Co.,  Col.  Has  lower  refractive  indices  and'  bire- 
fringence than  cancrinite. 

Microsommite.  Near  cancrinite;  perhaps  (Na,Et)i0Ca4Ali2Sii2O52SCl4).  In  minute 
colorless  prismatic  crystals  (hexagonal.  See  Fig.  30,  p.  19).  From  Vesuvius  (Monte 
Somma).  H.  =6.  G.  =  2'42-2'53.  co  =  1-521.  e  =  1'529. 

Davyne.  Near  microsommite.  From  Mte.  Somma;  Laacher  See,  Germany.  o>  = 
1-518.  e  =  1'521. 


Sodalite  Group.     Isometric 

Sodalite  Na4(AlCl)Al2(SiO4)3 

Haiiynite  (Na2,Ca)2(NaSO4.Al)Al2(Si04)3 

Noselite  Na4(NaSO4.Al)Al2(Si04)3 

Lazurite  Na4(NaS3.Al)Al2(SiO4)3 

The  species  of  the  Sodalite  Group  are  isometric  in  crystallization  and  per- 
haps tetrahedral  like  the  following  group.  In  composition  they  are  peculiar 
(like  cancrinite  of  the  preceding  group)  in  containing  radicals  with  Cl,  S04  and 
S,  which  are  elements  usually  absent  in  the  silicates.  These  are  shown  in  the 


502  DESCRIPTIVE   MINERALOGY 

formulas  written  above  in  the  form  suggested  by  Brogger,  who  shows  that 
this  group  and  the  one  following  may  be  included  with  the  garnets  in  a  broad 
group  characterized  by  isometric  crystallization  and  a  close  resemblance  in 
composition.  See  further  under  the  GARNET  GROUP  proper,  p.  505. 

The  formulas  are  also  often  written  as  if  the  compound  consisted  of  a  sili- 
cate and  chloride  (sulphate,  sulphide)  —  thus  for  sodalite,  3NaAlSiO4  +  NaCl, 
etc. 

SODALITE. 

Isometric,  perhaps  tetrahedral.  Common  form  the  dodecahedron. 
Twins-  tw.  pi.  o  (111),  forming  hexagonal  prisms  by  elongation  in  the  direction 
of  an  octahedral  axis  (Fig.  406,  p.  165).  Also  massive,  in  embedded  grains;  in 
concentric  nodules  resembling  chalcedony,  formed  from  elaeolite. 

Cleavage:  dodecahedral,  more  or  less  distinct.  Fracture  conchoidal  to 
uneven.  Brittle.  H.  =  5-5-6.  G.  =  2'14-2'30.  Luster  vitreous,  sometimes 
inclining  to  greasy.  Color  gray,  greenish,  yellowish,  white;  sometimes  blue, 
lavender-blue,  light  red.  Transparent  to  translucent.  Streak  uncolored. 
n  =  1-4827. 

Comp.  —  Na4(AlCl)Al2(SiO4)3  =  Silica  37'2,  alumina  31*6,  soda  25'6, 
chlorine  7'3  =  1017,  deduct  (0  =  2C1)  17  =  100.  Potassium  replaces  a 
small  part  of  the  sodium.  The  formula  may  also  be  written  3NaAlSiO4  + 
NaCl. 

Pyr..  etc.  —  In  the  closed  tube  the  blue  varieties  become  white  and  opaque.  B.B. 
fuses  with  intumescence,  at  3 '5-4,  to  a  colorless  glass.  Soluble  in  hydrochloric  acid  and 
yields  gelatinous  silica  upon  evaporation. 

Diff.  —  Distinguished  from  much  analcite,  leucite  and  haiiynite  by  chemical  tests  alone; 
dissolving  the  mineral  in  dilute  nitric  acid  and  testing  for  chlorine  is  the  simplest  and 
best. 

Micro.  —  Recognized  in  thin  sections  by  its  very  low  refraction,  isotropic  character  and 
lack  of  good  cleavage;  also,  in  most  cases,  by  its  lack  of  color.  In  uncovered  rock  sections 
the  minerals  of  this  group  may  be  distinguished  from  each  other  by  covering  them  with  a 
little  nitric  acid  which  is  allowed  to  evaporate  slowly.  With  sodalite  crystals  of  sodium 
chloride  will  form;  with  haiiynite  crystals  of  gypsum;  with  noselite  crystals  of  both  com- 
pounds after  the  addition  of  calcium  chloride;  lazurite  will  evolve  hydrogen  sulphide  which 
will  blacken  silver. 

Aftif.  —  .Sodalite  can  be  obtained  by  fusing  nephelite  with  sodium  chloride;  also  by  the 
action  of  sodium  carbonate  and  caustic  soda  upon  muscovite  at  500°.  It  has  been  pro- 
duced also  in  various  artificial  magmas  at  temperatures  below  700°. 

Obs.  —  Sodalite  occurs  only  in  igneous  rocks  of  the  nephelite-syenite  and  related  rock 
groups,  as  a  product  of  the  crystallization  of  a  magma  rich  in  soda;  also  as  a  product  asso- 
ciated with  enclosed  masses  and  bombs  ejected  with  such  magmas  in  the  form  of  lava,  as  at 
Vesuvius.  Often  associated  with  nephelite  (or  elseolite),  cancrinite  and  eudialyte.  With 
sanidine  it  forms  a  sodalite-trachyte  at  Scarrupata  in  Ischia,  Italy,  in  crystals.  In  Sicily, 
Val  di  Noto,  with  nephelite  and  analcite.  At  Vesuvius,  in  bombs  on  Monte  Somma  in  white, 
translucent,  dodecahedral  crystals;  massive  and  of  a  gray  color  at  the  Kaiserstuhl  and  near 
Lake  Laach,  Germany.  A  variety  from  Monte  Somma  containing  2  per  cent  of  molybde- 
num trioxide  has  -been  called  molybdosodalite.  At  Ditro,  Transylvania,  in  an  elaeolite- 
syenite.  In  the  foyaite  of  southern  Portugal.  At  Miask,  in  the  Ilmen  Mts.,  Russia;  in 
the  augite-syenite  of  the  Langesund-fiord  region  in  Norway.  Further  in  West  Greenland 
in  sodalite-syenite;  the  peninsula  of  Kola,  Russia. 

A  blue  massive  variety  occurs  at  Litchfield  and  West  Gardiner,  Me.  Occurs  in  the 
theralite  of  the  Crazy  Mts.,  Mon.,  also  at  Square  Butte,  Highwood  Mts.,  and  in  the  Bear- 
paw  Mts.,  in  tinguaite.  Occurs  also  in  the  ela3olite-syenite  of  Brome,  Brome  Co.,  and  of 
Montreal  and  Beloeil,  province  of  Quebec;  at  Dungannon,  Ontario,  in  large  blue  masses 
and  in  small  pale  pink  crystals.  At  Kicking  Horse  Pass,  Bristish  Columbia. 

Hackmanite.  .  A  sodalite  containing  about  6  per  cent  of  the  molecule  Na4[Al(NaS)]Al2 
(biO4)3  trom  a  rock  called  tawite  from  the  Tawa  valley  on  the  Kola  peninsula,  Lapland. 


SILICATES 


503 


HAUYNITE.     Haiiyne. 

Isometric.     Sometimes  in  dodecahedrons,  octahedrons,  etc. 

Twins:  tw.  pi.  o  (111);  contact-twins,  also  poly  synthetic;  penetration- 
twins  (Fig.  405,  p.  165).  Commonly  in  rounded  grains,  o  ten  looking  like 
crystals  with  fused  surfaces. 

Cleavage:  dodecahedral,  rather  distinct.  Fracture  flat  .conchoidal  to 
uneven.  Brittle.  H.  =  5*5-6.  G.  =  2-4-2 -5.  Luster  vitreous,  to  some- 
what greasy.  Color  bright  blue,  sky  blue,  greenish  blue  ;  asparagus-green, 
red,  yellow.  Streak  slightly  bluish  to  colorless.  Subtransparent  to  translu- 
cent; often  enclosing  symmetrically  arranged  inclusions  (Fig.  840):  n  = 
T4961. 

Comp.  —  Na2Ca(NaSO4.Al)Al2(SiO4)3.  This  is  analogous  to  the  garnet 
formula  (Brogger)  where  the  place  of  the  R3  is  taken  by  Na2,  Ca  and  the 
group  Na-0-SO2-O-Al.  The  percentage  composition  is:  Silica  32*0,  sulphur 
trioxide  14-2,  alumina  27 -2,  lime  10*0,  soda  16*6  =  100.  The  ratio  of  Na*  :  Ca 
also  varies  from  3:2;  potassium  may  be  present  in  small  amount.  The 
formula  may  also  be  wr  tten  2(Na2,Ca)Al2(Si04)2  +  (Na  ,Ca)SO4. 

Pyr.,  etc.  —  In  the  closed  tube  retains  its  color.  B.B.  in  the  forceps  fuses  at  4*5  to  a 
white  glass.  Soluble  in  hydrochloric  acid  and  yields  gelatinous  silica  upon  evaporation. 
The  solution  gives  a -test  for  the  sulphate  radical  with  barium  chloride. 

Micro.  —  Similar  to  sodalite,  which  see. 

Artif .  —  Has  been  produced  artificially  in  the  same  ways  as  with  sodalite  with  the  use 
of  a  sulphate  instead  of  a  chloride. 

Obs.  —  Common  in  certain  igneous  rocks,  thus  in  hauynophyre,  in  phonolite,  tephrite ; 
very  commonly  associated  with  nephelite  and  leucite.  Occurs  in  the  Vesuvian  lavas,  on 
Mte.  Somma;  at  Melfi,  on  Mt.  Vultur,  Naples;  in  the  lavas  of  the  Campagna,  Rome,  also 


Section  of  crystals  of  haiiynite  (after  Mohl) 

in  a  basalt  tuff  near  Albano,  Italy;  at  Niedermendig,  in  the  Eifel,  Germany;  the  phonolites 
of  Hohentwiel,  Baden,  Germany. 

Noselite  or  Nosean.  Near  haiiynite,  but  contains  little  or  no  lime.  Color  grayish, 
bluish,  brownish;  sometimes  nearly  opaque  from  the  presence  of  inclusions  (cf.  Fig.  840). 
n  =  1-495.  Not  uncommon  in  phonolite.  In  Germany  at  Andernach,  the  Laacher  See, 
and  elsewhere. 

LAZURITE.     LAPIS-LAZULI.     Lasurite. 

Isometric.     In  cubes  and  dodecahedrons.     Common  y  massive,  compact. 

Cleavage:  dodecahedral,  imperfect.  Fracture  uneven.  H.  =  5-5*5. 
G.  =  2-38-2-45.  Luster  vitreous.  Color  rich  Berlin-blue  or  azure-blue, 
violet-blue,  greenish  blue.  Translucent,  n  =  1*500. 

Comp.  —  Essentia  ly  Na4(NaS  .Al)  Al2(SiO4)3,  but  containing  also  in  mo- 
lecular combination  haiiynite  and  sodalite.  The  percentage  composition  of 
this  ultramarine  compound  is  as  follows:  Si  ica  31*7,  alumina  26*9,  soda 
27*3,  sulphur  16*9  =  102*9,  or  deduct  (O  =  S)  2*9  =  100. 

The  heterogeneous  character  of  what  had  long  passed  as  a  simple  mineral  under  the  name 
Lapis-lazuli  was  shown  by  Fischer  (1869),  Zirkel  (1873),  and  more  fully  by  Vogelsang  (1873). 


504  DESCRIPTIVE   MINERALOGY 


amount ^  scapolite V  plagioclase,  orthoclase  (microperthite?),  apatite,  titanite,  zircon,  and 
n  undetermined'  mineral  optically  +  and  probably  uniaxial.     Regarded  by  Brogger  as 
a  result  of  contact  metamorphism  in  limestone. 
Micro.  _  Similar  to  sodalite,  which  see. 


Pvr  etc  —  Heated  in  the  closed  tube  gives  off  some  moisture;  the  variety  from  Chile 
clows  with  a  beetle-green  light,  but  the  color  of  the  mineral  remains  blue  on  cooling  Fuses 
easily  (3)  with  intumescence  to  a  white  glass.  Soluble  in  hydrochloric  acid  and  yields  gelati- 
nous silica  upon  evaporation  and  evolves  hydrogen  sulphide. 


Obs  —  Occurs  in  Badakshan,  India,  in  the  valley  of  the  Kokcha,  a  branch  of  the  Oxus, 
a  few  miles  above  Firgamu.  Also  at  the  south  end  of  Lake  Baikal  Siberia.  Further,  in 
Chile  in  the  Andes  of  Ovalle.  In  ejected  masses  at  Monte  Somma,  Vesuvius,  rare.  From 
Siberia  and  Persia. 

Use  —  The  richly  colored  varieties  of  lapis  lazuli  are  highly  esteemed  for  costly  vases 
and  ornamental  furniture;  also  employed  in  the  manufacture  of  mosaics;  and  when  pow- 
dered constitutes  the  rich  and  durable  paint  called  ultramarine.  This  has  been  replaced, 
however,  by  artificial  ultramarine,  now  an  important  commercial  product. 


£>,  Helvite  Group.     Isometric-tetrahedral 

Helvite  (Mn,Fe)2(Mn2S)Be3(Si04)3 

Danalite  (Fe,Zn,Mn)2(  (Zn,Fe)2S)Be3(Si04)3 

Eulytite  Bi4(SiO4)3 

Zunyite  (Al(OH,F,Cl)2)6Al2(SiO4)3 

The  HELVITE  GROUP  includes  several  rare  species,  isometric-tetrahedral  in 
crystallization  and  in  composition  related  to  the  species  of  the  SODALITE 
GROUP  and  also  to  those  of  the  GARNET  GROUP  which  follows: 

HELVITE. 

Isometric-tetrahedral.  Commonly  in  tetrahedral  crystals ;  also  in  spheri- 
cal masses. 

Cleavage:  octahedral  in  traces.  Fracture  uneven  to  conchoidal.  Brittle. 
H.  =  6-6*5.  G.  =  3'16-3'36.  Luster  vitreous,  inclining  to  resinous.  Color 
honey-yellow,  inclining  to  yellowish  brown,  and  siskin-green,  reddish  brown. 
Streak  uncolored.  Subtransparent.  n  =  1 739.  Pyroelectric. 

Comp.  —  (Be,Mn,Fe)7Si3Oi2S.  This  may  be  written  (Mn,Fe)2(Mn2S)Be3 
(SiO4)3  analogous  to  the  Garnet  Group,  the  bivalent  group  -Mn-S-Mn  taking 
the  place  of  a  bivalent  element,  R,  and  3Be  corresponding  to  2A1,  cf.  p.  505. 
Composition  also  written  3(Be,Mn,Fe)2SiO4.(Mn,Fe)S. 

Pyr.,  etc.  —  Fuses  at  3  in  R.F.  with  intumescence  to  a  yellowish  brown  opaque  bead, 
becoming  darker  in  R.F.  With  the  fluxes  gives  the  manganese  reaction.  Soluble  in  hydro- 
chloric acid,  giving  hydrogen  sulphide  and  yielding  gelatinous  silica  upon  evap9ration. 

Obs.  —  Occurs  at  Schwarzenberg  and  Breitenbrunn,  in  Saxony;  at  Kapnik,  Hungary; 
also  in  the  pegmatite  veins  of  the  augite-syenite  of  the  Langesund  fiord,  Norway;  in  the 
Ilmen  Mts.,  Russia,  near  Miask,  in  pegmatite.  In  the  United  States,  with  spessartite,  at  the 
mica  mines  near  Amelia  Court-House,  Amelia  Co.,  Va.;  etc.  Named  by  Werner,  in  allu- 
sion to  its  yellow  color,  from  -Xios,  the  sun. 

Danalite.  (Be,Fe,Zn,Mn)7Si3Oi2S.  In  octahedrons;  usually  massive.  H.  =  5'5-6. 
G.  =  3-427.  Color  flesh-red  to  gray.  Occurs  in  small  grains  in  the  Rockport  granite, 
Cape  Ann,  Mass.;  at  the  iron  mine  at  Bartlett,  N.  H.;  El  Paso  Co.,  Col.  In  England  at 

Eulytite.  Bi4Si3Oi2.  Usually  in  minute  tetrahedral  crystals;  also  in  spherical  forms. 
H.  =  4'5.  G.  =  6'106.  Color  dark  hair-brown  to  grayish,  straw-yellow,  or  colorless. 
n  ^  2?'  Found  witn  native  bismuth  near  Schneeberg,  Saxony;  also  at  Johanngeorgen- 
stadt,  Germany,  m  crystals  on  quartz. 


SILICATES 


505 


Zunyite.  —  A  highly  basic  orthosilicate  of  aluminium,  (Al(OH,F,Cl)2)6Al2Si3Oi2.  In 
minute  transparent  tetrahedrons.  H.  =7.  G.  =  2*875.  From  the  Zuni  mine,  near  Sil- 
verton,  San  Juan  Co.,  and  on  Red  Mountain,  Ouray  Co.,  Col. 


4.    Garnet  Group.     Isometric 

or    3RO.R2O3.3Si02. 

II  II       H  III  III 

R  =  Ca,Mg,Fe,Mn. 


Ill  III 

Al,Fe,Cr,Ti. 


Garnet 

A.  GROSSULARITE  Ca3Al2(SiO4)3 

B.  PYROPE  Mg3Al2(Si04)3 

C.  ALMANDITE  Fe3Al2(SiO4)3 

D.  SPESSARTITE  Mn3Al2(SiO4)3 


Schorlomite 


Ca3(Fe,Ti)2(  (Si,Ti)O4) 


E.  ANDRADITE       Ca3Fe2(SiO4); 
Also     (Ca,Mg)3Fe2(SiO4)3, 

Ca3Fe2((Si,Ti)04)3 

F.  UVAROVITE     Ca3Cr2(Si04)3, 


The  GARNET  GROUP  includes  a  series  of  important  sub-species  included 
under  the  same  specific  name.  They  all  crystallize  in  the  normal  class  of 
the  isometric  system  and' are  alike  in  habit,  the  dodecahedron  and  trapezo- 
hedron  being  the  common  forms.  They  have  also  the  same  general  formula, 
and  while  the  elements  present  differ  widely,  there  are  many  intermediate 
varieties.  Some  of  the  garnets  include  titanium,  replacing  silicon,  and  thus 
they  are  connected  with  the  rare  species  schorlomite,  which  probably  also  has 
the  same  general  formula. 

Closely  related  to  the  GARNET  GROUP  proper  are  the  species  of  the  Sodalite  and  llelvite 
Groups  (pp.  501,  504).  All  are  characterized  by  isometric  crystallization,  and  all  are 
orthosilicates,  with  similar  chemical  structure.  Thus  the  formula  of  the  Garnet  Group  is 
Hill 

R3R2(SiO4)3;  to  this  Sodalite  conforms  if  written  Na4(AlCl)Al2(SiO4)3,  where  Na4  and  the 
bivalent  radical  A1C1  are  equivalent  to  R3;  similarly  for  Noselite  (Haliynite)  if  the  presence 
of  the  bivalent  group  NaSO4-Al  is  assumed. 

In  the  Helvite  Group,  which  is  characterized  by  the  tetrahedral  character  of  the  species 
(perhaps  true  also  of  the  Sodalites),  the  chemical  relation  is  less  close  but  probably  exists, 
as  exhibited  by  writing  the  formula  of  Helvite  (Mn,Fe)(Mn2S)Be3(SiO4)3,  where  the  bivalent 
group  -S-Mn-S-  enters,  and  3Be  may  be  regarded  as  taking  the  place  of  2A1. 

GARNET. 

Isometric.     The  dodecahedron  and  trapezohedron,  n  (211),  the  common 
841  842  843 


simple  forms;   also  these  in  combination,  or  with  the  hexoctahedron  s  (321). 
Cubic  and  octahedral  faces  rare.     Often  in  irregular  embedded  grains.     Also 


506 


DESCRIPTIVE   MINERALOGY 


massive;   granular,  coarse  or  fine,  and  sometimes  friable;   lamellar,  lamellae 
thick  and  bent.     Sometimes  compact,  cryptocrystalline  like  nephrite. 

Parting:   d  (110)  sometimes  rather  distinct.     Fracture  subconchoidal  to 


844 


845 


846 


uneven.  Brittle,  sometimes  friable  when  granular  massive;  very  tough  when 
compact  cryptocrystalline.  H.  =  6'5-7'5.  G.  =  3-15-4-3,  varying  with  the 
composition.  Luster  vitreous  to  resinous.  Color  red,  brown,  yellow,  white, 
apple-green,  black;  some  red  and  green,  colors  often  bright.  Streak  white. 
Transparent  to  subtranslucent.  Often  exhibits  anomalous  double  refraction, 
especially  grossularite  (also  topazolite,  etc.),  see  Art.  429.  Refractive  index 
rather  high,  and  varying  directly  with  the  composition.  The  different  pure 
molecules  have  approximately  the  following  indices. 

Pyrope  1705,  Grossularite  1-735,  Spessartite  I'SOO,  Almandite  1'830,  Uvarovite  1'870, 
Andradite  1'895. 

II  III 

Comp.  —  An  orthosilicate  having  the  general  formula  R3R2(SiO4)3,  or 
3RO.R203.3Si02.  The  bivalent  element  may  be  calcium,  magnesium,  ferrous 
iron  or  manganese;  the  trivalent  element,  aluminium,  ferric  iron  or  chro- 
mium, rarely  titanium;  further,  silicon  is  also  sometimes  replaced  by  titanium. 
The  different  garnet  molecules  are  isomorphous  with  each  other  although 
there  are  apparently  definite  limits  to  their  miscibility.  The  greater  majority 
will  be  found  to  have  two  or  three  component  molecules ;  in  the  case,  however, 
where  three  are  present  one  is  commonly  in  subordinate  amount.  The  index 
of  refraction  and  specific  gravity  vary  directly  with  the  variation  in  composition. 

Var.  —  There  are  three  prominent  groups,  and  various  subdivisions  under 
each,  many  of  these  blending  into  each  other. 

I.   Aluminium  Garnet,  including 

A.  GROSSULARITE    Calcium- Aluminium  Garnet         Ca3Al2(Si04)3 

B.  PYROPE  Magnesium- Aluminium  Garnet  Mg3Al2(SiO4)3 

C.  ALMANDITE          Iron- Aluminium  Garnet  Fe3Al2(SiO4)3 

D.  SPESSARTITE       Manganese- Aluminium  Garnet  Mn3Al2(SiO4)3 
II.   Iron  Garnet,  including 

E.  ANDRADITE          Calcium-Iron  Garnet  Ca3Fe2(SiO4)3 
(1)  Ordinary.     (2)  Magnesian.   (3)  Titaniferous.   (4)  Yttriferous, 

III.   Chromium  Garnet. 

F.  UVAROVITE         Calcium-Chromium  Garnet         Ca3Cr2(SiO4)3 

The  name  Garnet  is  from  the  Latin  granatus,  meaning  like  a  grain,  and  directly  from 
pomegranate,  the  seeds  of  which  are  small,  numerous,  and  red,  in  allusion  to  the  aspect  oi 
the  crystals. 


SILICATES  507 

A.  GROSSULARITE.     Essonite  or  Hessonite.     Cinnamon-stone.     Calcium- 
aluminium  Garnet.     Formula  3CaO.Al2O3.3Si02  =  Silica  40 -0,  alumina  227, 
lime  37 '3  =  100.     Often  containing  ferrous  iron  replacing  the  calcium,  and 
ferric  iron  replacing  aluminium,  and  hence  graduating  toward  groups  C  and 
E.     G.  =  3-53.     Color  (a)  colorless  to  white;    (6)  pale  green;    (c)  amber- 
and  honey-yellow;    (d)  wine-yellow,  brownish  yellow,  cinnamon-brown;    (e) 
rose-red;    rarely  (/)  emerald-green  from  the  presence  of  chromium.     Often 
shows  optical  anomalies  (Art.  429). 

The  original  grossularite  (wiluite  in  part)  included  the  pale  green  from  Siberia,  and  was 
so  named  from  the  botanical  name  for  the  gooseberry;  G.  =  3-42-372.  Cinnamon-stone, 
or  essonite  (more  properly  hessonite),  included  a  cinnamon-colored  variety  from  Ceylon, 
there  called  hyacinth;  but  under  this  name  the  yellow  and  yellowish  red  kinds  are  usually 
included;  named  from  fjvauv,  inferior,  because  of  less  hardness  than  the  true  hyacinth 
which  it  resembles.  Succinite  is  an  amber-colored  kind  from  the  Ala  valley,  Piedmont, 
Italy.  Romanzovite  is  brown. 

Pale  green,  yellowish,  and  yellow-brown  garnets  are  not  invariably  grossularite;  some 
(including  topazolite,  demantoid,  etc.)  belong  to  the  group  of  Calcium-Iron  Garnet,  or 
Andradite. 

B.  PYROPE.     Precious  garnet  in  part.     Magnesium-aluminium  Garnet. 
Formula  3MgO.Al203.3Si02  =  Silica  44-8,    alumina  25*4,  magnesia  29*8  = 
100.     Magnesia  predominates,  but  calcium  and  iron  are   also   present;   the 
original  pyrope  also  contained  chromium.     G.  =  3'51.     Color  deep  red  to 
nearly  black.     Often  perfectly  transparent  and  then  prized  as  a  gem.     The 
name  pyrope  is  from  TTUPCOTTOS,  fire-like. 

Rhodolite,  of  delicate  shades  of  pale  rose-red  and  purple,  brilliant  by  reflected  light, 
corresponds  in  composition  to  two  parts  of  pyrope  and  one  of  almandite;  from  Macon  Co., 
N.  C. 

C.  ALMANDITE.     Almandine.     Precious  garnet  in  part.     Common  garnet 
in  part.     Iron-aluminium  Garnet.     Formula  3FeO.Al203.3SiO2  =  Silica  36 -2, 
alumina  20 '5,  iron  protoxide  43 '3  =  100.     Ferric  iron  replaces  the  aluminium 
to  a  greater  or  less  extent.     Magnesium  also  replaces  the  ferrous  iron,  and 
thus  it  graduates  toward  pyrope,  cf.  rhodolite  above.     G.  =  4-25.     Color  fine 
deep  red,  transparent,  in  precious  garnet;   brownish  red,  translucent  or  sub- 
translucent,  in  common  garnet;  black.     Part  of  common  garnet  belongs  to 
Andradite. 

The  Alabandic  carbuncles  of  Pliny  were  so  called  because  cut  and  polished  at  Alabanda. 
Hence  the  name  almandine  or  almandite,  now  in  use. 

D.  SPESSARTITE.     Spessartine.     Manganese-aluminium  Garnet.     Formula 
3MnO.Al2O3.3SiO2  =  Silica  36'4,  alumina  20'6,  manganese  protoxide  43'0  = 
100.     Ferrous  iron  replaces  the  manganese  to  a  greater  or  less  extent,  and 
ferric  iron  also  the  aluminium.     G.  =  4-18.     Color  dark  hyacinth-red,  some- 
times with  a  tinge  of  violet,  to  brownish  red. 

E.  ANDRADITE.     Common    Garnet,    Black    Garnet,    etc.      Calcium-iron 
Garnet.     Formula  3CaO.Fe2O3.3Si02  =  Silica  35'5,  iron  sesquioxide  31 -5,  lime 
33*0  =  100.     Aluminium  replaces  the  ferric  iron;   ferrous  iron,  manganese 
and  sometimes  magnesium  replace  the  calcium.     G.  =  375.     Colors  various: 
wine-,  topaz-  and  greenish  yellow,  apple-green  to  emerald-green;  brownish 
red,  brownish  yellow;  grayish  green,  dark  green;  brown;  grayish  black,  black. 

Named  Andradite  after  the  Portuguese  mineralogist,  d'Andrada,  who  in  1800  described 
and  named  one  of  the  included  subvarieties,  Allochroite.  Chemically  there  are  the  follow- 
ing varieties: 


508  DESCRIPTIVE   MINERALOGY 

1  Simple  Calcium-iron  Garnet,  in  which  the  protoxides  are  wholly  or  almost  wholly 
lime'    Includes-    (a)   Topazolite,  having  the  color  and  transparency  of  topaz,  and  also 
sometimes  green;  crystals  often  showing  a  vicinal  hexoctahedron.     Demantoid !  a  grass-green 

o  emerald-green  variety  with  brilliant  diamond-like  luster,  used  as  a  gem.  (6)  Colophonite, 
a  coarse  granular  kind,  brownish  yellow  to  dark  reddish  brown  in  color  resinous  in  luster, 
and  usually  with  iridescent  hues;  named  after  the  resin  colophony,  (c)  Melamte  (from 
ueXas  black]  black,  either  dull  or  lustrous;  but  all  black  garnet  is  not  here  included. 
Pyreneite  is  grayish  black  melanite.  (d)  Dark  green  garnet,  not  distinguishable  from  some 
allochroite  except  by  chemical  trials. 

2  Manganesian  Calcium-iron  Garnet,     (a)  Rothoffite.     The  original  allochroite  was  a 
manganesian  iron-garnet  of  brown  or  reddish  brown  color,  and  of  fine-grained  massive 
structure.     Rothoffite,  from  Langban,  Sweden,  is  similar,  yellowish  brown  to  liver-brown. 
Other  common  kinds  of  manganesian  iron-garnet  are  light  and  dark,  dusky  green  and  black, 
and  often  in  crystals.     Polyadelphite  is  a  massive  brownish  yellow  kind,  from  Franklin  Fur- 
nace N.  J.     Bredbergite,  from  Sala,  Sweden,  contains  a  large  amount  of  magnesia.     (6)  Ap- 
lome  (properly  haplome)  has  its  dodecahedral  faces  striated  parallel  to  the  shorter  diagonal, 
whence  Haiiy  inferred  that  the  fundamental  form  was  the  cube;  and  as  this  form  is  simpler 
than  the  dodecahedron,  he  gave  it  a  name  derived  from  airXoos,  simple.     Color  of  the  origi- 
nal aplome  (of  unknown  locality)  dark  brown;   also  found  yellowish  green  and  brownish 
green  at  Schwarzenberg  in  Saxony,  and  on  the  Lena  in  Siberia. 

3.  Titaniferous.     Contains  titanium  and  probably  both  TiO2  and  Ti2O3;  formula  hence 
3Ca6.(Fe,Ti,Al)2O3.3(Si,Ti)O2.     It  thus  graduates  toward  schorlomite.     Color  black. 

4.  Yttriferous  Calcium-iron  Garnet.     Contains  yttria  in  small  amount;   rare. 

F.   UVAROVITE.     Ouvarovite.     Uwarowit.     Calcium-chromium  Garnet. 
Formula  3CaO.Cr203.3SiO2  =  Silica  35'9,  chromium  sesquioxide  30*6,  lime 
33-5  =  100.     Aluminium  takes  the  place  of  the  chromium  in  part.     H.  =  7 '5. 
G.  =  3-41-3-52.     Color  emerald-green. 

Pyr.  etc.  —  Most  varieties  of  garnet  fuse  easily  to  a  light  brown  or  black  glass;  F.  =  3 
in  almandite,  spessartite,  and  grossularite;  3 '5  in  andradite  and  pyrope;  but  uvarovite,  the 
chrome-garnet,  is  almost  infusible,  F.  =  6.  Andradite  and  almandite  fuse  to  a  magnetic 
globule.  Reactions  with  the  fluxes  vary  with  the  bases.  Almost  all  kinds  react  for  iron; 
strong  manganese  reaction  in  spessartite,  and  less  marked  in  other  varieties;  a  chromium 
reaction  in  uvarovite,  and  in  most  pyrope.  Some  varieties  are  partially  decomposed  by 
acids;  all  except  uvarovite  after  ignition  become  soluble  in  hydrochloric  acid,  and  generally 
yield  gelatinous  silica  on  evaporation.  Decomposed  on  fusion  with  alkaline  carbonates. 

The  density  of  garnets  is  largely  diminished  by  fusion.  Thus  a  Greenland  garnet  fell 
from  3'90  to  3'05  on  fusion,  and  a  Vilui  grossularite  from  3'63  to  2'95. 

Diff.  —  Characterized  by  isometric  crystallization,  usually  in  isolated  crystals,  dode- 
cahedrons or  trapezohedrons;  massive  forms  rare,  then  usually  granular.  *  Also  distin- 
guished by  hardness,  vitreous  luster,  and  in  the  common  kinds  the  fusibility.  Vesuvianite 
Fuses  more  easily,  zircon  and  quartz  are  infusible;  the  specific  gravity  is  higher  than  for 
tourmaline,  from  which  it  differs  in  form;  it  is  much  harder  than  sphalerite. 

Micro.  —  Distinguished  in  thin  sections  by  its  very  high  relief;  lack  of  cleavage;  iso- 
tropic  character;  usually  shows  a  pale  pink  color;  sometimes  not  readily  told  from  some  of 
the  spinels. 

Artif.  —  While  members  of  the  garnet  group  have  been  formed  artificially  their  synthe- 
sis is  difficult.  Apparently  they  can  be  produced  only  under  exact  conditions  of  tempera- 
ture and  pressure  that  are  difficult  to  reproduce.  Natural  garnets  when  fused  break  down 
into  various  other  minerals. 

Obs.  —  Grossularite  is  especially  characteristic  of  metamorphosed  impure  calcareous 
rocks,  whether  altered  by  local  igneous  or  general  metamorphic  processes;  it  is  thus  com- 
monly found  in  the  contact  zone  of  intruded  igneous  rocks  and  in  the  crystalline  schists. 
Almandite  is  characteristic  of  the  mica  schists  and  metamorphic  rocks  containing  alumina 
and  iron;  it  occurs  also  in  some  igneous  rocks  as  the  result  of  later  dynamic  and  metamor- 
phic processes;  it  forms  with  the  variety  of  amphibole  called  smaragdite  the  rock  eclogite. 
Pyrope  is  especially  characteristic  of  such  basic  igneous  rocks  as  are  formed  from  magmas 
containing  much  magnesia  and  iron  with  little  or  no  alkalies,  as  the  peridotites,  dunites, 
etc.;  also  found  in  the  serpentines  formed  from  these  rocks;  then  often  associated  with 
spinel,  chromite,  etc.  Spessartite  occurs  in  granitic  rocks,  in  quartzite,  in  whetstone  schists 
(Belgium) ;  it  has  been  noted  with  topaz  in  lithophyses  in  rhyolite  (Colorado).  The  black 
variety  of  andradite,  melanite,  is  common  in  eruptive  rocks,  especially  with  nephelite,  leucite, 
thus  in  phonohtes,  leucitophyres,  nephelinites :  in  such  cases  often  titaniferous  or  associated 


SILICATES  509 

with  a  titaniferous  garnet,  sometimes  in  zonal  intergrowth;  it  also  occurs  as  a  product  of 
contact  metamorphism.  Demantoid  occurs  in  serpentine.  Uvarovite  belongs  particularly 
with  chromite  in  serpentine;  it  occurs  also  in  granular  limestone. 

Garnet  crystals  often  contain  inclusions  of  foreign  matter,  but  only  in  part  due  to  altera- 
tion; as,  vesuvianite,  calcite,  epidote,  quartz  (Fig.  486,  p.  180);  at  times  the  garnet  is  a 
mere  shell,  or  perimorph,  surrounding  a  nucleus  of  another  species.  A  black  garnet  from 
Arendal,  Norway,  contains  both  calcite  and  epidote; 
crystals  from  Tvedestrand,  Norway,  are  wholly  calcite 
within,  there  being  but  a  thin  crust  of  garnet.  Crystals 
from  East  Woodstock,  Me.,  are  dodecahedrons  with  a 
thin  shell  of  cinnamon-stone  enclosing  calcite;  others  from 
Raymond,  Me.,  show  successive  layers  of  garnet  and 
calcite.  Many  such  cases  have  been  noted. 

Garnets  are  often  altered,  thus  to  chlorite,  serpentine; 
even  to  limonite.  Crystals  of  pyrope  are  sometimes 
surrounded  by  a  chloritic  zone  (kelyphite  of  Schrauf) 
not  homogeneous,  as  shown  in  Fig.  847. 

Among  prominent  foreign  localities  of  garnets,  besides 
those  already  mentioned,  are  the  following  —  GROSS- 
ULARITE:  Fine  cinnamon-stone  comes  from  Ceylon;  on 
the  Mussa-Alp  in  the  Ala  valley  in  Piedmont,  Italy,  with 
clinochlore  and  diopside;  at  Zermatt,  Switzerland; 
pale  yellow  at  Auerbach,  Germany;  brownish  (romanzovite)  at  Kimito  in  Finland;  honey- 
yellow  octahedrons  in  Elba;  pale  greenish  from  the  banks  of  the  Vilui  in  Siberia,  in  serpentine 
with  vesuvianite;  also  from  Cziklowa  and  Orawitza  in  the  Banat,  Hungary;  with  vesu- 
vianite and  wollastonite  in  ejected  masses  at  Vesuvius;  in  white  or  colorless  crystals  in 
Tellemark,  in  Norway;  also  dark  brown  at  Mudgee,  New  South  Wales;  dark  honey-yellow 
at  Guadalcazar,  and  clear  pink  or  rose-red  dodecahedrons  at  Xalostoc,  Morelos,  Mexico, 
called  variously,  landerite,  xalostocite  and  rosolite. 

PYROPE:  In  serpentine  (from  peridotite)  near  Meronitz  and  the  valley  of  Krems,  in 
Bohemia  (used  as  a  gem);  at  Zoblitz  in  Saxony;  in  the  Vosges  Mts.;  in  the  diamond  dig- 
gings of  South  Africa  ("Cape  rubies").  ALMANDITE:  Common  in  granite,  gneiss,  eclogite, 
etc.,  in  many  localities  in  Saxony,  Silesia,  etc.;  at  Eppenreuth  near  Hof,  Bavaria;  in  large 
dodecahedrons  at  Falun  in  Sweden;  hyacinth-red  or  brown  in  the  Zillertal,  Tyrol,  Austria. 
Precious  garnet  comes  in  fine  crystals  from  Ceylon,  Pegu,  British  India,  Brazil,  and  Green- 
land. SPESSARTITE:  From  Aschaffenburg  in  the  Spessart,  Bavaria;  at  St.  Marcel,  Pied- 
mont, Italy;  near  Chanteloube,  Haute  Vienne,  France,  etc. 

ANDRADITE:  The  beautiful  green  demantoid  or  "Uralian  emerald"  occurs  in  transparent 
greenish  rolled  pebbles,  also  in  crystals,  in  the  gold  washings  of  Nizhni-Tagilsk  in  the  Ural 
Mts.;  green  crystals  occur  at  Schwarzenberg,  Saxony;  brown  to  green  at  Morawitza  and 
Dognacska,  Hungary;  emerald-green  at  Dobschau,  Hungary;  in  the  Ala  valley,  Piedmont, 
Italy,  the  yellow  to  greenish  topazolite.  Allochroite,  apple-green  and  yellowish,  occurs  at 
Zermatt,  Switzerland;  black  crystals  (melanite),  also  brown,  at  Vesuvius  on  Mte.  Somma; 
near  Bareges  in  the  Hautes-Pyrenees,  France,  (pyreneite).  Aplome  occurs  at  Schwarzen- 
berg in  Saxony,  in  brown  to  black  crystals.  Other  localities  are  Pfitschtal,  Tyrol,  Austria; 
Langban,  Sweden;  Pitkaranta,  Finland;  Arendal,  Norway.  UVAROVITE:  Found  at  Sara- 
novskaya  near  Bisersk,  also  in  the  vicinity  of  Kyshtymsk,  Ural  Mts.,  in  chromic  iron;  at 
Jordansmuhl,  Silesia;  Pic  Posets  near  Venasque  in  the  Pyrenees  on  chromite. 

In  North  America,  in  Me.,  beautiful  crystals  of  cinnamon-stone  (with  vesuvianite)  occur 
at  Parsonsfield,  Phippsburg,  and  Rumford,  at  Raymond.  In  N.  H.,  at  Hanover,  small 
clear  crystals  in  gneiss;  at  Warren,  cinnamon  garnets;  at  Graf  ton.  In  Ver.,  at  New  Fane, 
in  chlorite  slate.  In  Mass.,  in  gneiss  at  Brookfield;  in  fine  dark  red  or  nearly  black  trape- 
zohedral  crystals  at  Russell,  sometimes  very  large.  In  Conn.,  trapezohedrons,  in  mica 
slate,  at  Reading  and  Monroe;  dodecahedrons  at  Southbury  and  Roxbury;  at  Haddam, 
crystals  of  spessartite.  In  N.  Y.,  brown  crystals  at  Crown  Point,  Essex  Co.;  colophonite 
as  a  large  vein  at  Willsboro,  Essex  Co.;  in  Middletown,  Delaware  Co.,  large  brown  crystals; 
a  cinnamon  variety  at  Amity.  In  N.  J.,  at  Franklin,  black,  brown,  yellow,  red,  and  green 
dodecahedral  garnets;  also  near  the  Franklin  Furnace  (polyadelphite] .  In  Pa.,  in  Chester 
Co.,  at  Pennsbury,  fine  dark  brown  crystals;  near  Knauertown;  at  Chester,  brown;  in 
Concord,  on  Green's  Creek,  resembling  pyrope;  in  Leiperville,  red;  at  Mineral  Hill,  fine 
brown;  at  Avondale  quarry,  fine  hessonite;  uvarovite  at  Woods'  chrome  mine,  Lancaster 
Co.  In  Va.,  beautiful  transparent  spessartite,  used  as  a  gem,  at  the  mica  mines  at  Amelia 
Court-House.  In  N.  C.,  fine  cinnamon-stone  at  Bakers ville;  red  garnets  in  the  gold  wash- 
ings of  Burke,  McDowell,  and  Alexander  counties;  rhodolite  in  Macon  Co.;  also  mined  near 


510 


DESCRIPTIVE   MINERALOGY 


Morgantown  and  Warlich,  Burke  Co.,  to  be  used  as  "emery,"  and  as  " garnet-paper."  In 
Ky.,  fine  pyrope  in  the  peridotite  of  Ellis  Co.  In  Ark.,  at  Magnet  Cove,  a  titaniferous 
melanite  with  schorlomite.  Large  dodecahedral  crystals  altered  to  chlorite  occur  at  the 
Spurr  Mt.  iron  mine,  Lake  Superior,  Mich.  In  Col.,  at  Nathrop,  fine  spessartite  crystals 
in  lithophyses  in  rhyolite;  in  large  dodecahedral  crystals  at  Ruby  Mt.,  Salida,  Chaff ee  Co., 
the  exterior  altered  to  chlorite.  In  Ariz.,  .yellow-green  crystals  in  the  Gila  canon;  pyrope 
on  the  Colorado  river  in  the  western  part  of  the  territory.  N.  M.,  fine  pyrope  on  the 
Navajo  reservation  with  chrysolite  and  a  chrome-pyroxene.  In  Cal.,  green  with  copper 
ore,  Hope  Valley,  El  Dorado  Co.;  uvarovite,  in  crystals  on  chromite,  at  New  Idria.  Fine 
crystals  of  a  rich  red  color  and  an  inch  or  more  in  diameter  occur  in  the  mica  schists  at 
Fort  Wrangell,  mouth  of  the  Stickeen  river,  in  Alaska. 

In  Canada,  at  Marmora,  dark  red;  at  Grenville,  a  cinnamon-stone;  an  emerald-green 
chrome-garnet,  at  Orford,  Quebec,  with  millerite  and  calcite;  fine  colorless  to  pale  olive- 
green,  or  brownish  crystals,  at  Wakefield,  Ottawa  Co.,  Quebec,  with  white  pyroxene,  honey- 
yellow  vesuvianite,  etc.,  also  others  bright  green  carrying  chromium;  dark  red  garnet  in 
the  townships  of  Villeneuve  (spessartite)  and  Templeton;  at  Hull,  Quebec. 

Use.  —  The  various  colored  and  transparent  garnets  are  used  as  semiprecious  gem 
s'ones.  At  times  the  mineral  is  also  used  as  an  abrasive. 

Schorlomite.  Probably  analogous  to  garnet,  3CaO.(Fe,Ti)2O3.3(Si,Ti)O2.  Usually 
massive,  black,  with  conchoidal  fracture  and  vitreous  luster.  H.  =  7—7 '5.  G.  =  3'81— 
3*88.  From  Magnet  Cove,  Ark.;  in  nepheline-syenite  on  Ice  River,  British  Columbia. 


In  small  dull  crystals  (monoclinic). 
From  the  auriferous  sands  of  Oldh- 


Partschinite.  (Mn,Fe)3Al2Si3Oi2  like  spessartite. 
H.  =  6-5-7.  G.  =  4-006.  Color  yellowish,  reddish, 
pian,  Transylvania. 

Agricolite.     Same  as  for  eulytite,   Bi4Si3Oi2,  but  monoclinic.     In  globular  or  semi- 
globular  forms.     From  Johanngeorgenstadt,  Germany. 


Monticellite 

Forsterite 

Chrysolite 

Hortonolite 
Fayalite 
Knebelite 
Tephroite 


Chrysolite  Group.     R2Si04.     Orthorhombic 


GaMgSiO4 
Mg2SiO4 

(Mg,Fe)2SiO4 

(Fe,Mg,Mn)2SiO4 

Fe2SiO4 

(Fe,Mn)2SiO4 

Mn2Si04 


mm"1 
110  A  110 

hh' 
Oil  A  01 

I     a 

b 

:  c 

46°  54' 

59°  52' 

0-4337 

1 

:  0-5758 

49°  51' 

60°  43' 

0-4648 

1 

:  0-5857 

49°  57' 

60°  47' 

0-4656 

1 

:  0-5865 

49°  15' 

60°  10' 

0-4584 

1 

:  0-5793 

49°  24' 

61°  25' 

0-4600 

1 

:  0-5939 

The  CHRYSOLITE  GROUP  includes  a  series  .of  orthosilicates  of  magnesium 
calcium,  iron  and  manganese.     They  all  crystallize  in  the  orthorhombic  system 
with  but  little  variation  in  axial  ratio.     The  prismatic  angle  is  about  50°  and 
hat  of  the  unit  brachydome  about  60°;  corresponding  to  the  latter  threefold 
twms  are  observed.     The  type  species  is  chrysolite  (or  olivine),  which  contains 

t^^        /°V  m  Varylng  Pr°Porti°ns  and  is  hence  intermediate 
the  comparatively  rare  magnesium  and  iron  silicates 


SILICATES 


511 


CHRYSOLITE.    Olivine.     Peridot. 

Orthorhombic.     Axes  a  :  b  :  c  =  0-46575  :  1  :  0-5865. 

mm'",  110  A  1TO  =  49°  57' 
ss'    120  A  120  =  94°  4' 


dd', 
kk, 
eef", 
W", 


101  A  101 
021  A  021 
111  A  111 
121  A  121 


103°  6' 
99°  6' 
40°  5 

72°  13 


848 


/e\    a 

e  \ 

m     a 

in 

Twins  rare:  tw.  pi.  h  (Oil)  with  angle  between 
basal   planes   of  the  two  individuals  =  60°  47', 
penetration-twins,  sometimes  repeated;  tw.  pi.  w     \  d    \// 
(012),  the  vertical  axes  crossing  at  an  angle  of 
about  30°.      Crystals  often  flattened  ||  a  (100)    or  6  (010),  less   commonly 
elongated  ||  c  axis.     Massive,  compact,  or  granular;  in  embedded  grains. 

Cleavage:  b  (010)  rather  distinct;  a  (100)  less  so.  Fracture  conchoidal. 
Brittle.  H.  =  6'5-7.  G.  =  3-27-3-37,  increasing  with  the  amount  of  iron; 
3'57  for  hyalosiderite  (30  p.  c.  FeO).  Luster  vitreous.  Color  green  —  com- 
monly olive-green,  sometimes  brownish,  grayish  red,  grayish  green,  becoming 
yellowish  brown  or  red  by  oxidation  of  the  iron.  Streak  usually  uncolored, 
rarely  yellowish.  Transparent  to  translucent.  Optically  +  .  Ax.  pi.  || 
c  (001),  Bx  J_  a  (100).  Dispersion  p  <  v ,  weak.  Axial  angle  large,  a  = 
1-662.  /?  =  1-680.  7  =  1*699. 

Var.  —  Precious.  —  Of  a  pale  yellowish  green  color,  and  transparent.  G.  =  3-441, 
3'351.  Occasionally  seen  in  masses  as  large  as  "a  turkey's  egg,"  but  usually  much  smaller. 
It  has  long  been  brought  from  the  Levant  for  jewelry,  but  the  exact  locality  is  not  known. 

Common;  Olivine.  —  Dark  yellowish  green  to  olive-  or  bottle-green.  G.  =  3 '26-3 '40. 
Disseminated  in  crystals  or  grains  in  basic  igneous  rocks,  basalt  and  basaltic  lavas,  etc. 
Hyalosiderite  is  a  highly  ferruginous  variety. 

Comp.  —  (Mg,Fe)2Si04  or  2(Mg,Fe)O.Si02.  The  ratio  of  Mg  :  Fe 
varies  widely,  from  16  :  1,  12  :  1,  etc.,  to  2  :  1  in  hyalosiderite,  and  hence  pass- 
ing from  forsterite  on  the  one  side  to 
fayalite  on  the  other.  No  sharp  line  can 
be  drawn  on  either  side.  Titanium  dioxide 
is  sometimes  present  replacing  silica;  also 
tin  and  nickel  in  minute  quantities. 

Pyr.,  etc.  —  B.  B.  whitens,  but  is  infusible  in 
most  cases;  hyalosiderite  and  other  varieties  rich 
in  iron  fuse  to  a  black  magnetic  globule;  some  kinds 
turn  red  upon  heating.  With  the  fluxes  gives 
reactions  for  iron.  Some  varieties  give  reactions 
for  titanium  and  manganese.  Soluble  in  hydro- 
chloric acid  and  yields  gelatinous  silica  upon 
evaporation. 

Diff.  —  Characterized  by  its  infusibility,  the 
yellow-green  color,  granular  form  and  cleavage 
(quartz  has  none). 

Micro.  —  Recognized  in  thin  sections  by  its  high  relief;  lack  of  color;  its  few  but 
marked  rough  cleavage-cracks;  high  interference-colors,  which  are  usually  the  brilliant 
and  pronounced  tones  of  the  second  order;  parallel  extinction;  biaxial  character;  charac- 
teristic outlines  (usually  with  acute  terminations)  when  in  distinct  crystals  (Figs.  850-852), 
its  frequent  association  with  iron  ore  and  augite,  and  its  very  common  alteration,  in  a  greater 
or  less  degree,  to  serpentine,  the  first  stages  being  marked  by  the  separation  of  iron-ore 
grains  along  the  lines  of  fracture  (Fig.  853). 

Artif .  —  The  different  members  of  the  Chrysolite  Group  have  been  easily  synthesized 
in  various  ways.  They  are  often  observed  in  slags. 


010 


512 


DESCRIPTIVE    MINERALOGY 


Obs.  —  Chrysolite  (olivine)  has  two  distinct  methods  of  occurrence:  (a)  in  igneous 
rocks,  as  peridotite,  norite,  basalt,  diabase  and  gabbro,  formed  by  the  crystallization  of 
magmas  low  in  silica  and  rich  in  magnesia;  from  an  accessory  component  in  such  rocks 


852 


853 


the  olivine  may  increase  in  amount  until  it  is  the  mam  rock  constituent  as  in  the  dunites; 
also  (6)  as  the  product  of  metamorphism  of  certain  sedimentary  rocks  containing  magnesia 
and  silica,  as  in  impure  dolomites.  In  the  dunites  and  peridotites  of  igneous  origin  the 
chrysolite  is  commonly  associated  with  chromite,  spinel,  pyrope,  etc.,  which  are  valuable 
indications  also  of  the  origin  of  serpentines  derived  from  olivine.  In  the  metamorphic 
rocks  the  above  are  wanting,  and  carbonates,  as  dolomite,  breunnerite,  magnesite,  etc., 
are  the  common  associations;  chrysolitic  rocks  of  this  latter  kind  may  also  occur  altered 
to  serpentine. 

Chrysolite  also  occurs  in  grains,  rarely  crystals,  embedded  in  some  meteoric  irons. 
Also  present  in  meteoric  stones,  frequently  in  spherical  forms,  or  chondrules,  sometimes 
made  up  of  a  multitude  of  grains  with  like  (or  unlike)  optical  orientation  enclosing  glass 
between. 

Among  the  more  prominent  localities  are:  Vesuvius  in  lava  and  on  Monte  Somma  in 
ejected  masses,  with  augite,  mica,  etc.  In  Germany  observed  in  the  so  called  sanidine 
bombs  at  the  Laacher  See;  at  Forstberg  near  May  en  in  the  Eifel  and  forming  the  mass  of 
"olivine  bombs"  in  the  Dreiser  Weiher  near  Daun  in  the  same  region;  at  Sasbach  in  the 
Kaiserstuhl,  Baden  (hyalosiderite)  .  In  crystals  of  gem-quality  from  Egypt.  In  Sweden, 
with  ore-deposits,  as  at  Langban,  Pajsberg,  Persberg,  etc.  In  serpentine  at  Snarum,  Nor- 
way, in  large  crystals,  themselves  altered  to  the  same  mineral.  Common  in  the  volcanic 
rocks  of  Sicily,  the  Hawaiian  Islands,  the  Azores,  etc. 

In  the  United  States,  in  Thetford  and  Norwich,  Ver.,  in  boulders  of  coarsely  crystallized 
basalt,  the  crystals  or  masses  several  inches  through.  In  olivine-gabbro  of  Waterville,  in 
the  White  Mts.,  N.  H.;  at  Webster,  in  Jackson  Co.,  N.  C.,  with  serpentine  and  chromite; 
with  chromite  in  Loudon  Co.,  Va.;  in  Lancaster  Co.,  Pa.  In  small  clear  olive-green  grains 
with  garnet  at  some  points  in  Ariz,  and  N.  M.  In  basalt  in  Canada,  near  Montreal,  at 
Rougemont  and  Mounts  Royal  and  Montarville,  and  in  eruptive  rocks  at  other  points. 

Alteration  of  chrysolite  often  takes  place  through  the  oxidation  of  the  iron;  the  mineral 
becomes  brownish  or  reddish  brown  and  iridescent.  The  process  may  end  in  leaving  the 
cavity  of  the  crystal  filled  with  limonite  or  red  oxide  of  iron.  A  very  common  kind  of 
alteration  is  to  the  hydrous  magnesium  silicate,  serpentine,  with  the  partial  removal  of  the 
iron  or  its  separation  in  the  form  of  grains  of  magnetite,  also  as  iron  sesquioxide;  this 
change  has  often  taken  place  on  a  large  scale.  See  further  under  serpentine,  p.  573. 

Chrysolite  is  named  from  xpvris,  gold,  and  Al0os.  The  hyalosiderite,  from  oaXos, 
glass,  and  o-iSrjpos,  iron.  The  chrysolithus  of  Pliny  was  probably  our  topaz  ;  and  his  topaz 
our  chrysolite. 

Use.  —  The  clear,  fine  green  varieties  are  used  as  a  gem  stone;  usually  caUed  peridot. 

T^Y-*  Fr°m  *the  r°ck  ?armeloite  of  Carmelo  Bay,  Cal.;  a  silicate  resembling  an 
chrysolite,  exact  composition  undetermined.     Has  been  noted  as  a  pseudomorph 
h*  Mittelgebirge'  Bohemia.     Orthorhombic,  foliated  and 


cleavable^G 


SILICATES  513 

The  axial  ratios  of  the  other  members  of  the  Chrysolite  Group  are  given  in  the  table  on 
p.  510.  The  species  are  briefly  characterized  as  follows: 

Monticellite.  CaMgSiO4.  Occurs  in  colorless  to  gray  crystals  on  Mte.  Somma,  Vesu- 
vius; in  masses  (batrachite)  on  Mt.  Monzoni,  Tyrol,  Italy;  in  crystals  or  grains  in  lime- 
stone at  Magnet  Cove,  Ark.  G.  =  3'03-3'25.  Optically  -.  Indices,  1 '651-1 '668. 

Glaucochroite.  CaMnSiO4.  In  embedded  prismatic  crystals.  Crystal  constants  and 
optical  properties  near  those  of  Chrysolite  Group.  Color,  delicate  bluish  green.  Found 
at  Franklin  Furnace,  N.  J.  H.  =6.  G.  =  3 '4. 

Forsterite.  Mg2SiO4.  Occurs  in  white  crystals  at  Vesuvius;  in  greenish  or  yellowish 
embedded  grains  at  Bolton,  Mass,  (boltonite).  G.  =  3'21-3'33.  Optically  +.  ft  =  1'659. 

Hortonolite.  (Fe,Mg,Mn)2SiO4.  In  rough  dark-colored  crystals  or  masses.  Occurs  at 
the  iron  mine  of  Monroe,  Orange  Co.,  N.  Y. ;  Iron  Mine  Hill,  Cumberland,  R.  I.  G.  =  3'91. 
Optically  -.  Indices,  1768-1 '803. 

Fayalite.  Fe2SiO4.  From  the  Mourne  Mts.,  Ireland;  the  Azores;  the  Yellowstone 
Park;  Rockport,  Mass.,  etc.  From  Cuddia  Mida,  Island  of  Pantelleria,  Italy.  Crystals 
and  massive,  brown  to  black  on  exposure.  G.  =  4'1  Optically  — .  Indices,  1  '824-1  '874. 
Manganfayalite  is  a  manganese  variety  found  at  Sodermanland,  Sweden. 

Knebelite.     (Fe,Mn)2SiO4.     From  Dannemora,  and  elsewhere  in  Sweden.     G.  =  4-1. 

Tephroite.  MnoSiO4;  also  with  zinc,  in  the  variety  roeppetite.  From  Sterling  Hill  and 
Franklin  Furnace,  N.  J.;  also  from  Sweden;  from  Benderneer,  New  South  Wales.  Color 
flesh-red  to  ash-gray.  G.  =  41.  Optically  — .  Index  about  T80. 


Phenacite  Group.     R2Si04.     Tri-rhombohedral 

rr'  c 

Willemite  Zn2SiO4  64°  30'  0-6775 

Troostite  (Zn,Mn)2SiO4 

Phenacite  Be2SiO4  63°  24'  0-6611 

The  PHENACITE  GROUP  includes  the  above  orthosilicates  of  zinc  (man- 
ganese) and  beryllium.  Both  belong  to  the  tri-rhombohedral  class  of  the 
trigonal  division  of  the  hexagonal  system,  and  have  nearly  the  same  rhombo- 
hedral  angle.  The  rare  species  trimerite,  MnSiO4.BeSiO4,  which  is  pseudo- 
hexagonal  (triclinic)  is  probably  to  be  regarded  as  connecting  this  group  with 
the  preceding  Chrysolite  Group. 

The  following  rare  species  are  related: 

rr'  c 

Dioptase         H2CuSiO4  Tri-rhombohedral       54°     5'  0'5342 

Friedelite        H7(MnCl)Mn4(SiO4)4  56°  17'  0'5624 

Pyrosmalite    H7(  (Fe,Mn)Cl)(Fe,Mn)4(SiO4)4  53°  49'  0'5308 

These  species  are  very  near  to  each  other  in  form,  as  shown  in  the  above  axial  ratios; 
they  further  approximate  to  the  species  of  the  Phenacite  Group  proper.  They  are  also 
closely  related  among  themselves  in  composition,  since  they  are  all  acid  orthosilicates,  and 
have  the  general  formula  H2RSiO4  =  H8R4(SiO4)4,  where  (e.g.  for  Friedelite)  in  the  latter 
form  the  place  of  one  hydrogen  atom  is  taken  by  the  univalent  radical  (MnCl). 

WILLEMITE. 

Tri-rhombohedral.  Axis  c  =  0*6775;  rr'  (1011)  A  (IlOl)  =  64°  30';  eer 
(0112)  A  (1012)  =  36°  47'. 

In  hexagonal  prisms,  sometimes  long  and  slender,  again  short  and  stout; 
rarely  showing  subordinate  faces  distributed  according  to  the  phenacite  type. 
Also  massive  and  in  disseminated  grains;  fibrous. 

Cleavage:  c  (000 1)  easy,  Moresnet;  difficult,  N.  J.-;  a  (1120)  easy,  N.  J. 
Fracture  conchoidal  to  uneven.  Brittle.  H.  =  5'5.  G.  =  3 -89-4 -18.  Luster 


514 


DESCRIPTIVE   MINERALOGY 


vitreo-resinous,  rather  weak.     Color  white  or  greenish  yellow,  when  purest; 
apple-green,  flesh-red,  grayish  white,  yellowish  brown-    often   dark  brown 


854 


855 


856 


Figs.  854-857,  New  Jersey,     e  (0112),  s  (1123),  u  (2ll3),  x  (3121). 

when  impure.     Streak  uncolored.     Transparent  to  opaque.     Optically  +  . 
<o  =  1-693.     e  =  1712. 

Comp.  —  Zinc  orthosilicate,  Zn2Si04  or  2ZnO.Si02  =  Silica  27-0,  zinc 
oxide  73*0  =  100.  Manganese  often  replaces  a  considerable  part  of  the  zinc 
(in  troostite),  and  iron  is  also  present  in  small  amount. 

Pyr.,  etc.  —  B.B.  in  the  forceps  glows  and  fuses  with  difficulty  to  a  white  enamel;  the 
varieties  from  New  Jersey  fuse  from  3 '5  to  4.  The  powdered  mineral  on  charcoal  in  R.F. 
gives  a  coating,  yellow  while  hot  and  white  on  cooling,  which,  moistened  with  solution  of 
cobalt,  and  treated  in  O.F.,  is  colored  bright  green.  With  soda  the  coating  is  more  readily 
obtained.  Soluble  in  hydrochloric  acid  and  yields  gelatinous  silica  upon  evaporation. 

Obs.  —  From  Altenberg  near  Moresnet,  Belgium;  at  Stolberg,  near  Aix-la-Chapelle. 
From  Musartut,  Greenland;  Mindouli,  French  Congo;  Kristiania,  Norway.  In  N.  J. 
at  Mine  Hill,  Franklin  Furnace,  and  at  Sterling  Hill,  two  miles  distant.  Occurs  with  zincite 
and  franklinite,  varying  in  color  from  white  to  pale  honey-yellow  and  light  green  to  dark 
ash-gray  and  flesh-red;  sometimes  in  large  reddish  crystals  (troostite).  Rare  at  the  Merritt 
mine,  Socorro  Co.,  N.  M.;  also  at  the  Sedalia  mine,  Salida,  Col.  Named  by  Levy  after 
William  I.,  Kinfc  of  the  Netherlands. 

Use.  —  An  ore  of  zinc. 

PHENACITE. 

Tri-rhombohedral.     Axis  c  =  0-6611;  rr'  (1011)  A  (1101)  =  63°  24'. 
Crystals  commonly  rhombohedral  in  habit,  often  lenticular  in  form,  the 

858  859  860 


Miask. 


Florissant.  Col. 


Mt.  Antero,  Col.,  Pfd. 

prisms  wanting;   also  prismatic,  sometimes  terminated  by  the  rhombohedron 
of  the  third  series,  x  (see  further,  pp.  110-112). 


SILICATES 


515 


Cleavage:  a  (1120)  distinct;  r  (1011)  imperfect.  Fracture  conchoidal. 
Brittle.  H.  =  7 '5-8.  G.  =  2-97-3-00.  Luster  vitreous.  Colorless;  also 
bright  wine-yellow,  pale  rose-red;  brown.  Transparent  to  subtranslucent 
Optically  +  .  co  =  1'6540;  e  =  1'6697. 

Comp.  —  Beryllium  orthosilicate,  Be2SiO4  or  2BeO.SiO2  =  Silica  54*45,  glu- 
cina  45-55  =  100. 

Pyr.,  etc.  —  Alone  remains  unaltered;  with  borax  fuses  with  extreme  slowness,  unless 
pulverized,  to  a  transparent  glass.  With  soda  affords  a  white  enamel;  with  more,  intu- 
mesces  and  becomes  infusible.  Dull  blue  with  cobalt  solution. 

Obs.  —  Occurs  at  the  emerald  and  chrysoberyl  mine  of  Takovaya,  85  versts  east  of  Eka- 
terinburg, Ural  Mts.;  also  in  the  Ilmen  Mts.,  near  Miask,  Russia;  near  Framont  in  the 
Vosges  Mts.;  Kragero,  Norway;  at  the  Cerro  del  Mercado,  Durango,  Mexico;  crystals 
from  San  Miguel  di  Piracicaba,  Minas  Geraes,  Brazil. 

In  Col.,  on  amazon-stone,  at  Topaz  Butte,  near  Florissant,  16  miles  from  Pike's  Peak; 
also  on  quartz  and  beryl  at  Mt.  Antero,  Chaffee  county.  Occurs  at  Chatham,  N.  H. 
Named  from  (j>€va£,  a  deceiver,  in  allusion  to  its  having  been  mistaken  for  quartz. 


Trimerite.  (Mn,Ca)2SiO4.Be2SiO4.  In  thick  tabular  prismatic  crystals,  pseudo- 
hexagonal  (triclinic)  in  form  and  angle.  H.  =  6-7.  G.  =  3 '474.  Color  salmon-pink  to 
nearly  colorless  in  small  crystals.  Optically—.  Indices,  1715-1 725.  From  the  Harstig 
mine,  Wermland,  Sweden. 


861 


JDioptase.     H2CuSiO4  or  H2O.CuO.SiO2.     Commonly  in  prismatic  crystals  (ssr  0221 
A  2021  =84°  33$')  •     Also  in  crystalline  aggregates;    massive.     Cleavage:    r  (lOTl)  per- 
fect.     Fracture  conchoidal  to  uneven.      H.  =  5.      G.  = 
3 '28-3 '35.    Luster  vitreous.    Color  emerald-green.    Opti- 
cally +.     co  =  1-654.     e  =  1-707. 

Occurs  in  druses  of  well-defined  crystals  on  quartz, 
occupying  seams  in  a  compact  limestone  west  of  the  hill 
of  Altyn-Tiibe  in  the  Kirghiz  Steppe,  Russia;  in  the 
gold  washings  at  several  points  in  Siberia;  atRezbanya, 
Hungary.  From  Copiapo,  Chile,  on  quartz  with  other 
copper  ores.  In  fine  crystals  at  the  Mine  Mindouli,  two 
leagues  east  of  Comba,  in  the  French  Congo  State.  Also 
at  the  copper  mines  of  Clifton,  Graham  Co.,  and  from 
Metcalfe  and  near  Florence,  Ariz. 

Plancheite.      H2Cu7(Cu.OH)8(SiO3)i2.      Fibrous,   often 

mammillary.    Blue  color.    G,  =  3'4.     Found  associated  with  dioptase,  etc.,  at  Mindouli, 
French  Congo. 

Friedelite.  H7(MnCl)Mn4Si4Oi6.  Crystals  commonly  tabular  \\  c  (0001) ;  also  massive, 
cleavable  to  closely  compact.  H.  =  4-5.  G.  =  3'07.  Color  rose-red.  From  the  man- 
ganese mine  of  Adervielle,  vallee  du  Louron,  Hautes  Pyrenees,  France;  from  Sjo  mine, 
Wermland,  Sweden;  from  Franklin  Furnace,  N.  J. 

Pyrosmalite.  H7((Fe,Mn)Cl)(Fe,Mn)4Si4Oi6.  Crystals  thick  hexagonal  prisms  or 
tabular;  also  massive,  foliated.  H.  =  4-4'5.  G.  =  3*06-3 '19.  Color  blackish  green  to 
pale  liver-brown  or  gray.  Index  about  1'66.  From  the  iron  mines  of  Nordmark  in  Werm- 
land and  at  Dannemora,  Sweden. 


Meionite 
Wernerite 


Scapolite  Group. 

c  =  0-4393 
c  =  0-4384 


Tetragonal-pyramidal 

Mizzonite,  Dipyre 
Marialite 


c  =  0-4424 
c  =  0-4417 


The  species  of  the  SCAPOLITE  GROUP  crystallize  in  the  pyramidal  class  of 
the  tetragonal  system  with  nearly  the  same  axial  ratio.  They  are  white  or 
grayish  white  in  color,  except  when  impure,  and  then  rarely  of  dark  color. 


516  DESCRIPTIVE    MINERALOGY 

Hardness  =  5-6*5;  G.  =  2-5-2-8.  In  composition  they  are  silicates  of 
aluminium  with  calcium  and  sodium  in  varying  amounts;  chlorine  is  also 
often  present,  sometimes  only  in  traces.  Iron,  magnesia,  potash  are  not 
present  unless  by  reason  of  inclusions  or  of  alteration.  Carbon  dioxide  and 
sulphur  trioxide  have  been  noted  in  certain  analyses.  It  has  been  suggested 
that  these  radicals  enter  into  the  composition  in  the  same  manner  as  the 
chlorine. 

The  Scapolites  are  analogous  to  the  Feldspars  in  that  they  form  a  series 
with  a  gradual  variation  in  composition,  the  amount  of  silica  increasing  with 
the  increase  of  the  alkali,  soda,  being  40  p.  c.  in  meionite  and  64  p.  c.  in  mari- 
alite.  A  corresponding  increase  is  observed  also  in  the  amount  of  chlorine 
present.  Furthermore  there  is  also  a  gradual  change  in  specific  gravity,  in 
the  strength  of  the  double  refraction,  and  in  resistance  to  acids,  from  the  easily 
decomposed  meionite,  with  G.  =  2-72,  to  marialite,  which  is  only  slightly 
attacked  and  has  G.  =  2-63.  Tschermak  has  shown  that  the  variation  in 
composition  may  be  explained  by  the  assumption  of  two  fundamental  end 
compounds,  viz.  : 

Meionite  Ca4Al6Si6025  Me 

Marialite  NaiAlgSigC^Cl  Ma 


By  the  isomorphous  combination  of  these  compounds  the  composition  of 
the  species  mentioned  above  may  be  explained;  no  sharp  line  can,  however, 
be  drawn  between  them. 

Optically  the  series  is  characterized  by  the  decrease  in  the  strength  of  the  double  refrac- 
tion  in  passing  from  meionite  to  marialite.  Thus  (Lacroix)  for  meionite  «  —  e  =  0'036' 
for  typical  wernerite  0'03-0-02;  for  dipyre  0'015. 

The  tetragonal  species  melilite  and  gehlenite  are  near  the  Sca*polites  in  ' 
angle.     The  more  common  vesuvianite  is  also  related. 


MEIONITE. 


Tetragonal.  Axis  c  =  0-43925.  In  prismatic  crystals  (Fig.  201, "p.  86), 
either  clear  and  glassy  or  milky  white;  also  in  crystalline  grains  and  massive. 
Cleavage:  a  (100)  rather  perfect,  m  (110)  somewhat  less  so.  Fracture  con- 
choidal.  Brittle.  H.  =  5-5-6  G.  =  2-70-2-74.  Luster  vitreous.  Color- 
less to  white.  Transparent  to  translucent;  often  cracked  within.  Opticallv 
-.  co  =  1-597;  e  =  1-560. 

Comp.  —  Ca4Al6Si6025or4CaO.3Al2O3.6Si02  =  Silica  40-5,  alumina  34-4, 
hme  25' 1  =  100. 

The  varieties  included  here  range  from  nearly  pure  meionite  to  those  consisting:  of 
rneiomte  and  marialite  in  the  ratio  of  3  :  1,  i.e.,  Me  :  Ma  =  3  :  1.  No  sharp  line  can  be 
drawn  between  meionite  and  the  following  species. 

Obs.  —  Occurs  in  small  crystals  in  cavities,  usually  in  limestone  blocks,  on  Monte 
bomma  Vesuvius.  Also  in  ejected  masses  at  the  Laacher  See,  Germany.  A  mineral  in 

h«^11  "\neiSu       m  *h€lBlack  Foi>est,  Germany,  which  is  like  meionite  except  for  a 

basal  cleavage  has  been  called  pseudomeionite. 

WERNERITE.     COMMON  SCAPOLITE. 
Tetragonal-pyramidal.     Axis  c  =  0-4384. 

Crystals  prismatic,  usually  coarse,  with  uneven  faces  and  often  large.     The 
f  the  pyramidal  class  sometimes  shown  in  the  development  of  the 


SILICATES 


517 


faces  z  (311)  and  zx  (131).     Also  massive,  granular,  or  with  a  faint  fibrous 
appearance;  sometimes  columnar. 

eer,  101  A  Oil  =  32°  59'. 

rr',  111  A  111  =  43°  45'. 

mr,  110  A  111  =  58°  12'. 

zz'",  311  A  311  =  29°  43'. 

Cleavage:  a  (100)  and  m  (110)  rather  dis- 
tinct, but  interrupted.  Fracture  subconchoidal. 
Brittle.  H.  =  5-6.  G.  =  2-66-273.  Luster 
vitreous  to  pearly  externally,  inclining  to  res- 
inous; cleavage  and  cross-fracture  surface 
vitreous.  Color  white,  gray,  bluish,  greenish, 
and  reddish,  usually  light;  streak  uncolored. 
Transparent  to  faintly  subtranslucent.  Optically—,  co  =  1-570.  e  =  1-549. 

Comp.  —  Intermediate  between  meionite  and  marialite  and  correspond- 
ing to  a  molecular  combination  of  these  in  a  ratio  3  :  1  to  1  :  2.  The  silica 
varies  from  46  to  54  p.c.,  and  as  its  amount  increases  the  soda  and  chlorine 
also  increase.  Scapolites  with  silica  from  54  p.  c.  to  60  p.  c.  are  classed  with 
mizzonite;  they  correspond  to  Me  :  Ma  from  1  :  2  to  1  :  3  and  upwards. 

The  percentage  composition  for  a  common  compound  is  as  follows: 
Me  :  Ma  3  :  1       SiO2  46*10      A12O3  30'48       CaO  19'10       Na2O  3'54      Cl  1 -01  =100*23 

Pyr.,  etc.  —  B.B.  fuses  easily  with  intumescence  to  a  white  blebby  glass  giving  a  strong 
sodium  flame  color.  Imperfectly  decomposed  by  hydrochloric  acid. 

Diff .  —  Characterized  by  its  square  form  and  prismatic  cleavage  (90°) :  resembles 
feldspar  when  massive,  but  has  a  characteristic  fibrous  appearance  on  the  cleavage  surface; 
it  is  also  more  fusible,  and  has  a  higher  specific  gravity;  also  distinguished  by  fusibility 
with  intumescence  from  pyroxene  (which  see,  p.  478). 

Micro.  —  Recognized  in  thin  sections  by  its  low  refraction;  lack  of  color;  rather  high 
interference-colors  reaching  the  yellows  and  reds  of  the  first  order,  sections  showing  which 
extinguish  parallel  to  the  cleavage;  by  the  distinct  negative  axial  cross  of  basal  sections 
which  show  the  cleavage-cracks  crossing  at  right  angles. 

Obs.  —  Occurs  in  metamorphic  rocks,  crystalline  schists,  gneisses,  amphibolites  and 
most  abundantly  in  granular  limestone  near  its  junction  with  the  associated  granitic  or 
allied  rocks;  sometimes  in  beds  of  magnetite  accompanying  limestone.  It  is  often  asso- 
ciated with  a  light-colored  pyroxene,  amphibole,  garnet,  and  also  with  apatite,  titanite, 
zircon;  amphibole  is  a  less  common  associate  than  pyroxene,  but  in  some  cases  has  resulted 
from  the  alteration  of  pyroxene.  Scapolite  has  been^sjjown  also  to  be  frequently. a  com- 
ponent of  basic  igneous  rocks,  especially  those  rich  in  plaglOuLiuLj  uiwitaining  much  lime; 
it  is  regarded  as  a  secondary  product  through  a  certain  kind  of. alteration.  The  scapolites 
are  easily  altered;  pseudormorphs  of  mica,  more  rarely  other  minerals,  are  com- 
mon. 

Prominent  localities  are  at  Pargas,  Finland,  where  it  occurs  in  limestone;  Arendal  in 
Norway,  and  Malsjo  in  Wermland,  Sweden,  where  it  occurs  with  magnetite  in  limestone. 
Passauite  is  from  Obernzell,  near  Passau,  in  Bavaria.  The  pale  blue  or  gray  scapolite  from 
Lake  Baikal,  Siberia,  is  called  glaucolite.  In  the  United  States,  occurs  in  Ver.,  at  Marl- 
borough,  massive.  In  Mass.,  at  Bolton;  at  Chelmsford.  In  N.  Y.  in  Orange  Co.,  Essex 
Co.,  Lewis  Co.;  Grasse  Lake,  Jefferson  Co.;  at  Gouverneur,  in  limestone.  In  N.  J.,  at 
Franklin  and  Newton.  In  Pa.,  at  the  Elizabeth  mine,  French  Creek,  Chester  Co. 

In  Canada,  at  Calumet  Island,  massive;  at  Grenville;  .Templeton;  Wakefield,  Ottawa 
Co.;  at  Bedford  and  Bathurst,  Ont  :  Scapolite  rocks  occur  at  several  points. 

Mizzonite.  Dipyre.  Here  are  included  scapolites  with  54  to  57  p.  c.  SiO2,  correspond- 
ing to  a  molecular  combination  from  Me  :  Ma  =  1  :  2  to  Me  :  Ma  =  1:3.  Mizzonite 
occurs  in  clear  crystals  in  ejected  masses  on  Mte.  Somma,  Vesuvius. 

Dipyre  occurs  in  elongated  square  prisms,  often  slender,  sometimes  large  and  coarse,  in 
limestone  and  crystalline  schists,  chiefly  from  the  Pyrenees;  also  in  diorite  at  Bamle,  Nor- 
way; Saint-Nazaire,  France;  Algeria.  Couseranite  from  the  Pyrenees  is  a  more  or  less 
altered  form  of  dipyre. 


DESCRIPTIVE   MINERALOGY 

Marialite  Theoretically  Na4Al3Si9O24Cl,  see  p.  516.  Indices,  1- 541-1- 554.  The 
actual  iinerkl  corresponds  to  Me  :  Ma  =  1  :  4.  It  occurs  in  a  basalt  tuff,  at  Pianura, 
near  Naples. 

Sarcolite.  (Ca,Na,)3Al2(SiO4)3.  In  small  tetragonal  crystals.  H.  =  6.  G.  =  2-545- 
2-932.  Color  flesh-red.  Indices,  1 '640-1 '656.  From  Monte  Somma,  Vesuvius. 

MELILITE. 

Tetragonal.  Axis  c  =  0-4548.  Usually  in  short  square  prisms  (a  (100)) 
or  octagonal  prisms  (a,  m  (110)),  also  in  tetragonal  tables. 

Cleavage:  c  (001)  distinct;  a  (100)  indistinct.  Fracture  conchoidal  to 
uneven.  Brittle.  H.  =  5.  G.  =  2-9-3-10.  Luster  vitreous,  inclining  to 
resinous.  Color  white,  pale  yellow,  greenish,  reddish,  brown.  Pleochroism 
distinct  in  yellow  varieties.  Sometimes  exhibits  optical  anomalies.  Opti- 
cally -.  co  =  1-634.  €  =  1-629. 

Comp.  —  Perhaps  R12R4Si9036  or  Na2(Ca,Mg)i1(Al,Fe)4(Si04)9  for  meli- 
lite. If  Ca  :  Mg  =  8:3,  and  Al  :  Fe  =  1  :  1,  the  percentage  composition  is: 
Silica  37-7,  alumina  7'1,  iron  sesquioxide  11-2,  lime  31-3,  magnesia  8'4,  soda  4'3 
=  100.  Potassium  is  also  present. 

The  composition  of  the  melilite-gehlenite  group  can  be  explained  as  isomorphous  mix- 
tures of  the  three  compounds,  sarcolite,  3CaO.Al2O3.3SiO2  or  soda-sarcolite  3Na2O.Al2O3. 
3SiO2;  dkermanite,  8CaO.4MgO.9SiO2;  velardeiiite,  2CaO.Al2O3.SiO2.  The  last  is  noted  in 
large  amount  in  gehlenite  from  the  Velardena  mining  district,  Mexico. 

Artif.  —  Melilite  has  been  formed  artificially  by  fusing  together  its  constituent 
oxides.  It  is  found  in  slags  and  has  been  produced  in  various  artificial  magmas. 

Pyr.,  etc.  —  B.B.  fuses  at  3  to  a  yellowish  or  greenish  glass.  With  the  fluxes  reacts  for 
iron.  Soluble  in  hydrochloric  acid  and  yields  gelatinous  silica  upon  evaporation. 

Micro.  —  Distinguished  in  thin  sections  by  its  moderate  refraction;  very  low  interfer- 
ence-colors, showing  often  the  "ultra  blue"  (Capo  di  Bove);  parallel  extinction;  negative 
character;  usual  development  in  tables  parallel  to  the  base  and  very  common  "peg  struc- 
ture" due  to  parallel  rod-like  inclusions  penetrating  the  crystal  from  the  basal  planes 
inward:  this,  however,  is  not  always  easily  seen. 

Obs.  —  Melilite  is  a  component  of  certain  igneous  rocks  formed  from  magmas  very  low 
in  silica,  rather  deficient  in  alkalies,  and  containing  considerable  lime  and  alumina.  In 
such  cases  melilite  appears  to  crystallize  in  the  place  of  the  more  acid  plagioclase. 

Melilite  of  yellow  and  brownish  colors  is  found  at  Capo  di  Bove,  near  Rome,  in  leucito- 
phyre  with  nephelite,  augite,  hornblende;  at  Vesuvius  in  dull  yellow  crystals  (somervillite) ', 
not  uncommon  in  certain  basic  eruptive  rocks,  as  the  melilite-basalts  of  Hochbohl  near  Owen 
in  Wurttemberg,  of  the  Swabian  Alp,  of  Gorlitz,  the  Erzgebirge,  Germany;  also  in  the 
nephelite  basalts  of  the  Hegau,  of  Oahu,  Hawaiian  Islands,  etc.;  perovskite  is  a  common 
associate.  Occurs  as  chief  constituent  of  rock  on  Beaver  Creek,  Gunnison  Co.,  Col.  Com- 
mon in  furnace  slags.  Melilite  is  named  from  nf€\t,  honey,  in  allusion  to  the  color. 

Humboldtilite  occurs  in  cavernous  blocks  on  Monte  Somma,  Vesuvius,  with  greenish  mica, 
also  apatite,  augite;  the  crystals  are  often  rather  large,  and  covered  with  a  calcareous  coat- 
ing; less  common  in  transparent  lustrous  crystals  with  nephelite,  sarcolite,  etc.,  in  an 
augitic  rock.  Zurlite  is  impure  humboldtilite.  Deeckeite  is  a  pseudomorph  after  melilite 
with  the  composition  (H,K,Na)2(Mg,Ca)(Al,Fe)2(Si2O6)5.9H2O,  found  in  a  melilite  basalt 
from  the  Kaiserstuhl,  Baden,  Germany. 

Cebollite.  H2Ca5Al<>Si3Oi6.  Orthorhombic  (?).  Fibrous.  H.  =5.  G.  =  2'96.  Color 
white  to  greenish  gray.  Indices,  1 '59-1 '63.  Fusible  at  5.  Soluble  in  acids.  Found  as 
an  alteration  product  of  melilite  near  Cebolla  Creek,  Gunnison  Co.,  Col. 
^  Gehlenite.  Ca3Al2Si2Oi0.  Crystals  usually  short  square  prisms.  Axis  c  =  0-4001. 
y-  =  2 -9-3 '07.  Different  shades  of  grayish  green  to  liver-brown.  From  Mount  Monzoni, 
m  the  Fassatal,  in  Tyrol,  Austria.  From  Velardena  mining  district,  Mexico. 

FUGGERITE  Corresponds  to  a  member  of  the  gehlenite-akermanite  series,  3  ak  :  10  geh. 
From  Monzonite  of  Monzonital,  Tyrol,  Austria. 


SILICATES 


519 


AKERMANITE.     Tetragonal,  isomorphous  with  melilite  and  gehlenite. 
as.     See  further  under  Melilite. 


Found  in  certain 


VESUVIANITE.     Idocrase. 

Tetragonal.     Axis  c  =  0-5372. 

ce,  001  A  101  =  28°  15'. 
cp,  001  A  111  =  37°  13|'. 
ct,  001  A  331  =  66°  18'. 

865 


pp 


866 


111  A  Til  =  50°  39'. 
311  A  311  =  31°  38'. 


867 


Zermatt 


Sandford,  Me. 


Often  in  crystals,  prismatic  or  pyramidal.  Also  massive;  columnar, 
straight  and  divergent,  or  irregular;  granular  massive;  cryptocrystalline. 

Cleavage:  m  (110)  not  very  distinct;  a  (100)  and  c  (001)  still  less  so. 
Fracture  subconchoidal  to  uneven.  Brittle.  H.  =  6*5.  G.  =  3 '35-3 '45. 
Luster  vitreous;  often  inclining  to  resinous.  Color  brown  to  green,  and  the 
latter  frequently  bright  and  clear;  occasionally  sulphur-yellow,  and  also  pale 
blue.  Streak  white.  Subtransparent  to  faintly  subtranslucent.  Dichroism 
not  usually  strong.  Optically  — ;  also  -+-  rarely.  Birefringence  very  low. 
Sometimes  abnormally  biaxial.  Indices  variable,  from  1715  to  1720. 

Comp.  —  A  basic  calcium-aluminium  silicate,  but  of  uncertain  formula; 
perhaps  Ca6[Al(OH,F)]Al2(SiO4)5.  Ferric  iron  replaces  part  of  the  aluminium 
and  magnesium  the  calcium.  Fluorine  and  titanium  may  be  present. 

Another  general   formula  has  been  proposed,  RtCayALzSieO^,  in  which  R4 
may  be  Ca2,(AlOH)2,(A102H)4,  or  H4. 

Pyr.,  etc.  —  B.B.  fuses  at  3  with  intumescence  to  a  greenish  or  brownish  glass.  With 
the  fluxes  gives  reactions  for  iron,  and  some  varieties  a  strong  manganese  reaction.  Cyprine, 
a  blue  variety,  gives  a  reaction  for  copper  with  salt  of  phosphorus.  Partially  decomposed 
by  hydrochloric  acid,  and  completely  when  the  mineral  has  been  previously  ignited. 

Diff.  —  Characterized  by  its  tetragonal  form  and  easy  fusibility.  Resembles  some 
brown  varieties  of  garnet,  tourmaline,  and  epidote. 


520 


DESCRIPTIVE   MINERALOGY 


Micro.  —  Recognized  in  thin  sections  by  its  high  refraction  producing  a  very  strong 
relief  and  its  extremely  low  birefringence;  *  also  in  general  by  its  color,  pleochroism,  and 
uniaxial  negative  character;  the  latter,  on  account  of  the  low  birefringence,  being  difficult 
to  determine.  The  low  birefringence,  however,  aids  in  distinguishing  it  from  epidote,  with 
which  at  times  it  may  be  confounded. 

Obs.  —  Vesuvianite  was  first  found  among  the  ancient  ejections  of  Vesuvius  and  the 
dolomitic  blocks  of  Monte  Somma,  whence  its  name.  It  commonly  occurs  as  a  contact 
mineral  from  the  alteration  of  impure  limestones,  then  usually  associated  with  lime  garnet 
(grossularite),  phlogopite,  diopside,  wollastonite;  also  epidote;  also  in  serpentine,  chlorite 
schist,  gneiss  and  related  rocks. 

Prominent  localities  are  Vesuvius;  the  Albani  Mts.;  in  Switzerland  at  Zermatt,  etc.; 
the  Mussa  Alp  in  the  Ala  valley,  in  Piedmont,  Italy;  Mt.  Monzoni  in  the  Fassatal,  Austria; 
at  Orawitza  and  Dognaczka,  Hungary;  Haslau  near  Eger  in  Bohemia  (egeran);  near 
Jordansmiihl,  Silesia;  on  the  Vilui  river,  near  Lake  Baikal,  Siberia  (sometimes  called  wiluite 
or  viluite,  like  the  grossular  garnet  from  the  same  region);  Achmatovsk,  Ural  Mts.;  in 
Norway;  at  Arendal,  " colophonite" ;  at  Egg,  near  Christiansand;  at  Morelos,  Mexico. 

In  North  America,  in  Me.  at  Phippsburg  and  Rumford;  at  Sandford.  In  N.  H.,  at 
Warren  with  cinnamon-stone.  In  N.  Y.,  near  Amity.  In  N.  J.,  at  Newton.  In  Lewis 
and  Clark  Co.,  Mon.  In  Cal.  near  San  Carlos  in  Inyo  Co.;  at  Crestmore,  Riverside  Co. 
In  Canada,  at  Calumet  Falls,  Litchfield,  Pontiac  Co.;  at  Grenville  in  calcite;  at  Templeton, 
Ottawa  Co.,  Quebec.  A  lavender-colored  variety,  known  as  mangan-vesuvianite  comes 
from  near  Black  Lake,  Quebec. 

Californite  is  a  closely  compact  variety  of  an  olive-green  to  a  grass-green  color  from 
Siskiyou,  Fresno  and  Tulare  Cos.,  Cal. 


Zircon 
Thorite 


Zircon  Group. 

ZrSi04 
ThSiO4 


.     Tetragonal 


c  =  Q'6404 
c  =  0-6402 


This  group  includes  the  orthosilicates  of  zirconium  and  thorium,  both 
alike  in  tetragonal  crystallization,  axial  ratio  and  crystalline  habit. 

.These  species  are  sometimes  regarded  as  oxides  and  then  included  in  the  RUTILE  GROUP 
(p.  425),  to  which  they  approximate  closely  in  form.  A  similar  form  belongs  also  to  the 
tantalate,  Tapiolite,  and  to  the  phosphate,  Xenotime;  further,  compound  groups  consisting 
of  crystals  of  Xenotime  and  Zircon  in  parallel  position  are  not  uncommon  (Fig.  462,  p.  173) . 


ZIRCON. 

Tetragonal.     Axis  c  =  0-64037. 
ee',   101  A  Oil  =  44°  50' 
ee",  101  A  101  =  65°  16'. 
pp',  111  A  111  =  56°  40£'. 
uu'  331  A  331 


871 


83°  9' 
872 


mp  110  A  111  =  47°  50'. 
mu,  110  A  331  =  20°  12±' 
xx™,  311  A  311  =  32°  57'. 
ax,  100  A  311  =  31°  43'. 

873 


Frequently  minerals  which,  like  vesuvianite,  melilite  and  zoisite,  are  doubly  refract- 
ing but  of  extremely  low  birefringence  and  possibly  (where  they  are  positive  for  one  color 


SILICATES 


521 


Twins:  tw.  pi.  e  (101),  geniculated  twins  like  rutile  (Fig.  412,  p.  166). 
Commonly  in  square  prisms,  sometimes  pyramidal.  Also  in  irregular  forms 
and  grains. 

875  876  877 

c 

'Pi 


Colorado 

Cleavage:  m  (110)  imperfect;  p  (111)  less  distinct.  Fracture  conchoidal. 
Brittle.  H.  =  7*5.  G.  =  4-68-470  most  common,  but  varying  widely  to  4 '2 
and  4 '86.  Luster  adamantine.  Colorless,  pale  yellowish,  grayish,  yellowish 
green,  brownish  yellow,  reddish  brown.  Streak  uncolored.  Transparent  to 
subtranslucent  and  opaque.  Optically +.  Birefringence  high,  co  =  1-9239, 
e  =  1*9682,  Ceylon.  Sometimes  abnormally  biaxial. 

Hyacinth  is  the  orange,  reddish  and  brownish  transparent  kind  used  for  gems.  Jargon 
is  a  name  given  to  the  colorless  jor  smoky  zircons  of  Ceylon,  in  allusion  to  the  fact  that 
while  resembling  the  diamond  in  luster,  they  are  comparatively  worthless;  thence  came 
the  name  zircon. 


zirconia  67-2  =  100.     A 


Comp.  —  ZrSi04  or  Zr02.SiO2  =  Silica  32-8, 
little  iron  (Fe2O3)  is  usually  present. 

Pyr.,  etc.  —  Infusible;  the  colorless  varieties  are  unaltered,  the  red  become  colorless, 
while  dark-colored  varieties  are  made  white;  some  varieties  glow  and  increase  in  density 
by  ignition.  Not  perceptibly  acted  upon  by  salt  of  phosphorus.  In  powder  decomposed 
when  fused  with  soda  on  the  platinum  wire,  and  if  the  product  is  dissolved  in  dilute  hydro- 
chloric acid  it  gives  the  orange  color  characteristic  of  zirconia  when  tested  with  turmeric 
paper.  Not  acted  upon  by  acids  except  in  fine  powder  with  concentrated  sulphuric  acid. 
Decomposed  by  fusion  with  alkaline  carbonates  and  bisulphates. 

Diff.  —  Characterized  by  the  prevailing  square  pyramid  or  square  prism;  also  by  its 
adamantine  luster,  hardness,  high  specific  gravity,  and  infusibility;  the  diamond  is  optically 
isotropic. 

Micro.  —  Recognized  in  thin  sections  by  its  very  high  relief;  very  high  interference- 
colors,  which  approach  white  of  the  higher  order  except  in  very  thin  sections;  positive 
uniaxial  character.  It  is  distinguished  from  cassiterite  and  rutile  only  by  its  lack  of  color, 
and  from  the  1-itter  also  in  many  cases  by  method  of  occurrence. 

Artif .  —  Zircon  has  been  prepared  artificially  by  heating  zirconium  oxide  with  quartz 
in  gaseous  silicon  fluoride. 

Obs.  —  A  common  accessory  constituent  of  igneous  rocks,  especially  those  of  the  more 
acid  feldspathic  groups  and  particularly  the  kinds  derived  from  magmas  containing  much 
soda,  as  granite,  syenite,  diorite,  etc.  It  is  one  of  the  earliest  minerals  to  crystallize  from  a 
cooling  magma.  Is  generally  present  in  minute  crystals,  but  in  pegmatitic  facies  often  in 
large  and  well-formed  crystals.  Occurs  more  rarely  elsewhere,  as  in  granular  limestone, 
chloritic  and  other  schists;  gneiss;  sometimes  in  iron-ore  beds.  Crystals  are  common  in 
most  auriferous  sands.  Sometimes  found  in  volcanic  rocks,  probably  in  part  as  inclusions 
derived  from  older  rocks. 

Zircon  in  distinct  crystals  is  so  common  in  the  pegmatitic  forms  of  the  nephelite-syenite 

but  negative  for  another),  do  not  show  a  gray  color  between  crossed  nicols  but  a  curious 
blue,  at  times  an  intense  Berlin  blue,  which  is  quite  distinct  from  the  other  blues  of  the  color 
scale  and  is  known  as  the  "ultra  blue." 


522 


DESCRIPTIVE   MINERALOGY 


and  augite-syenite  of  southern  Norway  (with  segirite,  etc.)  that  this  rock  there  and  else- 
where has  sometimes  been  called  a  "  zircon-syenite." 

Found  in  alluvial  sands  in  Ceylon;  in  the  gold  regions  of  the  Ural  Mts.;  in  Norway,  at 
Laurvik,  at  Arendal,  in  the  iron  mines,  at  Fredriksyarn,  and  in  veins  in  the  augite-syenite 
of  the  Langesund  fiord;  Pfitschtal,  Tyrol,  Austria;  in  Germany  in  lava  at  Niedermendig  in 
the  Eifel,  red  crystals;  from  Madagascar;  from  Minas  Geraes,  Brazil. 

In  North  America,  in  Me.,  at  Litchfield;  in  N.  Y.,  in  Moriah,  Essex  Co.,  cinnamon- 
red;  near  the  outlet  of  Two  Ponds,  Orange  Co.,  with  scapolite,  pyroxene  and  titantite;  at 
Warwick,  chocolate-brown,  near  Amity;  in  St.  Lawrence  Co..  in  the  town  of  Hammond; 
at  Rossie,  Fine,  Pitcairn.  In  Pa.,  near  Reading.  In  N.  C.,  abundant  in  the  gold  sands  of 
Burke,  McDowell,  Polk,  Rutherford,  Henderson,  and  other  counties.  In  Col.,  with  astro- 
phyllite,  etc.,  in  the  Pike's  Peak  region  in  El  Paso  Co.;  at  Cheyenne  Mt.  In  CaL,  in  auri 
ferous  gravels. 

In  Canada,  at  Grenville,  Argenteuil  Co.;  in  Templeton  and  adjoining  townships  in 
Ottawa  Co.,  Quebec;  in  Renfrew  Co.,  sometimes  very  large;  in  North  Burgess,  Lanark  Co. 

Use.  —  Zircon  in  its  transparent  varieties  serves  frequently  as  a  gem  stone;  also  as  a 
source  of  zirconium  oxide  used  in  the  manufacture  of  the  incandescent  gas  mantles. 

Malacon  is  an  altered  zircon.  Cyrtolite  is  related  but  contains  uranium,  yttrium  and 
other  rare  elements. 

Naegite  is  apparently  zircon  with  yttrium,  niobium-tantalum,  thorium,  and  uranium 
oxides.  Occurs  in  spheroidal  aggregates  near  Takoyama,  Mino,  Japan.  Color  green,  gray 
brown.  H.  =  7'5.  G.  =  4'1. 

Thorite.  Thorium  silicate,  ThSiO4,  like  zircon  in  form;  usually  hydrated,  black  in 
color,  and  then  with  G.  =  4 '5-5;  also  orange-yellow  and- with  G.  =  5 '19-5 -40  (orangite). 
From  the  Brevik  region  and  Arendal,  Norway. 

Auerlite.  Like  zircon  in  form;  supposed  to  be  a  silico-phosphate  of  thorium.  Hender- 
son Co.,  N.  C. 


RR2(Si04)2  or  (RO)RSi04 


Danburite-Topaz  Group.     Orthorhombic. 

Danburite  CaB2(Si04)2  a  :  b 

Topaz  [Al(F,OH)2]AlSiO4  a  :  b 

Andalusite  (A10)AlSiO4  J  b  :  a  :  f  c  =  0'5070 

or     a  :  b  :  c  =  0'9861 


c  =  G'5444 
c  =  0-5285 


0-4807 
0-4770 
0-4749 
0-7025 


Sillimanite 
Cyanite 

a  :  b  :  c 


Al2SiO5 
Al2Si05     - 
0-8994  :  1  :  07090; 


Orthorhombic 
Triclinic 
a  =  90°  5J',  ft  =  101°  2' 


a  :b  =  0-970  :  1 


7  =  105°  44J'. 


DANBURITE. 

Orthorhombic. 
878 


in 


28-4 


Axes  a  :  b  :  c  =_0'5444  :  1  :  0-4807. 

mm'",  110  A  110  =  57°  8'.        dd',   101  A  101  =    82°  53' 
II',        120  A  120  =  85°  8'.        ww',  041  A  041  =  125°    3'.' 

Habit  prismatic,  resembling  topaz.     Also  in  indistinct 
embedded  crystals,  and  disseminated  masses. 

Cleavage:  c  (001)  very  indistinct.  Fracture  uneven 
to  subconchoidal.  Brittle.  H.  =  7-7-25.  G.  =  2*97- 
3-02.  Color  pale  wine-yellow  to  colorless,  yellowish  white, 
dark  wine-yellow,  yellowish  brown.  Luster  vitreous  to 
greasy,  on  crystal  surfaces  brilliant.  Transparent  to 
translucent.  Streak  white.  .  Optically  -  2V  =  88° 
a  =  1-632.  ft  =  1-634.  7  =  1-636. 

i  or  CaO.B2O3.2SiO2  =  Silica  48'8,  boron  trioxide 


SILICATES 


523 


Pyr.,  etc.  —  B.B.  fuses  at  3'5  to  a  colorless  glass,  and  imparts  a  green  color  to  the  O.  F. 
(boron).  Not  decomposed  by  hydrochloric  acid,  but  sufficiently  attacked  for  the  solution 
to  give  the  reaction  of  boric  acid  with  turmeric  paper.  When  previously  ignited  gelatinizes 
with  hydrochloric  acid.  Phosphoresces  on  heating,  giving  a  reddish  light. 

Obs.  —  Occurs  at  Danbury,  Conn.,  with  microcline  and  oligoclase  in  dolomite.  At 
Russell,  N.  Y.,  in  fine  crystals.  On  the  Piz  Valatscha,  the  northern  spur  of  Mt.  Skopi 
south  of  Dissentis  in  eastern  Switzerland,  in  slender  prismatic  crystals  and  elsewhere  in 
Switzerland.  In  crystals  from  Takachio,  Hinga,  and  from  Obira,  Bungo,  Japan.  From  Mt. 
Bity  and  Maharitra,  Madagascar. 

BARSOWITE.  This  doubtful  species,  occurring  with  blue  corundum  in  the  Ural  Mts.,  is 
by  some  authors  classed  with  danburite;  composition  CaAl2Si2Q8  like  anorthite. 

TOPAZ. 

Orthorhombic.     Axes  a  :  b  :  c  =  0-52854  :  1  :  047698. 

879  880  881  882 


^ 

I 

p 

in 

T 

m 

P> 

I 

1 

Brazil 

mm'",  110  A  1TO  =    55°  43'. 

II,         120  A  120  =    89°  49'. 

dd',       201  A  201  =  122°    1'. 

XX',    043  A  043  =    64°  55'. 

//',        021  A  021  =    87°  18'. 


Japan 


Durango 


yy',  041  A  041  =  124°  41'. 

ci,     001  A  223  =  34°  14'. 

^cu,    001  A  111  =  45°  35'. 

co,    001  A  221  •=  63°  54'. 


Ural 

uu',     111  A  Til  =    78°    20'. 

uu'",  111  A  111  =    39°      0'. 

oo',     221  A  221  =  105°      7'. 

oo'"    221  A  221  =    49°  37*'. 


883 


884 


Crystals  commonly  prismatic,  m  (110) 
predominating;  or  I  (120)  and  the  form 
then  a  nearly  square  prism  resembling 
andalusite.  Faces  in  the  prismatic  zone 
often  vertically  striated,  and  often  show- 
ing vicinal  planes.  Also  firm  columnar; 
granular,  coarse  or  fine. 

Cleavage:  c  (001)  highly  perfect. 
Fracture  subconchoidal  to  uneven. 
Brittle.  H.  =  8.  G.  =  3 -4-3 -6.  Luster 
vitreous.  Color  straw-yellow,  wine- 
yellow,  white,  grayish,  greenish,  bluish, 
reddish.  Streak  uncolored.  Trans- 
parent to  subtranslucent.  Optically  +.  Ax.  pi.  ||  6  (010).  Bx  J_  c  (001). 
Axial  angles  variable.  2V  =  49°  to  66°.  Refractive  indices,  Brazil: 

For  D        a  =  1-62936        ft  =  1  "63077         7  =  1 '63747        .'.     2V  =  49°  31' 

Var.  —  Ordinary.  In  prismatic  crystals  usually  colorless  or  pale  yellow,  less  often 
pale  blue,  pink,  etc.  The  yellow  of  the  Brazilian  crystals  is  changed  by  heating  to  a  pale 
rose-pink.  Often  contains  inclusions  of  liquid  CCV 

Physalite,  or  pyrophysalite,  is  a  coarse  nearly  opaque  variety,  from  Finbo,  Sweden; 
intumesces  when  heated,  hence  its  name  from  <£waXis,  bubble,  and  irvp,  fire.  Pycnite  has 
a  columnar,  very  compact  structure.  Rose  made  out  that  'the  cleavage  was  the  same,  and 


Ural 


Japan 


524 


DESCRIPTIVE    MINERALOGY 


the  form  probably  the  same;   and  Des  Cloizeaux  showed  that  the  optical  characters  were 
those  of  topaz. 

Comp.  —  (AlF)2SiO4;  usually  containing  hydroxyl  and  then  [A1(F,OH)]2 
SiO4  or  as  given  on  p.  522.  The  former  requires  Silica  32 '6,  alumina  55 '4, 
fluorine  207  =  1087,  deduct  (O  =  2F)  87  =  100. 

Pyr.,  etc.  —  B.B.  infusible.  Fused  in  the  closed  tube,  with  potassium  bisulphate  gives 
the  characteristic  fluorine  reactions.  With  cobalt  solution  the  pulverized  mineral  gives  a 
fine  blue  on  heating.  Only  partially  attacked  by  sulphuric  acid.  A  variety  of  topaz  from 
Brazil,  when  heated,  assumes  a  pink  or  red  hue,  resembling  the  Balas  ruby. 

Diff.  —  Characterized  by  its  prismatic  crystals  with  angles  of  56°  (124°)  or  87°  (93°); 
also  by  the  perfect  basal  cleavage;  hardness;  infusibility;  yields  fluorine  B.B. 

Artif.  —  Topaz  has  been  made  artificially  by  heating  a  mixture  of  silica  and  aluminium 
fluoride  and  then  igniting  this  mixture  in  silicon  fluoride  gas. 

Obs.  —  Topaz  occurs  especially  in  the  highly  acid  igneous  rocks  of  the  granite  family, 
as  granite  and  rhyolite,  in  veins  and  cavities,  where  it  appears  to  be  the  result  of  fumarole 
action  after  the  crystallization  of  the  magma;  sometimes  also  in  the  surrounding  schists, 
gneisses,  etc.,  as  a  result  of  such  action.  In  these  occurrences  often  accompanied  by  fluor- 
tie,  cassiterite,  tourmaline.  Frequently  occurs  in  tin-bearing  pegmatites.  Topaz  alters 
aesily  into  a  compact  mass  of  muscovite. 

Fine  topaz  comes  from  Russia  from  the  Ural  Mts.,  from  Alabashka,  in  the  region  of 
Ekaterinburg;  from  Miask  in  the  Ilmen  Mts.;  also  the  gold-washings  on  the  River  Sanarka 
in  Govt.  Orenburg;  in  Nerchinsk,  beyond  Lake  Baikal,  in  the  Adun-Chalon  Mts.,  etc.;  in 
the  province  of  Minas  Geraes,  Brazil,  at  Ouro  Preto  and  Villa  Rica,  of  deep  yellow  color;  in 
Germany  at  the  tin  mines  of  Zinnwald  and  Ehrenfriedersdorf,  and  smaller  crystals  at 
Schneckenstein  and  Altenberg;  sky-blue  crystals  in  Cairngorm,  Aberdeenshire,  Scotland; 
the  Mourne  mountains,  Ireland;  on  the  island  of  Elba.  Physalite  occurs  in  crystals  of 
great  size,  at  Fossum,  Norway;  Finbo,  Sweden.  Pycnite  is  from  the  tin  mine  of  Altenberg 
in  Saxony;  also  of  Schlackenwald,  Zinnwald,  etc.  Fine  crystals  occur  at  Durango,  Mexico, 
with  tin  ore;  at  San  Luis  Potosi  in  rhyolite.  Mt.  Bischoff,  Tasmania,  with  tin  ores; 
similarly  in  New  South  Wales.  In  Japan  in  pegmatite  from  Otani-yama,  Province  of  Omi, 
near  Kioto. 

In  the  United  States,  in  Me.,  at  Stoneham,  in  albitic  granite.  In  Conn.,  at  Trumbull, 
with  fluorite;  at  Willimantic.  In  N.  C.,  at  Crowder's  Mountain.  In  Col.,  in  fine  crystals 
colorless  or  pale  blue  from  the  Pike's  Peak  region;  at  Nathrop,  Chaff ee  Co.,  in  wine-colored 
crystals  with  spessartite  in  lithophyses  in  rhyolite;  similarly  in  the  rhyolite  of  Chalk  Mt. 
In  Texas  in  fine  crystals  at  Streeter.  In  Utah,  in  fine  transparent  colorless  crystals  with 
quartz  and  sanidine  in  the  rhyolite  of  the  Thomas  Range,  40  miles  north  of  Sevier  Lake. 
In  Col.  in  Ramona  Co. 

The  name  topaz  is  from  ro-n-a^os,  an  island  in  the  Red  Sea,  as  stated  by  Pliny.  But 
the  topaz  of  Pliny  was  not  the  true  topaz,  as  it  " yielded  to  the  file."  Topaz  was  included 
by  Pliny  and  earlier  writers,  as  well  as  by  many  later,  under  the  name  chrysolite. 

Use.  —  As  a  gem  stone. 

ANDALUSITE. 


Orthorhombic.     Axes  a  :  b  :  c  =  0-9861  :  1  :  070245. 


885 


886 


mm'",  110  A  110 

88'     Oil  A  Oil 


89°  12'. 
70°  10'. 


Usually  in  coarse  prismatic  forms,  the 
prisms  nearly  square  in  form.  Massive, 
imperfectly  columnar;  sometimes  radiated 
and  granular. 

Cleavage:  m  (110)  distinct,  sometimes 
perfect  (Brazil);  a  (100)  less  perfect; 
b  (010)  in  traces.  Fracture  uneven,  sub- 
conchoidal.  Brittle.  H.  =  7-5.  G  =  3'16 
-3 '20.  Luster  vitreous;  often  weak.  Color 
whitish,  rose-red,  flesh-red,  violet,  pearl-gray,  reddish  brown,  olive-green. 


SILICATES 


525 


887 


Streak  uncolored.     Transparent   to  opaque,  usually  sub  translucent.      Pleo- 
chroism  strong  in  some  colored  varieties.      Absorption  strong,  X  >  Y  >  Z. 
Sections  normal  to  an  optic  axis  are  idiophanous  or  show  the  polarization- 
brushes  distinctly  (p.  288).     Optically  — .     Ax.  pi. 
||  b  (010).     Bx  J_  c  (001).     2V  =  85°.     a  =  T632. 
0  =  1*638.     7  =  1-643. 

Var.  —  Chiastolite,  or  Made  is  a  variety  in  stout  crystals 
having  the  axis  and  angles  of  a  different  color  from  the  rest, 
owing  to  a  regular  arrangement  of  carbonaceous  impurities 
through  the  interior,  and  hence  exhibiting  a  colored  cross,  or 
a  tesselated  appearance  in  a  transverse  section.  Fig.  888 
shows  sections  of  a  crystal.  Viridine  is  a  green  variety  con- 
taining some  iron  and  manganese  from  near  Darmstadt,  Ger- 
many. 

Comp.  —  Al2SiO5  =  (A1O) AlSiO4  or  Al2O3.SiO2  = 
Silica  36-8,  alumina  63*2  =  100.  Manganese  is 
sometimes  present,  as  in  manganandalusite. 


100 


— *z 


Pyr.,  etc.  —  B.B.  infusible.     With  cobalt  solution  gives  a 


blue   color  after  ignition.     Not  decomposed  by  acids.     De- 
composed on  fusion  with  caustic  alkalies  and  alkaline  carbonates. 

Diff.  —  Characterized  by  the  nearly  square  prism,  plepchroism,  hardness,  infusibility; 
reaction  for  alumina  B.B. 

Micro.  —  Distinguished  in  thin  sections  by  its  high  relief;  low  interference-colors, 
which  are  only  slightly  above  those  of  quartz;  negative  biaxial  character;  negative  exten- 
sion of  the  crystals  (diff .  from  sillimanite) ;  rather  distinct  prismatic  cleavage  and  the  con- 
stant parallel  extinction  .(diff.  from  pyroxenes,  which  have  also  greater  birefringence);  also 
by  its  characteristic  arrangement  of  impurities  when  these  are  present  (Fig.  888).  The 
pleochroism,  which  is  often  lacking,  is,  when  present,  strong  and  characteristic. 

888 


Obs.  —  Most  common  in  argillaceous  schist,  or  other  scnists  imperfectly  crystalline; 
also  in  gneiss,  mica  schist  and  related  rocks;  rarely  in  connection  with  serpentine.  The 
variety  chiastolite  is  commonly  a  contact  mineral  in  clay-slates,  e.g.,  adjoining  granitic  dikes. 
Sometimes  associated  with  sillimanite  with  parallel  axes. 

Found  in  Spain,  in  Andalusia;  in  Austria  in  the  Tyrol,  Lisens  Alp;  in  Saxony,  at  Brauns- 
dorf ;  Bavaria,  at  Wunsiedel,  etc.  In  Brazil,  province  of  Minas  Geraes,  in  fine  crystals  and 
as  rolled  pebbles.  Remarkable  crystals  of  chiastolite  from  Mt.  Howden,  near  Bimbowrie, 
South  Australia. 

In  North  America,  in  Me.,  at  Standish.  N.  H.,  White  Mtn.  Notch;  Mass.,  at  West- 
ford;  Lancaster,  both  varieties;  Sterling,  chiastolite.  Conn.,  at  Litchfield  and  Washing- 
ton. Pa.,  in  Delaware  Co.,  near  Leiperville,  large  crystals;  Upper  Providence. 

Named  from  Andalusia,  the  first  locality  noted.  The  name  made  is  from  the  Latin 
macula,  a  spot.  Chiastolite  is  from  X«*O"TOS,  arranged  diagonally,  and  hence  from  chi, 
the  Greek  name  for  the  letter  X. 

Use.  —  When  clear  and  transparent  may  serve  as  a  gem  stone. 

Guarinite.  2(K,Na)2O.8CaO.5(Al,Fe,Ce)2O3.10SiO2.  Orthorhombic.  In  minute  thin 
tables,  flattened  ||  b  (010),  nearly  tetragonal  in  form.  H.  =  6'5.  G.  =  2 -9-3-3.  Color 
sulphur-yellow,  honey-yellow.  Pleochroic,  canary-yellow  to  colorless.  Found  in  a  grayish 
trachyte  on  Mte.  Somma,  Vesuvius.  Axial  ratio  and  optical  properties  agree  closely  with 
those  of  danburite. 


526  DESCRIPTIVE   MINERALOGY 

SILLIMANITE.     Fibrolite. 

Orthorhombic.  Axes  a  :  b  =  0'970  :  1.  mm'"  110  A  110  =  88°  15', 
hh'  230  A  230  =  69°.  Prismatic  faces  striated  and  rounded.  Commonly  in 
long  slender  crystals  not  distinctly  terminated;  often  in  close  parallel  groups, 
passing  into  fibrous  and  columnar  massive  forms;  sometimes  radiating. 

Cleavage:  b  (010)  very  perfect.  Fracture  uneven.  H.  =  6-7.  G.  = 
3-23-3-24.  Luster  vitreous,  approaching  subadamantine.  Color  hair-brown, 
grayish  brown,  grayish  white,  grayish  green,  pale  olive-green.  Streak  un- 
colored.  Transparent  to  translucent.  Pleochroism  sometimes  distinct. 
Optically  +.  Double  refraction  strong.  Ax.  pi.  ||  b  (010).  Bx  J_  c  (001). 
Dispersion  p  >  v.  Axial  angle  and  indices  variable.  2V  =  20°  (approx.). 
a  =  1-638.  0  =  1-642.  7  =  1*653. 

Comp.  —  Al2SiO5  =  (A10)AlSi04,  like  andalusite.  Silica  36'8,  alumina 
63'2  =  100. 

Sillimanite  is  the  most  stable  of  the  three  aluminium  silicates.  Both  andalusite  and 
cyanite  are  converted  into  sillimanite  when  strongly  heated. 

Pyr.  —  Same  as  andalusite. 

Diff.  —  Characterized  by  its  fibrous  or  columnar  form;  perfect  cleavage;  infusibility; 
reaction  for  alumina. 

Micro.  —  In  thin  sections  recognized  by  its  form,  usually  with  transverse  fractures; 
parallel  extinction;  high  interference-colors. 

Artif.  —  Sillimanite  has  been  made,  artificially  by  fusing  its  oxides  together.  Both 
andalusite  and  cyanite  are  converted  into  sillimanite  when  strongly  heated. 

Obs.  —  Often  present  in  the  quartz  of  gneisses  and  sometimes  granites  in  very  slender, 
minute  prisms  commonly  aggregated  together  and  sometimes  intergrown  with  andalusite; 
iolite  is  also  a  common  associate;  rarely  as  a  contact  mineral;  often  occurs  with  corundum. 

Observed  in  many  localities,  thus  near  Moldau  in  Bohemia;  at  Fassa  in  Tyrol,  Austria 
(bucholziie) ;  in  the  Carnatic,  India,  with  corundum  (fibrolite} ;  at  Bodenmais,  Bavaria; 
Freiberg,  Saxony;  in  France,  near  Pontgibaud  and  other  points  in  Auvergne;  forms  rolled 
masses  in  the  diamantiferous  sands  of  Minas  Geraes,  Brazil. 

In  the  United  States,  in  Mass.,  at  Worcester.  In  Conn.;  near  Norwich,  with  zircon, 
monazite  and  corundum;  at  Willimantic.  In  N.  Y.,  at  Yorktown,  Westchester  Co.;  in 
Monroe,  Orange  Co.,  (monrolite).  In  Pa.,  at  Chester  on  the  Delaware,  near  Queensbury 
forge;  in  Delaware  Co.;  Del.,  at  Brandy  wine  Springs.  With  corundum  in  N.  C. 

Named  fibrolite  from  the  fibrous  massive  variety;  sillimanite.  after  Prof.  Benjamin 
Silliman  of  New  Haven  (1779-1864). 

Bamlite,  xenolite,  worthite  probably  belong  to  sillimanite;  the  last  is  altered. 

CYANITE.    Kyanite.     Disthene. 

Triclinic.  Axes  a  :  b  :  c  =  0-8994  :  1  :  07090;  a  =  90°  5|',  0  =  101°  2', 
7  =  105°  44i'.  ac,  100  A  001  =  78°  30';  be,  010  A  001  =  86°  45'. 

889  Usually  in  long  bladed  crystals,  rarely  terminated.    Also 

>, ^    coarsely  bladed  columnar  to  subfibrous. 

Cleavage :  a  (100)  very  perfect ;  b  (010)  less  perfect ;  also 
parting  1 1  c  (001).  H.  =  5-7 -25;  the  least,  4-5,  on  a  (100) 
|  caxis;  6-7  on  a  (100)  ||  edge  a  (100)/ c  (001);  7  on 
b  (010).  G.  =  3-56-3-67.  Luster  vitreous  to  pearly. 
Color  blue,  white;  blue  along  the  center  of  the  blades  or 
crystals  with  white  margins;  also  gray,  green,  black. 
Streak  uncolored.  Translucent  to  transparent.  Pleo- 
chroism distinct  in  colored  varieties.  Optically  — . 
Ax.  pi.  nearly  1  a  (100)  and  inclined  to  edge  a/b  on  a  about  30°,  and 
about  7i°  on  6  (010),  cf.  Fig.  889.  2V  =  82°.  a  =  1-717.  B  =  1722. 
7  =  1'729. 


SILICATES  527 

Comp.  —  Empirical  formula  Al2SiO6  or  Al203.Si02,  like  andalusite  and 
sillimanite.  Perhaps  a  basic  metasilicate,  (A10)2Si03. 

Pyr.,  etc.  Same  as  for  andalusite.  At  a  high  temperature  cyanite  assumes  the  physical 
characters  of  sillimanite. 

Diff.  —  Characterized  by  the  bladed  form;  common  blue  color;  varying  hardness;  in- 
fusibility;  reaction -for  alumina. 

Obs.  —  Occurs  principally  in  gneiss  and  mica  schist  (both  the  ordinary  variety  with 
muscoyite  and  also  that  with  paragonite)  often  accompanied  by  garnet  and  sometimes  by 
staurolite;  also  in  eclogite  schist.  It  is  often  associated  with  corundum. 

Found  in  transparent  crystals  at  Monte  Campione  in  the  St.  Gothard  region  in  Switzer- 
land in  paragonite  schist;  on  Mt.  Greiner,  Zillertal,  and  in  the  Pfitschtal  (rhcetizite,  white) 
in  Tyrol,  Austria;  in  eclogite  of  the  Saualpe,  Carinthia;  Horrsjoberg  in  Wermland,  Sweden; 
Villa  Rica,  Brazil,  etc. 

In  Mass.,  at  Chesterfield,  with  garnet  in  mica  schist.  In  Conn.,  at  Litchfield,  Washing- 
ton, Canton,  Barkhamstead,  etc.  In  Ver.,  at  Thetford.  In  Pa.,  in  Chester  Co.  and  in 
Delaware  Co.  In  Va.,  Buckingham  Co.  In  N.  C.,  with  rutile,  lazulite,  etc.,  at  Crowder's 
Mt.,  Gaston  Co.;  in  Gaston  and  Rutherford  counties  associated  with  corundum,  damourite; 
beautiful  clear  green  in  Yancey  Co.  Named  from  KVCXVOS,  blue. 

Datolite  Group.     Monoclinic 

ii  in  ii  in 

Basic  Orthosilicates.    HRRSiO5  or  R3R2(SiO5)2.    Oxygen  ratio  for  R  :  Si  =  3  : 2. 
ii  in 

R  =  Ca,Be,Fe,  chiefly;  R  =  Boron,  the  yttrium  (and  cerium)  metals,  etc. 


a 


Datolite  0'6345 


HCaBSiO5  or  Ca(BOH)SiO 


1 


1-2657      89°  51 


1-2824  89°  21' 

4c  ft 

1-3330  79°  44' 

T3215  89°  26*' 


Homilite  0'6249 

CaaFeBsSisOig  or  Ca2Fe(BO)2(Si04)2 

2a 

Euclase  0'6474     1 

HBeAlSi05  or  Be(A10H)Si04  a 

Gadolinite  0'6273     1 

Be2FeY2Si2Oi0  or  Be2Fe(YO)2(Si04)2 

The  species  of  the  DATOLITE  GROUP  are  usually  regarded  as  basic  ortho- 
silicates,  the  formulas  being  taken  in  the  second  form  given  above.  They  all 
crystallize  in  the  monoclinic  system,  and  all  but  Euclase  conform  closely  in 
axial  ratio;  with  the  latter  there  is  also  a  distinct  morphological  relationship. 

DATOLITE. 

Monoclinic.     Axes  a  :  b  :  c  =  0'6345  :  1  :  1-2657;  ft  =  89°  51^'. 

mm'",   110  A  HO  =    64°  47'.  en,    001  A  111  =  66°  57'. 

ac,         100  A  001  =    89°  51'.  cm,  001  A  110  =  89°  53'. 

ax,        100  A  101  =    45°    0'.  ce,     001  A  Tl2  =  49°  49'. 

012  A  012  =    64°  39*'.  nn',  111  A  111  =  59°    4*'. 

Oil  A  Oil  =  103°  23'.  ce',    Tl2  A  U2  =  48°  19*'. 

Crystals  varied  in  habit;  usually  short  prismatic  with  either  m  (110)  or 
wx  (Oil)  predominating;  sometimes  tabular  ||  x  (201);  also  of  other  types, 
and  often  highly  modified  (Figs.  890-893).  Also  botryoidal  and  globular, 
having  a  columnar  structure;  divergent  and  radiating;  sometimes  massive, 
granular  to  compact  and  crypto-crystalline. 

Cleavage    not    observed.      Fracture    conchoidal  to    uneven.      Brittle. 


528 


DESCRIPTIVE   MINERALOGY 


H  =5-5-5.  G.  =  2-9-3-0.  Luster  vitreous,  rarely  subresinous  on  a  surface  of 
fracture.  Color  white;  sometimes  grayish,  pale  green,  yellow,  red,  or  ame- 
thystine, rarely  dirty  olive-green  or  honey-yellow.  Streak  white.  Trans- 

890  891 


Bergen  Hill 

parent  to  translucent;  rarely  opaque  white.     Optically  -.     2V  =  74°.  a 
1-625.    |8  =  1-653.     7  =  1*669. 


893 


Bergen  Hill 


Andreasberg 


Var.  —  1.  Ordinary.  In  glassy  crystals  of  varied  habit,  usually  with  a  greenish  tinge. 
The  angles  in  the  prismatic  and  clinodome  zones  vary  but  little/e.  g.,  110  A  110  =  64°  47, 
while  Oil  A  Oil  =  66°  37',  etc.  2.  Compact  massive.  White  opaque  cream-colored,  pink; 
breaking  with  the  surface  of  porcelain  or  Wedge  wood  ware.  From  the  Lake  Superior  region. 
3.  Betryoidal;  Botryolite.  Radiated  columnar,  having  a  botryoidal  surface,  and  containing 
more  water  than  the  crystals,  but  optically  identical. 

Comp.  —  A  basic  orthosilicate  of  boron  and  calcium;  empirically 
HCaBSiO5  or  H20.2CaO.B2O3.2SiO2;  this  may  be  written  Ca(BOH)Si04  = 
Silica  37-6,  boron  trioxide  21-8,  lime  35-0,  water  5'6  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  gives  off  much  water.  B.B.  fuses  at  2  with  intumescence 
to  a  clear  glass,  coloring  the  flame  bright  green.  Gelatinizes  with  hydrochloric  acid. 

Diff.  —  Characterized  by  its  glassy,  greenish,  complex  crystals;  easy  fusibility  and 
green  flame  B.  B. 

Obs.  —  Datolite  is  found  chiefly  as  a  secondary  mineral  in  veins  and  cavities  in  basic 
eruptive  rocks,  often  associated  with  calcite,  prehnite  and  various  zeolites;  sometimes 
associated  with  danburite;  also  in  gneiss,  diorite,  and  serpentine;  in  metallic  veins;  some- 
times in  beds  of  iron  ore.  Found  in  Scotland,  in  trap,  at  the  Kilpatrick  Hills,  etc.;  in 
a  bed  of  magnetite  at  Arendal  in  Norway  (botryolite) ;  at  Uto  in  Sweden;  at  Andreasberg, 
Germany,  in  diabase  and  in  veins  of  silver  ores;  in  Rhenish  Bavaria  (the  humboMtite) ;  at 
the  Seisser  Alp,  Tyrol,  Austria,  and  at  Theiss,  near  Claussen,  Hungary;  in  geodes in  amygda- 


SILICATES  529 

loid;  in  Italy,  in  granite  at  Baveno  near  Lago  Maggiore,  at  Toggiana  in  Modena,  in  serpen- 
tine, at  Monte  Catini  in  Tuscany. 

In  the  United  States  not  uncommon  with  the  diabase  of  Conn,  and  Mass.  Thus  at 
the  Rocky  Hill  quarry,  Hartford,  Conn.;  at  Middlefield  Falls  and  Roaring  Brook,  Conn.; 
Westfield,  Mass.  In  N.  J.,  at  Bergen  Hill  and  Great  Notch  in  splendid  crystals;  at  Pater- 
son,  Passaic  Co.  Both  crystals  and  the  opaque  compact  variety,  in  the  Lake  Superior  region. 

Named  from  daTeurdai,  to  divide,  alluding  to  the  granular  structure  of  a  massive 
variety. 

Homilite.  (Ca,Fe)3B2Si2Oi0  or  (Ca,Fe)3(BO)2(SiO4)2.  Crystals  often  tabular  || 
c  (001);  angles  near  those  of  datolite.  H.  =  5.  G.  =  3'38.  Color  black,  blackish  brown. 
Index  about  T68.  Found  on  Stoko  and  other  islands,  in  the  Langesund  fiord,  Norway. 

Euclase.  HBeAlSiO5  or  Be(AlOH)SiO4.  In  prismatic  crystals.  Cleavage  ||  6  (010) 
perfect.  H.  =  7*5.  G.  =  3'05-3'10.  Luster  vitreous.  Colorless  to  pale  green  or  blue. 
Optically  +.  0  =  1'655.  From  Brazil,  in  the  province  of  Minas  Geraes;  in  the  aurif- 
erous sands  of  the  Orenburg  district,  southern  Ural  Mts.,  near  the  river  Sanarka;  in  the 
Glossglockner  region  of  the  Austrian  Alps;  from  Epprechtstein,  Fichtelgebirge,  Bavaria. 

Gadolinite.  Be2FeY2Si2Oi0  or  Be2Fe(YO)2(SiO4)2.  Crystals,  often  prismatic,  rough 
and  coarse;  commonly  in  masses.  Cleavage  none.  Fracture  conchoidal  or  splintery. 
Brittle.  H.  =  6'5-7.  G.  =  4'0-4'5;  normally  4'36-4 '47  (anisotropic),  4'24-4 '29  (isotropic 
and  amorphous  from  alteration).  Luster  vitreous  to  greasy.  Color  black,  greenish  black, 
also  brown.  From  near  Falun  and  Ytterby,  Sweden;  Hittero,  Norway;  also  in  Llano  Co., 
Texas,  in  nodular  masses  and  rough  crystals,  sometimes  up  to  40  or  60  pounds  in  weight. 
Crystals  from  Kumak,  East  Greenland. 

The  yttrium  earths  or  "  gadolinite-earths "  (partly  replaced  by  the  oxides  of  cerium, 
lanthanum  and  didymium)  form  a  complex  group  which  contains  considerable  erbium, 
also  several  new  elements  (ytterbium,  scandium,  etc.)  of  more  or  less  definite  character. 

Yttrialite.  A  silicate  of  thorium  and  the  yttrium  metals  chiefly.  Massive;  amor- 
phous. G.  =  4-575.  Color  on  the  fresh  fracture  olive-green,  changing  to  orange-yellow 
on  surface.  Associated  with  the  gadolinite  of  Llano  Co.,  Texas. 

Rowlandite.  An  yttrium  silicate,  occurring  massive  with  gadolinite  of  Llano  Co., 
Texas;  color  drab-green. 

Thalenite.  An  yttrium  silicate.  In  tabular  or  prismatic  monoclinic  crystals.  H. 
=  6*5.  G.  =  4'2.  Color  flesh-red.  /3  =  174.  Found  in  Sweden  at  Osterby  in  Dale- 
carlia  and  at  Askagen  in  Wermland. 

Thortveitite.  A  silicate  of  the  yttrium  metals,  (Sc,Y)2Si2O7.  Orthorhombic.  In  radi- 
ating groups  of  large  tapering  crystals.  Prismatic  cleavage.  H.  =  6-7.  G.  =  3*57. 
Color  grayish  green  to  white  when  altered.  Usually  translucent.  Difficultly  fusible. 
Found  in  pegmatite  in  Iveland  parish,  Satersdalen,  Norway. 

Mackintoshite.  Silicate  of  uranium,  thorium,  cerium,  etc.  Massive.  Color  black. 
Llano  Co.,  Texas. 

Epidote  Group.    Orthorhombic  and  Monoclinic 

ii  in  ii    in         in 

Basic  Orthosilicates,  HR^R3Si3O13  or  R2(ROH)R2(SiO4)3 

ii  ii         in  in     in 

R  =  Ca,Fe;  R  =  Al,Fe,Mn,Ce,  etc. 

a.  Orthorhombic  Section 

a 
Zoisite  Ca2(AlOH)Al2(SiO4)3  0'6196     1     0'3429 


j8.  Monoclinic  Section 
mCa2(AlOH)Al2(SiO4)3 


Piedmontite         Ca2(AlOH)(Al,Mn)2(SiO4)3        1-6100 
Allanite  (Ca,Fe)2(A10H)  (Al,Ce,Fe)2 

(SiO4)3  1*5509 


1-8036  64°  37' 
1-8326  64°  39' 


1-7691    64°  59' 


530  DESCRIPTIVE    MINERALOGY 

The  EPIDOTE  GROUP  includes  the  above  complex  orthosilicates.  The 
monoclinic  species  agree  closely  in  form.  To  them  the  orthprhombic  species 
zoisite  is  also  related  in  angle,  its  prismatic  zone  corresponding  to  the  mono- 
clinic  orthodomes,  etc.  Thus  we  have: 

Zoisite    mm'",  110  A  110  =  63°  34'.         Epidote     cr,      001  A  101  =  63°  42'. 

.    uu',      021  A  021  =  68°  54'.  mm',  110  A  110  =  70°    4',  etc. 

There  seems  to  be,  however,  a  monoclinic  calcium  compound,  having  the  com- 
position of  zoisite,  but  monoclinic  and  strictly  isomorphous  with  ordinary 
epidote;  it  is  called  dinozoisite. 

ZOISITE. 

J    Orthorhombic.     Axes  a  :  b  :  c  =  0'6196  :  1  :  0-34295.  ^ 

mm'",  110  A  HO  =  63°  34'.  jf,     Oil  A  Oil  =  37°  52'. 

dd',       101  A  101  =  57°  56'.  oo'",  111  A  111  =  33°  24'. 

Crystals  prismatic,  deeply  striated  or  furrowed  vertically,  and  seldom 
distinctly  terminated.  Also  massive;  columnar  to  compact. 

Cleavage:  b  (010)  very  perfect.  Fracture  uneven  to  subconchoidal. 
Brittle.  H.  =  6-6 -5.  G.  =  3-25-3-37.  Luster  vitreous;  on  the  cleavage- 
face,  b  (010),  pearly.  Color  grayish  white,  gray,  yellowish  brown,  greenish 
gray,  apple-green;  also  peach-blossom-red  to  rose-red.  Streak  uncolored. 
Transparent  to  subtranslucent. 

i  Pleochroism  strong  in  pink  varieties.  Optically  +.  Ax.  pi.  usually  ||  b 
(010);  also  ||  c  (001).  Bx  _L  a  (100).  Dispersion  strong,  p  <  v;  also  p  >  v. 
Axial  angle  variable  even  in  the  same  crystal.  2V  =  0°-60°.  a  =  1-700. 
0  =  1-703.  7  =  1*706. 

Var.  —  1.  Ordinary.  Colors  gray  to  white  and  brown;  also  green.  Usually  in  indistinct 
prismatic  or  columnar  forms;  also  in  fibrous  aggregates.  G.  =  3'226-3'381.  Unionite  is  a 
very  pure  zoisite.  2.  Rose-red  or  Thulite.  Fragile;  pleochroism  strong.  3.  Compact, 
massive.  Includes  the  essential  part  of  most  of  the  mineral  material  known  as  saussurite 
(e.g.,  in  saussurite-gabbro),  which  has  arisen  from  the  alteration  of  feldspar. 

Comp.  —  HCa2Al3Si3013  or  4CaO.3Al2O3.6SiO2.H2O  =  Silica  397,  alu- 
mina 33-7,  lime  24-6,  water  2*0  =  100.  The  alumina  is  sometimes  replaced 
by  iron,  thus  graduating  toward  epidote,  which  has  the  same  general  for- 
mula. 

Pyr.,  etc.  —  B.B.  swells  up  and  fuses  at  3-3'5  to  a  white  blebby  mass.  Not  decom- 
posed by  acids;  when  previously  ignited  gelatinizes  with  hydrochloric  acid.  Gives  off  water 
when  strongly  ignited. 

Diff.  —  Characterized  by  the  columnar  structure;  fusibility  with  intumescence;  re- 
sembles some  amphibole. 

Micro.  —  Distinguished  in  thin  sections  by  its  high  relief  and  very  low  interference- 
colors;  lack  of  color  and  biaxial  character.  From  epidote  it  is  distinguished  by  its  lack  of 
color  and  low  birefringence;  from  vesuvianite  by  its  color  and  biaxial  character.  Thin 
sections  frequently  show  the  "ultra  blue"  (p.  520)  between  crossed  nicols. 

Obs.  —  Occurs  especially  in  those  crystalline  schists  which  have  been  formed  by  the 
dynamic  metamorphism  of  basic  igneous  rocks  containing  plagioclase  rich  in  lime.  Com- 
monly accompanies  some  one  of  the  amphiboles  (actinolite,  smaragdite,  glaucophane,  etc.); 
thus  in  amphibolite,  glaucophane  schist,  eclogite;  often  associated  with  corundum. 

The  original  zoisite  is  that  of  the  eclogite  of  the  Saualpe  in  Carinthia  (saualpite] .  Other 
localities  are:  Kauris  in  Salzburg;  Sterzing,  etc.,  in  Tyrol,  Austria;  the  Fichtelgebirge  in 
Bavaria;  Marschendorf  in  Moravia;  Saastal  in  Switzerland;  the  island  of  Syra,  one  of  the 
Cyclades,  in  glaucophane  schist.  In  crystals  from  Chester,  Mass..  Thulite  occurs  at 
Kleppan  in  Tellemarken,  Norway,  and  at  Traversella  in  Piedmont,  Italy. 


SILICATES 


531 


EPIDOTE.     Pistacite. 
Monoclinic.     Axes  a  :  b  :  c  —  1-5787  :  1 


mm' 

ca, 

ce, 

cr, 

ar'. 


894 


110  A  110  =  109°  56'. 


001  A  100  = 
001  A  101  = 
001  A  101  = 
100  A  101  = 


64°  37'. 
34°  43'. 
63°  42'. 
51°  41'. 


:  1-8036;  0_=  64°  37'. 

d,  001  A  201  =  89°  26' 
co,  001  A  Oil  =  58°  28' 
en,  001  A  111  =  75°  11' 
an"',  100  A  111  =  69°  2' 
rm"',  111  A  111  =  70°  29' 


897 


Twins:  tw.  pi.  a  (100)  common,  often  as  embedded  tw.  lamellae.  Crystals 
usually  prismatic  ||  the  ortho-axis  b  and  terminated  at  one  .extremity  only; 
passing  into  acicular  forms;  the  faces  in  the  zone  a  (100) /c  (001)  deeply 
striated.  Also  fibrous,  divergent  or  parallel;  granular,  particles  of  various 
sizes,  sometimes  fine  granular,  and  forming  rock-masses. 

Cleavage:  c  (001)  perfect;  a  (100)  imperfect.  Fracture  uneven.  Brittle. 
H.  =  6-7.  G.  =  3-25-3-5.  Luster  vitreous;  on  c  (001)  inclining  to  pearly 
or  resinous.  Color  pistachio-green  or  yellowish  green  to  brownish  green, 
greenish  black,  and  black;  sometimes  clear  red  and  yellow;  also  gray  and 
grayish  white,  rarely  colorless.  Streak  uncolored,  grayish.  Transparent  to 
opaque:  generally  subtranslucent. 

Pleochroism  strong :  vibrations  1 1  Z  green,  Y  brown  and  strongly  absorbed, 
X  yellow.  -  Absorption  usually  Y  >  Z  >  X]  but  sometimes  Z  >  Y  >  X  in 
the  variety  of  epidote  common  in  rocks.  Often 
exhibits  idiophano-us  figures;  best  in  sections 
normal  to  an  optic  axis,  but  often  to  be  observed 
in  natural  Crystals  (Sulzbach),  especially  if  flat- 
tened ||  r(101).  (See  p.  288.)  Optically-. 
Ax.  pi.  ||  b  (010).  Bx.a.r  A  c  axis  =  -  2°  56'. 
Hence  Z  J_  a  (100)  nearly.  Dispersion  inclined, 
strongly  marked;  of  the  axes  feeble,  p  >  v. 
Axial  angle  large,  a  =  1-729.  /3  =  1'754.  7  = 
1-768. 

Var.  —  Epidote  has  ordinarily  a  peculiar  yellowish  green 
(pistachio)  color,  seldom  found  in  other  minerals.  But 
this  color  passes  into  dark  and  light  shades  —  black  on  one 
side  and  brown  on  the  other;  red,  yellow  and  colorless 
varieties  also  occur. 

Var.  1.   Ordinary.     Color  green  of  some  shade,  as  described,  the 
absent,     (a)  In  crystals,     (b)  Fibrous,     (c)  Granular  massive,     (d) 


)istachio  tint  rarely 
>corza  is  epidote  sand 


from  the  gold  washings  in  Transylvania.     The  Arendal,  Norway,  epidote  (Arendalite)  is 
mostly  in  dark  green  crystals;   that  of  Bourg  d'Oisans,  Dauphine,  France,    (Thallite,  Del- 


532  DESCRIPTIVE   MINERALOGY 

phinite  Oisanite)  in  yellowish  green  crystals,  sometimes  transparent.  Puschkinite  includes 
crystals  from  the  auriferous  sands  of  Ekaterinburg,  Ural  Mts.  Achmatite  is  ordinary  epi- 
dote from  Achmatovsk,  Ural  Mts.  A  variety  from  Garda,  Hoste  Island,  Terra  del  Fuego, 
is  colorless  and  resembles  zoisite. 

2.  The  Bucklandite  from  Achmatovsk,  Ural  Mts.,  described  by  Hermann,  is  black  with 
a  tinge  of  green,  and  differs  from  ordinary  epidote  in  having  the  crystals  nearly  symmetrical 
and  not,  like  other  epidote,  lengthened  in  the  direction  of  the  ortho-axis.     G.  =  3  '51. 

3.  Withamite.     Carmine-red  to  straw-yellow,  strongly  pleochroic;    deep  crimson  and 
straw-yellow.     H.  =  6-6'5;    G.  =  3  '137;    in  small  radiated  groups.     From  Glencoe,  in 
Argyleshire,  Scotland.     Sometimes  referred  to  piedmontite,  but  contains  little  MnO. 

4.  Tawmanite  is  a  chromium-bearing  epidote  from  Tawman,  Kachin  Hills,  Upper  Burma. 
Deep  green  color  and  strong  pleochroism,  emerald-green  to  bright  yellow. 

Comp.  —  HCa*(Al,Fe)8Si«Oi8  or  H2O.4CaQ.3(Al>Fe8)2O8.6SiO2,  the  ratio 
of  aluminium  to  iron  varies  commonly  from  6  :  1  to  3  :  2.  Percentage  com- 
position: 

For  Al  :  Fe  =  3  :  1  SiO2  37'87,  A12O3  24'13,  Fe2O3  12'60,  CaO  23'51,  H2O  1'89  =  100 

Clinozoisite  is  an  epidote  without  iron,  having  the  composition  of  zoisite;  fouqueite  is 
probably  the  same  from  an  anorthite-gneiss  in  Ceylon.  Picroepidote  is  supposed  to  contain 
Mg  in  place  of  Ca. 

Pyr.,  etc.  —  In  the  closed  tube  gives  water  on  strong  ignition.  B.B.  fuses  with  in- 
tumescence at  3-3  '5  to  a  dark  brown  or  black  mass  which  is  generally  magnetic.  Reacts 
for  iron  and  sometimes  for  manganese  with  the  fluxes.  Partially  decomposed  by  hydro- 
chloric acid,  but  when  previously  ignited,  gelatinizes  with  acid.  Decomposed  on  fusion 
with  alkaline  carbonates. 

Diff  .  —  Characterized  often  by  its  peculiar  yellowish  green  (pistachio)  color  ;  readily 
fusible  and  yields  a  magnetic  globule  B.B.  Prismatic  forms  often  longitudinally  striated, 
but  they  have  not  the  angle,  cleavage  or  brittleness  of  tremolite;  tourmaline  has  no  distinct 
cleavage,  is  less  fusible  (in  common  forms)  and  usually  shows  its  hexagonal  form. 

Micro.  —  Recognized  in  thin  sections  by  its  high  refraction;  strong  interference-colors 
rising  into  those  of  the  third  order  in  ordinary  sections;  decided  color  and  striking  pleochro- 
ism; also  by  the  fact  that  the  plane  of  the  optic  axes  lies  transversely  to  the  elongation  of 
the  crystals. 

Obs.  —  Epidote  is  commonly  formed  by  the  metamorphism  (both  local  igneous  and  of 
general  dynamic  character)  of  impure  calcareous  sedimentary  rocks  or  igneous  rocks  con- 
taining much  lime.  It  thus  often  occurs  in  gneissic  rocks,  mica  schist,  amphibole  schist, 
serpentine;  so  also  in  quartzites,  sandstones  and  limestones  altered  by  neighboring  igneous 
rocks.  Often  accompanies  beds  of  magnetite  or  hematite  in  such  rocks.  Has  also  been 
found  in  granite  (Maryland),  and  regarded  as  an  original  mineral. 

It  is  often  associated  with  quartz,  feldspar,  actinolite,  axinite,  chlorite,  etc.  It  some- 
times forms  with  quartz  an  epidote  rock,  called  epidosite.  A  similar  rock  exists  at  Mel- 
bourne in  Canada.  A  gneissoid  rock  consisting  of  flesh-colored  orthoclase,  quartz  and 
epidote  from  the  Unaka  Mts.  (N.  C.  and  Tenn.)  has  been  called  unakyte. 

Beautiful  crystallizations  come  from  Bourg  d'Oisans,  Dauphine,  France;  the  Ala  valley 
and  Traversella,  in  Piedmont,  Italy;  Elba;  Zermatt,  Switzerland;  Zillertal  in  Tyrol, 
Austria;  also  in  fine  crystals  from  the  Knappenwand  in  the  Untersulzbachtal,  Pinzgau, 
Austria,  associated  with  asbestus,  adularia,  apatite,  titanite,  scheelite;  further  at  Striegau, 
Silesia;  Zoptau,  Moravia;  Arendal,  Norway;  the  Achmatovsk  mine  near  Zlatoust, 
Ural  Mts. 

In  North  America,  occurs  in  N.  H.,  at  Franconia  and  Warren.  In  Mass.,  at  Hadlyme 
and  Chester  in  crystals  in  gneiss;  at  Athol,  in  syenitic  gneiss,  in  fine  crystals;  Newbury, 
Sr  limestone-  In  Conn.,  at  Haddam,  in  large  splendid  crystals.  In  N.  Y.,  near  Amity; 
Monroe,  Orange  Co.;  Warwick,  pale  yellowish  green,  with  titanite  and  pyroxene.  In 
N.  C.,  at  Hampton's,  Yancey  Co.;  White's  mill,  Gaston  Co.;  Franklin,  Macon  Co.;  in 
crystals  and  crystalline  masses  in  quartz  at  White  Plains,  Alexander  Co.  In  Mich.,  in  the 
Lake  Superior  region,  at  many  of  the  mines.  Crystals  from  Seven  Devils  mining  district, 
Idaho;  from  Riverside,  Cal.;  from  Sulzer,  Prince  of  Wales  Island,  Alaska. 
((  Epidote  was  named  by  Haiiy,  from  the  Greek  e7ri5o<m,  increase,  translated  by  him, 
qui  a  recu  un  accroissement,"  the  base  of  the  prism  (rhomboidal  prism)  having  one  side 
than  the  other.  Pistacite,  from  TriaraKux,  the  pistachio-nut,  refers  to  the  color. 


?ie«d?10n?ite'    Similar  in  an8le  to  ordinary  epidote,  but  contains  5  to  15  p.  c.  Mn2O3. 
-  o'5.     G.  =  3'404.     Color  reddish  brown  and  reddish  black.     Pleochroism  strong. 


SILICATES  533 

Absorption  X  >  Y  >  Z.  Optically  +.  Ax.  pi.  ||  b  (010).  Bxa.r  A  c  axis  =  +  82°  34', 
X  A  caxis  =  -  6°  to  -  3°.  0  =  173.  Occurs  with  manganese  ores  at  St.  Marcel,  Pied- 
mont, Italy.  In  crystalline  schists  on  lie  de  Groix,  France;  in  glaucophane-schist  in  Japan. 
Occasionally  in  quartz  porphyry,  as  in  the  antique  red  porphyry  of  Egypt,  also  that  of 
South  Mountain,  Pa. 

Hancockite.  Belongs  in  Epidote  Group  containing,  PbO,  MnO,  CaO,  SrO,  MgO, 
A12O3,  Fe2O3,  Mn2Os.  Crystals  which  are  very  small  and  lath  shaped  show  characteristic 
epidote  habit  and  closely  related  angles.  Brownish  red.  H.  =  6-7.  G.  =  4'0.  Found 
at  Franklin,  N.  J. 

ALLANITE.     Orthite. 

Monoclinic.  Axes,  p.  529.  In  angle  near  epidote.  Crystals  often  tabu- 
lar 1 1  a  (100) ;  also  long  and  slender  to  acicular  prismatic  by  elongation  1 1  axis  b. 
Also  massive  and  in  embedded  grains. 

Cleavage:  a  (100)  and  c  (001)  in  traces;  also  m  (110)  sometimes  observed. 
Fracture  uneven  or  subconchoidal.  Brittle.  H.  =  5-5-6.  G.  =  3-0-4-2. 
Luster  submetallic,  pitchy  or  resinous.  Color  brown  to  black.  Subtranslu- 
cent  to  opaque.  Pleochroism  strong:  Z  brownish  yellow,  Y  reddish  brown, 
X  greenish  brown.  Optically  — .  Ax.  pi.  ||  b  (010).  Bxa  A  caxis  =  32J° 
approx.  j8  =  1*682.  Birefringence  variable.  Also  isotropic  and  amorphous 
by  alteration  analogous  to  gadolinite. 

Var.-^  Allanite.  The  original  mineral  was  from  East  Greenland,  in  tabular  crystals 
or  plates.  Color  black  or  brownish  black.  G.  =  3'50-3'95.  Bucklandite  is  anhydrous 
allanite  in  small  black  crystals  from  a  magnetite  mine  near  Arendal,  Norway.  Bagration- 
ite  occurs  in  black  crystals  which  are  like  the  bucklandite  of  Achmatovsk  (epidote). 

Orthite  included,  in  its  original  use,  the  slender  or  acicular  prismatic  crystals,  containing 
some  water,  from  Finbo,  near  Falun,  Sweden.  But  these  graduate  into  massive  forms,  and 
some  orthites  are  anhydrous,  or  as  nearly  so  as  most  allanite.  The  name  is  from  6p66s 
straight. 

ii  in  ii 

Comp.  —  Like   epidote   HRR3Si3Oi3  or   H20.4R0.3R203.6Si02  with   R 

m 

=  Ca  and  Fe,  and  R.  =  Al,Fe,  the  cerium  metals  Ce,  Di,  La,  and  in  smaller 
amounts  those  of  the  yttrium  group.  Some  varieties  contain  considerable 
water,  but  probably  by  alteration. 

Pyr.,  etc.  —  Some  varieties  give  much  water  in1  the  closed  tube,  and  all  kinds  yield  a 
small  amount  on  strong  ignition.  B.B.  fuses  easily  and  swells  up  (F.  =  2 '5)  to  a  dark, 
blebby,  magnetic  glass.  With  the  fluxes  reacts  for  iron.  Most  varieties  gelatinize  with 
hydrochloric  acid,  but  if  previously  ignited  are  not  decomposed  by  acid. 

Obs.  —  Occurs  in  albitic  and  common  feldspathic  granite,  gneiss,  syenite,  zircon  syenite, 
porphyry.  Thus  in  Greenland;  Norway;  Sweden;  Striegau,  Silesia.  Also  in  white  lime- 
stone as  at  Auerbach  on  the  Bergstrasse,  Germany;  often  in  mines  of  magnetic  iron.  Rather 
common  as  an  accessory  constituent  in  many  rocks,  as  in  andesite,  diorite,  dacite,  rhyolite, 
the  tonalite  of  Mt.  Adamello,  Austria,  the  scapolite  rocks  of  Odegaarden,  Norway,  etc. 
Sometimes  inclosed  as  a  nucleus  in  crystals  of  the  isomorphous  species,  epidote.  From 
Madagascar. 

At  Vesuvius  in  ejected  masses  with  sanidine,  sodalite,  nephelite,  hornblende,  etc. 
Similarly  in  trachytic  ejected  masses  at  the  Laacher  See,  Germany  (bucklandite). 

In  Mass.,  at  the  Bolton  quarry.  In  N.  Y.,  Moriah,  Essex  Co.,  with  magnetite  and 
apatite;  at  Monroe,  Orange  Co.  In  N.  J.,  at  Franklin  Furnace  with  feldspar  and  mag- 
netite. In  Pa.,  at  South  Mountain,  near  Bethlehem,  in  large  crystals;  at  East  Bradford; 
near  Eckhardt's  furnace,  Berks  Co.,  abundant.  In  Va.,  in  large  masses  in  Amherst  Co.; 
also  in  Bedford,  Nelson,  and  Amelia  counties.  In  N.  C.,  at  many  points.  At  the  Devil's 
Head  Mt.,  Douglas  Co.,  Col.  In  Texas  in  Llano  Co. 


534 


DESCRIPTIVE   MINERALOGY 


AXINITE. 

Triclinic.     Axes  a  :  b  :  c  =  04921  :  1  :  0-4797;   a  =  82°  54',  ft  =  91°  52', 
T  =  131°  32'. 

ftoa  900  901 


M 


Dauphine" 


Poloma 


Bethlehem,  P; 


am,    100  A  110  =  15°  34'. 

aM,  100  A  110  =  28°  55'. 

as,  100  A  201  =  21°  37'. 


Mr,  110  A  111  =  45°  15'. 

mr,  110  A  111  =  64°  22'. 
ras,  110  A  201  =  27°  57'. 


Also  mas- 


Crystals  usually  broad  and  acute-edged,  but  varied  in  habit, 
sive,  lamellar,  lamellae  often  curved;  sometimes  granular. 

Cleavage:  b  (010)  distinct.     Fracture  conchoidal.     Brittle.     H.  =  6'5-' 
G.  =  3-271-3-294.     Luster  highly  glassy.     Color   clove-brown,    plum-blue, 
and    pearl-gray;     also    honey-yellow,    greenish    yellow.     Streak  uncoloi 
Transparent  to  subtranslucent.     Pleochroism  strong.     Optically  — .     Ax.  pi. 
and  Bxa  approximately  J_  x  (111).     Axial  angles  variable.     2V  =  65°-70°. 
0  =  1-68  (approx.).     Pyroelectric  (p.  307). 

Comp.  —  A   boro-silicate   of    aluminium    and    catcium   with   varying 

amounts  of  iron  and  manganese.  Formula,  RyR^ (SiOJs.  R  =  Calcium 
chiefly,  sometimes  in  large  excess,  again  in  smaller  amount  and  manganese 
prominent;  iron  is  present  in  small  quantity,  also  magnesium  and  basic  hydro- 
gen. 

Pyr.,  etc.  —  B.B.  fuses  readily  with  intumescence,  imparts  a  pale  green  color  to  the 
O.F.,  and  fuses  at  2  to  a  dark  green  to  black  glass;  with  borax  in  O.F.  gives  an  amethystine 
bead  (manganese),  which  in  R.F.  becomes  yellow  (iron).  Fused  with  a  mixture  of  bisul- 
phate  of  potash  and  fluorite  on  the  platinum  loop  colors  the  flame  green  (boric  acid) .  Not 
decomposed  by  acids,  but  when  previously  ignited,  gelatinizes  with  hydrochloric  acid. 

Obs.  —  Axinite  occurs  in  clove-brown  crystals;  near  Bourg  d'Oisans  in  Dauphine, 
France;  at  Andreasberg,  Harz  Mts.,  Germany;  Striegau,  Silesia;  on  Mt.  Skopi,  in  eastern 
Switzerland;  Elba;  at  the  silver  mines  of  Kongsberg,  Norway;  Nordmark,  Sweden;  near 
Miask  in  the  Ural  Mts.;  in  Cornwall,  England,  of  a  dark  color,  at  the  Botallack  mine  near 
St.  Just,  etc.  From  Obira,  Japan. 

In  the  United  States,  at  Phippsburg,  Me.;  Franklin  Furnace,  N.  J.,  honey-yellow;  at 
Bethlehem,  Pa.;  in  Cal.  at  Bonsall,  San  Diego  Co.,  at  Riverside,  Riverside  Co.,  and  at 
Consumers  Mine,  Amador  Co. 

Named  from  a^lvij,  an  axe,  in  allusion  to  the  form  of  the  crystals. 


PREHNITE. 

Orthprhombic-hemimorphic.     Axes  a  :  b  :  c  =  0-8401  :  1  :  0-5549. 
Distinct  individual  crystals  rare;  usually  tabular  ||  c  (001);    sometimes 
prismatic,  mm7"  (110)  A  (HO)  =  80°  4';  again  acute  pyramidal.     Commonly 


SILICATES  535 

in  groups  of  tabular  crystals,  united  by  c  (001)  making  broken  forms,  often 
barrel-shaped.  Reniform,  globular,  and  stalactitic  with  a  crystalline  surface. 
Structure  imperfectly  columnar  or  lamellar,  strongly  coherent;  also  compact 
granular  or  impalpable. 

Cleavage:  c  (001)  distinct.  Fracture  uneven.  Brittle.  H.  =  6-6 '5. 
G.  =  2 -80-2 -95.  Luster  vitreous;  on  base  weak  pearly.  Color  light  green, 
oil-green,  passing  into  white  and  gray;  often  fading  on  exposure.  Sub- 
transparent  to  translucent.  Streak  uncolored. 

Comp.  —  An  acid  orthosilicate,  H2Ca2Al2(Si04)3  =  Silica  43*7,  alumina 
24-8,  lime  27'1,  water  4-4  =  100. 

Prehnite  is  sometimes  classed  with  the  zeolites,  with  which  it  is  often  associated;  the, 
water  here,  however,  has  been  shown  to  go  off  only  at  a  red  heat,  and  hence  plays  a  differ- 
ent part. 

Pyr.,  etc.  —  In  the  closed  tube  yields  water.  B.B.  fuses  at  2  with  intumescence  to  a 
blebby  enamel-like  glass.  Decomposed  slowly  by  hydrochloric  acid  without  gelatinizing; 
after  fusion  dissolves  readily  with  gelatinization. 

Diff.  —  B.B.  fuses  readily,  unlike  beryl,  green  quartz,  and  chalcedony.  Its  hardness  is 
greater  than  that  of  the  zeolites. 

Obs.  —  Occurs  chiefly  in  basic  eruptive  rocks,  basalt,  diabase,  etc.,  as  a  secondary  min- 
eral in  veins  and  cavities,  often  associated  with  some  of  the  zeolites,  also  datolite,  pectolite, 
calcite,  but  commonly  one  of  the  first  formed  of  the  series;  also  less  often  in  granite,  gneiss, 
syenite,  and  then  frequently  associated  with  epidote;  sometimes  associated  with  native 
copper,  as  in  the  Lake  Superior  region. 

At  St.  Christophe,  near  Bourg  d'Oisans  in  Dauphine,  France;  Fassatal,  Tyrol,  Austria; 
the  Ala  valley  in  Piedmont,  Italy;  in  the  Harz  Mts.  near  Andreasberg,  Germany;  in  granite 
at  Striegau,  Silesia;  Arendal,  Norway;  ^Edelfors  in  Sweden  (edelite)',  at  Corstorphine  Hill, 
near  Edinburgh,  Scotland;  Mourne  Mts.,  Ireland. 

In  the  United  States,  finely  crystallized  at  Farmington,  Conn.;  Paterson  and  Bergen 
Hill,  N.  J.;  in  syenite,  at  Somerville,  Mass.;  on  north  shore  of  Lake  Superior,  and  the 
copper  region. 

Named  (1790)  after  Col.  Prehn,  who  brought  the  mineral  from  the  Cape  of  Good  Hope. 

Harstigite.  An  acid  orthosilicate  of  manganese  and  calcium.  In  small  colorless  pris- 
matic crystals.  H.  =  5'5.  G.  =  3 '049.  Indices,  1 '678-1 '683.  From  the  Harstig  mine, 
near  Pajsberg,  Wermland,  Sweden. 

Cuspidine.  Contains  silica,  lime,  fluorine,  and  from  alteration  carbon  dioxide:  formula 
perhaps  Ca2Si(O,F2)4.  In  minute  spear-shaped  crystals.  H.  =  5-6.  G.  =  2-853-2'860. 
Color  pale  rose-red.  Indices,  1  '590-1  '602.  From  Vesuvius,  in  ejected  masses  in  the  tufa 
of  Monte  Somma.  From  Franklin,  N.  J. 


IV.   Subsilicates 

The  species  here  included  are  basic  salts,  for  the  most  part  to  be  referred 
either  to  the  metasilicates  or  orthosilicates,  like  many  basic  compounds  already 
included  in  the  preceding  pages.  Until  their  constitution  is  definitely  settled, 
however,  they  are  more  conveniently  grouped  by  themselves  as  SUBSILICATES. 
It  may  be  noted  that  those  species  having  an  oxygen  ratio  of  silicon  to  bases 
of  2  :  3,  like  topaz,  andalusite,  sillimanite,  datolite,  etc.,  also  calamine,  car- 
pholite,  and  perhaps  tourmaline,  are  sometimes  regarded  as  salts  of  the  hypo- 
thetical parasilicic  acid,  HeSiOs. 

The  only  prominent  group  in  this  subdivision  is  the  HUMITE  GROUP. 


536 


DESCRIPTIVE   MINERALOGY 


Humite  Group 


a  :b 


1-0803  :  1  :  T8861     90C 


1-0863 

6 

1-0802 


1  :  3-1447     90C 


c 
4-4033 


T0803  :  1  :  5'6588     90C 


Prolectite 

[Mg(F,OH)]2Mg[SiO4]i?     Monoclmic 

Chondrodite 

[Mg(F,OH)]2Mg3[Si04]2     Monoclmic 

Humite 

[Mg(F,OH)]2Mg5[Si04]3     Orthorhombic 

Clinohumite 

[Mg(F,OH)]2Mg7[SiO4]4      Monoclinic 

The  species  here  included  form  a  remarkable  series  both  as  regards  crys- 
talline form  and  chemical  composition.  In  crystallization  they  have  sensibly 
the  same  ratio  for  the  lateral  axes,  while  the  vertical  axes  are  almost  exactly 
in  the  ratio  of  the  numbers  3:5:7:9  (see  also  below).  Furthermore, 
though  one  species  is  orthorhombic,  the  others  monoclinic,  they  here  also 
correspond  closely,  since  the  axial  angle  0  in  the  latter  cases  does  not  sensibly 
differ  from  90°. 

In  composition,  as  shown  by  Penfield  and  Howe  (also  Sjogren),  the 
three  species  are  basic  orthosilicates  in  each  of  which  the  univalent  g 
(MgF)  or  (MgOH)  enters,  while  the  Mg  atoms  present  are  in  the  rati<^; 
3  :  5  :  7.     The  composition  given  for  Prolectite   is  theoretical  only,  1  -i 
that    which    would    be    expected    from    its    crystallization.     In   physr 
characters  these  species  are  very  similar,  and  several  of  them  may  o<|ij 
together    at    the    same    locality    and     even    intercrystallized    in    pa 
lamellae.  %  . 

The  species  of  the  group  approximate  closely  in  angle  to  chrysolite  and  chrysoi 
The  axial  ratios  may  be  compared  as  follows: 

Prolectite a 

Chondrodite. a 

Humite b 

Clinohumite a 

Chrysolite b 

Chrysoberyl b 

CHONDRODITE  —  HUMITE  —  CLINOHUMITE. 

Axial  ratios  as  given  above.  Habit  varied,  Figs.  902  to  910.  Twins 
common,  the  twinning  planes  inclined  60°,  also  30°,  to  c  (001)  in  the  brachy- 
dome  or  clinodome  zone,  hence  the  axes  crossing  at  angles  near  60°;  often 
repeated  as  trillings  and  as  polysynthetic  lamellae  (cf.  Fig.  609,  p.  299).  Also 
twins,  with  c  (001)  as  tw.  plane.  Two  of  the  three  species  are  often  twinned 
together. 

Cleavage:  c  (001)  sometimes  distinct.  Fracture  subconchoidal  to  uneven. 
Brittle.  H.  =  6-6-5.  G.  =  3-1-3-2.  Luster  vitreous  to  resinous.  Color 
white,  light  yellow,  honey-yellow  to  chestnut-brown  and  garnet-  or  hyacinth- 
red.  Pleochroism  sometimes  distinct.  Optically  .+  . 

Chondrodite.  Absorption  X  >  Z  >  Y.  Optically  +.  Ax.  pi.  and  Bxa  J_  b  (010). 
Bx0  A  c  axis  =  X  A  c  axis  =  +  25°  52'  Brewster;  28°  56'  Kafveltorp;  30°  approx.,  Mte. 
Somma.  0  =  1-619;  7  -  a  =  0'031.  2V  =  80°. 

Humite.     Ax.  pi.  ||  c  (001).     Bx  J_  a  (100).     0  =  1'643.     7  -  a  =  0'035. 

Clinohumite.  Ax.  pi.  and  Bxa  _L  b  (010).  Bx0  A  c  axis  =  +  11°-12°;  7^°  approx., 
Brewster.  2V  =  76°.  0  =  1-670.  7  -  a  =  0'038. 


b  :  \c  =  1-0803 

-i 

0-6287 

6  :\c  =  1-0863 

1 

0-6289 

a  :$c  =  1-0802 

1 

0-6291 

b  :  $c  =  1-0803 

-| 

0-6288 

2a  :     c  =  1-0735 

1 

0-6296 

2a:     c  =  1-0637 

i 

0-6170     % 

SILICATES 
903 


537 


904 


Figs.  902,  903,  Chondrodite,  Brewster,  N.  Y. 

906 
905 


103 


Chondrodite,  Sweden 
907 


Projection  on  (001) 

Projection  on  (Olb) 
Figs.  905,  906,  Chondrodite,  Mte.  Somma 


908 


Humite,  Sweden 
910 


Humite,  Vesuvius 


Clinohumite,  Brewster 


Projection  on  (010) 
Clinohumite,  Mte.  Somma 


Comp.  —  Basic  fluosilicates  of  magnesium  with  related  formulas  as 
shown  in  the  table  above.  Hydroxyl  replaces  part  of  the  fluorine,  and  iron 
often  takes  the  place  of  magnesium. 

Pyr.,  etc.  —  B.B.  infusible;  some  varieties  blacken  and  then  burn  white.  Fused  with 
potassium  bisulphate  in  the  closed  tube  gives  a  reaction  for  fluorine.  With  the  fluxes 
a  reaction  for  iron.  Gelatinizes  with  acids.  Heated  with  sulphuric  acid  gives  off  silicon 
fluoride. 


538  DESCRIPTIVE   MINERALOGY 

Obs.  -Chondrodite,  humite,  and  elinohumite  all  occur  at  Vesuvius  in  the  ejected 
masses  both  of  limestone  or  feldspathic  type  found  on  Monte  Somma.  They  are  associated 
with  chrysolite,  biotite,  pyroxene,  magnetite,  spinel,  vesuvianite,  calcite,  etc.;  also  less 
often  with  sanidine,  meionite,  nephelite.  Of  the  three  species,  humite  is  the  rarest  and 
elinohumite  of  most  frequent  occurrence.  They  seldom  all  occur  together  in  the  same 
mass,  and  only  rarely  two  of  the  species  (as  humite  and  elinohumite)  appear  together. 
Occasionally  elinohumite  interpenetrates  crystals  of  humite,  and  parallel  intergrowths  with 
chrysolite  have  also  been  observed. 

Chondrodite  occurs  at  Mte.  Somma,  Vesuvius,  as  above  noted;  at  Pargas,  Finland,  honey- 
yellow  in  limestone;  at  Kafveltorp,  Nya-Kopparberg,  Sweden,  associated  with  chalcopyrite, 
galena,  sphalerite.  At  Brewster,  N.  Y.,  at  the  Tilly  Foster  magnetic  iron  mine  in  deep 
garnet-red  crystals.  Also  probably  at  numerous  points  where  the  occurrence  of  "chon- 
drodite" has  been  reported. 

Humite  also  occurs  at  the  Ladu  mine  near  Filipstadt,  Sweden,  with  magnetite  in  crys- 
talline limestone.  In  crystalline  limestone  with  elinohumite  in  Andalusia,  Spain.  Also  in 
large,  coarse,  partly  altered  crystals  at  the  Tilly  Foster  iron-mine  at  Brewster,  N.  Y.  Noted 
at  Franklin  Furnace,  N.  J. 

Clinohumite  occurs  at  Mte.  Somma  and  in  Andalusia;  in  crystalline  limestone  near 
Lake  Baikal  in  East  Siberia;  at  Brewster,  N.  Y.,  in  rare  but  highly  modified  crystals. 

Hydroclinohumite  is  a  titaniferous  variety  (originally  called  titanolivine)  from  Ala 
Valley,  Piedmont,  Italy. 

Prolectite  is  from  the  Kq  mine,  Nordmark,  Sweden;   very  rare;   imperfectly  known. 

Numerous  other  localities  of  "chondrodite"  have  been  noted,  chiefly  in  crystalline 
limestone;  most  of  them  are  probably  to  be  referred  to  the  species  chondrodite,  but  the 
identity  in  many  cases  is  yet  to  be  proved.  At  Brewster  large  quantities  of  massive  "chon- 
drodite" occur  associated  with  magnetite,  enstatite,  ripidolite,  and  from  its  extensive 
alteration  serpentine  has  been  formed  on  a  large  scale.  The  granular  mineral  is  common 
in  limestone  in  Sussex  Co.,  N.  J.,  and  Orange  Co.,  N.  Y.,  associated  with  spinel,  and  occa- 
sionally with  pyroxene  and  corundum.  Also  in  Mass.,  at  Chelmsford,  with  scapolite; 
at  South  Lee,  in  limestone.  In  Canada,  in  limestone  at  St.  Jerome,  Grenville,  etc., 
abundant. 


The  name  chondrodite  is  from  xwSpos,  a  grain,  alluding  to  the  granular  structure. 
Humite  is  from  Sir  Abraham  Hume. 

Leucophcenicite.  Mn5(MnOH)2(SiO4)3,  similar  to  the  humite  type  of  formula. 
Monoclinic.  In  striated  crystals  elongated  parallel  to  ortho-axis.  Massive.  H.  =  5*5-6. 
G.  =  3'8.  Color  light  purplish  red.  Fusible.  From  Franklin,  N.  J.  . 


ILVAITE.     Lievrite.     Yenite. 

Orthorhombic.     Axes  a  :  b  :  c  =  0'6665  :  1  :  0*4427. 

oil  mm'",  110  A  lIO  =  67°  22'.  rr'    101  A  101  =  67°  11'. 

as',        120  A  120  =  73°  45'.  oo',  111  A  Til  =  62°  33'. 

Commonly  in  prisms,  with  prismatic  faces  vertically  striated. 
Columnar  or  compact  massive. 

Cleavage:  6(010),  c(001)  rather  distinct.  Fracture  uneven. 
Brittle.  H.  =  5-5-6.  G.  =  3'99-4'05.  Luster  submetallic. 
Color  iron-black  or  dark  grayish  black.  Streak  black,  inclining 
to  green  or  brown.  Opaque. 

^  Comp.  -  -  CaFe2(FeOH)  (SiO4)2      or     H2O.CaO.4FeO.Fe2O3. 
4SiO2  =  Silica  29 -3,  iron  sesquioxide  19 -6,  iron  protoxide  35  -2, 
lime    137,  water    2-2  =  100.      Manganese    may    replace    part 
of  the  ferrous  iron. 

Pyr.,  etc.  —  B.B.  fuses  quietly  at  2'5  to  a  black  magnetic  bead.  With  the  fluxes  reacts 
lor  iron.  Some  varieties  give  also  a  reaction  for  manganese.  Gelatinizes  with  hydro- 
chloric acid. 

Obs.  —  Found  on  Elba  in  dolomite;  on  Mt.  Mulatto  near  Predazzo,  Tyrol,  Austria,  in 
granite;  Schneeberg,  Saxony;  Fossum,  in  Norway.  In  crystals  from  Siorarsiut,  South 
Lrreenland.  Reported  as  formerly  found  at  Cumberland,  R.  I.;  also  at  Milk  Row  quarry, 


SILICATES 


539 


Somerville,  Mass.  In  fine  crystals  from  South  Mountain  mine,  Owyhee  Co.,  Idaho.  Named 
Ilvaite  from  the  Latin  name  of  the  island  (Elba). 

Ardennite.  Dewalquite.  A  vanadio-silicate  of  aluminium  and  manganese;  also  con- 
taining arsenic.  In  prismatic  crystals  resembling  ilvaite.  H.  =  6-7.  G.  =  3*620.  Yel- 
low to  yellowish  brown.  Index  about  179.  Found  at  Salm  Chateau  in  the  Ardennes, 
Belgium. 

Langbanite.  Manganese  silicate  with  ferrous  antimonate;  formula  doubtful.  Rhom- 
bohedral-tetartohedral.  In  iron-black  hexagonal  prismatic  crystals.  H.  =  6'5. 
G.  =  4'918.  Luster  metallic.  From  Langban,  Sweden. 

The  following  are  rare  lead  silicates.     See  also  p.  498. 

Kentrolite.  Probably  3PbO.2Mn2O3.3SiO2.  In  minute  prismatic  crystals;  often  in 
sheaf -like  forms;  also  massive.  H.  =5.  G.  =6'19.  Color  dark  reddish  brown;  black 
on  the  surface.  From  southern  Chile;  Langban  and  Jakobsberg,  Sweden;  Bena  Padru, 
near  Ozieri,  Sardinia. 

Melanotekite.  3PbO.2Fe2O3.3SiO2  or  (Fe4O8)Pb8(SiO4)s.  Orthorhombic;  prismatic. 
Massive;  cleavable.  H.  =  6'5.  G.  =  573.  Luster  metallic  to  greasy.  Color  black  to 
blackish  gray.  Occurs  with  native  lead  at  Langban,  Sweden.  Also  in  crystals  resembling 
kentrolite  at  Hillsboro,  N.  M. 


Bertrandite.  H2Be4Si?O9  or  H2O.4BeO.2SiO2.  Orthorhombic-hemimorphic.  In  small 
tabular  or  prismatic  crystals.  H.  =  6-7.  G.  =  2'59-2'60.  Colorless  to  pale  yellow. 
Optically  — .  0  =  T603.  Usually  occurs  in  feldspathic  veins,  often  with  other  beryllium 
minerals  as  a  result  of  the  alteration  of  beryl.  At  the  quarries  of  Barbin  near  Nantes, 
France;  Pisek,  Bohemia;  Irkutka  Mt.,  Altai  Mts.,  Russia;  Ireland,  Southern  Norway; 
Cornwall,  England;  Mt.  Antero,  Chaff ee  Co.,  Col.,  with  phenacite;  Amelia  Court-House, 
Va.;  Oxford  Co.,  Me. 


07834  :  1  :  04778. 


912 


913 


CALAMINE.     Smithsonite.     Hemimorphite. 

Orthorhombic-hemimorphic.     Axes  a  :  b  :  c 

mm'",  110  A  101  =    76°    9'. 

ss',  101  A  101  =    62°  46'. 

«',  301  A  301  =  122°  41'. 

ee',  Oil  A  Oil  =    51°    5'. 

w',  031  A  031  =  110°  12'. 

w'",  121  A  121  =    78°  26'. 

Crystals  often  tabular  ||  b  (010);  also  pris- 
matic; faces  6  vertically  striated.  Usually 
implanted  and  showing  one  extremity  only. 
Often  grouped  in  sheaf -like  forms  and  form- 
ing drusy  surfaces  in  cavities.  Also  stalac- 
titic,  mammillary,  botryoidal,  and  fibrous 
forms;  massive  and  granular. 

Cleavage:  m  (110)  perfect;  s(  101)  less  so; 

c  (001)  in  traces.  Fracture  uneven  to  subconchoidal.  Brittle.  H. 
the  latter  when  crystallized.  G.  =  3 -40-3 -50.  Luster  vitreous; 
subpearly,  sometimes  adamantine.  Color  white;  sometimes  with  a  delicate 
bluish  or  greenish  shade;  also  yellowish  to  brown.  Streak  white.  Trans- 
parent to  translucent.  Optically  +.  2V  =  46°.  a  =  1-614.  (3  =  1*617. 
7  =  1-636.  Strongly  pyroelectric. 

Comp.  —  H2ZnSiO5  or  (ZnOH)2SiO3  or  H2O.2ZnO.SiO2  =  Silica  25-0, 
zinc  oxide  67 -5,  water  7-5  =  100.  The  water  goes  off  only  at  a  red  heat; 
unchanged  at  340°  C. 

Pyr.,  etc.  —  In  the  closed  tube  decrepitates,  whitens,  and  gives  off  water.  B.B.  almost 
infusible  (F.  =6).  On  charcoal  with  soda  gives  a  coating  which  is  yellow  while  hot,  and 


=  4-5-5, 
c  (001) 


540  DESCRIPTIVE   MINERALOGY 

white  on  cooling  Moistened  with  cobalt  solution,  and  heated  in  O.F.,  this  coating  assumes 
a  bright  green  color,  but  the  ignited  mineral  itself  becomes  blue.  Gelatinizes  with  acids 
even  when  previously  ignited.  .  ,,..,.  .,,  ., 

f)iQ  Characterized  by  its  mfusibihty;  reaction  for  zinc;  gelatimzation  with  acids. 

Resembles  some  smithsonite  (which  effervesces  with  acid),  also  prehnite. 

Obs.  —  Calamine  and  smithsonite  are  usually  found  associated  in  veins  or  beds  in 
stratified  calcareous  rocks  accompanying  sulphides  of  zinc,  iron  and  lead.  Thus  at  Aix-la- 
Chapelle  Germany;  Raibel  and  Bleiberg,  in  Carinthia;  Moresnet  in  Belgium;  Rezbanya, 
and  Schemnitz,  Hungary.  At  Roughten  Gill,  in  Cumberland;  at  Alston  Moor,  white; 
near  Matlock,  in  Derbyshire;  Leadhill,  Scotland;  at  Nerchinsk,  m  eastern  Siberia.  From 
Santa  Eulalia,  Chihuahua,  Mexico. 

In  the  United  States  occurs  at  Sterling  Hill,  near  Ogdensburg,  N.  J.,  in  fine  clear  crystal- 
line masses.  In  Pa.,  at  the  Perkiomen  and  Phenixville  lead  mines;  at  Friedensville. 
Abundant  in  Va.,  at  Austin's  mines  in  Wythe  Co.  With  the  zinc  deposits  of  southwestern 
Missouri,  especially  about  Granby,  both  as  crystallized  and  massive  calamine.  Crystals 
from  Leadville,  Col;  from  Organ  Mts.,  N.  M.;  Elkhorn  Mts.,  Mon.  At  the  Emma  mine, 
Cottonwood  Canon,  Utah. 

The  name  Calamine  (with  Galmei  of  the  Germans)  is  commonly  supposed  to  be  a  cor- 
ruption of  Cadmia.  Agricola  says  it  is  from  calamus,  a  reed,  in  allusion  to  the  slender 
forms  (stalactitic)  common  in  the  cadmia  fornacum. 

Use.  —  An  ore  of  zinc. 

Clinohedrite.  H2CaZnSiO5.  Monoclinic-clinohedral  (see  Figs.  352,  353,  p.  138). 
H.  =  5'5.  G.  =  3'33.  Colorless  or  white  to  amethystine.  Index,  1 '67.  From  Franklin,  N.  J. 

Stokesite.  —  Perhaps  H^aSnSisOn.  Orthorhombic.  Prismatic  cleavage.  H.  =  6. 
G.  =  3'2.  Colorless.  0  =  1*61.  From  Roscommon  Cliff,  St.  Just,  Cornwall. 

Carpholite.  H4MnAlsSi2O10.  In  radiated  and  stellated  tufts.  G.  =  2'935.  Color 
straw-  to  wax-yellow.  Biaxial,  — .  0  =  1*63.  Occurs  at  the  tin  mines  of  Schlaggenwald, 
Bohemia;  Wippra,  in  the  Harz  Mts.,  on  quartz,  etc. 

Lawsonite.  H4CaAl2Si2Oio.  In  prismatic  orthorhombic  crystals;  mm'",  110  A  110 
=  67°  16'.  G.  =  3*09.  Luster  vitreous  to  greasy.  Colorless,  pale  blue  to  grayish  blue. 
Optically  -f-.  /3  =  1'669.  Occurs  in  crystalline  schists  of  the  Tiburn  peninsula,  Marin 
Co.,  Gal.;  also  in  the  schists  of  Pontgibaud,  France,  and  New  Caledonia. 

Hibschite.  Same  as  for  lawsonitc,  H4CaAl2Si2Oio.  In  minute  isometric  crystals,  usually 
octahedrons.  H.  =  6.  G.  =  3'0.  Colorless  or  pale  yellow.  Refractive  index,  1 '67.  In- 
fusible. From  the  phonolite  of  Marienberg,  Bohemia.  Associated  with  melanite. 

Cerite.  A  silicate  of  the  cerium  metals  chiefly,  with  water.  Crystals  rare;  commonly 
massive;  granular.  H.  =  5'5.  G.  =  4*86.  Color  between  clove-brown  and  cherry-red 
to  gray.  Indices,  1 '83-1 '93.  Occurs  at  Bastnas,  near  Riddarhyttan,  Sweden. 

Toernebohmite.  A  silicate  of  the  cerium  metals,  chiefly,  R3(OH)(SiO4)2.  Monoclinic? 
Color,  green  to  olive.  /3  =  1'81.  Biaxial,  +.  Strong  dispersion,  P  <  v.  Pleochroic,  rose 
to  blue-green.  From  Bastnas,  near  Riddarhytta.n,  Sweden. 

Beckelite.  Ca3(Ce,La,Di)4Si3O15.  Isometric  Crystals  small,  often  microscopic.  Cubic 
cleavage.  H.  =  5.  G.  =  4*1.  Color  yellow.  Infusible.  Occurs  with  nepheline  syenite 
rocks  near  Mariupol,  Russia. 

Hellandite.  A  basic  silicate  chiefly  of  the  cerium  metals,  aluminium,  manganese  and 
calcium.  Monoclinic.  Prismatic  habit.  H.  =  5*5.  G.  =  37.  Color  brown.  Fusible. 
Found  in  pegmatite  near  Kragero,  Norway. 

Bazzite.  A  silicate  of  scandium  with  other  rare  earth  metals,  iron  and  a  little  soda. 
Hexagonal.  In  minute  prisms,  often  barrel  shaped.  H.  =  6*5.  G.  =  2'8.  Color  azure- 
i  Transparent  in  small  individuals.  Optically  -.  Refractive  indices,  co  =  1'626. 
e  =  rb05.  Strongly  dichroic,  co  =  pale  greenish  yellow,  e  =  azure-blue.  Infusible.  In- 
soluble m  ordinary  acids.  Found  at  Baveno,  Italy. 

ANGARALITE  2(Ca,Mg)0.5(Al,Fe)2O.,.6SiO2.  In  thin  tabular  hexagonal(?)  crystals. 
U.  -  2-b2.  Color  black  from  carbonaceous  impurities.  Uniaxial,  +.  In  contact  zone  of 
limestone,  southern  part  of  Yenisei  District,  Siberia. 


TOURMALINE. 

Rhombohedral-hemimorphic._    Axis  c  =  0-4477. 

cr,  0001  A  lOll  =  27°  20'.       rr'    1011  A  1101   —  4fi°  W        im'     39^1   A  Q^91        AA°    T 
co,  0001  A  0221  =  45°  57'.      oof,  oil  A  20*1  =  #  %\      %i,  l|i  ^  1}  I4626»  gj/ 


SILICATES 


541 


Crystals  usually  prismatic  in  habit,  often  slender  to  acicular;    rarely 
flattened,  the  prism  nearly  wanting.     Prismatic  faces  strongly  striated  ver- 


914 


515 


916 


917 


918 


ma 


921 


tically,  and  the  crystals  hence  often  much  rounded  to  barrel-shaped.  The 
cross-section  of  the  prism  three-sided  (m,  Fig.  921),  six- 
sided  (a),  or  nine-sided  (m  and  a).  Crystals  commonly 
hemimorphic.  Sometimes  isolated,  but  more  com- 
monly in  parallel  or  radiating  groups.  Sometimes  mas- 
sive compact;  also  columnar,  coarse  or  fine,  parallel 
or  divergent. 

Cleavage :  a  (1 120) ,  r  (101 1)  difficult.  Fracture  sub- 
conchoidal  to  uneven.  Brittle  and  often  rather  friable. 
H.  =  7-7-5.  G.  =  2-98-3-20.  Luster  vitreous  to  res- 
inous. Colur  black,  brownish  black,  bluish  black, 
most  common;  blue,  green,  red,  and  sometimes  of  rich 
shades;  rarely  white  or  colorless;  some  specimens  red  internally  and  green 
externally;  and  others  red  at  one  extremity,  and  green,  blue  or  black  at 
the  other;  the  zonal  arrangement  of  different  colors  widely  various  both  as 
to  the  colors  and  to  crystallographic  directions.  Streak  uncolored.  Trans- 
parent to  opaque. 

Strongly  dichroic,  especially  in  deep-colored  varieties;  axial  colors  varying 
widely.  Absorption  for  co  much  stronger  than  for  e,  thus  sections  1 1  c  axis  trans- 
mit sensibly  the  extraordinary  ray  only,  and  hence  their  use  (e.g.,  in  the  tour- 
maline tongs  (p.  243)  )  for  giving  polarized  light.  Exhibits  idiophanous  figures 
(p.  288).  Optically  — .  Birefringence  rather  high,  co  —  e  =  OO2.  Indices: 
coy  =  1-6366,  ey  =  1-6193  colorless  variety;  o>r  =  1*6435,  er  =.  1-6222  blue- 


542  DESCRIPTIVE   MINERALOGY 

green.     Sometimes  abnormally  biaxial.     Becomes  electric  by  friction;    also 
strongly  pyroelectric. 

Var.  —  Ordinary.  In  crystals  as  above  described;  black  much  the  most  common, 
(a)  Rubellite;  the  red,  sometimes  transparent;  the  Siberian  is  mostly  violet-red  (siberite), 
the  Brazilian  rose-red;  that  of  Chesterfield  and  Goshen,  Mass.,  pale  rose-red  and  opaque; 
that  of  Paris,  Me.,  fine  ruby-red  and  transparent.  (6)  Indicolite,  or  indigolite;  the  blue, 
either  pale  or  bluish  black;  named  from  the  indigo-blue  color,  (c)  Brazilian  Sapphire  (in 
jewelry);  Berlin-blue  and  transparent,  (d)  Brazilian  Emerald,  Chrysolite  (or .Peridot)  of 
Brazil;  green  and  transparent,  (e)  Peridot  of  Ceylon;  honey-yellow.  (/)  Achroite;  color- 
less tourmaline,  from  Elba,  (g)  Aphrizite;  black  tourmaline,  from  Kragero,  Norway. 
(h)  Columnar  and  black;  coarse  columnar.  Resembles  somewhat  common  hornblende, 
but  has  a  more  resinous  fracture,  and  is  without  distinct  cleavage  or  anything  like  a  fibrous 
appearance  in  the  texture;  it  often  has  the  appearance  on  a  broken  surface  of  some  kinds  of 
soft  coal. 

Comp.  —  A  complex  silicate  of  boron  and  aluminium,  with  also  either 
magnesium,  iron  or  the  alkali  metals  prominent.  A  general  formula  may  be 
written  as  HgAlaCB.OH^Si^ip  (Penfield  and  Foote)  in  which  the  hyrogen 
may  be  replaced  by  the  alkalies  and  also  the  bivalent  elements,  Mg,Fe,Ca. 
Fluorine  is  commonly  present  in  small  amounts. 

The  varieties  based  upon  composition  fall  into  three  prominent  groups,  between  which 
there  are  many  gradations: 

1.  ALKALI  TOURMALINE.     Contains  sodium   or  lithium,   or  both;    also   potassium. 
G.  =  3-0-3-1.     Color  red  to  green;  also  colorless.     From  pegmatites. 

2.  IRON  TOURMALINE.     G.  =  3-1-3-2.     Color  usually  deep  black.     Accessory  mineral 
in  siliceous  igneous  rocks  and  in  mica  schists,  etc. 

3.  MAGNESIUM    TOURMALINE.     G.  =  3-0-3'09.     Usually    yellow-brown    to    brownish 
black;  also  colorless.     From  limestone  or  dolomite. 

A  chromium  tourmaline  also  occurs.  G.  =  3*120.  Color  dark  green. 
Pyr.,  etc.  —  The  magnesia  varieties  fuse  rather  easily  to  a  white  blebby  glass  or  slag; 
the  iron-magnesia  varieties  fuse  with  a  strong  heat  to  a  blebby  slag  or  enamel;  the  iron 
varieties  fuse  with  difficulty,  or,  in  some,  only  on  the  edges;  the  iron-magnesia-lithia 
varieties  fuse  on  the  edges,  and  often  with  great  difficulty,  and  some  are  infusible;  the  lithia 
varieties  are  infusible.  With  the  fluxes  many  varieties  give  reactions  for  iron  and  man- 
ganese. Fused  with  a  mixture  of  potassium  bisulphate  and  fluor-spar  gives  a  distinct  re- 
action for  boric  acid.  Not  decomposed  by  acids.  Crystals,  especially  of  the  lighter  colored 
varieties,  show  strong  pyroelectricity. 

Diff.  —  Characterized  by  its  crystallization,  prismatic  forms  usual,  which  are  three-, 
six-,  or  nine-sided,  and  often  with  rhombohedral  terminations;  massive  forms  with  colum- 
nar structure;  also  by  absence  of  cleavage  (unlike  amphibole  and  epidote);  in  the  common 
black  kinds  by  the  coal-like  fracture;  by  hardness;  by  difficult  fusibility  (common  kinds), 
compared  with  garnet  and  vesuvianite.  The  boron  test  is  conclusive. 

Micro.  —  Readily  distinguished  in  thin  sections  by  its  somewhat  high  relief;    rather 

u°nugin    i  erence~colors'  ne"gative  uniaxial  character;   decided  colors  in  ordinary  light  in 

which  basal  sections  often  exhibit  a  zonal  structure.     Also,  especially,  by  its  remarkable 

-bsorption  when  the  direction  of  crystal  elongation  is  _]_  to  the  vibration-plane  of  the  lower 

nicol;  this  with  its  lack  of  cleavage  distinguishes  it  from  biotite  and  amphibole,  which  alone 

among  rock-making  minerals  show  similar  strong  absorption. 

Ubs.  —  Commonly  found  in  granite  and  gneisses  as  a  result  of  fumarole  action  or  of 
legalizing  gases  m  the  fluid  magma,  especially  in  the  pegmatite  veins  associated  with 
icn  rocks;  at  the  periphery  of  such  masses  or  in  the  schists,  or  altered  limestones,  gneisses, 
!tc.,  immediately  adjoining  them.     It  marks  especially  the  boundaries  of  granitic  masses, 
its  associate  minerals  are  those  characteristic  of  such  occurrences;    quartz,  albite, 
microcline   muscovite   etc.     The  variety  in  granular  limestone  or  dolomite  is  commonly 
vn,    tne  bluish-black  variety  sometimes  associated  with  tin  ores;    the  brown  with 
e  lithium  variety  is  often  associated  with  lepidolite.     Red  or  green  varieties, 
d     Pp°n-CUrQnear     kat?F mburg  in  the  Ural  Mts-  Elba;  Campolongo  in  Tessin,  Switzer- 
^lr  ?:XOny;        -°  *he  Province  Minas  Geraes,  Brazil;    yellow  and  brown  from 
A™ br?Tn  ™netles  £rom  Eibenstock,  Saxony;    the  Zillertal,  Tyrol,  Austria; 
"        i dal'0N°.rway;    Snarum  and  Kragero,  Norway;    pale  yellowish  brown  at 

crystais  °ccur  in  c°™n  at  different  iocaiities- 


SILICATES 


543 


variety  from  the  chromite  beds  in  Montgomery  Co.,  Md.     In  N.  C.,  Alexander 
e  black  crystals  with  emerald  and  hiddenite.     In  Cal.,  fine  groups  of  rubellite  in 


In  the  United  States,  in  Me.  at  Paris  and  Hebron,  magnificent  red  and  green  tourmalines 
with  lepidolite,  etc.;  also  blue  and  pink  varieties;  and  at  Norway;  pink  at  Rumford,  em- 
bedded in  lepidolite;  at  Auburn  in  clear  crystals  of  a  delicate  pink  or  lilac  with  lepidolite, 
etc.;  at  Albany,  green  and  black.  In  Mass.,  at  Chesterfield,  red,  green,  and  blue;  at 
Goshen,  blue  and  green;  at  Norwich,  New  Braintree  and  Carlisle,  good  black  crystals.  In 
N.  H.,  Grafton,  Acworth;  at  Orford,  brownish  black  in  steatite.  In  Conn.,  at  Monroe, 
dark  brown  in  mica-slate;  at  Haddam,  black  in  mica  slate;  also  fine  pink  and  green;  at 
New  Milford,  black.  In  N.  Y.,  near  Gouverneur,  brown  crystals,  with  tremolite,  etc., 
in  granular  limestone;  black  near  Port  Henry,  Essex  Co.;  near  Edenville;  splendid  black 
crystals  at  Pierrepont,  St.  Lawrence  Co.;  colorless  and  glassy  at  De  Kalb;  dark  brown  at 
McComb.  In  N.  J.,  at  Hamburg  and  Newton,  black  and  brown  crystals  in  limestone, 
with  spinel;  also  grass-green  crystals  in  crystalline  limestone  near  Franklin  Furnace.  In 
Pa.,  at  Newlin,  Chester  Co.;  near  Unionville,  yellow;  at  Chester,  fine  black;  Middle- 
town,  black;  Marple,  green  in  talc;  near  New  Hope  on  thej)elaware,  large  black  crystals. 
A  chrome  y 
Co.,  in  fine 
lepidolite  from  Mesa  Grande,  Pala,  etc.  in  San  Diego  Co. 

In  Canada,  in  the  province  of  Quebec,  yellow  crystals  in  limestone  at  Calumet  Falls, 
Litchfield,  Pontiac  Co.;  at  Hunterstown;  fine  brown  crystals  at  Clarendon,  Pontiac  Co.; 
black  at  Grenville  and  Argenteuil,  Argenteuil  Co.  In  Ontario,  in  fine  crystals  at  North 
Burgess,  Lanark  Co.;  Gal  way  and  Stoney  Lake  in  Dummer,  Peterborough  Co. 

The  name  turmalin  from  Turamali  in  Cingalese  (applied  to  zircon  by  jewelers  of  Cey- 
lon) was  introduced  into  Holland  in  1703,  with  a  lot  of  gems  from  Ceylon. 

Use.  —  The  variously  colored  and  transparent  varieties  are  used  as  gem  stones;  see 
under  "Var."  above. 

Dumortierite.  A  basic  aluminium  borosilicate,  perhaps  SAloOs^Os.GSiC^.HaO  (Schaller) . 
The  water  and  boric  oxide  have  been  considered  as  variable  in  amount  and  basic  in  charac- 
ter with  the  general  formula,  (AlO)i6Al4(SiO4)7  (Ford). 

Orthorhombic.  Prismatic  angle  approximately  60°.  Usually  in  fibrous  to  columnar 
aggregates.  Cleavage:  a  (100),  distinct;  also  prismatic,  imperfect.  H.  =7.  G.  =  3'26- 
3'36.  Luster  vitreous.  Color  bright  smalt-blue  to  greenish  blue.  Transparent  to  trans- 
lucent. Pleochroism  very  strong:  X  deep-blue  or  nearly  colorless,  Y  yellow  to  red- violet 
or  nearly  colorless,  Z  colorless  or  pistachio-green.  Exhibits  idiophanous  figures,  analogous 
to  andalusite.  Optically  -.  Ax.  pi.  ||  b  (010).  Bx  J_  c  (001).  «  =  1-678.  0  =  1'686. 
7  =  1-689. 

Recognized  in  thin  section  by  its  rather  high  relief;  low  interference-colors  (like  those 
of  quartz);  occurrence  in  slender  prisms,  needles  or  fibers,  with  negative  optical  extension; 
parallel  extinction;  biaxial  character  and  "especially  by  its  remarkable  pleochroism. 

Found  embedded  in  feldspar  in  blocks  of  gneiss  at  Chaponost,  near  Lyons,  France; 
from  Wolfshau,  near  Schmiedeberg,  Silesia;  in  the  iolite  of  the  gneiss  of  Tvedestrand, 
Norway;  Rio  de  Janeiro,  Brazil.  In  the  United  States,  it  occurs  near  Harlem,  New  York 
Island,  in  the  pegmatoid  portion  of  a  biotite-gneiss ;  in  a  quartzose  rock  at  Clip,  Yuma  Co., 
Arizona;  from  San  Diego  Co.,  Cal.;  Woodstock,  Wash. 


STAUROLITE.     Staurotide. 
Orthorhombic.     Axes  a  :  b  :  c 

mm"',  110  A  110  =    50°  40'. 

rr',        101  A  101  =  110°  32'. 

922 


0-4734  :  1  :  0-6828. 


cr, 
m,r, 


001  A 
110  A 


101 
101 


923 


=  55°  16'. 
=  42°    2'. 

924 


Twins  cruciform:    tw.  pi.  x  (032),  the  crystals  crossing  nearly  at  right 
angles;   tw.  pi.  z  (232),  crossing  at  an  angle  of  60°  approximately;   tw.  pi. 


010 


544  DESCRIPTIVE    MINERALOGY 

y  (230)  rare,  also  in  repeated  twins  (cf.  Figs.  397,  p.  164;  439,  440,  441,  p.  170). 
Crystals  commonly  prismatic  and  flattened  ||  b  axis;  often  with  rough  surfaces. 
Cleavage:  b  (010)  distinct,  but  interrupted;  m  (110)  m  traces.  Fracture 
subconchoidal.  Brittle.  H.  =  7-7-5.  G.  =  3  '65-3  77.  Subvitreous,  inclin- 
ing to  resinous.  Color  dark  reddish  brown  to  brownish  black,  and  yellowish 
brown.  Streak  uncolored  to  grayish.  Translucent  to  nearly  or  quite  opaque. 

Pleochroism  distinct :    Z  ( =  c  axis)  hyacinth-red 
to  blood-red,  X,  Y  yellowish  red;  or  Z  gold-yellow, 
**&*»  x  Y  light  yellow  to  colorless.     Optically  +.     Ax. 

pi.   ||  a  (100).      Bx  _L  c  (001).      2V  =  88°   (ap- 
\      MI  I  /  prox.).     a  =  1-736.     ft  =  1741.     7  =  1*746. 

Comp.  —  HFeAl5Si2Oi3,  which    may    be  writ- 
ten (A10)4(AlOH)Fe(SiO4)2  or  H2O.2Fe0.5Al2O3. 
010  4SiO2  =  Silica  26*3,  alumina  55 '9,  iron  protoxide 
>x    15-8,  water  2'0  =  100.     Magnesium    (also  man- 
ganese) replaces  a  little  of  the  ferrous  iron;  ferric 
iron  part  of  the  aluminium. 

Nordmarkite  from  Nordmark,  Sweden,  contains  man- 

/\  ganese  in  large  amounts. 

\g  Pyr.,  etc.  —  B.B.  infusible,  excepting  the  manganesian 

&  variety,  which  fuses  easily  to  a   black  magnetic  glass. 

Z  With  the  fluxes  gives  reactions  for  iron,  and  sometimes 

for  manganese.    Imperfectly  decomposed  by  sulphuric  acid. 

Diff.  —  Characterized  by  the  obtuse  prism  (unlike  andalusite,  which  is  nearly  square) ; 
by  the  frequency  of  twinning  forms;  by  hardness  and  infusibility. 

Micro.  —  Under  the  microscope,  sections  show  a  decided  color  (yellow  to  red  or  brown) 
and  strong  pleochroism  (yellow  and  red);  also  characterized  by  strong  refraction  (high 
relief),  rather  bright  interference-colors,  parallel  extinction  and  biaxial  character  (generally 
positive  in  the  direction  of  elongation).  Easily  distinguished  from  rutile  (p.  427)  by  its 
biaxial  character  and  lower  interference-colors. 

Obs.  —  Usually  found  in  crystalline  schists,  as  mica  schist,  argillaceous  schist,  and 
gneiss,  as  a  result  of  regional  or  contact  metamorphism;  often  associated  with  garnet,  silli- 
manite,  cyanite,  and  tourmaline.  Sometimes  encloses  symmetrically  arranged  carbon- 
aceous impurities  like  andalusite  (p.  524) .  Other  impurities  are  also  often  present,  especially 
silica,  sometimes  up  to  30  to  40  p.  c.;  also  garnet,  mica,  and  perhaps  magnetite,  brookite. 

Occurs  with  cyanite  in  paragonite  schist,  at  Mt.  Campione,  Switzerland;  in  the  Zillertal, 
Tyrol,  Austria;  Goldenstein  in  Moravia;  Aschaffenburg,  Bavaria;  in  large  twin  crystals  in 
the  mica  schists  of  Brittany  and  Scotland.  In  the  province  of  Minas  Geraes,  Brazil. 

Abundant  throughout  the  mica  schists  of  New  England.  In  Me.,  at  Windham.  In 
N.  H.,  brown  at  Franconia;  at  Lisbon;  on  the  shores  of  Mink  Pond,  loose  in  the  soil.  In 
Mass.,  at  Chesterfield,  in  fine  crystals.  In  Conn.,  at  Bolton,  Vernon,  etc.;  Southbury  with 
garnets;  at  Litchfield,  black  crystals.  In  N.  C.,  near  Franklin,  Macon  Co.;  also  in  Madi- 
son and  Clay  counties.  In  Ga.,  in  Fannin  Co.,  loose  in  the  soil  in  fine  crystals.  In  large 
crystals  from  Ducktown,  Tenn. 

Named  from  (rravpos,  a  cross. 

Use.  —  Occasionally  a  transparent  stone  is  cut  for  a  gem. 

Kornerupine.  Near  MgAl2SiO6.  In  fibrous  to  columnar  aggregates,  resembling  silli- 
mamte.  H.  =  6'5.  G.  =  3'273  kornerupine;  3'341  prismatine.  Colorless  to  white,  or 
brown.  Biaxial,  -.  Indices,  1 '669-1 '682. 

Kornerupine  occurs  at  Fiskernas  on  the  west  coast  of  Greenland.  Prismatine  is  from 
Waldheim,  Saxony.  Found  in  large,  clear  crystals  of  a  sea-green  color  and  gem  quality 
trom  near  Betroka,  Madagascar. 

Sapphirine.  Mg6Ali2Si2O27.  In  indistinct  tabular  crystals.  Usually  in  disseminated 
grains,  or  aggregations  of  grains.  H.  =  7'5.  G.  =  3'42-3'48.  Color  pale  to  dark  blue  or 
green.  Biaxial,  -.  Indices,  1705-1711.  From  Fiskernas,  southwestern  Greenland. 
Occurs  near  Betroka,  Madagascar.  From  St.  Urbain,  Quebec. 

r\  .p^didierite.    A  basic  silicate  of  aluminium,  ferric  iron,  magnesium,  ferrous  iron,  etc. 
Orthornombic.     In  elongated  crystals.     Two  cleavages.     G.  =  3'0.     Color  bluish  green. 


SILICATES  545 

/3  =  1-64.  Strongly  pleochroic.  Found  in  pegmatite  at  Andrahomana  in  southern 
Madagascar. 

Serendibite.  10(Ca,Mg)O.5Al2p3.B2O3.6SiO2.  In  irregular  grains  showing  polysyn- 
thetic  twinning;  probably  monoclinic  or  triclinic.  H.  =  6*7.  G.  =  3*4.  Color  blue. 
Pleochroism  marked.  Refractive  index,  17.  Infusible.  From  Gangapitiya  near  Am- 
bakotte,  Ceylon. 

Silicomagnesipfluorite.  A  fluosilicate  of  calcium  and  magnesium,  perhaps,  H2Ca4Mg3 
Si2O7Fi0.  Radiating  fibrous  in  spherical  forms.  H.  =  2'5.  G.  =  2'9.  Color  ash-gray, 
light  greenish  or  bluish.  Fusible.  From  Lupikko,  near  Pitkaranta,  Finland. 

Grothine.  A  silicate  of  calcium  with  aluminium  and  a  little  iron  of  uncertain  compo- 
sition. Orthorhombic.  In  small  tabular  crystals.  Colorless.  Transparent.  G.  =  3'09. 
Optically  +.  Infusible.  Decomposed  by  sulphuric  acid.  Found  with  microsommite  on 
limestone  near  Nocera  and  Sarno,  Campagna,  Italy. 

ALOISIITE.  Luigite.  A  basic  silicate  containing  ferrous  oxide,  lime,  magnesia,  and 
soda.  Amorphous.  Color,  brown  to  violet.  Acts  as  a  cement  in  a  tuff  found  at  Fort 
Portal,  Uganda. 

POCHITE.  Hi6Fe8Mn2Si3O29.  Amorphous.  H.  =  3'5-4.  G.  =  370.  Color  reddish 
brown.  Opaque.  Found  in  iron  ore  near  Vares,  Bosnia. 


SILICATES 
Section  B.     Chiefly  Hydrous  Species 

The  SILICATES  of  this  second  section  include  the  true  hydrous  compounds, 
that  is,  those  which  contain  water  of  crystallization,  like  the  zeolites;  also  the 
hydrous  amorphous  species,  as  the  clays,  etc.  There  are  also  included  certain 
species  —  as  the  Micas,  Talc,  Kaolinite  —  which,  while  they  yield  water  upon 
ignition,  are  without  doubt  to  be  taken  as  acid  or  basic  metasilicates,  orthosili- 
cates,  etc.  Their  relation,  however,  is  so  close  to  other  true  hydrous  species 
that  it  appears  more  natural  to  include  them  here  than  to  have  placed  them 
in  the  preceding  chapter  with  other  acid  and  basic  salts.  Finally,  some 
species  are  referred  here  about  whose  chemical  constitution  and  the  part 
played  by  the  water  present  there  is  still  much  doubt.  The  divisions  recog- 
nized are  as  follows: 

I.   Zeolite  Division 
1.    Introductory  Subdivision.     2.    Zeolites 

II.   Mica  Division 
1.    Mica  Group.     2.    Clintonite  Group.     3.    Chlorite  Group 

III.   Serpentine  and  Talc  Division 

Chiefly  Silicates  of  Magnesium. 

IV.   Kaolin  Division 

Chiefly  Silicates  of  Aluminium;  for  the  most  part  belonging  to  the  group 
of  the  clays. 

V.   Concluding  Division 

Species  not  included  in  the  preceding  divisions;  chiefly  silicates  of  the 
heavy  metals,  iron,  manganese,  etc. 


546 


DESCRIPTIVE    MINERALOGY 


I.   Zeolite  Division 
1.    Introductory  Subdivision 

Of  the  species  here  included,  several,  as  Apophyllite,  Okenite,  etc.,  while  not  strictly 
ZEOLITES,  are  closely  related  to  them  in  composition  and  method  of  occurrence.  Pectolite 
(p.  483)  and  Prehnite  (p.  534)  are  also  sometimes  classed  "here. 

Inesite.  H2(Mn,Ca)6Si6Oi9.3H2O.  Crystals  small,  prismatic;  also  fibrous,  radiated  and 
spherulitic.  H.  =  6.  G.  =  3'029.  Color  rose-  to  flesh-red.  Occurs  at  the  manganese 
mines  near  Dillenburg,  Germany.  Rhodotilite  is  the  same  species  from  the  Harstig  mine, 
Pajsberg,  Sweden.  From  Jakobsberg  and  Langban,  Sweden ;  Villa  Corona,  Durango,  Mexico. 

Hillebrandite.  Ca2SiO4.H2O.  Orthorhombic;  radiating  fibrous.  H.  =  5'5.  G.=  27. 
Refractive  index  =  1*61.  Color  white.  Fusible  with  difficulty.  Found  in  contact  zone 
between  limestone  and  diorite  in  the  Velardena  mining  district,  Mexico. 

Crestmoreite.  Probably  4H2CaSiO4.3H2O.  Compact.  Color,  snow-white.  H.  =  3. 
G.  =  2'2.  ft  =  T59.  An  alteration  product  of  Wilkeite.  From  Crestmore,  Riverside  Co., 

Riversideite.  2CaSiO6.H2O.  In  compact  fibrous  veinlets.  Silky  luster.  H.  =  3. 
G.  =  2-64.  Indices,  1  "59-1 '60.  Easily  fusible.  From  Crestmore,  Riverside  Co.,  Cal. 

Ganophyllite.  7MnO.Al2O3.8SiO2.6H2O.  In  short  prismatic  crystals;  also  foliated, 
micaceous.  Color  brown.  H.  =  4~4'5.  G.  =  2'84.  Biaxial,  -.  Indices,  17Q5-1730. 
From  the  Harstig  mine,  near  Pajsberg,  Sweden. 

Lotrite.  3(Ca,Mg)O.2(Al,Fe)2O3.4SiO2.2H2O.  Massive,  in  an  aggregate  of  small 
grains  and  leaves.  One  cleavage.  H.  =  7'5.  G.=  3'2.  Color  green.  Refractive  index, 
1'67.  Found  in  small  veins  in  a  chlorite  schist  in  the  valley  of  the  Lotru,  Transylvania. 

.  Okenite.  H2CaSi2O6.H2O.  Commonly  fibrous;  also  compact.  H.  =  4'5-5.  G.  =  2'28- 
2 '36.  Color  white,  with  a  shade  of  yellow  or  blue.  Biaxial,  — .  Index,  1'556.  Occurs  in 
basalt  or  related  eruptive  rocks;  as  in  the  Faroe  Islands;  Iceland;  Disko,  Niorkornat,  etc., 
Greenland;  Poona,  India.  From  Crestmore,  Riverside  Co.,  Cal. 

Gyrolite.  H2Ca2Si3O9.H2O.  Rhombohedral-tetartohedral.  In  white  concretions, 
lamellar-radiate  in  structure.  Optically  -.  co  =  1'56.  From  the  Isle  of  Skye,  with 
stilbite,  laumontite,  etc.;  in  India,  etc.  With  apophyllite  of  New  Almaden,  California; 
also  Nova  Scotia.  Found  also  at  various  places  in  Bohemia;  from  Scotland  and  the  Faroe 
Islands;  Sao  Paulo,  Brazil.  Reyerite  from  Greenland  is  similar  to  gyrolite.  Zeophyllite  is 
a  similar  species  which  may  be  identical  with  gyrolite.  Rhombohedral.  In  spherical 
forms  with  radiating  foliated  structure.  Perfect  basal  cleavage.  H.  =  3.  G.  =  2*8. 
Color  white,  u  =  1'56.  From  various  localities  in  Bohemia  and  elsewhere. 

APOPHYLLITE. 

Tetragonal.     Axis  c  =  1  -2515. 

926  927  928  929 


ay,  100  A  310 
cp,  001  A  111 


18°  26'. 
60°  32'. 


op,    100  A  111 
pp',  111  A  Til 


52°  0'. 
76°  0'. 


/™it  Taried'  in  scluare  Prisms  («  (100))  usually  short  and  terminated  by 
-)  or  by  o  and  p  (111),  and  then  resembling  a  cube  or  cubo-octahedron; 


SILICATES  547 

also  acute  pyramidal  (p  (111))  with  or  without  c  and  a;  less  often  thin  tabu- 
lar II  c.  Faces  c  often  rough;  a  bright  but  vertically  striated;  p  more  or  less 
uneven.  Also  massive  and  lamellar;  rarely  concentric  radiated. 

Cleavage:  c  (001)  highly  perfect;  m  (110)  less  so.  Fracture  uneven. 
Brittle.  H.  =  4-5-5.  G.  =  2-3-2-4.  Luster  of  c  pearly;  of  other  faces 
vitreous.  Color  white,  or  grayish;  occasionally  with  a  greenish,  yellowish,  or 
rose-red  tint,  flesh-red.  Transparent;  rarely  nearly  opaque.  Birefringence 
low;  usually  +,  also  — .  Often  shows  anomalous  optical  characters  (Art. 
429,  Fig.  617).  Indices,  1-535-1-537. 

Comp.  —  H7KCa4(SiO3)8.4fH20  or  K20.8Ca0.16SiO2.16H20  =  Silica 
537,  lime  25-0,  potash  5-2,  water  16*1  =  100.  A  small  amount  of  fluorine 
replaces  part  of  the  oxygen. 

The  above  formula  differs  but  little  from  H2CaSi2O6.H2O,  in  which  potassium  replaces 
part  of  the  basic  hydrogen.  The  form  often  accepted,  H2(Ca,K)Si2O6.H2O,  corresponds 
less  well  with  the  analyses. 

Pyr.,  etc.  —  In  the  closed  tube  exfoliates,  whitens,  and  yields  water,  which  reacts  acid. 
B.B.  exfoliates,  colors  the  flame  violet  (potash),  and  fuses  to  a  white  vesicular  enamel. 
F.  =  1*5.  Decomposed  by  hydrochloric  acid,  with  separation  of  slimy  silica. 

Diff.  —  Characterized  by  its  tetragonal  form,  the  square  prism  and  pyramid  the  com- 
mon habits;  by  the  perfect  basal  cleavage  and  pearly  luster  on  this  surface. 

Obs.  —  Occurs  commonly  as  a  secondary  mineral  in  basalt  and  related  rocks,  with 
various  zeolites,  also  datolite,  pectolite,  calcite;  also  occasionally  in  cavities  in  granite, 
gneiss,  etc.  Greenland,  Iceland,  the  Faroe  Islands,  and  British  India,  especially  at  Poonah, 
afford  fine  specimens  of  apophyllite  in  amygdaloidal  basalt  or  diabase.  Occurs  also  at 
Andreasberg,  Harz  Mts.,  Germany,  of  a  delicate  pink;  Radautal  in  the  Harz  Mts.;  at 
Orawitza,  Hungary,  with  wollastonite;  Uto,  Sweden;  on  the  Seisser  Alp  in  Tyrol,  Austria; 
Guanajuato,  Mexico,  often  of  a  beautiful  pink  upon  amethyst. 

In  the  United  States,  large  crystals  occur  at  Bergen  Hill,  Paterson,  West  Paterson, 
and  Great  Notch,  N.  J.;  in  Pa.,  at  the  French  Creek  mines,  Chester  Co.;  at  the  Cliff, 
Phoenix  and  other  mines,  Lake  Superior  region;  Table  Mt.  near  Golden,  Col.;  in  Cal., 
at  the  mercury  mines  of.  New  Almaden  often  stained  brown  by  bitumen;  also  from  Nova 
Scotia  at  Cape  Blomidon,  and  other  points. 

Named  by  Haiiy  in  allusion  to  its  tendency  to  exfoliate  under  the  blowpipe,  from  airb 
and  (f>v\\oi>,  a  leaf.  Its  whitish  pearly  aspect,  resembling  the  eye  of  a  fish  after  boiling,  gave 
rise  to  the  earlier  name  Ichthyophthalmite,  from  ixOvs,  fish,  6<f>da\iJi6s,  eye, 

2.  Zeolites 

The  ZEOLITES  form  a  family  of  well-defined  hydrous  silicates,  closely  re- 
lated to  each  other  in  composition,  in  conditions  of  formation,  and  hence  in 
mode  of  occurrence.  They  are  often  with  right  spoken  of  as  analogous  to 
the  Feldspars,  like  which  they  are  all  silicates  of  aluminium  with  sodium  and 
calcium  chiefly,  also  rarely  barium  and  strontium;  magnesium,  iron,  etc.,  are 
absent  or  present  only  through  impurity  or  alteration.  Further,  the  com- 
position in  a  number  of  cases  corresponds  to  that  of  a  hydrated  feldspar;  while 
fusion  and  slow  recrystallization  result  in  the  formation  from  some  of  them  of 
aiiorthite  (CaAl2Si2Og)  or  a  calcium-albite  (CaA^SieOie)  as  shown  by  Doelter. 
The  Zeolites  do  riot,  however,  form  a  single  group  of  species  related  in  crystal- 
lization, like  the  Feldspars,  but  include  a  number  of  independent  groups 
widely  diverse  in  form  and  distinct  in  composition;  chief  among  these  are 
the  monoclinic  PHILLIPSITE  GROUP;  the  rhombohedral  CHABAZITE  GROUP, 
and  the  orthorhombic  (and  monoclinic)  NATROLITE  GROUP.  A  transition  in 
composition  between  certain  end  compounds  has  been  more  or  less  well- 
established  in  certain  cases,  but,  unlike  the  Feldspars,  with  these  species  cal- 
cium and  sodium  seem  to  replace  one  another  and  an  increase  in  alkali  does  not 
necessarily  go  with  an  increase  in  silica. 


548  DESCRIPTIVE   MINERALOGY 

Like  other  hydrous  silicates  they  are  characterized  by  inferior  hardness, 
chiefly  from  3-5  to  5-5,  and  the  specific  gravity  is  also  lower  than  with  corre- 
sponding anhydrous  species,  chiefly  2  -0  to  2  -4.  Corresponding  to  these  charac- 
ters; they  are  rather  readily  decomposed  by  acids,  many  of  them'  with  gela- 
tinization.  The  intumescence  B.B.,  which  gives  the  name  to  the  family  (from 
fefi>,  to  boil,  and  \iBos,  stone)  is  characteristic  of  a  large  part  of  the  species. 

The  Zeolites  are  all  secondary  minerals,  occurring  most  commonly  in 
cavities  and  veins  in  basic  igneous  rocks,  as  basalt,  diabase,  etc.;  less  fre- 
quently in  granite,  gneiss,,  etc.  In  these  cases  the  lime  and  the  soda  in  part 
have  been  chiefly  yielded  by  the  feldspar;  the  soda  also  by  elseolite,  sodalite, 
etc. ;  potash  by  leucite,  etc.  The  different  species  of  the  family  are  often  asso- 
ciated together;  also  with  pectolite  and  apophyllite  (sometimes  included  with 
the  zeolites),  datolite,  prehnite  and,  further,  calcite.  Many  of  the  zeolites 
have  been  produced  synthetically  by  various  hydrochemical  reactions.  In 
general  they  appear  to  have  been  formed  in  nature  by  reactions  upon  the  feld- 
spar or  feldspathoid  minerals. 


Ptilolite.  RAl2SiioO24.5H2O.  Here  R  =  Ca  :  K2  :  Na2  =  6  :  2  :  1  approx.  In  short 
capillary  needles,  aggregated  in  delicate  tufts.  Colorless,  white.  Biaxial,  +.  Indices, 
1 '480-1 '485.  Occurs  upon  a  bluish  chalcedony  in  cavities  in  a  vesicular  augite-andesite 
found  in  fragments  in  the  conglomerate  beds  of  Green  and  Table  mountains,  Jefferson  Co., 
and  from  Silver  Cliff,  Custer  Co.,  Col.,  also  from  Elba  and  Iceland. 

Mordenite.  -  3RAl2Si10p24.20H;.O,  where  R  =  K2  :  Na2  :  Ca  =  1  :  1  :  1.  In  minute 
crystals  resembling  heulandite  in  habit  and  angles;  also  in  small  hemispherical  or  reniform 
concretions  with  fibrous  structure.  H.  =  3-4.  G.  =  215.  Color  white,  yellowish  or 
pinkish.  Occurs  near  Morden,  King's  Co.,  Nova  Scotia,  in  trap;  also  in  western  Wyoming 
near  Hoodoo  Mt.,  on  the  ridge  forming  the  divide  between  Clark's  Fork  and  the  East  Fork 
of  the  Yellowstone  river.  Also  from  Seiseralpe,  Tyrol,  Austria  and  the  Faroe  Islands. 


HEULANDITE.     Stilbite  some  authors. 

Monoclinic.     Axes  a  :  b  :  c  =  0-4035  :  1  :  0-4293;  0  =  88°  34J'. 

mm'",  110  A  1TO  =  43°  56'.  cs,   001  A  201  =  66°    0'. 

ct,         001  A  201  =  63°  40'.  ex,  001  A  021  =  40°  38|' 

v£ 


t 


»  Crystals  sometimes  flattened  1 1  b  (010),  the  surface  of  pearly 

\  luster  (Fig.  930;  also  Fig.  21,  p.  12);  form  often  suggestive  of 
the  orthorhombic  system,  since  the  angles  cs  and  ct  differ  but 
little.  Also  in  globular  forms;  granular. 

Cleavage:  b  (010)  perfect.  Fracture  subconchoidal  to  un- 
even. Brittle.  H.  =  3-5-4.  G.  =  2-18-2-22.  Luster  of  6 
strong  pearly;  of  other  faces  vitreous.  Color  various  shades 
of  wmte,  passing  into  red,  gray  and  brown.  Streak  white. 
Transparent  to  subtranslucent.  Optically  +.  Ax.  pi.  and 
Bxa  _L  b  (010).  Ax.  pi.  and  Bx0  for  some  localities  nearly  ||  c 
also  for  others  nearly  _L  c  in  white  light.  Bx0  A  c  axis  =  +  57J° 
Axial  angle  variable,  from  0°  to  92°;  usually  2Er  =  52°.  a  =  1-498. 
P  =  1-^:99.  7  =  1-505. 

Comp.  —  H4CaAl2(Si03)6.3H20  or  5H2O.CaO.Al2O3.6SiO2  =  Silica  59'2, 
alumina  16'8,  lime  9'2,  water  14'8  =  100. 


Strontia  is  usuaUy  present,  sometimes  up  to  3 '6  p.  c. 
Pyr.  —  As  with  stilbite,  p.  551. 


SILICATES 


549 


Obs.  —  Heulandite  occurs  principally  in  basaltic  rocks,  associated  with  chabazite,  stil- 
bite and  other  zeolites;  also  in  gneiss,  and  occasionally  in  metalliferous  veins. 

The  finest  specimens  of  this  species  come  from  Berufiord,  and  elsewhere  in  Iceland; 
the  Faroe  Islands;  in  British  India,  near  Bombay;  also  in  railroad  cuttings  in  the  Bhor 
and  Thul  Ghats.  Also  occurs  in  the  Kilpatrick  Hills,  near  Glasgow;  on  the  Island  of 
Skye;  Fassatal,  Tyrol,  Austria;  Andreasberg,  Harz  Mts.,  Germany;  Viesch  and  elsewhere, 
Switzerland. 

In  the  United  States,  in  diabase  at  Bergen  Hill,  West  Paterson  and  Great  Notch,  N.  J.; 
on  north  shore  of  Lake  Superior;  with  haydenite  at  Jones's  Falls  near  Baltimore  (beau- 
montite),  Md.  At  Peter's  Point,  Nova  Scotia;  also  at  Cape  Blomidon,  and  other  points. 

Named  after  the  English  mineralogical  collector,  H.  Heuland,  whose  cabinet  was  the 
basis  of  the  classical  work  (1837)  of  Levy. 

Brewsterite.  H4(Sr,Ba,Ca)Al2(SiO3)6.3H2O.  In  prismatic  crystals.  H.  =5.  G.  =  2-45. 
Color  white,  inclining  to  yellow  and  gray.  Biaxial,  +.  Index,  1*45.  From  Strontian 
in  Argyleshire,  Scotland;  near  Freiburg  in  Breisgau,  Germany. 

Epistilbite.  Probably  like  heulandite,  H4CaAl2(SiO3)6.3H2O.  Crystals  monoclinic, 
uniformly  twins;  habit  prismatic.  In  radiated  spherical  aggregations;  also  granular. 
G.  =  2-25.  Color  white.  Biaxial,-.  Indices,  1 '502-1 '512.  Occurs  with  scolecite  at  the, 
Berufiord,  Iceland;  the  Faroe  Islands;  Poona,  India;  in  small  reddish  crystals,  at  Mar- 
garet ville,  Nova  Scotia,  etc.  Reissite  is  from  Santorin  Island. 


Wellsite 
Phillipsite 
Harmotome 
Stilbite 


Phillipsite  Group. 

Monoclinic 

a 

6 

c 

(Ba,Ca,K2)Al2Si3010.3H2O 

0-768 

1 

1-245 

(K2,Ca)Al2Si4012.4iH2O 

0-7095 

1 

1-2563 

(K2,Ba)Al2Si5O14.5H20 

0-7032 

1 

1-2310 

(Na2,Ca)Al2Si6O16.6H2O 

0-7623 

1 

1-1940 

53° 
55° 
55° 
50° 


27' 
37' 
10' 
50' 


The  above  species,  while  crystallizing  in  the  monoclinic  system,  are  remark- 
able for  the  pseudo-symmetry  exhibited  by  their  twinned  forms.  Certain  of 
these  twins  are  pseudo-orthorhombic,  others  pseudo-tetragonal  and  more  com- 
plex twins  even  pseudo-isometric. 

Fresenius  has  shown  that  the  species  of  this  group  may  be  regarded  as  forming  a  series, 
in  which  the  ratio  of  RO  :  A12O3  is  constant  (=  1  :  1),  and  that  of  SiO2  :  H2O  also  chiefly 
1:1.  The  end  compounds  assumed  by  him  are: 

RAl2Si6Oi6.6H2O;  R2Al4Si4O16.6H2O. 

Here  R  =  Ca  chiefly,  in  phillipsite  and  stilbite,  Ba  in  harmotome,  while  in  wellsite  Ba, 
Ca,  and  K2  are  present;  also  in  smaller  amounts  Na2,  Sr2.  The  first  of  the  above  compounds 
may  be  regarded  as  a  hydrated  calcium  albite, 
the  second  as  a  hydrated  anorthite.  Pratt 
and  Foote,  however,  show  that  the  anorthite 
end  compound  more  probably  has  the  for- 
mula RAl2Si2O  ;.2H2O  (or  this  doubled) .  The 
formulas  given  beyond  are  those  correspond- 
ing to  reliable  analyses  of  certain  typical 
occurrences. 


931 


932 


Wellsite.  RAl2Si3Oio.3H2O  with  R  =  Ca  : 
Ba  :  K2  =  3  :  1  :  3;  Sr  and  Na  also  present 
in  small  amount.  Percentage  composition: 
SiO2  42-9,  A12O3  24-3,  BaO6'6,  CaO  7'3,  K2O 
6'  1,  H2O  12-8  =  100.  Monoclinic  (axes  above) ; 
in  complex  twins,  analogous  to  those  of 
phillipsite  and  harmotome  (Figs.  931,  932). 

Brittle.     No  cleavage.     H.  =  4-4'5.     G.  =  2'278-2'366.     Luster  vitreous.     Colorless  to 
white.     Optically  +.     Bx  _L  b  (010).     Birefringence  weak. 

Occurs  at  the  Buck  Creek  (Cullakanee)  corundum  mine  in  Clay  Co.,  N.  C.;  in  isolated 
crystals  attached  to  feldspar,  also  to  hornblende  and  corundum;  intimately  associated  with 
chabazite.  Also  found  at  Kurzy  near  Simferopol,  Crimea,  Russia. 


550 


DESCRIPTIVE    MINERALOGY 


PHILLIPSITE. 

Monoclinic.     Axes  a  :  b  :  c  =  07095  :  1  :  1-2563;  ft  =  55°  37'. 

mm"'    110  A  HO  =  60°  42'.  cm,  001  A  110  =  60°  50'. 

a/,         100  A  101  =  34°  23'.  ee',   Oil  A  Oil  =  92°    4'. 


933 


Crystals  uniformly  penetration-twins,  but  often 
simulating  orthorhombic  or  tetragonal  forms.  Twins 
sometimes,  but  rarely,  simple  (1)  with  tw.  pi.  c  (001) . 
and  then  cruciform  so  that  diagonal  parts  on  b  (010) 
belong  together,  hence  a  fourfold  striation,  ||  edge 
b/m,  may  be  often  observed  on  b.  (2)  Double  twins, 
the  simple  twins  just  noted  united  with  e  (Oil)  as 
tw.  pi.,  and,  since  ee'  varies  but  little  from  90°, 
the  result  is  a  nearly  square  prism,  terminated 
by  what  appear  to  be  pyramidal  faces  each  with  a 
double  series  of  striations  away  from  the  medial  line. 
See  Figs.  452-454,  p.  172;  also  Fig.  400,  p.  164. 
Faces  6  (010)  often  finely  striated  as  just  noted,  but  striations  sometimes 
absent  and  in  general  not  so  distinct  as  with  harmotome;  also  m  (110) 
striated  ||  edge  b/m.  Crystals  either  isolated,  or  grouped  in  tufts  or  spheres, 
radiated  within  and  bristled  with  angles  at  surface. 

Cleavage:  c  (001),  6  (010),  rather  distinct.  Fracture  uneven.  Brittle. 
H.  =  4-4-5.  G.  =  2-2.  Luster  vitreous.  Color  white,  sometimes  reddish. 
Streak  uncolored.  Translucent  to  opaque.  Optically  +.  Ax.  pi.  and  Bx0 
J_  b  (010) .  The  ax.  pi.  lies  in  the  obtuse  angle  of  the  a-c  axes,  and  is  usually 
inclined  to  a  axis  about  15°  to  20°,  or  75°  to  70°  to  the  normal  to  c  (001) .  The 
position,  however,  is  variable.  2Ha.r  =  71°-84°.  Indices,  1-48-1-57. 

Comp.  —  In  some  cases  the  formula  is  (K2,Ca) Al2Si4Oi2.4H2O  =  Silica 
48-8,  alumina  207,  lime  7-6,  potash  6-4,  water  16-5  =  100.  Here  Ca  :  K2 
=  2:1. 

Pyr.,  etc.  —  B.B.  crumbles  and  fuses  at  3  to  a  white  enamel.  Gelatinizes  with  hydro- 
chloric acid. 

Obs.  —  In  translucent  crystals  in  basalt,  at  the  Giant's  Causeway.  Ireland;  at  Capo  di 
Bove,  near  Rome;  Aci  Castello  and  elsewhere  in  Sicily;  among  the  lavas  of  Mte.  Somma, 
Vesuvius;  in  Germany  at  Stempel,  near  Marburg;  Annerod,  near  Giessen;  in  the  Kaiser- 
stuhl,  with  faujasite,  at  Salesl,  Bohemia;  in  the  ancient  lavas  of  the  Puy-de-D6me,  France; 
from  Richmond,  Victoria.  Pseudophillipsite,  found  near  Rome,  Italy,  differs  from  phillips- 
ite  only  in  the  manner  in  which  it  loses  water  on  heating. 


HARMOTOME. 


934 


Monoclinic.  Axes  a  :  b  :  c  =  0*7031  :  1  :  1-2310;  ft  = 
55°  10'. 

Crystals  uniformly  cruciform  penetration-twins  with  c 
(001)  as  tw.  pi;  either  (1)  simple  twins  (Fig.  934)  or  (2) 
united  as  fourlings  with  tw.  pi.  e  (Oil).  These  double 
twins  often  have  the  aspect  of  a  square  prism  with  diag- 
onal pyramid,  the  latter  with  characteristic  feather-like 
striations  from  the  medial  line.  Also  in  more  complex 
groups  analogous  to  those  of  phillipsite. 

Cleavage:  b  (010)  easy,  c  (001)  less  so.  Fracture 
uneven  to  subconchoidal.  Brittle.  H.  =  4-5.  G.  =  2-44- 
2-50.  Luster  vitreous.  Color  white;  passing  into  gray, 
yellow,  red  or  brown.  Streak  white.  Subtransparent  to  translucent, 


SILICATES  551 

Ax.  pi.  and  Bxa  J_  b  (010).  Ax.  pi.  in  obtuse  angle  a-c  axes  and  inclined  about 
65°  to  a  axis  and  60°  to  c  axis.  Optically  +  .  2V  =  43°.  a  =  1-503.  ft  = 
1-505.  7  =  1-508. 

Comp.  —  In  part  H2(K2,Ba)Al2Si5Oi5.4H2O  or  (K2,Ba)O.Al2O3.5SiO2. 
5H2O  =  Silica  47-1,  alumina  16-0,  baryta  20'6,  potash  2-1,  water  14-1  =  100. 

Pyr.,  etc.  —  B.B.  whitens,  then  crumbles  and  fuses  without  intumescence  at  3'5  to  a 
white  translucent  glass.  Some  varieties  phosphoresce  when  heated.  Decomposed  by 
hydrochloric  acid  without  gelatinizing. 

Obs.  —  Occurs  in  basalt  and  similar  eruptive  rocks,  also  phonolite,  trachyte;  not  infre- 
quently on  gneiss,  and  in  some  metalliferous  veins.  AtStrontian,  in  Scotland;  in  a  metal- 
liferous vein  at  Andreasberg  in  the  Harz  Mts.,  Germany;  at  Rudelstadt,  Silesia;  Oberstein, 
Germany,  on  agate  in  siliceous  geodes;  at  Kongsberg,  Norway. 

In  the  United  States,  in  small  brown  crystals  with  stilbite  on  the  gneiss  of  New  York 
Island;  near  Port  Arthur,  Lake  Superior. 

Named  from  ap/zos,  joint,  and  r'env&v,  to  cut,  alluding  to  the  fact  that  the  pyramid 
(made  by  the  prismatic  faces  in  twinning  position)  divides  parallel  to  the  plane  that  passes 
through  the  terminal  edges. 

STILBITE.     Desmine. 

Monoclinic.     Axes  a:b:.c  =  0-7623  :  1  :  1-1940;  ft  =  50°  50'. 
Crystals  uniformly  cruciform  penetration-twins  with  tw.  pi.  c  (001),  analo- 
gous to  phillipsite  and  harmotome.     The  apparent  form  a  rhombic  pyramid 
whose  faces  are  in  fact  formed  by  the  prism  faces  of  the  two  individuals;  the 
vertical  faces  being  then  the  pinacoids  6  (010)  and  c  (001)  (cf. 
Figs.  613-615,  p.  299).     Usually  thin  tabular  ||  b  (010).     These          935 
compound  crystals  are  often  grouped  in  nearly  parallel  position, 
forming  sheaf -like  aggregates  with  the  side  face   (b),   showing 
its  characteristic  pearly  luster,  often  deeply  depressed.     Also 
divergent  or  radiated;    sometimes  globular  and  thin  lamellar- 
columnar. 

Cleavage:  6  (010)  perfect.  Fracture  uneven.  Brittle. 
H.  =  3-5-4.  G.  =  2-094-2-205.  Luster  vitreous;  of  b  (010) 
pearly.  Color  white;  occasionally  yellow,  brown  or  red,  to 
brick-red.  Streak  uncolored.  Transparent  to  translucent. 
Optically  — .  Ax.  pi.  ||  b  (010).  Bxa  inclined  5°  to  axis  a  in 
obtuse  angle  a-c  axes;  hence  Bxa  A  caxis  =  —  55°  50'.  2V  = 
33°  (approx.).  a  =  1-494.  ft  =  1-498.  7  =  I'SOO. 

Comp.  —  For  most  varieties  H4(Na2,Ca)Al2Si6Oi8.4H2O  or 
(Na2,Ca)O.Al2O3.6SiO2.6H2O  =  Silica   57-4,    alumina   16-3,   lime  7-7,   soda 
1-4,  water  17 -2  =  100.     Here  Ca  :  Na,  =  6  :  1. 

Some  kinds  show  a  lower  percentage  of  silica,  and  these  have  been  called  hypostilbite. 

Pyr.,  etc.  —  B.B.  exfoliates,  swells  up,  curves  into  fan-like  or  yermicular  forms,  and 
fuses  to  a  white  enamel.  F.  =  2-2*5.  Decomposed  by  hydrochloric  acid,  without  gelati- 
nizing. 

Diff.  —  Characterized  by  the  frequency  of  radiating  or  sheaf-like  forms;  by  the  pearly 
luster  on  the  clinopinacoid.  Does  not  gelatinize  with  acids. 

Obs.  —  Stilbite  occurs  mostly  in  cavities  in  amygdaloidal  basalt,  and  similar  rocks.  It 
is  also  found  in  some  metalliferous  veins,  and  in  granite  and  gneiss. 

Abundant  on  the  Faroe  Islands;  in  Iceland;  on  the  Isle  of  Skye,  in  amygdaloid ;  also  in 
Dumbartonshire,  Scotland,  in  red  crystals;  the  Giant's  Causeway,  Ireland;  at  Andreas- 
berg  in  the  Harz  Mts.,  Germany,  and  Kongsberg  and  Arendal  in  Norway,  with  iron  ore; 
on  the  Seisser  Alp  in  Tyrol,  Austria,  and  at  the  Puflerloch  (puflerite) ;  on  the  granite  of 
Striegau,  Silesia.  A  common  mineral  in  the  Deccan  trap  area  of  British  India. 

In  North  America,  sparingly  in  small  crystals  at  Chester  and  at  the  Somerville  syenite 
quarries,  Mass.;  at  Phillipstown,  N.  Y.;  and  at  Bergen  Hill,  West  Paterson  and  Great 
Notch,  N.  J.;  also  at  the  Michipicoten  Islands,  Lake  Superior.  In  Nova  Scotia  at  Part- 
ridge Island,  also  at  Isle  Haute,  Two  Islands,  Digby  Neck,  Cape  Blomidon,  etc. 

The  name  stilbite  is  from  arlX^rj,  luster,  and  desmine  from  d'caw,  a  bundle. 


552  DESCRIPTIVE   MINERALOGY 

Flokite.  H8(Ca,Na2)Al2Si9026.2H20.  Monoclinic.  In  slender  prismatic  crystals. 
Perfect  cleavages  parallel  to  (100)  and  (010).  H.  =  5.  G.  =  2 -10.  Colorless  and  trans- 
parent. Indices,  1  '472-1  '474.  Fuses  with  intumescence.  From  Iceland. 

Gismondite.  Perhaps  CaAl2Si2O8.4H2O.  In  pyramidal  crystals,  pseudo-tetragonal. 
H  =  4'5  G.  =  2-265.  Colorless  or  white,  bluish  white,  grayish,  reddish.  Biaxial.  -. 
Index  1-539.  Occurs  in  the  leucitophyre  of  Mt.  Albano,  near  Rome,  at  Capo  di  Bove, 
and  elsewhere,  etc.;  on  the  Gorner  glacier,  near  Zermatt,  Switzerland;  Schlauroth  near 
Gorlitz  in  Silesia;  Salesl,  Bohemia,  etc. 

LAUMONTITE.     Leonhardite.     Caporcianite. 

Monoclinic.     Axes  a  :  b  :  c  =  M451  :  1  :  0-5906;  0  =  68°  46'. 

Twins-  tw.  pi.  a  (100).  Common  form  the  prism  m  (mm'"  110  A  110  = 
93°  440  with  oblique  termination  e,  201  (ce  001  A  201  =  56°  55').  Also 
columnar,  radiating  and  divergent. 

Cleavage:  6  (010)  and  m  (110)  very  perfect;  a  (100)  imperfect.  Fracture 
uneven.  Not  very  brittle.  H.  =  3 -5-4.  G.  =  2-25-2-36.  Luster  vitreous, 
inclining  to  pearly  upon  the  faces  of  cleavage.  Color  white,  passing  into 
yellow  or  gray,  sometimes  red.  Streak  uncolored.  Transparent  to  trans- 
lucent; becoming  opaque  and  usually  pulverulent  on  exposure.  Optically  — . 
Ax.  pi.  ||  b  (010).  Bxa  A  c  axis  =  +  65°  to  70°.  Dispersion  large,  p  <  v; 
inclined,  slight.  2Er  =  52°  24'.  a  =  1-513.  0  =  1'524.  7  =  1*525. 

Comp.  —  H4CaAl2Si4Oi4.2H20  =.  4H2O.CaO.Al2O3.4SiO2  =  Silica  51% 
alumina  217,  lime  11-9,  water  15-3  =  100. 

Var.  —  Leonhardite  is  a  laumontite  which  has  lost  part  of  its  water  (to  one  molecule), 
and  the  same  is  probably  true  of  caporcianite.  Schneiderite  is  laumontite  from  the  serpen- 
tine of  Monte  Catini,  Italy,  which  has  undergone  alteration  through  the  action  of  magnesian 
solutions. 

Pyr.,  etc.  —  B.B.  swells  up  and  fuses  at  2'5-3  to  a  white  enamel.  Gelatinizes  with 
hydrochloric  acid. 

Obs.  —  Occurs  in  the  cavities  of  basalt  and  similar  eruptive  rocks;  also  in  porphyry 
and  syenite,  and  occasionally  in  veins  traversing  clay  slate  with  calcite. 

Its  principal  localities  are  the  Faroe  Islands;  Disko  in  Greenland;  in  Bohemia,  at  Eule 
in  clay  slate;  St.  Gothard  in  Switzerland;  Baveno,  Italy;  Nagyag,  Transylvania;  the 
Fassatal,  Tyrol,  Austria;  the  Kilpatrick  hills,  near  Glasgow,  Scotland;  the  Hebrides,  and 
the  north  of  Ireland.  In  India,  in  the  Deccan  trap  area,  at  Poona,  etc. 

Peter's  Point,  Nova  Scotia,  affords  fine  specimens  of  this  species.  Found  at  Phipps- 
burg,  Me.  Abundant  in  many  places  in  the  copper  veins  of  Lake  Superior  in  trap,  and  on 
Isle  Royale;  on  north  shore  of  Lake  Superior,  between  Pigeon  Bay  and  Fond  du  Lac. 
Found  also  at  Bergen  Hill,  N.  J.;  at  the  Tilly  Foster  iron  mine,  Brewster,  N.  Y. 

Laubanite.  CaaAUSuOu.GHjjO.  Resembles  stilbite.  H.  =  4'5-5.  G.  =  2'23.  Color 
snow-white.  Occurs  upon  phillipsite  in  basalt  at  Lauban,  Silesia. 

Chabazite  Group.     Rhombohedral 

rr'.  c 

Chabazite         (Ca,Na2)Al2Si4012.6H20        85°  14'       1;0860 
Gmelinite         (Na2Ca)Al2Si4Oi2.6H20         68°     8'      07345  or  fc  =  1*1017 
Levynite  CaAl2Si3Oi0.5H20  73°  56'      0'8357        fc  =  1-1143 

The  Chabazite  Group  includes  these  three  rhombohedral  species.  The 
fundamental  rhombohedrons  have  different  angles,  but,  as  shown  in  the  axial 
ratios  above,  they  are  closely  related,  since,  taking  the  rhombohedron  of 
Chabazite  as_  the  basis,  that  of  Gmelinite  has  the  symbol  (2023)  and  of 
Levynite  (3034). 

The  variation  in  composition  often  observed  in  the  first  two  species  has  led  to  the  rather 


SILICATES  553 

plausible  hypothesis  that  they  are  to  be  viewed  as  isomorphous  mixtures  of  the  feldspar-like 
compounds 

(Ca,Na2)Al2Si2O8.4H2O,  (Ca,Na2)Al2Si6Oi6.8H2O. 

CHABAZITE. 
Rhombohedral.     Axis  c  =  1-0860;  0001  A  1011  =  51°  25f. 

936  937  938 


Phacolite 


Twins:  (1)  tw.  axis  c  axis,  penetration-twins  common.  (2)  Tw.  pi. 
r(1011);  contact-twins,  rare.  Form  commonly  the  simple  rhombohedron 
varying  little  in  angle  from  a  cube  (rrf  1101  A  1101  =  85°  14');  also  r  and 
e  (0112),  (eef '  =  54°  47').  Also  in  complex  twins.  Also  amorphous. 

Cleavage:  r  (1011)  rather  distinct.  Fracture  uneven.  Brittle.  H.  = 
4-5.  G.  =  2-08-2-16.  Luster  vitreous.  Color  white,  flesh-red;  streak 
uncolored.  Transparent  to  translucent.  Optically  — ;  also  +  (Andreas- 
berg,  also  haydenite).  Birefringence  low.  The  interference-figure  usually 
confused;  .sometimes  distinctly  biaxial;  basal  sections  then  divided  into 
sharply  defined  sectors  with  different  optical  orientation.  These  anomalous 
optical  characters  probably  secondary  and  chiefly  conditioned  by  the  variation 
in  the  amount  of  water  present.  Mean  refractive  index  1-5. 

Var.  —  1.  Ordinary.  The  most  common  form  is  the  fundamental  rhombohedron,  in 
which  the  angle  is  so  near  90°  that  the  crystals  were  at  first  mistaken  for  cubes.  Acadialite, 
from  Nova  Scotia  (Acadia  of  the  French  of  18th  century),  is  a  reddish  chabazite;  sometimes 
nearly  colorless.  Haydenite  is  a  yellowish  variety  in  small  crystals  from  Jones's  Falls,  near 
Baltimore,  Md.  2.  Phacolite  is  a  colorless  variety  occurring  in  twins  of  hexagonal  form 
(Fig.  938),  and  lenticular  in  shape  (whence  the  name,  from  0a/c6s,  a  bean)',  the  original 
was  from  Leipa  in  Bohemia.  Here  belongs  also  herschelite  (seebachite)  from  Richmond, 
Victoria;  the  composite  twins  of  great  variety  and  beauty.  Probably  also  the  original 
herschelite  from  Sicily.  It  occurs  in  flat,  almost  tabular,  hexagonal  prisms  with  rounded 
terminations  divided  into  six  sectors. 

Comp.  —  Somewhat  uncertain,  since  a  rather  wide  variation  is  often 
noted  even  among  specimens  from  the  same  locality.  The  ratio  of 
(Ca,Na2,K2)  :  Al  is  nearly  constant  (=  1  :  1),  but  of  A12  :  Si  varies  from  1  :  3 
to  1  :  5 ;  the  water  also  increases  with  the  increase  in  silica.  The  composition 
usually  corresponds  to  (Ca,Na2)Al2Si4Oi2.6H2O,  which,  if  calcium  alone  is 
present,  requires:  Silica  47 -4,  alumina  20'2,  lime  11-1,  water  21 -3  =  100.  If 
Ca  :  Nao  =  1:1,  the  percentage  composition  is:  Silica  47*2,  alumina  20*0, 
lime  5-5,  soda  6-1,  water  21-2  =  100. 

Potassium  is  present  in  small  amount,  also  sometimes,  barium  and  strontium.  Streng 
explains  the  supposed  facts  most  satisfactorily  by  the  hypothesis  that  the  members  of  the 
group  are  isomorphous  mixtures  analogous  to  the  feldspars,  as  noted  above. 

Pyr.,  etc.  —  B.B.  intumesces  and  fuses  to  a  blebby  glass,  nearly  opaque.  Decomposed 
by  hydrochloric  acid,  with  separation  of  slimy  silica. 


554  DESCRIPTIVE   MINERALOGY 

Diff  —Characterized  by  rhombohedral  form  (resembling  a  cube).  It  is  harder  than 
calcite  and  does  not  effervesce  with  acid;  unlike  calcite  and  fluonte  in  cleavage;  fuses  B.B. 
with  intumescence  unlike  analcite. 

Obs.  —  Occurs  mostly  in  basaltic  rocks,  and  occasionally  m  gneiss,  syenite,  mica  schist, 
hornblendic  schist.  Occurs  at  the  Faroe  Islands,  Greenland,  and  Iceland,  associated  with 
chlorite  and  stilbite;  at  Aussig  in  Bohemia;  in  Germany  at  Oberstem,  with  harmotome, 
and  at  Annerod,  near  Giessen;  at  the  Giant's  Causeway,  Antrim,  Ireland,  and  Renfrew- 
shire, Scotland;  Isle  of  Skye,  etc.  In  Australia  (phacolite)  at  Richmond,  near  Melbourne, 

etc 

In  the  United  States,  in  syenite  at  Somerville,  Mass.;  at  Bergen  Hill  and  West  Paterson, 
N.  J.,  in  crystals;  at  Jones's  Falls  near  Baltimore,  Md.  (haydenite).     In  Nova  Scotia,  wine 
yellow  or  flesh-red  (the  last  the  acadialite),  associated  with  heulandite,  analcite  and  calcite, 
at  Five  Islands,  Swan's  Creek,  Digby  Neck,  Two  Islands,  Wasson's  Bluff,  etc. 
The  name  chabazite  is  from  x<*/3«^os,  an  ancient  name  of  a  stone. 

GMELINITE. 

Rhombohedral.     Axis  c  =  0*7345. 

Crystals    usually    hexagonal    in    aspect;     sometimes    p    (0111)    smaller 

than  r(1011),_and  habit  rhombo- 

939  940  hedral;  rr'  10_11  A  1101  =  68°  8', 

rp  1011  A  0111  =  37°  44'. 

Cleavage:     m    (1010)    easy; 
c  (0001)  sometimes  distinct.  Frac- 
ture uneven.    Brittle.    H.  =  4*5. 
G.  =  2-04-2-17.     Luster  vitreous. 
Colorless,  yellowish  white,  green- 
ish white,  reddish   white,  flesh- 
red.    Transparent  to  translucent. 
Optically    positive,    also     nega- 
tive.    Birefringence  very  low.     Interference-figure  often  disturbed,  and  basal 
sections  divided  optically  into  sections  analogous  to  chabazite.     Mean  refrac- 
tive index,  1'47. 

Comp.  —  In  part  (Na2,Ca)Al2Si40i2.6H2O.  If  sodium  alone  is  present 
this  requires:  Silica  46-9,  alumina  19-9,  soda  12-1,  water  21-1  =  100.  See  also 
p.  552. 

Pyr.,  etc.  —  B.B.  fuses  easily  (F.  =  2'5-3)  to  a  white  enamel.  Decomposed  by  hydro- 
chloric acid  with  separation  of  silica. 

Obs.  —  Occurs  in  flesh-red  crystals  in  amygdaloidal  rocks  at  Montecchio  Maggiore, 
Italy;  at  Andreasberg,  Germany;  in  Transylvania;  Antrim,  Ireland;  Talisker  in  Isle  of 
Skye,  in  large  colorless  crystals.  In  Australia  at  Flinders,  Victoria. 

In  the  United  States  in  fine  white  crystals  at  Bergen  Hill,  Great  Notch  and  Paterson, 
N.  J.  At  Cape  Blomidon,  Nova  Scotia  (ledererite) ;  also  at  Two  Islands  and  Five  Islands. 

Named  Gmelinite  after  Prof.  Gmelin  of  Tubingen  (1792-1860). 

Levynite.  CaAl2Si3Oi0.5H.,p.  In  rhombohedral  crystals.  H.  =  4-4'5.  G.  =  2'09-2'lG. 
Colorless,  white,  grayish,  reddish,  yellowish.  Optically  — .  co  =  T50.  Found  at  Glen- 
arm  and  at  Island  Magee,  Antrim,  Ireland;  at  Dalsnypen,  Faroe  Islands,  in  Iceland;  in 
East  Greenland;  in  the  basalt  of  Table  Mountain  near  Golden,  Col. 

Offretite.  A  potash  zeolite,  related  to  the  species  of  the  chabazite  group.  In  basalt 
of  Mont  Simiouse,  France. 


ANALCITE.     Analcime. 


Isometric.  Usually  in  trapezohedrons;  also  cubes  with  faces  n  (211); 
again  the  cubic  faces  replaced  by  a  vicinal  trisoctahedron.  Sometimes  in 
composite  groups  about  a  single  crystal  as  nucleus  (Fig.  389,  p.  161).  -Also 
massive  granular;  compact  with  concentric  structure. 


SILICATES 


555 


942 


Cleavage:  cubic,  in  traces.  Fracture  subconchoidal.  Brittle.  H.  = 
5-5  -5.  G.  =  2-22-2-29.  Luster  vitreous.  Colorless,  white;  occasionally 
grayish,  greenish,  yellowish,  or  reddish  white.  Transparent  to  nearly  opaque. 
Often  shows  weak  double  refrac- 
tion, which  is  apparently  con- 
nected with  loss  of  water  and 
consequent  change  in  molecular 
structure  (Art.  429).  n  =  1-4874. 
Comp.  —  Na  AlSi2  O6  H2  O  = 
Na20.Al2O3.4Si02.2H2O  =  Silica 
54.5,  alumina  23-2,  soda  14-1, 
water  8-2  =  100. 

Analyses    show    always  a  varying 
excess    of     silica     and     water    above 
amounts  required  by  formula.     It  has 
been  assumed  that  a  molecule  containing  the  acid  H2Si2O6  is  present  in  soild  solution  in 
small  amounts. 

Pyr.,  etc.  —  Yields  water  in  the  closed  tube.  B.B.  fuses  at  2'5  to  a  colorless  glass. 
Gelatinizes  with  hydrochloric  acid. 

Diff.  —  Characterized  by  trapezohedral  form,  but  is  softer  than  garnet,  and  yields  water 
B.B.,  unlike  leucite  (which  is  also  infusible);  fuses  without  intumescence  to  a  clear  glass 
unlike  chabazite.  From  leucite  and  spdalite  surely  distinguished  only  by  chemical  tests, 
i.e.,  absence  of  chlorine  in  the  nitric-acid  test  (see  sodalite,  p.  502),  absence  of  much  potash 
and  abundance  of  soda  in  the  solution,  anol  evolution  of  much  water  from  the  powder  in  a 
closed  glass  tube  below  a  red  heat. 

Micro.  —  Recognized  in  thin  sections  by  its  very  low  relief  and  isotropic  character; 
often  shows  optical  anomalies. 

Obs.  —  Occurs  frequently  with  other  zeolites.,  also  prehnite,  calcite,  etc.,  in  cavities  and 
seams  in  basic  igneous  rocks,  as  basalt,  diabase,  etc.:  also  in  granite,  gneiss,  etc.  Recently 
shown  to  be  also  a  rather  widespread  component  of  the  groundmass  of  various  basic 
igneous  rocks,  at  times  being  the  only  alkali-alumina  silicate  present,  as  in  the  so-called 
analcite-basalts.  Has  been  held  in  such  cases  to  be  a  primary  mineral  produced  by  the 
crystallization  of  a  magma  containing  considerable  soda  and  .water  vapor  held  under  pres- 
sure. 

The  Cyclopean  Islands,  near  Catania,  Sicily,  afford  pellucid  crystals;  also  the  Fassatal 
in  Tyrol,  Austria;  other  localities  are,  in  Scotland,  in  the  Kilpatrick  Hills;  Co.  Antrim, 
etc.,  in  Ireland;  the  Faroe  Islands;  Iceland;  near  Aussig,  Bohemia;  at  Arendal,  Norway, 
in  beds  of  iron  ore;  at  Andreasberg,  in  the  Harz  Mts.,  Germany,  in  silver  mines. 

In  the  United  States,  occurs  at  Bergen  Hill  and  West  Paterson,  N.  J.;  in  gneiss  near 
Yonkers,  Westchester  Co.,  N.  Y.;  abundant  in  fine  crystals  with  prehnite,  datolite,  and 
calcite,  in  the  Lake  Superior  region;  at  Table  Mt.  near  Golden,  Col.,  with  other  zeolites. 
Nova  Scotia  affords  fine  specimens. 

The  name  analcime  is  from  avaXms,  weak,  and  alludes  to  its  weak  electric  power 
when  heated  or  rubbed.  The  correct  derivative  is  analcite,  as  here  adopted  for  the  species. 


Faujasite.     Perhaps 

In  isometric  octahedrons.  H.  =5.  G.  =  1'923.  Colorless,  white,  n  =  1'48.  Oc- 
curs with  augite  in  the  limburgite  of  Sasbach  in  the  Kaiserstuhl,  Baden,  Germany,  etc. 

Edingtonite.  Perhaps  BaAl2Si3Oio.3H2O.  Crystals  pyramidal  in  habit  (orthorhombic, 
pseudo-tetragonal);  also  massive.  H.  =  4-4  -5.  G.  =  2*694.  White,  grayish  white,  pink. 
Optically  —  .  Indices,  1*538-1  '554.  Occurs  in  the  Kilpatrick  Hills,  near  Glasgow,  Scot- 
land, with  harmotome.  From  Bohlet,  Sweden. 


Natrolite  Group.     Orthorhombic  and  Monoclinic 


Natrolite 

Scolecite 
Mesolite 


Ca(A10H)2(SiO3)3.2H2O 
(Na2Al2Si3O10.2H2O 
[2[CaAl2Si3Oio.3H2O] 


a 
0*9785 

a 
0-9764 


0-3536 

c 

0-3434 


89°    18' 


556 


DESCRIPTIVE   MINERALOGY 


The  three  species  of  the  NATROLITE  GROUP  agree  closely  in  angle,  though  varying  m 
crystalline  system;  Natrolite  is  orthorhombic  usually,  also  rarely  monoclmic ;  fecolecite  is 
monoclinic,  perhaps  also  in  part  triclinic;  Mesolite  seems  to  be  both  monoclmic  and  tn- 
clinic.  Fibrous,  radiating  or  divergent  groups  are  common  to  all  these  species. 

The  Natrolite  Group  includes  the  sodium  silicate,  Natrolite,  with  the  empirical  formula 
Na2Al2Si3Oi0.2H2O;  the  calcium  silicate,  Scolecite,  CaAlaSigOio.SHaO;  also  Mesolite 

, .  \  mNa2  Al2Si3Oio.2H2O 

intermediate  between  these  and  corresponding  to      nCaAl2Si3Oio.3H2O. 


NATROLITE. 
Orthorhombic.* 

943 


Axes  a  :  b 


944 


c  =  0-9785  :  1  :  0*3536. 

mm"',  110  A  1TO  =  88' 
mo,       110  A  111  =  63 


oo 
oo' 


111  A  111 
111  A  111 


11'. 

37°  38'. 
36°  47£'. 


Crystals  prismatic,  usually  very  slender  to 
acicular;  frequently  divergent,  or  in  stellate 
groups.  Also  fibrous,  radiating,  massive,  gran- 
ular, or  compact. 

Cleavage:  m  (110)  perfect;  b  (010)  imper- 
fect, perhaps  only  a  plane  of  parting.  Frac- 
ture uneven.  H.  =•  5-5'5.  G.  =  2'20-2'25. 
Luster  vitreous,  sometimes  inclining  to  pearly, 
especially  in  fibrous  varieties.  Color  white,  or  colorless;  to  grayish,  yellow- 
ish, reddish  to  red.  Transparent  to  translucent.  Optically  +.  Ax.  pi.  || 
6  (010).  Bx  _L  c  (001).  2V  =  63°.  a  =  1'480.  ft  =  T482.  7  =  T493. 

Var.  —  Ordinary.  Commonly  either  (»)  in  groups  of  slender  colorless  prismatic  crys- 
tals, varying  but  little  in  angle  from  square  prisms,  often  acicular,  or  (6)  in  fibrous  diver- 
gent or  radiated  masses,  vitreous  in  luster,  or  but  slightly  pearly  (these  radiated  forms  often 
resemble  those  of  thomsonite  and  pectolite) ;  often  also  (c)  solid  amygdules,  usually  radiated 
fibrous,  and  somewhat  silky  in  luster  within;  (d)  rarely  compact  massive.  Galactite  is 
ordinarily  natrolite,  in  colorless  needles  from  southern  Scotland. 

Bergmannite,  spreustein,  brevicite,  are  names  which  have  been  given  to  the  natrolite 
from  the  augite-syenite  of  southern  Norway,  on  the  Langesund  fiord,  in  the  "Brevik" 
region,  where  it  occurs,  fibrous,  massive,  and  in  long  prismatic  crystallizations,  and  from 
white  to  red  in  color.  Derived  in  part  from  elaeolite,  in  part  from  sodalite.  Iron-natrolite 
is  a  dark  green  opaque  variety,  either  crystalline  or  amorphous,  from  the  Brevik  region;  the 
iron  is  due  to  inclusions. 

Comp.  —  Na2Al2Si3Oio.2H20  or  Na2O.Al203.3Si02.2H20  =  Silica  474,  alu- 
mina 26-8,  NasO  16-3,  water  9-5  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  whitens  and  becomes  opaque.  B.B.  fuses  quietly  at  2 
to  a  colorless  glass.  Fusible  in  the  flame  of  an  ordinary  wax  candle.  Gelatinizes  with  acids. 

Diff.  —  Distinguished  from  aragonite  and  pectolite  by  its  easy  fusibility  and  gelati- 
nization  with  acid. 

Obs.  —  Occurs  in  cavities  in  amygdaloidal  basalt,  and  other  related  igneous  rocks; 
sometimes  in  seams  in  granite,  gneiss,  and  syenite.  Found  at  Aussig  and  Teplitz  in  Bohe- 
mia; in  fine  crystals  in  Auvergne,  France;  Fassatal,  Tyrol,  Austria;  Kapnik,  Hungary.  In 
red  amygdules  (crocalite)  in  amygdaloid  of  Ireland,  Scotland  and  Tyrol;  the  amygdaloid  of 
Bishopton,  Scotland  (galactite)  and  at  Glen  Farg  (fargite)  in  Fifeshire.  Common  in  the 
augite-syenite  of  the  Langesund  fiord,  near  Brevik,  southern  Norway.  From  various  local- 
ities in  Greenland. 

In  North  America,  in  the  trap  of  Nova  Scotia;  at  Bergen  Hill  and  West  Paterson,  N.  J.; 
at  Copper  Falls,  Lake  Superior;  from  benitoite  locality,  San  Benito  Co.,  Cal. 

Named  Mesotype  by  Haiiy,  from  Me<n>s,  middle,  and  TVTTOS,  type,  because  the  form  of 
the  crystal  —  in  his  view  a  square  prism  —  was  intermediate  between  the  forms  of  stilbite 

*  In  rare  cases  the  crystals  seem  to  be  monoclinic. 


SILICATES  557 

and  analcite.     Natrolite,  of  Klaproth,  is  from  natron,  soda;  it  alludes  to  the  presence  of  soda, 
whence  also  the  name  soda-mesotype,  in  contrast  with  scolecite,  or  lime-mesotype. 

SCOLECITE. 

Monoclinic.     Axes  a  :  b  :  c  =  0-9764  :  1  :  0*3434;  /3  =  89°  18'. 

Crystals  slender  prismatic  (mm'"  110  A  110  =  88°  37%'),  twins  showing  a 
feather-like  striation  on  b  '(010),  diverging  upward;  also  as  penetration-twins. 
Crystals  in  divergent  groups.  Also  massive,  fibrous  and  radiated,  and  in 
nodules. 

Cleavage:  m  (110)  nearly  perfect.  H.  =  5-5-5.  G.  =  2-16-2-4.  Luster 
vitreous,  or  silky  when  fibrous.  Transparent  to  subtranslucent.  Optically  —  . 
Ax.  pi.  and  Bx0  J_  b  (010).  Bxa  A  c  axis  =  15°-16°.  2V  =  36°  (approx.). 
a  -  1-512.  |8  =  1-519.  7  =  1'519. 

Comp.  —  CaAl2Si3O10.3H2O  or  CaO.Al2O3.3SiO2.3H20  =  Silica  45'9,  alu- 
mina 26-0,  lime  14-3,  water  13*8  =  100. 


Pyr.,  etc.  —  B.B.  sometimes  curls  up  like  a  worm  (whence  the  name  from  o-KuXqg,  a 
worm,  which  gives  scolecite,  and  not  scolesite  or  scolezite)',  other  varieties  intumesce  but 
slightly,  and  all  fuse  at  2-2*2  to  a  white  blebby  enamel.  Gelatinizes  with  acids  like  natrolite. 

Obs.  —  Occurs  in  the  Berufiord,  Iceland;  in  Scotland  in  amygdaloid  at  Staffa  Island 
and  in  Isle  of  Skye,  at  Talisker;  near  Eisenach,  Saxony;  in  Auvergne,  France;  common  in 
fine  crystallizations  in  the  Deccan  trap  area,  in  British  India.  In  crystals  from  Karsanan- 
guit-Kakait,  Greenland.  In  the  United  States,  in  Col.  at  Table  Mountain  near  Golden 
in  cavities  in  basalt.  In  Canada,  at  Black  Lake,  Megantic  Co.,  Quebec. 

Mesolite.  Intermediate  between  natrolite  and  scolecite  (see  p.  556).  In  acicular  and 
capillary  crystals;  delicate  divergent  tufts,  etc.  G.  =  2  -29.  White  or  colorless.  Indices, 
1  '505-1  '506.  In  amygdaloidal  basalt  at  numerous  points.  Crystals  from  Faroe  Islands 
appear  to  be  triclinic,  pseudomonoclinic  through  twinning.  Pseudomesolite  is  name  given 
to  a  zeolite  from  Carlton  Peak,  Minn.,  like  mesolite  except  for  its  optical  characters. 

Gonnardite.  (Ca,Na2)2Al2Si5Oi5.5£H2O.  In  spherules  with  radiating  structure. 
G.  =  2-25-2-35.  From  basalt  of  Gignat,  Puy-de-D6me,  France. 


THOMSONITE. 

Orthorhombic.     Axes  a  :  b  :  c  =  0-9932  :  1  :  1-0066. 

Distinct  crystals  rare;  in  prisms,  mm'"  110  A ,110  =  89°  37'.  Commonly 
columnar,  structure  radiated;  in  radiated  spherical  concretions;  also  closely 
compact. 

Cleavage:  6  (010)  perfect;  a  (100)  less  so;  c  (001)  in  traces.  Fracture 
uneven  to  subconchoidal.  Brittle.  H.  =  5-5*5.  G.  =  2-3-2-4.  Luster 
vitreous,  more  or  less  pearly.  Snow-white;  reddish,  green;  impure  varieties 
brown.  Streak  uncolored.  Transparent  to  translucent.  Pyroelectric.  Op- 
tically +  .  Ax.  pi.  1 1  c  (001).  Bx  J_  6  (010).  Dispersion  p  >  v  strong.  2V  = 
54°  (approx.).  a  =  1-497.  ft  =  1-503.  7  =  1'525. 

Var.  —  1.  Ordinary,  (a)  In  regular  crystals,  usually  more  or  less  rectangular  in  out- 
line, prismatic  in  habit.  (6)  Prisms  slender,  often  vesicular  to  radiated,  (c)  Radiated 
fibrous,  (d)  Spherical  concretions,  consisting  of  radiated  fibers  or  slender  crystals.  Also 
massive,  granular  to  impalpable,  and  white  to  reddish  brown,  less  often  green  as  in  Union- 
ite.  The  spherical  massive  forms  also  radiated  with  several  centers  and  of  varying  colors, 
hence  of  much  beauty  when  polished.  Ozarkite  is  a  white  massive  thomsonite  from  Arkan- 
sas. 

Comp.  —  (Na2,Ca)  Al2Si2O8.2JH20  or  (Na2,Ca)O.Al2O3.2SiO2.2iH20.  The 
ratio  of  Na2  :  Ca  varies  from  3  :  1  to  1  :  1.  If  Ca  :  Na^  =  3:1  the  percentage 
composition  requires:  SiO2  37'0,  A12O3  31-4,  CaO  12'9,  NaaO  4-8,  H20  13'9  = 
100. 


558  DESCRIPTIVE   MINERALOGY 

Pyr.,  etc. B.B.  fuses  with  intumescence  at  2  to  a  white  enamel.     Gelatinizes  with 

hydrochloric  acid. 

'    Diff. Resembles  some  natrolite,  but  fuses  to  an  opaque,  not  to  a  clear  glass. 

Obs.  —  Found  in  cavities  in  lava  in  amygdaloidal  igneous  rocks,  sometimes  with 
elseolite  as  a  result  of  its  alteration.  Occurs  near  Kilpatrick,  Scotland;  in  the  lavas  of 
Mte  Somma  (comptonite) ,  Vesuvius;  in  basalt  at  the  Pflasterkaute  in  Saxe  Weimar,  Ger- 
many in  Bohemia,  in  phonolite;  the  Cyclopean  islands,  Sicily;  near  Brevik,  Norway;  the 
Faroe' Islands;  Iceland  (carphostilbite,  straw-yellow);  at  Mt.  Monzoni,  Fassatal,  Tyrol, 

Occurs  at  Peter's  Point,  Nova  Scotia.  In  the  United  States,  at  West  Paterson,  N.  J.; 
at  Magnet  Cove  (ozarkite)  in  the  Ozark  Mts,,  Ark.;  in  the  amygdaloid  of  Grand  Marais, 
Lake  Superior,  which  yields  the  water-worn  pebbles  resembling  agate,  in  part  green  (linton- 
ite) ;  in  the  basalt  of  Table  Mt.  near  Golden,  Col. 

HYDROTHOMSONITE.  (H2,Na2)Ca)Al2Si2O8.5H2O.  An  alteration  product  of  thomsonite 
or  scolecite  from  Tschakwa  near  Batum  on  the  Black  Sea. 

Arduinite.  A  zeolite  containing  lime  and  soda.  In  radiating  fibrous  aggregates. 
G.  =  2-26.  Color  red.  From  Val  dei  Zuccanti,  Venetia,  Italy. 

Echellite.  (Ca,Na2)O.2Al2O3.3SiO2,4H2O.  In  radiating,  fibrous,  spheroidal  masses. 
White.  H.  =  5.  ft  =  T533.  Elongated  |[  Y.  From  Sextant  Portage,  Abitibi  River, 
Northern  Ontario. 

Epidesmine.  Comp.  same  as  for  stilbite.  Orthorhombic.  In  minute  crystals,  only  the 
three  pinacoids  showing.  Cleavages  parallel  to  both  vertical  pinacoids.  Colorless  to  yel- 
low. Index  =  1 '50.  Bxa  perpendicular  to  c  (001).  Optically-.  G.  =2*16.  Easily 
fusible  with  intumescence.  Occurs  as  a  crust  on  calcite  from  Schwarzenberg,  Saxony. 

Stellerite.  CaAl2Si7Oi8.7H2O.  Orthorhombic.  Crystals  tabular  parallel  to  b  (010). 
Cleavage  perfect  parallel  to  b  (010),  imperfect  parallel  to  a  (100)  and  c  (001).  H.  =  3 '5-4. 
G.  =  2*12.  Indices,  1  '48-1  '50.  Found  in  cavity  in  a  diabase  tuff,  Copper  Island,  Com- 
mander Islands. 

Erionite.  H2CaK2Na2Al2Si6Oi7.5H2O.  Orthorhombic.  In  aggregates  of  very  slender 
fibers,  resembling  wool.  G.  =  1'997.  White.  Occurs  in  cavities  in  rhyolite  from  Durkee, 
Oregon. 

Bavenite.  Ca3Al2(SiO3)6.H2O.  Monoclinic.  Fibrous-radiated  groups  of  prismatic 
crystals.  One  cleavage.  H.  =  5'5.  G.  =  2*7.  Color  white.  0  =  1'58.  Occurs  in  peg- 
matitic  druses  in  the  granite  of  Baveno,  Italy. 

Bityite.  A  hydrous  silicate  of  calcium  and  aluminium,  with  small  amounts  of  the 
alkalies.  Pseudo-hexagonal.  In  minute  hexagonal  plates  which  in  polarized  light  show 
division  into  six  biaxial  sectors.  Cleavage  parallel  to  base.  H.  =  5*5.  G.  =  3*0.  In- 
dices 1 '62-1 '64.  Found  as  crystal  crusts  in  pegmatite  veins  at  Maharitra,  Madagascar. 

Hydronephelite.  HNa2Al3Si3Oi2.3H2O.  Massive,  radiated.  H.  =  4'5-6.  G.  =  2'263. 
Color  white;  also  dark  gray.  Index,  1'50.  From  Litchfield,  Me.;  said  however  to  be  a 
mixture  of  natrolite,  hydrargillite  and  diaspore.  Ranite  from  the  Langesund  fiord,  Norway, 
is  similar. 


II.   Mica  Division 

The  species  embraced  under  this  Division  fall  into  three  groups:  1,  the 
MICA  GROUP,  including  the  Micas  proper;  2,  the  CLINTONITE  GROUP,  or  the 
Brittle  Micas;  3,  the  CHLORITE  GROUP.  Supplementary  to  these  are  the 
Vermiculites,  hydrated  compounds,  chiefly  results  of  the  alteration  of  some 
one  of  the  micas. 

All  of  the  above  species  have  the  characteristic  micaceous  structure,  that 
is,  they  have  highly  perfect  basal  cleavage  and  yield  easily  thin  laminae.  They 
belong  to  the  monoclinic  system,  but  the  position  of  the  bisectrix  in  general 
deviates  but  little  from  the  normal  to  the  plane  of  cleavage;  all  of  them  show 
on  the  basal  section  plane  angles  of  60°  or  120°,  marking  the  relative  position 
of  the  chief  zones  of  forms  present,  and  giving  them  the  appearance  of  hex- 


SILICATES 


559 


agonal  or  rhombohedral  symmetry;  further,  they  are  more  or  less  closely 
related  among  themselves  in  the  angles  of  prominent  forms. 

The  species  of  this  Division  all  yield  water  upon  ignition,  the  micas  mostly 
from  4  to  5  p.  c.,  the  chlorites  from  10  to  13  p.  c.;  this  is  probably  to  be 
regarded  in  all  cases  as  water  of  constitution,  and  hence  they  are  not  properly 
hydrous  silicates. 

More  or  less  closely  related  to  these  species  are  those  of  the  Serpentine  and 
Talc  Division  and  the  Kaolin  Division  following,  many  of  which  show  dis- 
tinctly a  mica-like  structure  and  cleavage  and  also  pseudo-hexagonal  sym- 
metry. 


1.    Mica  Group.     Monoclinic 


Muscovite 


Paragonite 
Lepidolite 
Zinnwaldite 
Biotite 

Phlogopite 


H2KAl3(Si04)3 
c  =  0-57735  :  1  :  3-3128 

H2NaAl3(SiO4)3 
KLi[Al(OH,F)2]Al(Si03)3  in  part. 


ft  =  89°  54' 


Potassium  Mica 

a  :  b 

Sodium  Mica 
Lithium  Mica 
Lithium-iron  Mica 

Magnesium-iron  Mica  (H,K)2(Mg,Fe)2(Al,Fe)2(SiO4)3  in  part. 
a  :  b  :  c  =  0-57735  :  1  :  3-2743         0  =  90°  0' 

(H,K,(MgF))3Mg3Al(Si04)3 

Magnesium  Mica;  usually  containing  fluorine,  nearly  free  from  iron. 
Lepidomelane  Annite. 

Iron  Micas.     Contain  ferric  iron  in  large  amount. 

The  species  of  the  MICA  GROUP  crystallize  in  the  monoclinic  system,  but 
with  a  close  approximation  to  either  rhombohedral  or  orthorhombic  symmetry; 
the  plane  angles  of  the  base  are  in  all  cases  60°  or  120°.  They  are  all  charac- 
terized by  highly  perfect  basal  cleavage,  yielding  very  thin,  tough,  and  more 
or  less  elastic  laminae.  The  negative  bisectrix,  X,  is  very  nearly  normal  to  the 
basal  plane,  varying  at  most  but  a  few  degrees  from  this;  hence  a  cleavage 
plate  shows  the  axial  interference-figure,  which  for  the  pseudo-rhombohedral 
kinds  is  often  uniaxial  or  nearly  uniaxial.  Of  the  species  named  above, 
biotite  has  usually  a  very  small  axial  angle,  and  is  often  sensibly  unaxial;  the 
axial  angle  of  phlogopite  is  also  small,  usually  10°  to  12°;  for  muscovite,  para- 
gonite,  lepidolite  the  angle  is  large,  in  air  commonly  from  50°  to  70°. 

The  Micas  may  be  referred  to  the  same  fundamental  axial  ratio  with  an 
angle  of  obliquity  differing  but  little  from  90°; 
they  show  to  a  considerable  extent  the  same 
forms,  and  their  isomorphism  is  further  indicated 
by  their  not  infrequent  intercrystallization  in  par- 
allel position,  as  biotite  with  muscovite,  lepidolite 
with  muscovite,  etc. 

A  blow  with  a  somewhat  dull-pointed  instrument 
on  a  cleavage  plate  of  mica  develops  in  all  the 
species  a  six-rayed  percussion-figure  (Fig.  945,  also 
Fig.  491,  p.  189),  two  lines  of  which  are  nearly  par- 
allel to  the  prismatic  edges ;  the  third,  which  is  the 
most  strongly  characterized,  is  parallel  to  the  clino- 

pinacoid  or  plane  of  symmetry.     The  micas  are  often  divided  into  two  classes, 
according  to  the  position  of  the  plane  of  the  optic  axes.     In  the  first  class 


945 


560  DESCRIPTIVE    MINERALOGY 

belong  those  kinds  for  which  the  optic  axial  plane  is  normal  to  b  (010),  the 
plane  of  symmetry  (Fig.  945) ;  in  the  second  class  the  axial  plane  is  parallel  to 
the  plane  of  symmetry.  The  percussion  figure  serves  to  fix  the  crystallo- 
graphic  orientation  when  crystalline  faces  are  wanting.  A  second  series  of 
lines  at  right  angles  to  those  mentioned  may  be  more  or  less  distinctly  developed 
by  pressure  of  a  dull  point  on  an  elastic  surface,  forming  the  so-called  pressure- 
figure;  this  is  sometimes  six-rayed,  more  often  shows  three  branches  only,  and 
sometimes  only  two  are  developed.  In  Fig.  945  the  position  of  the  pressure- 
figure  is  indicated  by  the  broken  lines.  These  lines  are  connected  with  gliding- 
planes  inclined  some  67°  to  the  plane  of  cleavage  (see  beyond). 

The  micas  of  the  first  class  include :  Muscovite,  paragonite,  lepidolite,  also 
some  rare  varieties  of  biotite  called  anomite. 

The  second  class  embraces:  Zinnwaldite  and  most  biotite,  including 
lepidomelane  and  phlogopite. 

Chemically  considered,  the  micas  are  silicates,  and  in  most  cases  orthosili- 
cates,  of  aluminium  with  potassium  and  hydrogen,  also  often  magnesium, 
ferrous  iron,  and  in  certain  cases  ferric  iron,  sodium,  lithium  (rarely  rubidium 
and  caesium);  further,  rarely,  barium,  manganese,  chromium.  Fluorine  is 
prominent  in  some  species,  and  titanium  is  also  sometimes  present.  Other 
elements  (boron,  etc.)  may  be  present  in  traces.  All  micas  yield  water  upon 
ignition  in  consequence  of  the  hydrogen  (or  hydroxyl)  which  they  contain. 

MUSCOVITE.     Common  Mica.     Potash  Mica. 

Monoclinic.     Axes  a    b  :  c  =  0*57735  :  1  :  3-3128;  /3  =  89°  54'. 

Twins  common  according  to  the  mica-law:  tw.  pi.  a  plane  in  the  zone 
cM  001  A  221  normal  to  c  (001)  the  crystals  often  united  by  c.  Crystals 
rhombic  or  hexagonal  in  outline  with  plane  angles  of  60°  or  120°.  Habit 
tabular,  passing  into  tapering  forms  with  planes  more  or  less  rough  and 
strongly  striated  horizontally;  vicinal  forms  common.  Folia  often  very  small 
and  aggregated  in  stellate,  plumose,  or  globular  forms;  or  in  scales,  and  scaly 
massive;  also  cryptocrystalline  and  compact  massive. 

Cleavage :  basal,  eminent.  Also  planes  of  secondary  cleavage  as  shown  in 
the  percussion-figure  (see  pp.  559  and  189) ;  natural  plates  hence  often  yield 

•  cM,     001  A  221  =  85°  36'. 

CM,       001  A  111  =  81°  30'. 

MM',  221  A  221  =  59°  48'. 

MM',      HI  A  111  =  59°  16£'. 

narrow  strips  or  thin  fibers 
||  axis  b,  and  less  distinct  in 
directions  inclined  60°  to  this. 

Inin L  laminae  flexible  and  elastic  when  bent,  very  tough,  harsh  to  the 
touch,  passing  into  kinds  which  are  less  elastic  and  have  a  more  or  less 
unctuous  or  talc-like  feel.  Etching-figures  on  c  (001) ,  monoclinic  in  symmetry 
(rig.  495,  p.  190). 

.«~~'  T*  i  ^*'     ^'  =  ^ '76-3.     Luster  vitreous  to  more  or  less  pearly  or 
Iky.     Colorless,  gray,  brown,  hair-brown,  pale  green,  and  violet,  yellow, 
dark  olive-green,  rarely  rose-red.     Streak  uncolored.     Transparent  to  trans- 
lucent. 

Pleochroism  usually  feeble;    distinct  in  some  deep-colored  varieties  (see 

>eyond).     Absorption  in  the  direction  normal  to  the  cleavage  plane  (vibra- 

X ,  aj  strong,  much  more  so  than  transversely  (vibrations  1 1  X) ;  hence  a 


• 

'i  SILICATES  561 

crystal  unless  thin  is  nearly  or  quite  opaque  in  the  first  direction  though 
translucent  through  the  prism.  Optically  — .  Ax.  pi.  J_  b  (010)  and  nearly 
J_  c  (001).  Bxa  (=  X)  inclined  about  --  1°  (behind)  to  a  normal  to  c  (001). 
Dispersion  p  >  v.  2V  variable,  usually  about  40°,  but  diminishing  in  kinds 
(phengite)  relatively  high  in  silica,  a  —  1*561.  ft  =  T590.  7  =  T594. 

Var.  —  1.  Ordinary  Muscovite.  In  crystals  as  above  described,  often  tabular  ||  c  (001), 
also  tapering  with  vertical  faces  rough  and  striated;  the  basal  plane  often  rough  unless  as 
developed  by  cleavage.  More  commonly  in  plates  without  distinct  outline,  except  as 
developed  by  pressure  (see  above) ;  the  plates  sometimes  very  large,  but  passing  into  fine 
scales  arranged  in  plumose  or  other  forms.  In  normal  muscovite  £he  thin  laminae  spring 
back  with  force  when  bent,  the  scales  are  more  or  less  harsh  to  the  touch,  unless  very  small, 
and  a  pearly  luster  is  seldom  prominent. 

2.  DAMOURITE.  Including  margarodite,  gilbertite,  hydro-muscovite,  and  most  HYDRO- 
MICA  in  general.  Folia  less  elastic;  luster  somewhat  pearly  or  silky  and  feel  unctuous  like 
talc.  The  scales  are  usually  small  and  it  passes  into  forms  which  are  fine  scaly  or  fibrous, 
as  sericite,  and  finally  into  the  compact  crypto-crystalline  kinds  called  oncosine,  including 
much  pinite.  Often  derived  by  alteration  of  cyanite,  topaz,  corundum,  etc.  Although 
often  spoken  of  as  hydrous  micas,  it  does  not  appear  that  damourite  and  the  allied  varieties 
necessarily  contain  more  water  than  ordinary  muscovite;  they  may,  however,  give  it  off 
more  readily. 

Margarodite,  as  originally  named,  was  the  talc-like  mica  of  Mt.  Greiner  in  the  Zillertal, 
Tyrol,  Austria;  granular  to  scaly  in  structure,  luster  pearly,  color  grayish  white.  Gilbertite 
occurs  in  whitish,  silky  forms  from  the  tin  mine  of  St.  Austell,  Cornwall.  Sericite  is  a  fine 
scaly  muscovite  united  in  fibrous  aggregates  and  characterized  by  its  silky  luster  (hence  the 
name  from  O-T/PIKOS,  silky}. 

Comp.  —  For  the  most  part  an  orthosilicate  of  aluminium  and  potas- 
sium (H,K)AlSiO4.  If,  as  in  the  common  kinds,  H  :  K  =  2  :  1,  this  becomes 
H2KAl3(SiO4)3  =  2H2O.K2O.3Al2O3.6SiO2  =  Silica  45-2,  alumina  38*5,  potash 
11-8,  water  4-5  =  100. 

Some  kinds  give  a  larger  amount  of  silica  (47  to  49  p.  c.)  than  corresponds  to  a  normal 
orthosilicate,  and  they  have  been  called  phengite.  As  shown  by  Clarke,  these  acid  mus- 
covites  can  be  most  simply  regarded  as  molecular  mixtures  of  H^KA^SiO^s  and 
H2KAl3(Si308)3. 

Iron  is  usually  present  in  small  amount  only.  Barium  is  rarely  present,  as  in  oellacherite. 
G.  =  2'88-2*99.  Chromium  is  also  present  in  fuchsite  from  Schwarzenstein,  Zillertal, 
Tyrol,  and  elsewhere. 

Pyr.,  etc.  —  In  the  closed  tube  gives  water.  B.B.  whitens  and  fuses  on  the  thin  edges 
(F.  =  5'7)  to  a  gray  or  yellow  glass.  With  fluxes  gives  reactions  for  iron  and  sometimes 
manganese,  rarely  chromium.*  Not  decomposed  by  acids.  Decomposed  on  fusion  with 
alkaline  carbonates. 

.  Diff.  —  Distinguished  in  normal  kinds  from  all  but  the  species  of  this  division  by  the 
perfect  basal  cleavage  and  micaceous  structure,  the  pale  color  separates  it  from  most  biotite; 
the  laminae  are  more  flexible  and  elastic  than  those  of  phlogopite  and  still  more  than  those  of 
the  brittle  micas  and  the  chlorites. 

Micro.  —  In  thin  sections  recognized  by  want  of  color  and  by  the  perfect  cleavage 
shown  by  fine  lines  (as  in  Fig.  951,  p.  564)  in  sections  _1_  c  (001),  in  a  direction  parallel  to  c. 
By  reflected  light  under  the  microscope  the  same  sections  show  a  peculiar  mottled  surface 
with  satin-like  luster;  birefringence  rather  high,  hence  interference-colors  bright. 

Obs.  —  Muscovite  is  the  most  common  of  the  micas.  It  is  an  essential  constituent  of 
mica  schist  and  related  rocks,  and  is  a  prominent  component  of  certain  common  varieties 
of  granite  and  gneiss;  also  found  at  times  in  fragmental  rocks  and  limestones;  in  volcanic 
rocks  it  is  rare  and  appears  only  as  a  secondary  product.  The  largest  and  best  developed 
crystals  occur  in  the  pegmatite  dikes  associated  with  granitic  intrusions,  either  directly 
cutting  the  granite  or  in  its  vicinity.  Often  in  such  occurrences  in  enormous  plates  from 
which  the  mica  or  "isinglass"  of  commerce  is  obtained.  It  is  then  often  associated  with 
crystallized  orthoclase,  quartz,  albite;  also  apatite,  tourmaline,  garnet,  beryl,  columbite, 
etc.,  and  other  mineral  species  characteristic  of  granitic  veins.  Further,  muscovite  often 
encloses  flattened  crystals  of  garnet,  tourmaline,  also  quartz  in  thin  plates  between  the 
sheets;  further  not  infrequently  magnetite  in  dendrite-like  forms  following  in  part  the  direc- 
tions of  the  percussion-figure. 


562  DESCRIPTIVE   MINERALOGY 

Some  of  the  best  known  localities,  are:  Abiihl  in  the  Sulzbachtal,  Austrian  Tyrol;  with 
adularia;  Rothenkopf  in  the  Zillertal,  Tyrol;  Soboth,  Styria;  St.  Gothard,  Binnental,  and 
elsewhere  in  Switzerland;  Mourne  Mts.,  Ireland;  Cornwall;  Uto,  Falun,  Sweden;  Skut- 
terud,  and  Bamble,  Norway.  Obtained  in  large  plates  from  Greenland  and  the  East  Indies. 

In  Me.,  at  Mount  Mica  in  the  town  of  Paris;  at  Buckfield,  in  fine  crystals.  In  N.  H.,  at 
Acworth,  Graf  ton.  In  Mass.,  at  Chesterfield;  South  Royalston;  at  Goshen,  rose-red.  In 
Conn.,  at  Monroe;  at  Litchfield,  with  cyanite;  at  the  Middletown  feldspar  quarry;  at 
Haddam;  at  Branch ville,  with  albite,  etc.;  New  Milford.  In  N.  Y.,  near  Warwick;  Eden- 
ville;  Edwards.  In  Pa.,  at  Pennsbury,  Chester  Co.;  at  Unionville,  Delaware  Co.,  and  at 
Middletown.  In  Md.,  at  Jones's  Falls,  Baltimore.  In  Va.,  at  Amelia  Court-Hquse.  In 
N.  C.,  extensively  mined  at  many  places  in  the  western  part  of  the  state;  the  chief  mines 
are  in  Mitchell,  Yancey,  Jackson  and  Macon  Cos.;  crystals  from  Lincoln  Co.  The  mica 
mines  have  also  afforded  many  rare  species,  as  columbite,  samarskite,  hatchettolite,  uran- 
inite,  etc.;  in  good  crystals  in  Alexander  Co.  In  S.  C.,  there  are  also  muscovite  deposits; 
also  in  Ga.  and  Ala. 

Mica  mines  have  also  been  worked  to  some  extent  in  the  Black  Hills,  S.  D.;  in  Wash., 
at  Rockford,  Spokane  Co.;  in  Col.  The  important  states  for  the  production  of  mica  are 
North  Carolina,  New  Hampshire,  Idaho,  South  Dakota,  Virginia,  Alabama,  New  York, 
Connecticut. 

Muscovite  is  named  from  Vitrum  Muscoviticum  or  Muscovy-glass,  formerly  a  popular 
name  of  the  mineral. 

Use.  —  As  an  insulating  material  in  electrical  apparatus;  as  a  non-inflammable  trans- 
parent material  for  furnace  doors,  etc.;  in  a  finely  divided  form  as  a  non-conductor  of  heat 
and  fireproofing  material;  mixed  with  oil  as  a  lubricant,  etc. 

Finite.  A  general  term  used  to  include  a  large  number  of  alteration-products  especially 
of  iolite,  also  spodumene,  nephelite,  scapolite,  feldspar  and  other  minerals.  In  composi- 
tion essentially  a  hydrous  silicate  of  aluminium  and  potassium  corresponding  more  or  less 
closely  to  muscovite,  of  which  it  is  probably  to  be  regarded  as  a  massive,  compact  variety, 
usually  very  impure  from  the  admixture  of  clay  and  other  substances.  Characters  as  fol- 
lows: Amorphous;  granular  to  cryptocrystalline.  Rarely  a  submicaceous  cleavage.  H.  = 
2'5-3'5.  G.  =  2'6-2'85.  Luster  feeble,  waxy.  Color  grayish  white,  grayish  green,  pea- 
green,  dull  green,  brownish,  reddish.  Translucent  to  opaque.  The  following  are  some  of 
the  minerals  also  classed  as  pinite:  gigantolite,  gieseckite  (see  p.  500),  liebenerite,  dysyntribite, 
par  ophite,  rosite,  polyargite,  wilsonite,  killinite. 

Agalmatolite  (pagodite)  is  like  ordinary  massive  pinite  in  its  amorphous  compact  texture, 
luster,  and  other  physical  characters,  but  contains  more  silica,  which  may  be  from  free 
quartz  or  feldspar  as  impurity.  The  Chinese  has  H.  =  2-2'5;  G.  =  2785-2'815.  Colors 
usually  grayish,  grayish  green,  brownish,  yellowish.  Named  from  aja\na,  an  image; 
pagodite  is  from  pagoda,  the  Chinese  carving  the  soft  stone  into  miniature  pagodas,  images, 
etc.  Part  of  the  so-called  agalmatolite  of  China  is  true  pinite  in  composition,  another  part 
is  compact  pyrophyllite,  and  still  another  steatite  (see  these  species). 

Paragonite.  A  sodium  mica,  corresponding  to  muscorite  in  composition;  formula, 
HaNaAlsCSiCMs.  In  fine  pearly  scales;  also  compact.  G.  =  278-2-90.  Index,  1'60. 
Color  yellowish,  grayish,  greenish;  constitutes  the  mass  of  the  rock  at  Monte'Campione  near 
Faido  in  Canton  Tessin,  Switzerland,  containing  cyanite  and  staurolite;  called  paragonite- 
schist.  Occurs  associated  with  tourmaline  and  corundum  at  Unionville,  Delaware  Co.,  Pa. 
Hallerite,  a  mica  with  an  iridescent  silver  color  and  pearly  luster.  Perhaps  a  lithium-bear- 
ing paragonite.  Found  at  Mesores,  near  Autun,  France. 

BADDECKITE,  an  iron  mica  related  to  muscovite.  In  small  scales  with  a  copper-red  color. 
From  near  Baddeck,  Nova  Scotia. 

LEPIDOLITE.    LithiaMica. 

In  aggregates  of  short  prisms,  often  with  rounded  terminal  faces.  Crys- 
tals sometimes  twins  or  trillings  according  to  the  mica  law.  Also  in  cleavable 
plates,  but  commonly  massive  scaly-granular,  coarse  or  fine. 

Cleavage:  basal,  highly  eminent.  H.  =  2-5-4.  G.  =  2 -8-2 -9.  Luster 
pearly  Color  rose-red,  violet-gray  or  lilac,  yellowish,  grayish  white,  white. 
Translucent  Optically  -.  Ax.  pi.  usually  ±  b  (010);  rarely  ||  6.  Bxa  (X) 

in       Si1 7oJ  f d'  *nd  T  33*'  "ellow  to  normal  to  c 
irom  ou  —  iZ  ,  p  =  1'5975. 


SILICATES 


563 


Comp.  —  In  part  a  metasilicate,  R3Al(SiO3)3  or  KLi[Al(OH,F)2]Al(Si03)3. 
The  ratio  of  fluorine  and  hydroxyl  is  variable. 

It  has  been  suggested  that  the  puro  lepidolite  molecule  is  represented  by  3Li2O.2K2O. 
3Al2O3.8F.12SiO2  and  that  most  lepidolites  are  mixtures  of  this  and  the  muscovite  molecule. 

Pyr.,  etc.  —  In  the  closed  tube  gives  water  and  reaction  for  fluorine.  B.B.  fuses  with 
intumescence  at  2-2 '5  to  a  white  or  grayish  glass  sometimes  magnetic,  coloring  the  flame 
purplish  red  at  the  moment  of  fusion  (lithia) .  With  the  fluxes  some  varieties  give  reactions 
for  iron  and  manganese.  Attacked  but  not  completely  decomposed  by  acids.  After  fusion, 
gelatinizes  with  hydrochloric  acid. 

Obs.  —  Occurs  in  granite  and  gneiss,  especially  in  granitic  veins;  often  associated  with 
lithia-tourmaline;  also  with  amblygonite,  spodumene,  cassiterite,  etc.;  sometimes  associ- 
ated with  muscovite  in  parallel  position. 

Found  near  TJto  in  Sweden;  Penig,  Saxony;  Rozena  (or  Rozna),  Moravia;  Madagascar, 
etc.  In  the  United  States,  common  in  the  western  part  of  Me.,  in  Hebron,  Auburn,  Paris, 
etc.;  at  Chesterfield,  Mass.;  Middletown  and  Haddam  Neck,  Conn.;  with  rubellite  near 
San  Diego,  Cal. 

Named  lepidolite  from  XeTm,  scale,  after  the  earlier  German  name  Schuppenstein,  allud- 
ing to  the  scaly  structure  of  the  massive  variety  of  Rozena. 

Use.  —  As  a  source  of  lithium  compounds. 

COOKEITE  is  a  micaceous  mineral  occurring  in  rounded  aggregations  on  rubellite,  also 
with  lepidolite,  tourmaline,  etc.,  at  Hebron,  Me.  An  alteration  of  lepidolite  or  tourmaline. 
Composition  Li[Al(OH)2l3(SiO3)2. 

Zinnwaldite.  An  iron-lithia  mica  in  form  near  biotite.  Color  pale  violet,  yellow  to 
brown  and  dark  gray.  Occurs  at  Zinnwald  and  Altenberg,  Germany;  similarly  in  Corn- 
wall, England.  From  Narsarsuk,  Greenland,  and  the  York  region,  Alaska. 

Cryophyllite  is  a  related  lithium  mica  from  Rockport,  Mass.  Polylithionite  is  a  lithium 
mica  from  Kangerdluarsuk,  Greenland.  Irvingite  is  an  alkalie  mica  containing  lithium  from 
near  Wausau,  Wis. 

Manandonite.  A  basic  boro-silicate  of  lithium  and  aluminium,  H24Li4Ali4B4Si6O53. 
Micaceous.  In  lamellar  aggregates  or  mammillary  crusts  of  hexagonal  plates.  Perfect 
basal  cleavage.  Color  white.  Luster  pearly.  Optically  +.  Axial  angle  small  and  vari- 
able. Easily  fusible  giving  red  flame.  Unattacked  by  acids.  Found  in  pegmatite  at  An- 
tandrokomby,  near  the  Manandona  River,  Madagascar. 

BIOTITE. 

Monoclinic;  pseudo-rhombohedral.  Axes  a  :  b  :  c  =  0-57735  :  1  :  3 -2743; 
0  =  90°. 

Habit  tabular  or  short  prismatic;  the  pyramidal  faces  often  repeated  in 
oscillatory  combination.  .Crystals  often  apparently  rhombohedral  in  sym- 
metry since  r  (101)  and  z  (132),  z'  (132),  which  are  inclined  to  c  (001)  at  sen- 
sibly the  same  angle,  often  occur  together;  further,  the  zones  to  which  these 
faces  belong  are  inclined  120°  to  each  other,  hence  the  hexagonal  outline  of 
basal  sections.  Twins,  according  to  the  mica  law,  tw.  pi.  a  plane  in  the 
prismatic  zone  _L  c  (001) .  Often  in  disseminated  scales,  sometimes  in  massive 
aggregations  of  cleavable  scales. 


948 


M 


960 


co,  001  A  112 
cM,  001  A  221 
c/*,  001  A  111 


73°  1'.  cr,  001  A  T01  =  80°  0'. 
85°  38'.  cz,  001  A  132  =  80°  0'. 
81°  19'.  MM',  221  A  221  =  59°  48*'. 


564  DESCRIPTIVE   MINERALOGY 

Cleavage:  basal,  highly  perfect;  planes  of  separation  shown  in  the  percus- 
sion-figure; also  gliding-planes  />  (205), ,  f  (135)  shown  in  the  pressure-figure 
inclined  about  66°  to  c  (001)  and  yielding  pseudo-crystalline  forms  (Fig.  489, 
p.  188).  H.  =  2-5-3.  G.  =  27-3-1.  Luster  splendent,  and  more  or  less 
pearly  on  a  cleavage  surface,  and  sometimes  submetallic  when  black;  lateral 
surfaces  vitreous  when  smooth  and  shining.  Colors  usually  green  to  black, 
often  deep  black  in  thick  crystals,  and  sometimes  even  in  thin  laminae, 
unless  the  lamina?  are  very  thin;  such  thin  lamina?  green,  blood-red,  or  brown 
by  transmitted  light;  also  pale  yellow  to  dark  brown;  rarely  white.  Streak 
uncolored.  Transparent  to  opaque. 

Pleochroism  strong;  absorption  Y  =  Z  nearly,  for  X  much  stronger. 
Hence  sections  ||  c  (001)  dark  green  or  brown  to  opaque;  those  J_  c  lighter  and 
deep  brown  or  green  for  vibrations  1 1  c,  pale  yellow,  green  or  red  for  vibrations 
J_  c.  Pleochroic  halos  often  noted,  particularly  about  microscopic  inclusions. 
Optically  — .  Ax.  pi.  usually  ||  b  (010),  rarely  _L  b.  Bxa  (=X)  nearly  coinci- 
dent with  the  normal  to  c  (001),  but  inclined  about  half  a  degree,  sometimes 
to  the  front,  sometimes  the  reverse.  Axial  angle  usually  very  small,  and  often 
sensibly  uniaxial;  also  up  to  50°.  Birefringence  high,  y  —  a  =  0*04  to  0-06. 
Comp.  —  In  most  cases  an  orthosilicate,  chiefly  ranging  between  (H,K)2 
(Mg,Fe)4(Al,Fe)2(Si04)4  and  (H,K)2(Mg,Fe)2Al2(SiO4)3.  Of  these  the  second 
formula  may  be  said  to  represent  typical  biotite.  The  amount  of  iron  varies 
widely. 

Var.  —  Biotite  is  divided  into  two  classes  by  Tschermak: 

I.  MEROXENE.  Axial  plane  ||  6  (010).  II.  ANOMITE.  Ax.  pi.  J_  6  (010).  Of  these 
two  kinds,  meroxene  includes  nearly  all  ordinary  biotite,  while  anomite  is,  so  far  as  yet 
observed,  of  restricted  occurrence,  the  typical  localities  being  Greenwood  Furnace,  Orange 
Co.,  N.  Y.,  and  Lake  Baikal  in  East  Siberia.  Meroxene  is  a  name  early  given  to  the  Vesu- 
vian  biotite.  Anomite  is  from  aw^tos,  contrary  to  law. 

Haughtonite  and  Siderophyllite  are  kinds  of  biotite  containing  much  iron. 
Manganophyllite  is  a  manganesian  biotite.     Occurs  in  aggregations  of  thin  scales.     Color 
bronze-  to  copper-red.     Streak  pale  red.     From  Pajsberg  and  Langban,  Sweden;  Pied- 
mont, Italy. 

Pyr.,  etc.  —  In  the  closed  tube  gives  a  little  water.  Some  varieties  give  the  reaction  for 
fluorine  in  the  open  tube;  some  kinds  give  little  or  no  reaction  for  iron  with  the  fluxes,  while 

others  give  strong  reactions  for  iron.  B.  B. 
whitens  and  fuses  on  the  thin  edges.  Completely 
decomposed  by  sulphuric  acid,  leaving  the  silica  in 
thin  scales. 

DM.  —  Distinguished  by  its  dark  green  to  brown 
and  black  color  and  micaceous  structure,  usually 
nearly  uniaxial. 

Micro.  —  Recognized    in   thin   sections  by  'its 

^      brown   (or  green)  color;    strong   pleochroism  and 

strong  absorption  parallel  to  the  elongation  (unlike 
tourmaline).  Sections  |  c  (001)  are  non-pleochroic, 
commonly  exhibit  more  or  less  distinct  hexagonal 
outlines  and  yield  a  negative  sensibly  uniaxial  figure. 
Sections  _|_  c  are  strongly  pleochroic  and  are  marked 

±by  fine  parallel,  cleavage  lines  (Fig.  951);  they  also 
have  nearly  parallel  extinction,  and  show  high 

,.  polarization  colors;    by  reflected  light  they  exhibit 

them  from  ^ro       u01'  Vvha1tered  sheen  which  is  veiT  characteristic  and  aids  in  distinguishing 

°^i  ~V?iotitr  is  an,  imP°rtant  constituent  of  many  different  kinds  of  igneous  rocks, 

illy  those  formed  from   magmas   containing   considerable   potash   and   magnesia 

non  in  certain  varieties  of  granites,  syenite,  diorite,  etc.,  of  the  massive  granular  type; 

i  rhyohte  trachyte,  and  andesite  among  the  lavas;  in  minettes,  kersantites,  etc.     It 

.curs  also  as  the  product  of  metamorphic  action  in  a  variety  of  rocks.     It  is  not  infre- 


SILICATES  565 

quently  associated  in  parallel  position  with  muscovite,  the  latter,  for  example,  forming  the 
outer  portions  of  plates  having  a  nucleus  of  biotite. 

Some  of  the  prominent  localities  of  crystallized  biotite  are  as  follows:  Vesuvius,  com- 
mon particularly  in  ejected  limestone  masses  on  Monte  Somma,  with  augite,  chrysolite, 
nephelite,  humite,  etc.  The  crystals  are  sometimes  nearly  colorless  or  yellow  and  then 
usually  complex  in  form;  also  dark  green  to  black;  Mt.  Monzoni  in  the  Fassatal  and 
Schwarzenstein,  Zillertal,  Tyrol,  Austria;  Rezbanya  and  Morawitza  in  Hungary;  in  Ger- 
many at  Schelingen  and  other  points  in  the  Kaiserstuhl  and  the  Laacher  See;  on  the  west 
side  of  Lake  Ilmen  near  Miask,  Russia. 

In  the  United  States  ordinary  biotite  is  common  in  granite,  gneiss,  etc.;  but  notable 
localities  of  distinct  crystals  are  not  numerous.  It  occurs  with  muscovite  (which  see)  as  a 
more  or  less  prominent  constituent  of  the  pegmatite  veins  in  the  New  England  States;  also 
Pennsylvania,  Virginia,  North  Carolina.  From  Greenwood,  Orange  Co.,  N.  Y.  Sidero- 
phyllite  is  from  the  Pike's  Peak  region,  Col. 

CASWELLITE.     An  altered  biotite  from  Franklin  Furnace,  N.  J. 

PHLOGOPITE. 

Monoclinic.  In  form  and  angles  near  biotite.  Crystals  prismatic,  taper- 
ing; often  large  and  coarse;  in  scales  and  plates. 

Cleavage:  basal,  highly  eminent.  Thin  laminae  tough  and  elastic.  H.  = 
2-5-3.  G.  =  278-2-85.  Luster  pearly,  often  submetallic  on  cleavage  surf  ace. 
Color  yellowish  brown  to  brownish  red,  with  often  something  of  a  copper-like 
reflection;  also  pale  brownish  yellow,  green,  white,  colorless.  Often  exhibits 
asterism  in  transmitted  light,  due  to  regularly  arranged  inclusions.  Pleo- 
chroism  distinct  in  colored  varieties:  Z  brownish  red,  Y  brownish  green,  X 
yellow.  Absorption  Z  >  Y  >  X.  Optically-.  Ax.  pi.  ||  b  (010).  Bxa 
nearly  _!_  c  (001).  Axial  angle  small  but  variable  even  in  the  same  specimen, 
from  0°  to  50°.  Dispersion  p  <  v.  The  axial  angle  appears  to  increase  with 
the  amount  of  iron.  Indices  variable,  from  1-541-1-638. 

Comp.  —  A  magnesium  mica,  near  biotite,  but   containing   little   iron; 

potassium  is  prominent  as  in  all  the  micas,  and  in  most  cases  fluorine.     Typi- 
i  i 

cal  phlogopite  is  R3Mg3Al(SiO4)3,  where  R  =  H,K,MgF. 

Obs.  —  Phlogopite  is  especially  characteristic  of  crystalline  limestone  or  dolomite.  It 
is  often  associated  with  pyroxene,  amphibole,  serpentine,  etc.  Thus  as  at  Pargas,  Fin- 
land; in  St.  Lawrence  Co.  and  Jefferson  Co.,  N.  Y.;  Franklin,  N.  J.;  also  Burgess,  Ontario, 
and  elsewhere  in  Canada. 

Named  from  </>Xoyco7r6s,  fire-like,  in  allusion  to  the  color. 

The  asterism  of  phlogopite,  seen  when  a  candle-flame  is  viewed  through  a  thin  sheet,  is 
a  common  character,  particularly  prominent  in  the  kinds  from  northern  New  York  and 
Canada.  It  has  been  shown  to  be  due  to  minute  acicular  inclusions,  rutile  or  tourmaline, 
arranged  chiefly  in  the  direction  of  the  rays  of  the  pressure-figure,  producing  a  distinct  six- 
rayed  star:  also  parallel  to  the  lines  of  the  percussion-figure,  giving  a  secondary  star,  usually 
less  prominent  than  the  other. 

Taeniolite.  Essentially  a  potassium-magnesium  silicate.  Monoclinic,  belonging  to  the 
mica  group.  Perfect  basal  cleavage.  Folia  somewhat  elastic.  H.  =  2 '5-3.  G.  =  2 "9. 
Colorless.  Fusible.  From  Narsarsuk,  southern  Greenland. 

Lepidomelane.  Near  biotite,  but  characterized  By  the  large  amount  of  ferric  iron 
present.  From  Langesund  fiord,  Norway;  Haddam,  Conn.  Annite  from  Cape  Ann,  Mass., 
belongs  here.  In  small  six-sided  tables,  or  an  aggregate  of  minute  scales.  H.  =  3.  G. 
=  3 '0-3 -2.  Color  black,  with  occasionally  a  leek-green  reflection. 

Alurgite.  A  manganese  mica  from  St.  Marcel,  Piedmont,  Italy.  Color  copper-red. 
Index,  1'59.  Mariposite  may  belong  here. 


Roscoelite.     A  vanadium  mica;  essentially  a  muscovite  in  which  vanadium  has  partly 
replaced  the  aluminium.     In  minute  scales;  structure  micaceous.     G.  =  2'92-2'94.     Color 


566  DESCRIPTIVE   MINERALOGY 

clove-brown  to  greenish  brown.     Indices,  1  '610-1 704.     Occurs  in  Cal.  at  the  gold  mine  at 
Granite  Creek,  Placerville,  and  elsewhere,  El  Dorado  Co. 


2.    Clintonite  Group.     Monoclinic 

The  minerals  here  included  are  sometimes  called  the  Brittle  Micas.  They 
are  near  the  micas  in  cleavage,  crystalline  form  and  optical  properties,  but  are 
marked  physically  by  the  brittleness  of  the  laminae,  and  chemically  by  their 
basic  character. 

In  several  respects  they  form  a  transition  from  the  micas  proper  to  the 
chlorites.  Margarite,  or  calcium  mica,  is  a  basic  silicate  of  aluminium  and 
calcium,  while  Chloritoid  is  a  basic  silicate  of  aluminium  and  ferrous  iron 
(with  magnesium),  like  the  chlorites. 


MARGARITE. 

Monoclinic.  Rarely  in  distinct  crystals.  Usually  in  intersecting  or 
aggregated  laminae;  sometimes  massive,  with  a  scaly  structure. 

Cleavage:  basal,  perfect.  Laminae  rather  brittle.  H.  =  3  -5-4*5.  G.  = 
2-99-3-08.  Luster  of  base  pearly,  of  lateral  faces  vitreous.  Color  grayish, 
reddish  white,  pink,  yellowish.  Translucent,  subtranslucent. 

Optically  —  .  Ax.  pi.  J_  b  (010).  Bxa  approximately  J_  c  (001),  but  vary- 
ing more  widely  than  the  ordinary  micas.  X  A  c  axis  =  +  6^°.  Dispersion 
p  <  v.  Axial  angle  large,  from  76°  to  128°  in  air.  Refractive  index  ft  =1-64- 
1-65. 

Comp.  —  H2CaAl4Si2Oi2  =  Silica  30'2,  alumina  51  '3,  lime  14'0,  water 
4'5  =  100. 

Pyr.,  etc.  —  Yields  water  in  the  closed  tube.  B.B.  whitens  and  fuses  on  the  edges. 
Slowly  and  imperfectly  decomposed  by  boiling  hydrochloric  acid. 

Obs.  —  Associated  commonly  with  corundum,  and  in  many  cases  obviously  formed 
directly  from  it;  thus  at  the  emery  deposits  of  Gumuch-dagh  in  Asia  Minor,  the  islands 
Naxos,  Nicaria,  etc.  Occurs  in  chlorite  of  Mt.  Greiner,  Sterzing,  Tyrol.  In  the  United 
States  at  the  emery  mine  at  Chester,  Mass.;  at  Unionville,  Chester  Co.,  Pa.;  with  corun- 
dum in  Madison  Co.  and  elsewhere  in  N.  C.;  at  Gainesville,  Hall  Co.,  Ga.;  at  Dudley  ville, 
Ala. 
.  Named  Margarite  from  fj.apyapiTt]s,  pearl. 

SEYBERTITE.     Clintonite.     Brandisite. 

Monoclinic,  near  biotite  in  form.  Also  foliated  massive;  sometimes 
lamellar,  radiate. 

Cleavage:  basal,  perfect.  Structure  foliated,  micaceous.  Laminae  brittle. 
Percussion-  and  pressure-figures,  as  with  mica.  H.  =  4-5.  G.  =  3-3-1. 
Luster  pearly  submetallic.  Color  reddish  brown,  yellowish,  copper-red. 
Streak  uncolored,  or  slightly  yellowish  or  grayish.  Pleochroism  rather  feeble. 
Optically  —  .  Ax.  pi.  J_  6  (010)  seybertite;  \\  b  brandisite.  Bxa  nearly  J_  c 
(001).  Axial  angles  variable,  but  not  large,  a  =  1*646.  ft  =  1-657.  7  = 
1  '658. 

y**-  —  !•  The  Amity  seybertite  (dintonite}  is  in  reddish  brown  to  copper-red  brittle  foli- 
ated masses;  the  surfaces  of  the  folia  often  marked  with  equilateral  triangles  like  some 
mica  and  chlorite.  Axial  angle  3°-13°. 

2.   Brandisite  (disterrite)  ,  from  the  Fassatal,  Tyrol,  is  in  hexagonal  prisms  of  a  yellowish 


ffT  ?m°m  ^T^en  ™lor  to  reddish  gray;    H.  =  5  of  base;    of  sides,   6-6-5.     Ax.   pi. 
||  b  (010).    Axial  angle  15°-30°.     Some  of  it  pseudomorphous,  after  fassaite. 


SILICATES  567 

Comp.  —  In  part  H3(Mg,Ca)5Al5Si2O18  =  3H20.10(Mg,Ca)0.5Al2O3. 
4SiO2. 

Pyr.,  etc.  —  Yields  water.  B.B.  infusible  but  whitens.  In  powder  acted  on  by  con- 
centrated acids. 

Obs.  —  Seybertite  occurs  at  Amity,  N.  Y.,  in  limestone  with  serpentine,  associated  with 
amphibole,  spinel,  pyroxene,  graphite,  etc.;  also  a  chlorite  near  leuchtenbergite.  Brandis- 
ite  occurs  on  Mt.  Monzoni  in  the  Fassatal,  Tyrol,  Austria,  in  white  limestone,  with  fassaite 
and  black  spinel. 

Xanthophyllite.  Perhaps  HsCMgjCa^Al^SisOsa.  The  original  xanthophyllite  is  in 
crusts  or  in  implanted  globular  forms.  Optically  negative.  Axial  angle  usually  very  small, 
or  sensibly  uniaxial;  sometimes  20°.  Indices,  -1 '649-1 '661.  From  near  Zlatoust  in  the 
Ural  Mts.  Found  at  Crestmore,  Riverside  Co.,  Cal. 

Waluewite  is  the  same  species  occurring  in  distinct  pseudo-rhombohedral  crystals.  Folia 
brittle.  H.  =  4'6.  G.  =  3 '093.  Luster  vitreous;  on  cleavage  plane  pearly.  Color  leek- 
to  bottle-green.  Transparent  to  translucent.  Pleochroism  rather  feeble:  ||  c  axis  fine 
green;  _L  c  axis  reddish  brown.  Optically  — .  Ax.  pi.  ||  b  (010).  Bx  sensibly  J_  c  (001). 
Axial  angle  17°  to  32°.  Found  with  perovskite  and  other  species  in  chloritic  schists  near 
Achmatovsk,  in  the  southern  Ural  Mts. 

CHLORITOID.     Ottrelite.     Phyllite. 

Probably  triclinic.  Rarely  in  distinct  tabular  crystals,  usually  hexagonal 
in  outline,  often  twinned  with  the  individuals  turned  in  azimuth  120°  to  each 
other.  Crystals  grouped  in  rosettes.  Usually  coarsely  foliated  massive; 
folia  often  curved  or  bent  and  brittle;  also  in  thin  scales  or  small  plates  dis- 
seminated through  the  containing  rock. 

Cleavage:  basal,  but  less  perfect  than  with  the  micas;  also  imperfect 
parallel  to  planes  inclined  to  the  base  nearly  90°  and  to  each  other  about  60° ; 
b  (010)  difficult.  Laminae  brittle.  H.  =  6'5.  G.  =  3'52-3'57.  Color  dark 
gray,  greenish  gray,  greenish  black,  grayish  black,  often  grass-green  in  very 
thin  plates.  Streak  uncolored,  or  grayish,  or  very  slightly  greenish.  Luster 
of  surface  of  cleavage  somewhat  pearly. 

Pleochroism  strong:  Z  yellow  green,  Y  indigo-blue,  X  olive-green.  Opti- 
cally +  .  Ax.  pi.  nearly  ||  b  (010).  Bxa  inclined  about  12°  or  more  to  the  nor- 
mal to  c  (001).  Dispersion  p  >  v,  large,  also  horizontal.  Axial  angles,  in  air 
65°  to  120°.  0  =  175.  Birefringence  low,  7  -  a  =  0'007-0'016. 

Comp.  —  For  chloritoid  H2(Fe,Mg)Al2Si07.  If  iron  alone  is  present, 
this  requires:  Silica  23 '8,  alumina  40'5,  iron  protoxide  28*5,  water  7-2  =  100. 

Micro.  —  Recognized  in  thin  sections  by  the  crystal  outlines  and  general  micaceous 
appearance;  high  relief ;  green  colors;  distinct  cleavage;  frequent  twinning;  strong  phleo- 
chroism  and  low  interference-colors.  By  the  last  character  readily  distinguished  from  the 
micas;  also  by  the  high  relief  and  extinction  oblique  to  the  cleavage  from  the  chlorites. 

Obs:  —  Chloritoid  (ottrelite,  etc.)  are  characteristic  of  sedimentary  rocks  which  have 
suffered  dynan^c  metamorphism,  especially  in  the  earlier  stages;  thus  found  in  argillites, 
conglomerates,  etc.,  which  have  assumed  the  schistose  condition.  With  more  advanced 
.degree  of  metamorphism  it  disappears.'  Often  grouped  in  fan-shaped,  sheaf -like  forms,  also 
in  irregular  or  rounded  grains. 

The  original  chloritoid  from  Kosoibrod,  near  Ekaterinburg  in  the  Ural  Mts.,  is  in  large 
curving  laminae  or  plates,  grayish  to  blackish  green  in  color,  often  spotted  with  yellow  from 
mixture  with  limonite.  Other  localities  are  He  le  Groix  (Morbihan),  France;  embedded  in 
large  crystals  at  Vanlup,  Shetland;  Ardennes,  France,  and  Belgium,  in  schists  with  ottrelite; 
also  from  Upper  Michigan;  Leeds,  Canada,  etc. 

Sismondine  (HnFeyAlieSigOs-i)  is  from  St.  Marcel,  Piedmont,  Italy;  it  occurs  also  with 
glaucophane  at  Zermatt  in  the  Valais,  Switzerland,  and  elsewhere. 

Salmite  is  a  manganesian  variety  occurring  in  irregular  masses,  having  a  coarse  saccha- 
roidal  structure  and  grayish  color.  G.  =  3'38.  From  Vielsalm,  Belgium. 

Masonite,  from  Natic,  R.  I.,  is  in  very  broad  plates  of  a  dark  grayish  green  color,  but 
bluish  green  in  very  thin  laminae  parallel  to  c  (001)  and  grayish  green  at  right  angles  to  this; 
occurs  in  argillaceous  schist. 


568  DESCRIPTIVE   MINERALOGY 

Ottrelite  is  generally  classed  with  chloritoid,  though  it  is  not  certain  that  they  are  iden- 
tical; it  seems  to  have  the  composition  H2(Fe,Mn)Al2Si2O9.  It  occurs  in  small,  oblong, 
shining  scales  or  plates,  more  or  less  hexagonal  in  form  and  gray  to  black  in  color;  in  argil- 
laceous schist  near  Ottrez,  on  the  borders  of  Luxemburg,  and  from  the  Ardennes,  France, 
and  Belgium;  also  near  Serravezza,  Tuscany,  Italy;  Tintagel  in  Cornwall.  Venasquite  is 
from  Venasque  in  the  Pyrenees,  and  from  Teule,  Finistere,  France.  Phyllite  is  from  the 
schists  of  New  England. 


3.    Chlorite  Group.     Monoclinic 

The  CHLORITE  GROUP  takes  its  name  from  the  fact  that  a  large  part  of  the 
minerals  included  in  it  are  characterize^  by  the  green  color  common  with  sili- 
cates in  which  ferrous  iron  is  prominent.  The  species  are  in  many  respects 
closely  related  to  the  micas.  They  crystallize  in  the  monoclinic  system,  but 
in  part  with  distinct  monoclinic  symmetry,  in  part  with  rhombohedral  symme- 
try, with  corresponding  uniaxial  optical  character.  The  plane  angles  of  the 
base  are  also  60°  or  120°,  marking  the  mutual  inclinations  of  the  chief  zones 
of  forms.  The  mica-like  basal  cleavage  is  prominent  in  distinctly  crystallized 
forms,  but  the  laminae  are  tough  and  comparatively  inelastic.  Percussion 
and  pressure-figures  may  be  obtained  as  with  the  micas  and  have  the 
same  orientation.  The  etching-figures  are  in  general  monoclinic  in 
symmetry,  in  part  also  asymmetric,  suggesting  a  reference  to  the  triclinic 
system. 

Chemically  considered  the  chlorites  are  silicates  of  aluminium  with  ferrous 
iron  and  magnesium  and  chemically  combined  water.  Ferric  iron  may  be 
present  replacing  the  aluminium  in  small  amount ;  chromium  enters  similarly 
in  some  forms,  which  are  then  usually  of  a  pink  instead  of  the  more  common 
green  color.  Manganese  replaces  the  ferrous  iron  in  a  few  cases.  Calcium 
and  alkalies  —  characteristic  of  all  the  true  micas  —  are  conspicuously  absent, 
or  present  only  in  small  amount. 

The  only  distinctly  crystallized  species  of  the  Chlorite  Group  are  Clino- 
chlore  and  Penninite.  These  seem  to  have  the  same  composition,  but  while 
the  former  is  monoclinic  in  form  and  habit,  the  latter  is  pseudo-rhombohedral 
and  usually  uniaxial.  Prochlorite  (including  some  ripidolite)  and  Corundo- 
philite  also  occur  in  distinct  cleavage  masses. 

Besides  the  species  named  there  are  other  kinds  less  distinct  in  form,  occur- 
ring in  scales,  also  fibrous  to  massive  or  earthy;  they  are  often  of  more  or  less 
undetermined  composition,  but  in  many  cases,  because  of  their  extensive  occur- 
rence, of  considerable  geological  importance.  These  latter  forms  occur  as 
secondary  minerals  resulting  from  the  alteration  especially  of  ferro-magnesian 
silicates,  such  as  biotite,  pyroxene,  amphibole;  also  garnet,  vesuvianite, 
tc.  I  hey  are  often  accompanied  by  other  secondary  minerals,  as  ser- 
pentine, hmonite,  calcite,  etc.,  especially  in  the  altered  forms  of  basic 
rocks.  .  • 

The  rock-making  chlorites  are  recognized  in  thin  sections  by  their  charac- 
teristic appearance  in  thin  leaves,  scales  or  fibers,  sometimes  aggregated  into 

irulites;  by  their  greenish  color;  pleochroism;  extinction  parallel  to  the 
cleavage  (unlike  choritoid  and  ottrelite);  low  relief  and  extremely  low  inter- 
ference-colors, which  frequently  exhibit  the  "  ultra-blue."  By  this  latter  char- 

?r  they  are  readily  distinguished  from  the  micas,  which  they  strongly 
resemble  and  with  which  they  are  frequently  associated. 


SILICATES 


569 


CLINOCHLORE.     Ripidolite  in  part. 

Monoclinic.     Axes  a  :  b  :  c  =  0-57735  :  1  :  2-2772;  0  =  89°  40'. 
952  953  954 


/         m< 


Pfitsch 


Wchwarzenstem 


Zillertal 


955 


Achmatovsk 


Crystals  usually  hexagonal  in  form,  often  tabular  ||  c  (001).  Plane  angles 
of  the  basal  section  =  60°  or  120°,  and  since  closely  similar  angles  are  found  in 
the  zones  which  are  separated  by  60°,  the  symmetry 
approximates  to  that  of  the  rhombohedral  system. 

Twins:  (1)  Mica  law,  tw.  pi.  _L  c  (001)  in  the  zone 
cmo  001  A  112;  sometimes  contact-twins  with  c  as  com- 
position face,  the  one  part  revolved  60°  or  a  multiple  of 
60°  in  azimuth  with  reference  to  the  other;  also  in  three- 
fold twins.  (2)  Penninite  law,  tw.  pi.  c,  contact-twins 
also  united  by  c  (Fig.  954);  here  corresponding  faces 
differ  180°  in  position.  Massive,  coarse  scaly  granular 
to  fine  granular  and  earthy. 

Cleavage:  c  (001)  highly  perfect.  Laminae  flexible 
tough,  and  but  slightly  elastic.  Percussion-figure  and 
pressure-figures  orientated  as  with  the  micas  (p.  559).  H.  =  2-2*5. 
G.  =  2-65-2-78.  Luster  of  cleavage-face  somewhat  pearly.  Color 
deep  grass-green  to  olive-green;  pale  green  to  yellowish  and  white; 
also  rose-red.  Streak  greenish  white  to  uncolored.  Transparent  to 
translucent.  Pleochroism  not  strong,  for  green  varieties  usually  X  green,  Z 
yellow.  Optically  usually  +.  Ax.  pi.  in  most  cases  ||  6  (010).  Bxa  inclined 
somewhat  to  the  normal  to  c  (001),  forward;  for  Achmatovsk  2°  30'.  Disper- 
sion p  <  v.  Axial  angles  variable,  even  in  the  same  crystal,  0°-90°;  some- 
times sensibly  uniaxial.  Birefringence  low.  Indices  approximately;  a  = 
1-585.  0  =  1-586.  7  =  1-596. 

Var.  —  1.  Ordinary;  green  clinochlore,  passing  into  bluish  green;  (a)  in  crystals,  as 
described,  usually  with  distinct  monoclinic  symmetry;  (6)  foliated;  (c)  massive. 

Leuchtenbergiie.  Contains  usually  little  or  no  iron.  Color  white,  pale  green,  yellowish; 
often  resembles  talc.  From  near  Zlatoust  in  the  Ural  Mts. 

Kotschubeite.  Contains  several  per  cent  of  chromium  oxide.  Crystals  rhombohedral 
in  habit.  Color  rose-red.  From  the  southern  Ural  Mts. 

Manganiferous.  Manganchlorite.  A  chlorite  from  the  Harstig  mine  near  Pajsberg, 
Sweden,  is  peculiar  in  containing  2 -3  p.  c.  MnO. 

Comp.  —  Normally  H8Mg5Al2Si3Oi8  =  4H2O.5MgO.Al2O3.3SiO2  =  Silica 
32-5,  alumina  18-4,  magnesia  36-1,  water  13-0  =  100.  Ferrous  iron  usually 
replaces  a  small  part  of  the  magnesia,  and  the  same  is  true  of  manganese  rarely; 
sometimes  chromium  replaces  the  aluminium. 

Pyr.,  etc.  —  Yields  water.  B.B.  in  the  platinum  forceps  whitens  and  fuses  with  diffi- 
culty on  the  edges  to  a  grayish  black  glass.  With  borax,  a  clear  glass  colored  by  iron, 
and  sometimes  chromium.  In  sulphuric  acid  wholly  decomposed. 

Micro.  —  In  thin  sections  characterized  by  pale  green  color  and  pleochroism;  dis- 
tinctly biaxial  and  usually  +. 


570 


DESCRIPTIVE   MINERALOGY 


Orr-nrs  in  connection  with  chloritic'and  talcose  rocks  or  schists  and  serpen- 

tine;  iswasSffislfii  ^^u^Tys:  ssr  £ 


Texas 


Zermatt 


u      Marienberg,  Saxony;  Zoptau,  Moravia.     A  manganesian  vanety  occurs 

at  ^niStherilJteddStates,  at  Westchester,  Pa.,  in  large  crystals  and  plates;  also  Unionville 
and  Tex^,  Pa  fat  the  magnetic  iron  mine  at  Brewster,  N.  Y,  in  part  changed  to  serpen- 
tine; near'  Lowell,  Ver.,  in  crystals. 

PENNINITE.     Pennine. 
Apparently  rhombohedral  in  form  but  strictly  pseudo-rhombohedral  and 

L°^abitCr'hombohedral:    sometimes  thick  tabular  with  c  (001)  prominent, 

again  steep  rhombohedral;  also  in 
tapering  six-sided  pyramids.  Rhombo- 
hedral faces  often  horizontally  striated. 
Crystals  often  in  crested  groups. 
Also  massive,  consisting  of  an  aggre- 
gation of  scales;  also  compact  crypto- 
crystalline. 

Cleavage:  c  (001)  highly  perfect. 
Laminae  flexible.  Percussion-figure 
and  pressure-figure  as  with  clinochlore 
but  less  easy  to  obtain;  not  elastic. 
H.  =  2-2-5.  G.  =  2-6-2-85.  Luster  of  cleavage-surface  pearly;  of  lateral 
plates  vitreous,  and  sometimes  brilliant.  Color  emerald-  to  olive-green; 
also  violet,  pink,  rose-red,  grayish  red;  occasionally  yellowish  and  silver- 
white.  Transparent  to  subtranslucent.  Pleochroism  distinct:  usually  ||  c 
(001)  green;  _L  c  yellow.  Optically  +,  also  —  ,  and  sometimes  both  in  adja- 
cent lamina  of  the  same  crystal.  Usually  sensibly  uniaxial,  but  sometimes 
distinctly  biaxial  (occasionally  2E  =  61°)  and  both  in  the  same  section. 
Sometimes  a  uniaxial  nucleus  while  the  border  is  biaxial  with  2E  =  36°,  the 
latter  probably  to  be  referred  to  clinochlore.  Indices  1-576  and  1-579. 

Var.  —  1.  Penninite,  as  first  named,  included  a  green  crystallized  chlorite  from  the 
Penninine  Alps. 

Kammererite.  In  hexagonal  forms  bounded  by  steep  six-sided  pyramids.  Color 
kermes-red;  peach-blossom-red.  Pleochroism  distinct.  Optically  —  from  Lake  Itkul, 
Bisersk,  Perm,  Russia;  +  Texas,  Pa.  Uniaxial  or  biaxial  with  axial  angle  up  to  20°.  Rho- 
dophyllite  from  Texas,  Pa.,  and  rhodochrome  from  Lake  Itkul  belong  here. 

Pseudophite  is  compact  massive,  without  cleavage,  and  resembles  serpentine. 

Comp.  —  Essentially  the  same  as  clinochlore,  H8(Mg,Fe)5Al2Si3Oi8. 

Pyr.,  etc.  —  In  the  closed  tube  yields  water.  B.B.  exfoliates  somewhat  and  is  diffi- 
cultly fusible.  With  the  fluxes  all  varieties  give  reactions  for  iron,  and  many  varieties  react 
for  chromium.  Partially  decomposed  by  hydrochloric  and  completely  by  sulphuric  acid. 

Micro.  —  In  thin  sections  shows  pale  green  color  and  pleochroism  ;  usually  nearly 
uniaxial,  —  . 

Obs.  —  Occurs  with  serpentine  in  the  region  of  Zermatt,  Valais,  Switzerland,  near 
Mt.  Rosa,  especially  in  the  moraines  of  the  Findelen  glacier;  crystals  from  Zermatt  are 
sometimes  2  in.  long  and  H  in.  thick;  also  at  the  foot  of  the  Simplon  Pass,  Switzerland;  at 
Ala,  Piedmont,  Italy,  with  clinochlore;  at  Schwarzenstein  in  Tyrol,  Austria;  at  Taberg 
in  Wermland,  Sweden;  at  Snarum,  Norway,  greenish  and  foliated. 

Kammererite  is  found  at  the  localities  already  mentioned;  also  near  Miask  in  the  Ural 
Mts.;  at  Haroldswick  in  Unst,  Shetland  Isles.  In  large  crystals  enclosed  in  the  talc  in 
crevices  of  the  chromite  from  Kraubat,  Styria.  Abundant  at  Texas,  Lancaster  Co.,  Pa., 
along  with  clmochlore,  some  crystals  being  embedded  in  clinochlore,  or  the  reverse.  Also 


SILICATES  571 

in  N.  C.,  with  chromite  at  Culsagee,  Macon  Co.;  Webster,  Jackson  Co.;  and  other  points. 
From  Washington,  Cal. 

PROCHLORITE.     Ripidolite  in  part. 

Monoclinic.  In  six-sided  tables  or  prisms,  the  side  planes  strongly  fur- 
rowed and  dull.  Crystals  often  implanted  by  their  sides,  and  in  divergent 
groups,  fan-shaped,  vermicular,  or  spheroidal.  Also  in  large  folia.  Massive, 
foliated,  or  granular. 

H.  =  1-2.  G.  =  278-2-96.  Translucent  to  opaque;  transparent  only  in 
very  thin  folia.  Luster  of  cleavage  surface  feebly  pearly.  Color  green,  grass- 
green,  olive-green,  blackish  green;  across  the  axis  by  transmitted  light  some- 
times red.  Streak  uncolored  or  greenish.  Laminae  flexible,  not  elastic. 
Pleochroism  distinct.  Optically  +  in  most  cases.  Bx  inclined  to  the  normal 
to  c  (001)  some  2°.  Axial  angle  small,  often  nearly  uniaxial;  again  2E  =  23°- 
30°.  Dispersion  p  <  v. 

Comp.  —  Lower  in  silicon  than  clinochlore,  and  with  ferrous  iron  usu- 
ally, but  not  always,  in  large  amount. 

Obs.  —  Like  other  chlorites  in  modes  of  occurrence.  Occasionally  formed  from  amphi- 
bole.  Sometimes  in  implanted  crystals,  as  at  St.  Gothard,  Switzerland,  enveloping  often 
adularia,  etc.;  Mt.  Greiner  in  the  Zillertal,  Tyrol,  Austria;  Rauris  in  Salzburg,  Austria; 
Traversella  in  Piedmont,  Italy;  at  Mts.  Sept  Lacs  and  St.  Cristophe  in  Dauphine,  France; 
in  Styria,  Bohemia.  Also  massive  in  Cornwall,  England,  in  tin  veins;  at  Arendal  in  Nor- 
way; Salberg  and  Dannemora,  Sweden;  Dognacska,  Hungary.  In  Scotland  at  various 
points.  In  the  United  States,  near  Washington,  D.  C.;  on  Castle  Mt.,  Batesville,  Va.,  a 
massive  form  resembling  soapstone,  color  grayish  green,  feel  greasy;  Steele's  mine,  Mont- 
gomery Co.,  N.  C.;  also  with  corundum  at  the  Culsagee  mine,  in  broad  plates  of  a  dark 
green  color  and  fine  scaly;  it  differs  from  ordinary  prochlorite  in  the  small  amount  of  ferrous 
iron. 

Corundophilite.  A  chlorite  occurring  in  deep  green  laminae  resembling  clinochlore  but 
more  brittle;  contains  but  24  p.  c.  SiO2.  /3  =  1'583.  Occurs  with  corundum  at  Chester, 
Mass. 

AMESITE.  H4(Mg,Fe)2Al2SiO9.  Silica  21'4  p.  c.  In  hexagonal  plates,  foliated,  resem- 
bling the  green  talc  from  the  Tyrol.  H.  =  2-5-3.  G.  =  271.  Color  apple-green.  Luster 
pearly  on  cleavage  face.  Optically  +,  sensibly  uniaxial.  Occurs  with  diaspore  at  Chester, 
Mass. 

SHERIDANITE.  A  chlorite  from  Sheridan  Co.,  Wy.,  containing  only  little  iron. 
OTHER  CHLORITES.  Besides  the  chlorites  already  described  which  occur  usually  in 
distinct  crystals  or  plates,  there  are,  as  noted  on  p.  568,  forms  varying  from  fine  scaly  to 
fibrous  and  earthy,  which  are  prominent  in  rocks.  In  some  cases  they  may  belong  to  the 
species  before  described,  but  frequently  the  want  of  sufficient  pure  material  has  left  their 
composition  in  doubt.  These  chlorites  are  commonly  characterized  by  their  green  color, 
distinct  pleochroism  and  low  birefringence  (p.  568). 

The  follow, ng  are  names  which  have  been  given  particularly  to  the  chlorites  filling 
cavities  or  seams  in  basic  igneous  rocks :  aphrosiderite,  diabantite,  delessite,  epichlorite,  eural- 
ite,  chlorophceite,  hullite,  pycnochlorite. 

The  following  are  other  related  minerals. 

Moravite.  2FeO.2(Al,Fe)oO3.7SiO2.2H2O.  In  lamellar,  scaly  and  granular  forms  with 
perfect  basal  cleavage.  H.  =  3"5.  G.  =  2'4.  Color  iron-black.  Fuses  difficultly. 
Found  at  iron  mines  of  Gobitschau  near  Sternberg,  Moravia. 

Cronstedite.  4FeO.2Fe2O3.3SiO2.4H2O.  Occurs  tapering  in  hexagonal  pyramids;  also 
in  diverging  groups;  amorphous.  Cleavage:  basal,  highly  perfect.  Thin  laminae  elastic. 
G.  =  3 '34-3 '35.  Color  coal-black  to  brownish  black;  by  transmitted  light  in  thin  scales 
emerald-green.  Streak  dark  olive-green.  /3  =  1*80.  From  Pfibram  in  Bohemia;  also  in 
Cornwall,  England. 

Thuringite.  8FeO.4(Al,Fe)2O3.6SiO2.9H2O.  Massive;  an  aggregation  of  minute  pearly 
scales.  Color  olive-green  to  pistachio-green.  /3  =  1*63.  From  near  Saalfeld,  in  Thurin- 
gia;  Hot  Springs,  Ark.,  etc.;  from  the  metamorphic  rocks  on  the  Potomac,  near  Harper's 


572  DESCRIPTIVE   MINERALOGY 

Ferry  (owenite).  Stilpnochloran  is  name  given  to  an  alteration  product  of  thuringite  from 
Gobitschau,  near  Sternberg,  Moravia.  In  yellow  to  bronze-red  scales. 

Brunsvigite.  9(Fe,Mg)O.2Al2O3.6SiO2.8H2O.  In  cryptocrystalline  and  foliated  masses 
sometimes  forming  spherical  radiated  aggregates.  Under  microscope  folia  show  hexagonal 
outline.  Color  olive-green  to  yellow-green.  H.  =  1-2.  G.  =  3U  Occurs  in  cavities  in 
the  gabbro  of  the  Radautal  in  the  Harz  Mts.,  Germany. 

Griffithite.  4(Mg,Fe,Ca)O.(Al,Fe)2O3.5SiO2.7H2O.  A  member  of  the  Chlorite  Group. 
Color  dark  green.  H.  =  1.  G.  =  2 '31.  Fusible  to  magnetic  slag.  Pleochroic,  pale  yel- 
low, olive-green,  brown-green.  Indices  1  '48-1  '57.  Occurs  in  amygdaloidal  cavities  in  a 
basalt  from  Cahuenga  Pass,  Griffith  Park,  Los  Angeles,  Cal. 

CHAMOSITE.  Contains  iron  (FeO)  with  but  little  MgO.  Occurs  compact  or  oolitic 
with  H.  about  3;  G.  =  3-3'4;  color  greenish  gray  to  black.  From  Chamoson,  near  St. 
Maurice,  in  the  Valais,  Switzerland. 

Stilpnomelane.  An  iron  silicate.  In  foliated  plates;  also  fibrous,  or  as  a  velvety  coat- 
ing. G.  =  2 '77-2 '96.  Color  black,  greenish  black.  Occurs  at  Obergrund  and  elsewhere 
in  Silesia;  also  hi  Moravia;  near  Weilburg,  Nassau,  Germany.  Chalcodite,  from  the  Sterling 
Iron  mine,  in  Antwerp,  Jefferson  Co.,  N.  Y.,  coating  hematite  and  calcite,  is  the  same 
mineral  in  velvety  coating  of  mica-like  scales  with  a  bronze  color. 

Minguetite.  A  member  of  Chlorite  Group.  A  silicate  of  ferric  and  ferrous  iron,  inter- 
mediate between  stilpnomelane  and  lepidomelane.  G.  =  2'86.  Color  blackish  green. 
Strongly  pleochroic,  light  yellow  to  opaque  black.  Optically  — .  Fuses  to  a  black  mag- 
netic enamel.  Decomposed  by  hydrochloric  acid.  From  Minguet  mine,  near  Segre, 
Maine-et-Loire,  France. 

Strigovite.  H4Fe2(Al,Fe)2Si2Oii.  In  aggregations  of  minute  crystals.  Color  dark 
green.  Occurs  as  a  fine  coating  over  the  minerals  in  cavities  in  the  granite  of  Striegau  in 
Silesia. 

Rumpfite.  Probably  a  variety  of  clinochlore.  Massive;  granular,  consisting  of  very 
fine  scales.  Color  greenish  white.  Occurs  with  talc  near  St.  Michael  and  elsewhere  in 
Styria. 

Spodiophyllite.  (Na2,K2)2(Mg,Fe)3(Fe,Al)2(SiO3)8.  In  rough  hexagonal  prisms.  Mica- 
ceous cleavage.  Laminae  brittle.  H.  =  3-3'2.  G.  =  2 '6.  Color  ash-jgray.  Fusible. 
From  Narsarsuk,  southern  Greenland. 

APPENDIX  TO  THE   MICA  DIVISION.  —  VERMICULITES. 

The  VERMICULITE  GROUP  includes  a  number  of  micaceous  minerals,  all  hydrated  sili- 
cates, in  part  closely  related  to  the  chlorites,  but  varying  somewhat  widely  in  composi- 
tion. They  are  alteration-products  chiefly  of  the  micas,  biotite,  phlogopite,  etc.,  and  retain 
more  or  less  perfectly  the  micaceous  cleavage,  and  of  ten-show  the  negative  optical  character 
and  small  axial  angle  of  the  original  species.-  Many  of  them  are  of  a  more  or  less  indefinite 
chemical  nature,  and  the  composition  varies,  with  that  of  the  original  mineral  and  with  the 
degree  of  alteration. 

The  laminae  in  general  are  soft,  pliable,  and  inelastic;  the  luster  pearly  or  bronze-like, 
and  the  color  varies  from  white  to  yellow; and  brown.  Heated  to  100°-110°  or  dried  over 
sulphuric  acid  most  of  the  vermiculites  lose  considerable  water,  up  to  10  p.  c.,  which  is 
probably  hygroscopic;  at  300°  another  portion  is  often  given  off;  and  at  a  red  heat  a  some- 
what larger  amount  is  expelled.  Connected  with  the  loss  of  water  upon  ignition  is  the 
common  physical  character  of  exfoliation;  some  of  the  kinds  especially  show  this  to  a 
marked  degree,  slowly  opening  out,  when  heated  gradually,  into  long  worm-like  threads. 
Ihis  character  has  given  the  name  to  the  group,  from  the  Latin  vermiculari,  to  breed  worms. 
Ihe  minerals  included  can  hardly  rank  as  distinct  species  and  only  their  names  can  be 
given  here:  Jefferisite,  vermiculite,  culsageeite,  kerrite,  lennilite,  hallite,  philadelphite,  vaalite, 
macomte,  dudleyite,  pyrosclerite. 


HI.   Serpentine  and  Talc  Division 

The  leading  species  belonging  here,  Serpentine  and  Talc,  are  closely  related 

Chlorite  Group  of  the  Mica  Division  preceding,  as  noted  beyond. 

borne  other  magnesium  silicates,  in  part  amorphous,  are  included  with  them. 


SILICATES  ,  573 

SERPENTINE. 

Monoclinic.  In  distinct  crystals,  but  only  as  pseudomorphs.  Sometimes 
foliated,  folia  rarely  separable;  also  delicately  fibrous,  the  fibers  often  easily 
separable,  and  either  flexible  or  brittle.  Usually  massive,  but  microscopically 
finely  fibrous  and  felted,  also  fine  granular  to  impalpable  or  cryptocrystalline ; 
slaty.  Crystalline  in  structure  but  often  by  compensation  nearly  isotropic; 
amorphous. 

Cleavage  b  (010),  sometimes  distinct;  also  prismatic  (50°)  in  chrysotile. 
Fracture  usually  conchoidal  or  splintery.  Feel  smooth,  sometimes  greasy. 
H.  =  2-5-4,  rarely  5-5.  G.  =  2-50-2-65;  some  fibrous  varieties  2-2-2-3; 
retinalite,  2-36-2-55.  Luster  subresinous  to  greasy,  pearly,  earthy;  resin-like, 
or  wax-like;  usually  feeble.  Color  leek-green,  blackish  green;  oil-  and  siskin- 
green;  brownish  red,  brownish  yellow;  none  bright;  sometimes  nearly  white. 
On  exposure,  often  becoming  yellowish  gray.  Streak  white,  slightly  shining. 
Translucent  to  opaque. 

Pleochroism  feeble.  Optically  - ,  perhaps  also  +  in  chrysotile.  Double 
refraction  weak.  Ax.  pi.  |  a  (100).  Bx  (X)  J_  6  (010)  the  cleavage  surface; 
Z  ||  elongation  of  fibers.  Biaxial,  angle  variable,  often  large;  2V  =  20°  to  90°. 
Indices  variable,  from  1*490-1' 571. 

Var.  —  Many  unsustained  species  have  been  made  out  of  serpentine,  differing  in  struc- 
ture (massive,  slaty,  foliated,  fibrous),  or,  as  supposed,  in  chemical  composition;  and  these 
now,  in  part,  stand  as  varieties,  along  with  some  others  based  on  variations  in  texture,  etc. 

A.  IN  CRYSTALS  —  PSEUDOMORPHS.     The  most  common  have  the  form  of  chrysolite. 
Other  kinds  are  pseudomorphs  after  pyroxene,  amphibole,  spinel,  chondrodite,  garnet, 
phlogopite,  etc.     Bastite  or  Schiller  Spar  is  enstatite  (hypersthene)  altered  more  or  less 
completely  to  serpentine.     See  p.  474. 

B.  MASSIVE.     1.   Ordinary  massive,     (a)  Precious  or  Noble  Serpentine  is  of  a  rich  oil- 
green    color,    of   pale   or    dark   shades,    and   translucent    even   when   in    thick   pieces. 
(b)  Common  Serpentine  is  of  dark  shades  of  color,  and  sub  translucent.     The  former  has  a 
hardness  of  2*5-3;  the  latter  often  of  4  or  beyond,  owing  to  impurities. 

Resinous.  Retinalite.  Massive,  honey-yellow  to  light  oil-green,  waxy  or  resin-like 
luster. 

Bowenite  (Nephrite  Bowen) .  Massive,  of  very  fine  granular  texture,  and  much  resembles 
nephrite,  and  was  long  so  called.  It  is  apple-green  or  greenish  white  in  color;  G.  =  2 '594- 
2*787;  and  it  has  the  unusual  hardness  5 "5-6.  From  Smithfield,  R.  I..;  also  a  similar  kind 
from  New  Zealand. 

Ricolite  is  a  banded  variety  with  a  fine  green  color  from  Mexico. 

C.  LAMELLAR.     Antigorite,  thin  lamellar  in  structure,  separating  into  translucent  folia. 
H.  =  2-5;  G.  =  2*622;  color  brownish  green  by  reflected  light;  feel  smooth,  but  not  greasy. 
From  Antigorio  valley,  Piedmont,  Italy. 

D.  THIN  FOLIATED.     Marmolite,   thin  foliated;    the  laminae  brittle  but  separable. 
G.  =  2*41;   colors  greenish  white,  bluish  white  to  pale  asparagus-green.     From  Hoboken, 
N.  J. 

E.  FIBROUS.     Chrysotile.     Delicately  fibrous,   the  fibers  usually  flexible  and  easily 
separating;  luster  silky,  or  silky  metallic;   color  greenish  white,  green,  olive-green,  yellow 
and  brownish;   G.  =  2 -2 19.     Often  constitutes  seams  in  serpentine.     It  includes  most  of 
the  silky  amianthus  of  serpentine  rocks  and  much  of  what  is  popularly  called  asbestus 
(asbestos).     Cf.  p.  489. 

Picrolite,  columnar,  but  fibers  or  columns  not  easily  flexible,  and  often  not  easily  sepa- 
rable, or  affording  only  a  splintery  fracture;  color  dark  green  to  mountain-green,  gray, 
brown.  The  original  was  from  Taberg,  Sweden.  Baltimorite  is  picrolite  from  Bare  Hills, 
Md. 

Radiotine  is  like  serpentine  except  in  regard  to  its  solubility  and  specific  gravity.  In 
spherical  aggregates  of  radiating  fibers  from  near  Dillenburg,  Nassau. 

F.  SERPENTINE    ROCKS.     Serpentine   often    constitutes   rock-masses.     It   frequently 
occurs  mixed  with  more  or  less  of  dolomite,  magnesite,  or  calcite,  making  a  rock  of  clouded 
green,  sometimes  veined  with  white  or  pale  green,  called  verd  antique,  ophiolite,  or  ophicalcite. 
Serpentine  rock  is  sometimes  mottled  with  red,  or  has  something  of  the  aspect  of  a  red 


574  DESCRIPTIVE   MINERALOGY 

porphyry;  the  reddish  portions  containing  an  unusual  amount  of  oxide  of  iron.  Any  ser- 
pentine rock  cut  into  slabs  and  polished  is  called  serpentine  marble. 

Microscopic  examination  has  established  the  fact  that  serpentine  in  rock-masses  has  been 
largely  produced  by  the  alteration  of  chrysolite,  and  many  apparently  homogeneous  ser- 
pentines show  more  or  less  of  this  original  mineral.  In  other  cases  it  has  resulted  from  the 
alteration  of  pyroxene  or  amphibole.  Sections  of  the  serpentine  derived  from  chrysolite 
often  show  a  peculiar  structure,  like  the  meshes  of  a  net  (Fig.  958)  ;  the  lines  marked  by 
grains  of  magnetite  also  follow  the  original  cracks  and  cleavage  directions  of  the  chrysolite 
(Fig.  959,  a).  The  serpentine  from  amphibole  and  pyroxene  commonly  shows  an  analogous 

structure;  the  iron  particles  following  the  former  cleav- 
968  age  lines.     Hence  the  nature  of  the  original  mineral  can 

often  be  inferred.     Cf.  Fig.  959,  a,  b,  c  (Pirsson). 

Comp.  —  A  magnesium  silicate,  H4Mg3Si209 
or  3MgO.2SiO2.2H20  =  Silica  44.1,  magnesia 
43-0,  water  12-9  =  100.  Iron  protoxide  often 
replaces  a  small  part  of  the  magnesium  ;  nickel 
in  small  amount  is  sometimes  present.  The 
water  is  chiefly  expelled  at  a  red  heat. 

Pyr.,  etc.  -<-  In  the  closed  tube  yields  water.  B.  B. 

fuses  on  the  edges  with  difficulty.  F.  ==6.  Gives  usually  an  iron  reaction.  Decom- 
posed by  hydrochloric  and  sulphuric  acids.  From  chrysotile  the  silica  is  left  in  fine 
fibers. 

Diff.  —  Characterized  by  softness,  absence  of  cleavage  and  feeble  waxy  or  oily  luster; 
low  specific  gravity;  by  yielding  much  water  B.B. 

Micro.  —  Readily  recognized  in  thin  sections  by  its  greenish  or  yellowish  green  color; 
low  relief  and  aggregate  polarization  due  to  its  fibrous  structure.  When  the  fibers  are 
parallel,  the  interference-colors  are  not  very  low,  but  the  confused  aggregates  may  show 


..Mife 


<lMii$ 

\M  i 


a,  Serpentine  derived  from  chrysolite;  6,  from  amphibole;  c,  from  pyroxene 

the  "ultra  blue"  or  even  be  isotropic.  The  constant  association  with  other  magnesia  bear- 
ing minerals  like  chrysolite,  pyroxene,  hornblende,  etc.,  is  also  characteristic.  The  presence 
oi  lines  of  iron  oxide  particles  as  noted  above  (Fig.  959)  is  characteristic. 

Obs.  —  Serpentine  is  always  a  secondary  mineral  resulting,  as  noted  above,  from  the 
alteration  of  silicates  containing  magnesia,  particularly  chrysolite,  amphibole  or  pyroxene. 

frequently  torms  large  rock-masses,  then  being  derived  from  the  alteration  of  peridotites 
dumtes  and  other  basic  rocks  of  igneous  origin;  also  of  amphibolites,  or  pyroxene  and 
chrysolite  rocks  of  metamorphic  origin.  In  the  first  case  it  is  usually  accompanied  by 
spinel,  garnet,  chromite  and  sometimes  nickel  ores;  in  the  second  case  by  various  carbo- 
nates such  as  dolomite,  magnesite,  breunnerite,  etc. 

Crystals  of  serpentine,  pseudomorphous  after  monticellite,  occur  in  the  Fassatal  Tyrol 
Austria.  A  variety  containing  soda  from  the  Zillertal,  Tyrol,  is  called  nemaphyllite  Near 
Miask  at  Lake  Aushkul,  Barsovka,  Ekaterinburg,  and  elsewhere  in  Russia;  in  Norway, 
iL  of  M?'  ?vT  Fine  precious  serpentines  come  from  Falun  and  Gulsjo  in  Sweden,  the 
w^l  F^lAn  Pnei^b0^od  ofQPorts°y  in  Aberdeenshire,  Scotland;  the  Lizard  in  Corn- 
wall, England;  Corsica,  Siberia,  Saxony,  etc. 

Roxbnrv0^  Al?erlf  '  m  ^e''  aVDef  Isle'  Precious  serpentine.  In  Ver,  at  New  Fane, 
Roxbury,  etc.  In  Mass,  fine  at  Newburyport.  In  R.  I,  at  Newport;  bowenite  at  Smith- 


SILICATES  575 

field.  In  Conn.,  near  New  Haven  and  Milford,  at  the  verd-antique  quarries.  In  N.  Y., 
at  Port  Henry,  Essex  Co.;  at  Antwerp,  Jefferson  Co.,  in  crystals;  in  Gouverneur  St! 
Lawrence  Co.,  in  crystals;  in  Cornwall,  Monroe,  and  Warwick,  Orange  Co.,  sometimes  in 
large  crystals  at  Warwick;  and  from  Richmond  to  New  Brighton,  Richmond  Co.;  Brew- 
sters.  In  N.  J.,  at  Hoboken,  with  brucite,  magnesite,  etc.;  at  Montville,  Morris  Co., 
chrysotile  and  retinalite,  with  common  serpentine,  produced  by  the  alteration  of  pyroxene! 
In  Pa.,  massive,  fibrous,  and  foliated,  at  Texas,  Lancaster  Co.;  at  West  Chester,  Chester 
Co.,  williamsite;  at  Mineral  Hill,  Newtown,  Marple,  and  Middletown,  Delaware  Co.  In 
Md.,  at  Bare  Hills;  at  Cooptown,  Harford  Co.,  with  diallage.  In  Cal.,  at  various  points 
in  the  Coast  Range.  Asbestus  in  notable  deposits  is  found  in  the  Grand  Canyon,  Ash 
Creek  and  Sierra  Ancha  Mts.,  Ariz. 

In  Canada,  abundant  among  the  metamorphic  rocks  of  the  Eastern  Townships  and 
Gaspe  peninsula,  Quebec;  at  Thetford,  Coleraine,  Broughton,  Orford,  South  Ham,  Bolton, 
Shipton,  Melbourne,  etc.  The  fibrous  variety  chrysotile  (asbestus,  bostonite)  often  forms 
seams  several  inches  in  thickness  in  the  massive  mineral,  and  is  now  extensively  mined  for 
technical  purposes.  Massive  Laurentian  serpentine  also  occurs  in  Grenville,  ArgenteuU 
Co.,  Quebec,  and  North  Burgess,  Lanark  Co.,  Ontario.  In  New  Brunswick,  at  Crow's 
Nest  in  Portland. 

The  names  Serpentine,  Ophite,  Lapis  colubrinus,  allude  to  the  green  serpent-like  cloud- 
ings of  the  serpentine  marble.  Retinalite  is  from  perivr),  resin;  Picrolite,  from  TTLKPOS, 
bitter,  in  allusion  to  the  magnesia  (or  Bittererde)  present;  Thermophyllite,  from  depurj,  heat, 
and  <t>v\\ov,  leaf,  on  account  of  the  exfoliation  when  heated;  Chrysotile,  from  XPWOS,  golden, 
and  rtXos,  fibrous;  Metaxite,  from  nerafe,  silk;  Marmolite,  from  juap/xmpco,  to  shine,  in  allu- 
sion to  its  peculiar  luster. 

Use.  —  As  an  ornamental  stone;  the  fibrous  variety  furnishes  the  greater  part  of  the 
heat  insulating  material  known  as  asbestus. 

Deweylite.  A  magnesian  silicate  near  serpentine  but  with  more  water.  Formula 
perhaps  4MgO.3SiO2.6H2O.  Amorphous,  resembling  gum  arabic,  or  a  resin.  H.  =  2-3 -5. 
G.  =  2'0-2'2.  Color  whitish,  yellowish,  reddish,  brownish.  Index,  1/55.  Occurs  with 
serpentine  in  the  Fleimstal,  Tyrol,  Austria;  also  at  Texas,  Pa.,  and  the  Bare  Hills,  Md. 
Gymnite  of  Thomson,  named  from  yvnvos,  naked,  in  allusion  to  the  locality  at  Bare  Hills, 
Md.,  is  the  same  species. 

Genthite.  Nickel  Gymnite.  A  gymnite  with  pait  of  the  magnesium  replaced  by  nickel, 
2NiO.2MgO.3SiO2.6H2O.  Amorphous,  with  a  delicate  stalactitic  surface,  incrusting. 
H.  =  3-4;  sometimes  very  soft.  G.  =  2 -409.  Luster  resinous.  Color  pale  apple-green, 
or  yellowish.  From  Texas,  Lancaster  Co.,  Pa.,  in  thin  crusts  on  chromite. 

Nepouite.  3(Ni,Mg)O.2SiO2.2H2O.  In  microscopic  crystal  plates  with  hexagonal  out- 
line. Good  cleavages.  H.  =  2-2;5.  G.  =  2*5-3-2.  Color  pale  to  deep  green.  0  =  1'62- 
1'63.  Occurs  in  the  nickel  deposits  of  New  Caledonia. 

Garnierite.  Noumeite.  An  important  ore  of  nickel,  consisting  essentially  of  a  hy- 
drated  silicate  of  magnesium  and  nickel,  perhaps  H2(Ni,Mg)SiO4  +  water,  but  very  variable 
in  composition,  particularly  as  regards  the  nickel  and  magnesium;  not  always  homogene- 
ous. Amorphous.  Soft  and  friable.  G.  =  2'3-2'8.  Luster  dull.  Color  bright  apple- 
green,  pale  green  to  nearly  white.  Index,  1/59.  In  part  unctuous;  sometimes  adheres  to 
the  tongue.  Occurs  in  serpentine  rock  near  Noumea,  capital  of  New  Caledonia,  associated 
with  chromic  iron  and  steatite,  where  it  is  extensively  mined.  A  similar  ore  occurs  at  Riddle 
in  Douglas  County,  southern  Oregon;  also  at  Webster,  Jackson  Co.,  N.  C. 


TALC. 

Orthorhombic  or  monoclinic.  Rarely  in  tabular  crystals,  hexagonal  or 
rhombic  with  prismatic  angle  of  60°.  Usually  foliated  massive;  sometimes  in 
globular  and  stellated  groups;  also  granular  massive,  coarse  or  fine;  fibrous 
(pseudomorphous) ;  also  compact  or  cryptocrystalline. 

Cleavage:  basal,  perfect.  Sectile.  Flexible  in  thin  laminse,  but  not 
elastic.  Percussion-figure  a  six-rayed  star,  oriented  as  with  the  micas.  Feel 
greasy.  H.  =  1-1-5.  G.  =  27-2-8.  Luster  pearly  on  cleavage  surface. 
Color  apple-green  to  white,  or  silvery  white;  also  greenish  gray  and  dark 
green;  sometimes  bright  green  perpendicular  to  cleavage  surface,  and  brown 


576  DESCRIPTIVE   MINERALOGY 

and  less  translucent  at  right  angles  to  this  direction;  brownish  to  blackish 
green  and  reddish  when  impure.  Streak  usually  white;  of  dark  green  varie- 
ties lighter  than  the  color.  Subtransparent  to  translucent.  Optically  nega- 
tive Ax.  pi.  1  1  a  (100).  Bx  _L  c  (001).  Axial  angle  small,  variable.  Indices 
approx.;  a  =  1'539.  0  =  1-589.  7  =  1'589. 

Var.  —  Foliated,  Talc.  Consists  of  folia,  usually  easily  separated,  having  a  greasy  feel, 
and  presenting  ordinarily  light  green,  greenish  white,  and  white  colors.  G.  =  2'55-278. 

Massive,  Steatite  or  Soapstone.  a.  Coarse  granular,  grayish  green,  and  brownish  gray 
in  color;  H.  =  l-2'5.  Pot-stone  is  ordinary  soapstone,  more  or  less  impure.  6.  Fine  granu- 
lar or  cryptocrystalline,  and  soft  enough  to  be  used  as  chalk;  as  the  French  chalk,  which  is 
milk-white  with  a  pearly  luster,  c.  Indurated  talc.  An  impure  slaty  talc,  harder  than 
ordinary  talc. 

Pseudomorphous.  a.  Fibrous,  fine  to  coarse,  altered  from  enstatite  and  tremohte. 
6.  Rensselaerite,  having  the  form  of  pyroxene  from  northern  New  York  and  Canada. 

Comp.  —  An  acid  metasilicate  of  magnesium,  H2Mg3(SiO3)4  or  H2O. 
3MgO.4Si02  =  Silica  63  -5,  magnesia  317,  water  4*8  =  100.  The  water  goes 
off  only  at  a  red  heat.  Nickel  is  sometimes  present  in  small  amount. 

Pyr.,  etc.  —  In  the  closed  tube  B.B.,  when  intensely  ignited,  most  varieties  yield  water. 
In  the  platinum  forceps  whitens,  exfoliates,  and  fuses  with  difficulty  on  the  thin  edges  to  a 
white  enamel.  Moistened  with  cobalt  solution,  assumes  on  ignition  a  pale  red  color.  Not 
decomposed  by  acids.  Rensselaerite  is  decomposed  by  concentrated  sulphuric  acid. 

Diff.  —  Characterized  by  extreme  softness,  soapy  feel;  common  foliated  structure; 
pearly  luster;  it  is  flexible  but  inelastic.  Yields  water  only  on  intense  ignition. 

Obs.  —  Talc  or  steatite  is  a  very  common  mineral,  and  in  the  latter  form  constitutes 
extensive  beds  in  some  regions.  It  is  often  associated  with  serpentine,  talcose  or  chloritic 
schist,  and  dolomite,  and  frequently  contains  crystals  of  dolomite,  breunnerite,  also  asbes- 
tus,  actinolite,  tourmaline,  magnetite. 

Steatite  is  the  material  of  many  pseudomorphs,  among  which  the  most  common  are 
those  after  pyroxene,  hornblende,  mica,  scapolite,  and  spinel.  The  magnesian  minerals  are 
those  which  commonly  afford  steatite  by  alteration;  while  those  like  scapolite  and  nephelite, 
which  contain  soda  and  no  magnesia,  most  frequently  yield  pinite-like  pseudomorphs. 
There  are  also  steatitic  pseudomorphs  after  quartz,  dolomite,  topaz,  chiastolite,  staurolite, 
cyanite,  garnet,  vesuvianite,  chrysolite,  gehlenite.  Talc  in  the  fibrous  form  is  pseudomorph 
after  enstatite  and  tremolite. 

Apple-green  talc  occurs  at  Mt.  Greiner  in  the  Zillertal,  Tyrol,  Austria;  in  the  Valais  and 
St.  Gothard  in  Switzerland;  in  Cornwall,  England,  near  Lizard  Point,  with  serpentine;  the 
Shetland  islands. 

In  North  America,  foliated  talc  occurs  in  Me.,  at  Dexter.  In  Ver.,  at  Bridgewater, 
handsome  green  talc,  with  dolomite;  Newfane.  In  Mass.,  at  Middlefield,  Windsor,  Blan- 
fprd,  Andover,  and  Chester.  In  R.  I.,  at  Smithfield,  delicate  green  and  white  in  a  crystal- 
line limestone.  In  N.  Y.,  at  Edwards,  St.  Lawrence  Co.,  a  fine  fibrous  talc  (agalite)  asso- 
ciated with  pink  tremolite;  on  Staten  Island.  In  N.  J.,  Sparta.  In  Pa.,  at  Texas, 
Nottingham,  Unionville;  in  South  Mountain,  ten  miles  south  of  Carlisle;  at  Chestnut  Hill, 
on  the  Schuylkill,  talc  and  also  soapstone,  the  latter  quarried  extensively.  In  Md.,  at 
Cooptown,  of  green,  blue,  and  rose  colors.  In  N.  C.,  at  Webster,  Jackson  Co.  The  im- 
portant states  for  the  production  of  talc  and  soapstone  are  New  York,  Vermont  and  Virginia. 
In  Canada,  in  the  townships  Bolton,  Button,  and  Potton,  Quebec,  with  steatite  in  beds  of 
Cambrian  age;  in  the  township  of  Elzevir,  Hastings  Co.,  Ontario,  an  impure  grayish  variety 
in  Archaean  rocks. 

Use.  —  In  the  form  of  soapstone  used  for  wash  tubs,  sinks,  table  tops,  switchboards, 
hearth  stones,  furnace  linings,  etc.;  the  tips  of  gas  burners,  tailors'  chalk,  slate  pencils, 
etc™  3rnaments'  etc>  ;  m  Powdered  form  as  filler  in  papers,  as  a  lubricant,  in  toilet  powders, 


%    G^?M®  is  aPPa.rently  a  variety  of  talc,  differing  in  the  amount  of  water  present  and  in 
its  solubility  in  acids.     From  Gava  valley,  Italy. 

SEPIOLITE.     Meerschaum. 

Compact,  with  a  smooth  feel,  and  fine  earthy  texture,  or  clay-like;   also 
rarely  fibrous.     H.  =  2-2-5.     G.  =  2.     Impressible   by   the   nail.     In   dry 


SILICATES  577 

masses  floats  on  water.     Color  grayish  white,  white,  or  with  a  faint  yellowish 
or  reddish  tinge,  bluish  green.     Opaque.     Biaxial,—.     /3  =  1-55. 

Comp.  —  H4Mg2Si3O10  or  2H2O.2MgO.3SiO2  =  Silica  60-8,  magnesia 
27-1,  water  12-1  =  100.  Some  analyses  show  more  water,  which  is  probably 
to  be  regarded  as  hygroscopic.  Copper  and  nickel  may  replace  part  of  the 
magnesium. 

Pyr.,  etc.  —  In  the  closed  tube  yields  first  hygroscopic  moisture,  and  at  a  higher  tem- 
perature gives  much  water  and  a  burnt  smell.  B.B.  some  varieties  blacken,  then  burn 
white,  and  fuse  with  difficulty  on  the  thin  edges.  With  cobalt  solution  a  pink  color  on 
ignition.  Decomposed  by  hydrochloric  acid  with  separation  of  silica. 

Obs.  —  Occurs  in  Asia  Minor,  in  masses  in  stratified  earthy  or  alluvial  deposits  at  the 
plains  of  Eskihi  sher;  at  Hrubschitz  in  Moravia;  in  Morocco,  called  in  French  Pierre  de 
Savon  de  Maroc;  at  Vallecas  in  Spain,  in  extensive  beds. 

A  fibrous  mineral,  having  the  composition  of  sepiolite,  occurs  in  Utah. 

The  word  meerschaum  is  German  for  sea-froth,  and  alludes  to  its  lightness  and  color. 
Sepiolite  is  from  <rr}Tria,  cuttle-fish,  the  bone  of  which  is  light  and  porous. 

Connarite.  A  hydrous  nickel  silicate,  perhaps  H^N^SisOio.  In  small  fragile  grains. 
G.  =  2'459-2'619.  Color  yellowish  green.  From  Rottis,  in  Saxon  Voigtland. 

Spadaite.  Perhaps  5MgO.6SiOa.4H2O.  Massive,  amorphous.  Color  reddish.  From 
Capo  di  Bove,  near  Rome. 


SAPONITE.     Piotine. 

Massive.  In  nodules,  or  filling  cavities.  Soft,  like  butter  or  cheese,  but 
brittle  on  drying.  G.  =  2 '24— 2 '30.  Luster  greasy.  Color  white,  yellowish, 
grayish  green,  bluish,  reddish.  Does  not  adhere  to  the  tongue. 

Comp.  —  A  hydrous  silicate  of  magnesium  and  aluminium;  but  the 
material  is  amorphous  and  probably  always  impure,  and  hence  analyses  give 
no  uniform  results.  Contains  SiO2  40-45  p.  c.,  A12O3  5-10  p.  c.,  MgO  19-26 
p.  c.,  H20  19-21  p.  c.;  also  Fe2O3,  FeO,  etc. 

Pyr.,  etc.  —  B.B.  gives  out  water  very  readily  and  blackens;  thin  splinters  fuse  with 
difficulty  on  the  edge.  Decomposed  by  sulphuric  acid. 

Obs.  —  Occurs  in  cavities  in  basalt,  diabase,  etc.;  also  with  serpentine.  Thus  at  Lizard 
Point,  Cornwall,  in  veins  in  serpentine;  at  various  localities  in  Scotland,  etc. 

Saponite  is  from  sapo,  soap;  and  piotine  from  TTIOT^S,  fat. 

LASSALLITE.  Composition  perhaps  3MgO.2Al2p3.12SiO2.8H2O.  In  snow-white  fibrous 
masses.  G.  =  1.5.  From  the  antimony  mine  at  Miramont  and  at  Can  Pey  near  Arles-sur- 
Tech,  France. 

Celadonite.  A  silicate  of  iron,  magnesium  and  potassium.  Earthy  or  in  minute 
scales.  Very  soft.  Color  green.  Index,  1 '63.  From  cavities  in  amygdaloid  at  Mte.  Baldo 
near  Verona,  Italy. 

Glauconite.  Essentially  a  hydrous  silicate  of  iron  and  potassium.  Amorphous,  and 
resembling  earthy  chlorite;  either  in  cavities  in  rocks,  or  loosely  granular  massive.  Color 
dull  green.  Index,  1'61.  Occurs  in  rocks  of  nearly  all  geological  ages;  abundant  in  the 
"green  sand,"  of  the  Chalk  formation,  sometimes  constituting  75  to  90  p.  c.  of  the  whole. 
Found  abundantly  in  ocean  sediments  near  the  continental  shores.  A  manganese  glauco- 
nite  from  the  Marsjat  forest,  Ural  Mts.,  has  been  called  marsjatskite.  Greenalite  is  a  green 
hydrated  ferrous  silicate  found  as  granules  in  the  cherty  rock  associated  with  iron  ores  of  the 
Mesabi  district,  Minn.  Resembles  glauconite  but  contains  no  potash. 

Pholidolite.  Corresponds  approximately  to  K2q.l2(Fe,Mg)O.Al2O3.13SiO2.5H2O.  In 
minute  crystalline  scales.  G.  =  2*408.  Color  grayish  yellow.  From  Taberg  in  Werm- 
land,  Sweden,  with  garnet,  diopside,  etc. 


578  DESCRIPTIVE   MINERALOGY 

IV.   KAOLIN  DIVISION 

KAOLINITE.     Kaolin. 

Monoclinic;  in  thin  rhombic,  rhomboidal  or  hexagonal  scales  or  plates 
with  angles  of  60°  and  120°.  Usually  constituting  a  clay-like  mass,  either 
compact,  friable  or  mealy. 

Cleavage:  basal,  perfect.  Flexible,  inelastic.  H.  =  2-2-5.  G.  =  2-6-2-63. 
Luster  of  plates,  pearly;  of  mass,  pearly  to  dull  earthy.  Color  white,  grayish 
white,  yellowish,  sometimes  brownish,  bluish  or  reddish.  Scales  transparent 
to  translucent;  usually  unctuous  and  plastic. 

Optically  biaxial,  negative.  Bx0  _L  b  (010).  Bxa  and  ax.  pi.  inclined 
behind  some  20°  to  normal  to  c  (001).  Axial  angle  large,  approx.  90°.  0  = 
1-482. 

Var.  —  1.  Kaolinite.  In  crystalline  scales,  pure  white  and  with  a  satin  luster  in  the 
mass.  2.  Ordinary.  Common  kaolin,  in  part  in  crystalline  scales  but  more  or  less  impure 
including  the  compact  lithomarge. 

Comp.  —  H4Al2Si209,  or  2H2O.Al203.2SiO2  =  Silica  46.5,  alumina  39.5, 
water  14-0  =  100.  The  water  goes  off  at  a  high  temperature,  above  330°. 

Pyr.,  etc.  —  Yields  water.  B.B.  infusible.  Gives  a  blue  color  on  ignition  with  cobalt 
solution.  Insoluble  in  acids. 

Diff.  —  Characterized  by  unctuous,  soapy  feel  and  the  alumina  reaction  B.B.  Re- 
sembles infusorial  earth,  but  readily  distinguished  under  the  microscope. 

Obs.  —  Ordinary  kaolin  is  a  result  of  the  decomposition  of  aluminous  minerals,  espe- 
cially the  feldspar  of  granitic  and  gneissoid  rocks  and  porphyries.  In  some  regions  where 
these  rocks  have  decomposed  on  a  large  scale,  the  resulting  clay  remains  in  vast  beds  of 
kaolin,  usually  more  or  less  mixed  with  free  quartz,  and  sometimes  with  oxide  of  iron  from 
some  of  the  other  minerals  present.  Pure  kaolinite  in  scales  often  occurs  in  connection  with 
iron  ores  of  the  Coal  formation.  It  sometimes  forms  extensive  beds  in  the  Tertiary  forma- 
tion, as  near  Richmond,  Va.  Also  met  with  accompanying  diaspore  and  emery  or 
corundum. 

Occurs  in  the  coal  formation  in  Belgium;  Schlan  in  Bohemia;  in  argillaceous  schist  at 
Lodeve,  Dept.  of  H6rault,  France;  as  kaolin  at  Diendorf  (Bodenmais)  in  Bavaria;  at 
Schemnitz,  Hungary;  with  fluoriteat  Zinnwald,  Germany.  Yrieix,  near  Limoges,  France, 
is  the  best  locality  of  kaolin  in  Europe  (a  discovery  of  1765) ;  it  affords  material  for  the 
famous  Sevres  porcelain  manufactory.  Large  quantities  of  clay  (kaolin)  are  found  in  Corn- 
wall and  West  Devon,  England. 

In  the  United  States,  kaolin  occurs  at  Newcastle  and  Wilmington,  Del.;  at  various 
localities  in  the  limonite  region  of  Ver.  (at  Brandon,  etc.),  Mass.,  Delaware  Co.,  Pa.;  Jack- 
sonville, Ala.;  near  Webster,  N.  C.;  Edgefield,  S.  C.;  near  Augusta,  Ga.  In  crystal  plates 
from  National  Belle  mine,  Silverton,  Col.  From  Lawrence  Co.,  Ind. 

The  name  Kaolin  is  a  corruption  of  the  Chinese  Raiding,  meaning  high-ridge,  the  name 
of  a  hill  near  Jauchau  Fu,  where  the  material  is  obtained. 

Use.  —  The  finer,  purer  grades  used  in  the  manufacture  of  porcelain,  china,  etc.;  in  the 
form  of  clay  in  pottery,  stoneware,  bricks,  etc. 

Pholerite.  Near  kaolinite,  but  some  analyses  give  15  p.  c.  water.  The  original  was 
from  the  coal  mines  of  Fins,  Dept.  of 'Allier,  France. 

Faratsihite.  (Al,Fe)2O?.2SiO2.2H2O.  Intermediate  between  kaolinite  and  chloropal. 
Monoclinic.  In  microscopic  hexagonal  plates.  Soft.  G.  =  2.  Color  pale  yellow.  Index 
a  little  higher  than  that  of  kaolinite.  Difficultly  fusible.  Decomposed  by  hydrochloric 
acid.  From  Faratsiho,  Madagascar. 

HALLOYSITE. 

Massive.     Clay-like  or  earthy. 

Fracture  conchoidal.  Hardly  plastic.  H.  =  1-2.  G.  =  2-0-2-20.  Luster 
somewhat  pearly,  or  waxy,  to  dull.  Color  white,  grayish,  greenish,  yellowish, 


SILICATES  579 

bluish,  reddish.     Translucent  to  opaque,  sometimes  becoming  translucent  or 
even  transparent  in  water,  with  an  increase  of  one-fifth  in  weight. 

Var.  —  Ordinary.  Earthy  or  waxy  in  luster  and  opaque  massive.  Galapectite  is  hal- 
loysite  of  Angleur,  Belgium.  Pseudosteatite  is  an  impure  variety,  dark  green  in  color,  with 
H.  =  2'25.  G.  =  2'469.  Indianaite  is  a  white  porcelain  clay  from  Lawrence  Co.,  Indiana, 
where  it  occurs  with  allophane  in  beds  four  to  ten  feet  thick. 

Smectite  is  greenish,  and  in  certain  states  of  humidity  appears  transparent  and  almost 
gelatinous;  it  is  from  Conde,  near  Houdan,  France. 

Bole,  in  part,  may  belong  here;  that  is  those  colored,  unctuous  clays  containing  more 
or  less  iron  oxide,  which  also  have  about  24  p.  c.  of  water;  the  iron  gives  them  a  brownish, 
yellowish  or  reddish  color;  but  they  may  be  mixtures.  Here  belongs  Bergseife  (mountain- 
soap). 

Comp.  —  A  silicate  of  aluminium  (Al2O3.2SiO2)  like  kaolinite,  but  amor- 
phous and  containing  more  water;  the  amount  is  somewhat  uncertain,  but  the 
formula  is  probably  to  be  taken  as  H4Al2Si2O9.H2O  or  2H2O.Al2O3.2SiO2.H2O 
=  Silica  43-5,  alumina  36 -9,  water  19 -6  =  100. 

Pyr.,  etc.  —  Yields  water.  B.B.  infusible.  A  fine  blue  on  ignition  with  cobalt  solu- 
tion. Decomposed  by  acids. 

Obs.  —  Occurs  often  in  veins  or  beds  of  ore,  as  a  secondary  product;  also  in  granite 
and  other  rocks,  being  derived  from  the  decomposition  of  some  aluminous  minerals. 

TERMIERITE.  A  clay-like  substance  resembling  halloysite  of  uncertain  composition  from 
the  antimony  mines  of  Miramont,  France. 

Newtonite.  HgA^Si^On-H^O.  In  soft  white  compact  masses  resembling  kaolin. 
Found  on  Sneed's  Creek  in  the  northern  part  of  Newton  Co.,  Ark. 


BATCHELORITE.  Al2O3.2SiO2.H2O.  A  green  foliated  mineral  from  Mt.  Lyell  mine, 
Tasmania. 

Cimolite.  A  hydrous  silicate  of  aluminium,  2Al2O3.9SiO2.6H2O.  Amorphous  clay- 
like,  or  chalky.  Very  soft.  G.  =  2' 18-2*30.  Color  white,  grayish  white,  reddish.  From 
the  island  of  Argentiera  (Kimolos  of  the  Greeks). 

Montmorillonite.  Probably  H2Al2SLiOi2.nH2O.  Massive,  clay-like.  Very  soft  and 
tender.  Luster  feeble.  Color  white  or  grayish  to  rose-red,  and  bluish ;  also  pistachio-green. 
Unctuous.  Montmorillonite,  from  Montmorillon,  France,  is  rose-red.  Confolensite  is  paler 
rose-red;  from  Confolens,  Dept.  of  Charente  at  St.  Jean-de-Cole,  near  Thiyiers. 

Stolpenite  is  a  clay  from  the  basalt  of  Stolpen,  Germany.  Saponite  of  Nickl&s  is  a  white, 
plastic,  soap-like  clay  from  the  granite  from  which  issues  one  of  the  hot  springs  of  Plom- 
bieres,  France,  called  Soap  Spring;  it  was  named  smegmatite  by  Naumann. 

PYROPHYLLITE. 

Monoclinic?  Foliated,  radiated  lamellar  or  somewhat  fibrous;  also  granu- 
lar to  compact  or  cryptocrystalline;  the  latter  sometimes  slaty. 

Cleavage:  basal,  eminent.  Laminae  flexible,  not  elastic.  Feel  greasy. 
H.  =  1-2.  G.  =  2 -8-2 -9.  Luster  of  folia  pearly;  of  massive  kinds  dull  and 
glistening.  Color  white,  apple-green,  grayish  and  brownish  green,  yellowish 
to  ocher-yellow,  grayish  white.  Subtransparent  to  opaque.  Optically  — . 
Bx  _L  cleavage.  Ax.  angle  large,  to  108°.  Mean  index,  1*58. 

Var.  —  (1)  Foliated,  and  often  radiated,  closely  resembling  talc  in  color,  feel,  luster  and 
structure.  (2)  Compact  massive,  white,  grayish  and  greenish,  somewhat  resembling  com- 
pact steatite,  or  French  chalk.  This  compact  variety  includes  part  of  what  has  gone  under 
the  name  of  agalmatolite,  from  China;  it  is  used  for  slate-pencils,  and  is  sometimes  called 
pencil-stone. 

Comp.  —  H2Al2(SiO3)4  or  H2O.Al2O3.4SiO2  =  Silica  667,  alumina  28*3, 
water  5'0  =  100. 

Pyr.,  etc.  —  Yields  water,  but  only  at  a  high  temperature.  B.B.  whitens,  and  fuses 
with  difficulty  on  the  edges.  The  radiated  varieties  exfoliate  in  fan-like  forms,  swelling 


580  DESCRIPTIVE   MINERALOGY 

UD  to  many  times  the  original  volume  of  the  assay  Moistened  with  cobalt  solution  and 
heated  gives  a  deep  blue  color  (alumina).  Partially  decomposed  by  sulphuric  acid,  and 
completely  on  fusion  with  alkaline  carbonates. 

Diff.  —  Resembles  some  talc,  but  distinguished  by  the  reaction  for  alumina  with  cobalt 

Obs  —  Compact  pyrophyllite  is  the  material  or  base  of  some  schistose  rocks.  The  foli- 
ated variety  is  often  the  gangue  of  cyanite.  Occurs  in  the  Ural  Mts.;  at  Westana,  Sweden; 
near  Ottrez,  Luxemburg;  Ouro  Preto,  Brazil. 

Also  in  white  stellate  aggregations  in  Cottonstone  Mt.,  Mecklenburg  Co.,  N.  C.;  in 
Chesterfield  Dist.,  S.  C.,  with  lazulite  and  cyanite;  in  Lincoln  Co.,  Ga.,  on  Graves  Mt. 
The  compact  kind,  at  Deep  River,  N.  C.,  is  extensively  used  for  making  slate-pencils  and 
resembles  the  so-called  agalmatolite  or  pagodite  of  China,  often  used  for  ornamental 
carvings. 

USe.  —  For  the  same  purposes  as  talc,  which  see. 

ALLOPHANE. 

Amorphous.  In  incrustations,  usually  thin,  with  a  mammillary  surface, 
and  hyalite-like;  sometimes  stalactitic.  Occasionally  almost  pulverulent. 

Fracture  imperfectly  conchoidal  and  shining,  to  earthy.  Very  brittle. 
H.  =  3.  G.  =  1-85-1-89.  Luster  vitreous  to  subresinous;  bright  and  waxy 
internally.  Color  pale  sky-blue,  sometimes  greenish  to  deep  green,  brown, 
yellow  or  colorless.  Streak  uncolored.  Translucent,  n  =  1*49. 

Comp.  —  Hydrous  aluminium  silicate,  Al2Si05.5H20  =  Silica  23'8,  alu- 
mina 40-5,  water  35-7  =  100.  Some  analyses  give  6  equivalents  of  water  = 
Silica  22-2,  alumina  37-8,  water  40'0  =  100. 

Impurities  are  often  present.  The  coloring  matter  of  the  blue  variety  is  due  to  traces 
of  chrysocolla,  and  substances  intermediate  between  allophane  and  chrysocolla  (mixtures) 
are  not  uncommon.  The  green  variety  is  colored  by  malachite,  and  the  yellowish  and 
brown  by  iron. 

Pyr.,  etc.  —  Yields  much  water  in  the  closed  tube.  B.B.  crumbles  but  is  infusible. 
Gives  a  blue  color  on  ignition  with  cobalt  solution.  Gelatinizes  with  hydrochloric  acid. 

Obs.  —  Allophane  is  regarded  as  a  result  of  the  decomposition  of  some  aluminous  sili- 
cate (feldspar,  etc.);  and  it  often  occurs  incrusting  fissures  or  cavities  in  mines,  especially 
those  of  copper  and  limonite,  and  even  in  beds  of  coal. 

Named  from  aXXos,  other,  and  ^aiveadai,  to  appear,  in  allusion  to  its  change  of  appear- 
ance under  the  blowpipe. 

Melite.  2(Al,Fe)2O3.SiO2.8H2O.  In  imperfect  prisms.  Stalactitic,  massive.  H.  =  3. 
2-2.  Color  bluish  brown.  Infusible.  From  Saalfield,  Thuringia. 

Collyrite.  2Al2O3.SiO2.9H2O.  A  clay-like  mineral,  white,  with  a  glimmering  luster, 
greasy  feel,  and  adhering  to  the  tongue.  G.  =  2-2  -15.  From  Ezquerra  in  the  Pyrenees. 

SchrStterite.  8Al2O3.3SiO2.30H2O.  Resembles  allophane;  sometimes  like  gum  in 
appearance.  H.  =  3-3 -5.  G.  =  1-95-2 -05.  Color  pale  green  or  yellowish.  From  Dollin- 
ger  mountain,  near  Freienstein,  in  Styria;  at  the  Falls  of  Little  River,  on  the  Sand  Mt., 
Cherokee  Co.,  Ala. 

The  following  are  clay-like  minerals  or  mineral  substances:    Sinopite,  smectite,  catlinite. 


Cenosite.  I^Ca^Er^CSi^n.  Orthorhombic.  G.  =  3'38.  Color  yellowish  brown. 
From  Hittero,  Norway;  Nordmark,  Sweden. 

Britholite.  A  complex  silicate  and  phosphate  of  the  cerium  metals  and  calcium.  Hex- 
agonal. In  minute  crystals.  •  H.  =  5'5.  G.  =  4-4.  Color  brown.  From  nepheline 
syenite  region  of  Julianehaab,  South  Greenland. 

Erikite.     Composition  uncertain;   essentially  a  silicate  and  phosphate  of  the  cerium 
rthorhombic.     In  prismatic  crystals.     H.  =  5'5.     G.  =  3'5.     Color  light  yel- 
low-brown to  dark  gray-brown.     From  nepheline-syenite  in  South  Greenland. 

Plazolite     3CaO  Al20A2(Si02,C02).2H20.       Isometric.       In    minute    dodecahedrons. 
b5.    G.  =3-13.    Colorless  to  light  yellow,     n  =  171.     From  Crestmore,  Cal. 


SILICATES  581 

Thaumasite.  CaSiO3.CaCO3.CaSO4.15H2O.  Massive,  compact,  crystalline.  Cleavage 
in  traces.  H.  =  3'5.  G.  =  1-877.  Color  white.  Uniaxial,o-.  co  =  1'507,  «  =  1'468. 
Occurs  filling  cavities  and  crevices  at  the  Bjelke  mine,  near  Areskuta,  Jemtland,  Sweden; 
at  first  soft  but  hardens  on  exposure  to  the  air.  Also  in  fibrous  crystalline  masses  at  Pat- 
erson,  N.  J.;  from  Beaver  Co.,  Utah. 

Spurrite.  2Ca2SiO4.CaCO3.  Probably  monoclinic.  In  granular  cleavable  masses. 
H.  =  5.  Color  pale  gray,  ft  =  T67.  Infusible.  .From  contact  zone  between  limestone 
and  diorite  in  Velardena  mining  district,  Mexico. 

Uranophane.  Uranotil.  CaO.2UO3.2'SiO2.GH2O.  In  radiated  aggregations;  massive, 
fibrous.  G.  =  3-81-3-90.  Color  yellow.  Biaxial,-.  Indices,  1'650-1'670.  From  the 
granite  of  Kupferberg,  Silesia.  Uranotil  occurs  at  Wolsendorf,  Bavaria;  Mitchell  Co., 

Dixenite.  MnSiO3.2Mn2(OH)AsO3.  Hexagonal.  In  aggregates  of  thin  folia. 
H.  =  3-4.  Basal  cleavage.  Color  nearly  black,  red  by  transmitted  light.  Optically 
+  .  n  =  1*96.  From  Langban,  Sweden. 

Bakerite.  A  hydrated  calcium  borosilicate,  8CaO.5B2O3.6SiO2.6H2O.  In  compact 
masses  resembling  unglazed  porcelain.  H.  =  4'5.  G.  =  2'7-2'9.  Color  white.  Fusible. 
From  borax  deposits  in  Mohave  desert,  16  miles  N.  E.  of  Daggett,  San  Bernardino  Co., 
Cal.  

CHRYSOCOLLA. 

Cryptocrystalline;  often  opal-like  or  enamel-like  in  texture;  earthy.  In- 
crusting  or  filling  seams.  Sometimes  botryoidal.  In  microscopic  acicular 
crystals  from  Mackay,  Idaho. 

Fracture  conchoidal.  Rather  sectile;  translucent  varieties  brittle.  H.  = 
2-4.  G.  =  2-2*238.  Luster  vitreous,  shining,  earthy.  Color  mountain- 
green,  bluish  green,  passing  into  sky-blue  and  turquois-blue;  brown  to  black 
when  impure.  Streak,  when  pure,  white.  Translucent  to  opaque.  Crystals 
from  Idaho  gave:  Uniaxial,  +;  w  =  1-46;  e  =  1-57;  weakly  pleochroic, 
co  =  colorless,  e  =  pale  blue-green. 

Comp.  —  True  chrysocolla  appears  to  correspond  to  CuSiO3.2H2O  = 
Silica  34-3,  copper  oxide  45 -2,  water  20 -5  =  100,  the  water  being  double  that  of 
dioptase. 

Composition  varies  much  through  impurities;  free  silica,  also  alumina,  black  oxide  of 
copper,  oxide  of  iron  (or  limonite)  and  oxide  of  manganese  may  be  present;  the  color  con- 
sequently varies  from  bluish  green  to  brown  and  black.  It  has  been  suggested  that  the 
composition  of  most  chrysocolla  is  not  definite  but  that  it  is  usually  in  the  form  of  a  mineral 
gel  with  copper  oxide,  silica  and  water  occurring  in  varying  proportions  according  to  the 
conditions  of  formation. 

Pyr.,  etc.  —  In  the  closed  tube  blackens  and  yields  water.  B.B.  decrepitates,  colors  the 
flame  emerald-green,  but  is  infusible.  With  the  fluxes  gives  the  reactions  for  copper. 
With  soda  and  charcoal  a  globule  of  metallic  copper.  Decomposed  by  acids  without 
gelatinization. 

Obs.  —  Accompanies  other  copper  ores,  occurring  especially  in  the  upper  part  of  veins. 
Found  in  copper  mines  in  Cornwall,  England;  Hungary;  Siberia;  Saxony;  South  Australia; 
Chile,  etc. 

In  the  United  States,  similarly  at  the  Schuyler's  mines,  N.  J.;  at  Morgantown,  Pa.;  at 
the  Clifton  mines,  Graham  Co.,  'in  Gila  Co.,  Ariz.;  Emma  mine,  Utah.  In  crystals  from 
Mackay,  Idaho. 

Chrysocolla  is  from  XPV(TOS,  gold,  and  KO\\<X,  glue,  and  was  the  name  of  a  material  used 
in  soldering  gold.  The  name  is  often  applied  now  to  borax,  which  is  so  employed. 

Use.  —  Chrysocolla  may  serve  as  a  minor  ore  of  copper. 

Shattuckite.  2CuSiO3.H2O.  Compact,  granular,  fibrous.  G.  =  3-8.  Color  blue. 
Indices,  1 '73-1 '80.  Pleochroic,  dark  to  light  blue.  Found  at  Shattuck  mine,  Bisbee, 
Ariz.,  forming  pseudomorphs  after  malachite. 

Bisbeeite.  CuSiO3.H2O.  Orthorhombic,  fibrous.  Color  pale  blue  to  nearly  white; 
Elongation  of  fibers  positive.  Indices  1-59  to  1-65.  Pleochroic,  very  pale  green  to  pale 
olive-brown.  Found  at  Shattuck  mine  at  Bisbee,  Ariz.,  resulting  from  the  hydration  of 
shattuckite. 


582  DESCRIPTIVE   MINERALOGY 

CHLOROPAL. 

Compact  massive,  with  an  opal-like  appearance;  earthy. 

H.  =  2-5^-5.  G.  =  1727-1-870,  earthy  varieties,  the  second  a  conchoidal 
specimen;  2-105,  Ceylon.  Color  greenish  yellow  and  pistachio-green. 
Opaque  to  subtranslucent.  Fragile.  Fracture  conchoidal  and  splintery 
to  earthy.  Adheres  feebly  to  the  tongue. 

Var.  —  Chloropal  has  the  above-mentioned  characters,  and  was  named  from  the  Hunga- 
rian mineral  occurring  at  Unghwar. 

Nontronite  is  pale  straw-yellow  or  canary-yellow,  and  greenish,  with  an  unctuous  feel; 
flattens  and  grows  lumpy  under  the  pestle,  and  is  polished  by  friction;  from  Nontron, 
Dept.  of  Dordogne,  France.  Pinguite  is  siskin-  and  oil-green,  extremely  soft,  like  ftew- 
made  soap,  with  a  slightly  resinous  luster,  not  adhering  to  the  tongue;  from  Wolkenstein 
in  Saxony.  Graminite  has  a  grass-green  color  (whence  the  name),  and  occurs  at  Menzen- 
berg,  in  the  Siebengebirge,  Germany;  in  thin  fibrous  seams,  or  as  delicate  lamellaB. 

Comp.  —  A  hydrated  silicate  of  ferric  iron,  perhaps  with  the  general 
formula  HeF^CSiO^a^I^O  or  Fe2O3.3SiO2.5H2O  =  Silica  41-9,  iron  sesqui- 
oxide  37 -2,  water  20*9  =  100.  Alumina  is  present  in  some  varieties. 

The  water  and  silica  both  vary  much.  The  Hungarian  chloropal  occurs  mixed  with 
opal,  and  graduates  into  it,  and  this  accounts  for  the  high  silica  of  some  of  its  analyses. 

Obs.  —  Localities  mentioned  above.  Chloropal  occurs  also  at  Meenser  Steinberg  near 
Gottingen,  Germany;  pinguite  at  Sternberg,  Moravia.  On  Lehigh  Mt.,  Pa.,  south  of 
Allentown,  occurs  in  connection  with  iron  deposits.  From  Palmetto  Mts.,  Esmeralda  Co., 
Nev. 

HCBFERITE.     An  iron  silicate  near  chloropal.     Color  green.     From  Kfitz,  Bohemia. 

Miillerite.  Zamboniniie.  Fe2Si3O9.2H2O.  Massive.  Resembles  nontronite.  Soft. 
G.  =  2-0.  Color  yellowish  green.  Infusible.  From  Nontron,  Dordogne,  France. 

Hisingerite.  A  hydrated  ferric  silicate,  of  uncertain  composition.  Amorphous,  com- 
pact. Fracture  conchoidal.  H.  =3.  G.  =  2'5-3'0.  Luster  greasy.  Color  black  to 
brownish  black.  Streak  yellowish  brown.  From  Riddarhyttan,  Tunaberg,  Sweden; 
Langban,  etc.,  Norway;  from  Greenland. 

Morencite.  A  hydrated  ferric  silicate  of  uncertain  composition.  Fibrous.  Color 
brownish  yellow.  From  Morenci,  Ariz. 


The  following  are  hydrous  manganese  silicates. 

Bementite.  HeMn^SiO^.  Orthorhombic.  Cleavages  ||  to  three  pinacoids.  In  soft 
radiated  masses  resembling  pyrophyllite.  G.  =  2  "981.  Color  pale  grayish  yellow.  From 
the  zinc  mines  of  Franklin  Furnace,  N.  J.  . 

T  EcJr°P^e-     Mn*Si8O28.7H2O.    Monoclinic(?).    In  thin  tabular  crystals.    Good  cleavage. 

H.  =4.     G.  =  2-46.    Color  brown.    Opaque.    Indices,  1  "62-1  -63.     From  Langban,  Sweden. 

Agnolite.     H2Mn3(SiO3)4.H2O.     Name  given  to  the  manganese  silicate  occurring  as 

part  of  the  material  from  Schemnitz,  Hungary,  known  as  manganocalcite.     Triclinic.     In 

radiating  fibrous  masses.    Color  flesh-red  to  rose.     H.  =5.     G.  =  3'0. 

Orientite.    Ca4Mn4(SiO4)5.4H2O.      Orthorhombic.      Radiating  prismatic.      Brown  to 

77«          ^I7&  ^  opaq;f  ••       H-  =  4-&-5.      G.  =  3.      Optically  +.      «  =  1758. 
776.    y  =  1795.     From  Onente  Province,  Cuba. 


PprS?tdh^10n?te'  3<z*LMn)9|iO*-H*>.  Monoclinic.  In  acute  pyramidal  crystals. 
Perfect  basal  cleavage.  H=  4-5-5.  G.  =  3*91.  Color,  bright  pink  to  reddish  brown. 
-  1  76.  crepitates  and  then  fuses  readily.  Soluble  in  acids.  From  Franklin,  N.  J. 
ran,??;™*6'  ~  A  1}ydrojf  sjjicate  of  manganese,  magnesium  and  zinc,  8RO.3SiO2.2H2O.  In 
radiating  groups  of  needle-like  crystals.  Colorless  and  transparent.  From  Franklin,  N.  J. 

G   -^T^-Qi    %£&?***  iMn0-3SKV3H20.     In  stalactitic  and  reniform  shapes. 
~  olor  brown.     From  the  Harstig  mine  near  Pajsberg,  Sweden. 

allv  dee°rivedefrnm  &?!]£*  ?ica11  °[  manSanese  and  iron,  of  doubtful  composition,  usu- 
and  liverTbro^n  alteration  of  rhodonite.     Amorphous.     Color  black  to  dark  brown 


TITANO-SILICATES,    TITANATES 


583 


Searlesite.  NaB(SiO3)2.H2O.  Monoclinic  (?).  In  minute  spherulites  composed  of 
radiating  fibers.  Color  white.  Indices,  1-52-1-53.  Fusible.  Decomposed  by  hydro- 
chloric acid.  Found  at  Searles  Lake,  San  Bernardino  Co.,  Cal. 

Colerainite.  4MgO.Al2O3.2SiO2.5H2O.  Hexagonal.  In  minute,  thin,  hexagonal  plates. 
H.  =  2-5-3.  G.  =  2-51.  Colorless  or  white.  Optically +.  Index,  1*56.  Found  in  Black 
Lake  area,  Coleraine  township,  Quebec. 

TARTARKAITE.  A  complex  hydrous  silicate  of  aluminium,  magnesium,  etc.  Tabular 
crystals.  G.  =  27.  Color  dark  gray  to  black.  Uniaxial,  +.  In  limestone  on  the  Tar- 
tarka  river,  Yenisei  District,  Siberia. 


ITANO-SILICATES,  TITANATES 

This  section  includes  the  common  calcium  titano-silicate,  Titanite;  also  a 
number  of  silicates  which  contain  titanium,  but  whose  relations  are  not  alto- 
gether clear;  further  the  titanate,  Perovskite,  and  niobo-titanate,  Dysanalyte, 
which  is  intermediate  between  Perovskite  and  the  species  Pyrochlore,  Micro- 
lite,  Koppite  of  the  following  section. 

In  general  the  part  played  by  titanium  in  the  many  silicates  in  which  it  enters  is  more 
or  less  uncertain.  It  is  probably  in  most  cases,  as  shown  in  the  preceding  pages,  to  be  taken 
as  replacing  the  silicon;  in  others,  however,  it  seems  to  play  the  part  of  a  basic  element;  in 
schorlomite  (p.  510)  it  may  enter  in  both  relations. 


TITANITE.     Sphene. 

Monoclinic.     Axes  a 

110  A  110  = 
001  A  102 


mm 
ex. 


b:c  =  0-7547 

66°  29'. 
21°    0'. 


1  :  0-8543;  p  =  60( 


nri 


960 


021  A  021  =  112°  3'. 
Ill  A  111  =  43°  49'. 


IV, 
en, 
cm, 
dt 


Tl2  A  112 
001  A  111  = 
001  A  110  = 
001  A  112  = 


961 


17'. 

46°    7*'. 
38°  16'. 
65°  30'. 
40°  34'. 

962 


963 


964 


Twins:  tw.  pi.  a  (100)  rather  common,  both  contact-twins  and  cruciform 
penetration-twins.     Crystals  very  varied  in  habit;   often  wedge-shaped  and 


584  DESCRIPTIVE    MINERALOGY 

flattened  ||  c  (001);    also  prismatic.     Sometimes  massive,  compact;    rarely 

1  $}  in  f*l  1 1\  T* 

Cleavage-  m  (110)  rather  distinct;  a  (100),  I  (112)  imperfect;  in  greeno- 
vite n  (111)  easy,  t  (111)  less  so.  Parting  often  easy  1 1  77  (221)  due  to  twinning 
lamellae.  H.  =  5-5'5.  G.  =  3 -4-3 -56.  Luster  adamantine  to  resinous. 
Color  brown,  gray,  yellow,  green,  rose-red  and  black.  Streak  white,  slightly 
reddish  in  greenovite.  Transparent  to  opaque. 

Pleochroism  in  general  rather  feeble,  but  distinct  in  deep-colored  kinds: 
Z  red  with  tinge  of  yellow;.  7,  yellow,  often  greenish;  X,  nearly  colorless. 
Optically  +  .  Ax.  pi.  ||  b  (010).  Bx  nearly  J_  x  (102),  i.e.,  Bx  A  c  axis  = 
+  51°.  Dispersion  p  >  v  very  large,  and  hence  the  peculiarity  of  the  axial 
interference-figure  in  white,  light.  Axial  angles  variable.  2V  =  27°.  a  = 
1-900.  ft  =  1-907.  7  =  2-034. 

Var.  —  Ordinary,  (a)  Titanite;  brown  to  black,  the  original  being  thus  colored,  also 
opaque  or  subtranslucent.  (6)  Sphene  (named  from  a^v,  a  wedge)',  of  light  shades,  as 
yellow,  greenish,  etc.,  and  often  translucent;  the  original  was  yellow.  Ligurite  is  an  apple- 
green  sphene.  Spinthere  (or  Semeline)  a  greenish  kind.  Lederite  is  brown,  opaque,  or  sub- 
translucent,  of  the  form  in  Fig.  960. 

Titanomorphite  is  a  white  mostly  granular  alteration-product  of  rutile  and  ilmemte,  not 
uncommon  in  certain  crystalline  rocks;  here  also  belongs  most  leucoxene  (see  p.  418). 

Manganesian;  Greenovite.  Red  or  rose-colored,  owing  to  the  presence  of  a  little  man- 
ganese; from  St.  Marcel,  Piedmont,  Italy;  from  Jothvad  in  Narukot,  India. 

Containing  yttrium  or  cerium.     Here  belong  grothite,  alshedite,  eucolite-titanite. 

Comp.  —  CaTiSiO5  or  CaO.TiO2.Si02  =  Silica  30-6,  titanium  dioxide 
40-8,  lime  28*6  =  100.  Iron  is  present  in  varying  amounts,  sometimes  man- 
ganese and  also  yttrium  in  some  kinds. 

Pyr.,  etc.  —  B.B.  some  varieties  change  color,  becoming  yellow,  and  fuse  at  3  with 
intumescence,  to  a  yellow,  brown  or  black  glass.  With  borax  they  afford  a  clear  yellowish 
green  glass.  Imperfectly  soluble  in  heated  hydrochloric  acid;  and  if  the  solution  be  con- 
centrated along  with  tin,  it  assumes  a  fine  violet  color.  With  salt  of  phosphorus  in  R.  F. 
gives  a  violet  bead;  varieties  containing  much  iron  require  to  be  treated  with  the  flux  on 
charcoal  with  metallic  tin.  Completely  decomposed  by  sulphuric  and  hydrofluoric  acids. 

Diff.  —  Characterized  by  its  oblique  crystallization,  a  wedge-shaped  form  common;  by 
resinous  (or  adamantine)  luster;  hardness  less  than  that  of  staurolite  and  greater  than  that 
of  sphalerite.  The  reaction  for  titanium  is  distinctive,  but  less  so  in  varieties  containing 
much  iron. 

Micro.  —  Distinguished  in  thin  sections  by  its  acute-angled  form,  often  lozenge-shaped; 
its  generally  pale  brown  tone;  very  high  relief  and  remarkable  birefringence,  causing  the 
section  to  show  white  of  the  higher  order;  by  its  biaxial  character  (showing  many  lemnis- 
cate  curves);  and  by  its  great  dispersion,  which  produces  colored  hyperbolas. 

Artif.  —  Titanite  is  apparently  produced  artificially  only  with  difficulty.  It  has  been 
obtained  by  fusing  together  silica  and  titanic  oxide  with  calcium  chloride. 

Obs.  —  Titanite,  as  an  accessory  component,  is  widespread  as  a  rock  forming  mineral, 
though  confined  mostly  to  the  acidic  feldspathic  igneous  rocks;  it  is  much  more  common 
in  the  plutonic  granular  types  than  in  the  volcanic  forms.  Thus  it  is  found  in  the  more 
basic  hornblende  granites,  syenites,  and  diorites,  and  is  especially  common  and  character- 
istic in  the  nephelite-syenites.  It  occurs  also  in  the  metamorphic  rocks  and  especially  in 
the  schists,  gneisses,  etc.,  rich  in  magnesia  and  iron  and  in  certain  granular  limestones.  It 
is  also  found  in  beds  of  iron  ore;  commonly  associated  minerals  are  pyroxene,  amphibole, 
chlorite,  scapolite,  zircon,  apatite,  etc.  In  cavities  in  gneiss  and  granite,  it  often  accom- 
panies adularia,  smoky  quartz,  apatite,  chlorite,  etc. 

Occurs  at  various  points  in  the  Grisons,  Switzerland,  associated  with  feldspar  and 
chlorite;  Tavetsch;  Binnental;  in  the  St.  Gothard  region;  Zermatt  in  the  Valais ;  Mader- 
anertal  in  Uri;  also  elsewhere  in  the  Alps;  in  Dauphine  (spinthere),  France;  in  Italy  at 
Ala  (hgunte)  and  at  St.  Marcel,  in  Piedmont;  at  Schwarzenstein  and  Rothenkopf  in  the 
XT  /uif  i  r'  Tyro1'  z°Ptau,  Moravia;  near  Tavistock,  England;  near  Tremadoc,  in 
JNorth  Wales;  from  Kragero  and  in  titanic  iron  at  Arendal,  Norway;  with  magnetite  at 


TITANO-SILICATES,    TITANATES  585 

Nordmark,  Sweden;   Achmatovsk,  Ural  Mts.     Occasionally  found  among  volcanic  rocks, 
as  at  Lake  Laach  (semeline)  and  at  Andernach  on  the  Rhine. 

In  Me.,  in  fine  crystals  at  Sandford.  In  Mass.,  in  gneiss,  in  the  east  part  of  Lee;  at 
Bolton  with  pyroxene  and  scapolite  in  limestone.  In  N.  Y.,  at  Roger's  Rock  on  Lake 
George,  abundant  in  small  brown  crystals;  at  Gouverneur,  in  black  crystals  in  granular 
limestone;  in  Diana  near  Natural  Bridge,  Lewis  Co.,  in  large  dark  brown  crystals,  among 


Statesville,  Iredell  Co.,  yellowish  white  with  sunstone;  also  Buncombe  Co.,  Alexander  Co., 
and  other  points. 

Occurs  in  Canada  in  Quebec  at  Grenyille,  Argenteuil  Co.;  also  Buckingham,  Templeton, 
Wakefield,  Hull,  Ottawa  Co.;  in  Ontario  at  North  Burgess,  honey-yellow;  near  Eganville, 
Renfrew  Co.,  in  very  large  dark  brown  crystals  with  apatite,  amphibole,  zircon. 

Molengraaffite.  A  titano-silicate  of  lime  and  soda.  Monoclinic  (?).  In  imperfect  pris- 
matic crystals.  Cleavage  (100)  perfect.  Color  yellow-brown.  Indices,  173-177.  From 
a  rock,  "lujaurite,"  in  Pilandsberg,  near  Rustenberg,  Transvaal. 

Keilhauite.  A  titano-silicate  of  calcium,  aluminium,  ferric  iron,  and  the  yttrium 
metals.  Crystals  near  titanite  in  habit  and  angles.  H.  =  6'5.  G.  =  3'52-377.  Color 
brownish  black.  From  near  Arendal,  Norway. 

Tscheffkinite.  A  titano-silicate  of  the  cerium  metals,  iron,  etc.,  but  an  alteration 
product,  more  or  less  heterogeneous,  and  the  composition  of  the  original  mineral  is  very 
uncertain.  Massive,  amorphous.  H.  =  5-5'5.  G.  =  4'508-4'549.  Color  velvet-black. 
From  the  Ilmen  mountains  in  the  Ural  Mts.  Also  from  South  India,  Kanjamalai  Hill, 
Salem  district.  An  isolated  mass  weighing  20  Ibs.  has  been  found  on  Hat  Creek,  near  Mas- 
sie's  Mills,  Nelson  Co.,  Va.;  also  found,  south  of  this  point,  in  Bedford  Co. 

Astrophyllite.  Probably  R4R4Ti(SiO4)4  with  R  =  H,  Na,  K,  and  R  =  Fe,  Mn  chiefly, 
including  also  Fe2O3.  Orthorhombic.  In  elongated  crystals;  also  in  thin  strips  or  blades; 
sometimes  in  stellate  groups.  Cleavage:  6  (010)  perfect  like  mica,  but  laminae  brittle. 
H.  =  3.  G.  =  3 '3-3 '4.  Luster  submetallic,  pearly.  Color  bronze-yellow  to  gold-yellow. 
Optically  +.  Indices,  1 '678-1733. 

Occurs  on  the  small  islands  in  the  Langesund  fiord,  near  Brevik,  Norway,  in  elseolite- 
syenite,  embedded  in  feldspar,  with  catapleiite,  segirite,  black  mica,  etc.  Similarly  at 
Kangerdluarsuk  and  Narsarsuk,  Greenland.  Also  with  arfvedsonite  and  zircon  at  St. 
Peter's  Dome,  Pike's  Peak,  El  Paso  Co.,  Col. 


Johnstrupite.  A  silicate  of  the  cerium  metals,  calcium  and  sodium  chiefly,  with  titan- 
ium and  fluorine.  In  prismatic  monoclinic  crystals.  G.  =  3 '29.  Color  brownish  green. 
Index,  1  -646.  From  near  Barkevik,  Norway. 

Mosandrite.     Near  Johnstrupite  in  form  and  composition  and  from  the  same  region. 

Rinkite,  also  near  Johnstrupite,  is  from  Greenland.       ••  f«« 

Narsarsukite.  A  highly  acidic  titano-silicate  of  ferric  iron  and  sodium.  Tetragonal. 
In  tabular  crystals.  Fine  prismatic  cleavage.  H.  =7.  G.  =  27.  Color  honey-yellow, 
on  weathering  brownish  gray  or  ocher-yellow.  w  =  T55.  Fusible.  In  pegmatite  at 
Narsarsuk,  southern  Greenland. 

Neptunite.  A  titano-silicate  of  iron  (manganese)  and  the  alkali  metals.  In  prismatic 
monoclinic  crystals.  H.  =  5-6.  G.  =  3 '23.  Color  black.  Streak,  cinnamon-brown. 
Mean  index,  170.  Pleochroic,  yellow  to  deep-red.  Found  at  Narsarsuk  and  elsewhere, 
southern  Greenland,  and  at  the  benitoite  locality  in  San  Benito  Co.,  Cal.  (originally  called 
carlosite) . 

Benitojte.  BaTiSi3O9.  Hexagonal,  trigonal  (ditrigonal-bipyramidal) .  In  crystals 
with  p(1011)  prominent.  H.  =  6'2-6'5.  G  .=  3'6.  Color  sapphire-blue  to  light  blue  and 
colorless.  Transparent.  Strongly  dichroic,  deep  blue  to  colorless,  co  =  177.  Fusible 
at  3.  Found  associated  with  neptunite  and  natrolite  near  the  headwaters  of  the  San  Benito 
River  in  San  Benito  Co.,  Cal. 

Leucosphenite.  Na4Ba(TiO)2(Si2O5)5.  Monoclinic.  In  minute  wedge-shaped  crystals. 
Distinct  cleavage.  H.  =  6'5.  G.  =  3'0.  Color  white.  /8  =  1'66.  Difficultly  fusible. 
From  Narsarsuk,  southern  Greenland. 


586  DESCRIPTIVE   MINERALOGY 

Lorenzenite.  Nao(TiO)2Si2O7.  Contains  considerable  zirconia.  Orthorhombic.  In 
minute  acicular  crystals.  Distinct  cleavage.  H.  =  6.  G.  =  3 -4.  /3  about  1  '78.  Fusible. 
From  Narsarsuk,  southern  Greenland. 

Joaquinite.  A  titano-silicate  of  calcium  and  iron.  Orthorhombic.  Color,  honey- 
yellow.  Associated  with  benitoite  from  San  Benito  Co.,  Cal. 

PEROVSKITE.     Perofskite. 

Isometric  or  pseudo-isometric.  Crystals  in  general  (Ural  Mts.,  Zermatt, 
Switzerland)  cubic  in  habit  and  often  highly  modified,  but  the  faces  often 
irregularly  distributed.  Cubic  faces  striated  parallel  to  the  edges  and  appar- 
ently penetration-twins,  as  if  of  pyritohedral  individuals.  Also  in  reniform 
masses  showing  small  cubes. 

Cleavage:  cubic,  rather  perfect.  Fracture  uneven  to  subconchoidal. 
Brittle.  H.  =  5*5.  G.  =  4-017-4-039.  Luster  adamantine  to  metallic-ada- 
mantine. Color  pale  yellow,  honey-yellow,  orange-yellow,  reddish  brown, 
grayish  black.  Streak  colorless,  grayish.  Transparent  to  opaque.  Usually 
exhibits  anomalous  double  refraction.  Mean  index,  about  2*38. 

Geometrically  considered,  perovskite  conforms  to  the  isometric  system;  optically,  how- 
ever, it  is  uniformly  biaxial  and  usually  positive.  The  molecular  structure  (also  as  devel- 
oped by  etching)  seems  to  correspond  to  Orthorhombic  symmetry.  Cf.  Art.  429. 

Comp.  —  Calcium  titanate,  CaTiO3  =  Titanium  dioxide  58-9,  lime  41-1 
=  100.  Iron  is  present  in  small  amount  replacing  the  calcium. 

Pyr.,  etc.  —  In  the  forceps  and  on  charcoal  infusible.  With  salt  of  phosphorus  in  O.F. 
dissolves  easily,  giving  a  greenish  bead  while  hot,  which  becomes  colorless  on  cooling;  in 
R.F.  the  bead  changes  to  grayish  green,  and  on  cooling  assumes  a  violet-blue  color.  En- 
tirely decomposed  by  boiling  sulphuric  acid. 

Obs.  —  Occurs  in  small  crystals,  associated  with  chlorite,  and  magnetic  iron  in  chlorite 
slate,  at  Achmatovsk,  near  Zlatoust,  in  the  Ural  Mts.;  at  Schelingen  in  the  Kaiserstuhl, 
Germany,  in  granular  limestone;  in  the  valley  of  Zermatt,  Switzerland,  near  the  Findelen 
glacier;  at  Wildkreuzjoch,  between  Pfitsch  and  Pfunders  in  Tyrol,  Austria;  various 
localities,  Piedmont,  Italy.  Sometimes  noted  in  microscopic  octahedral  crystals  as  a  rock 
constituent;  thus  in  nephelite-  and  melilite-basalts;  also  in  serpentine  (altered  peridotite) 
at  Syracuse,  N.  Y.;  in  igneous  rocks,  Beaver  Creek,  Gunnison  Co.,  Col. 

Knopite.  Near  perovskite  but  contains  cerium.  In  black  isometric  crystals.  From 
Alno,  Sweden. 

Dysanalyte.  A  titano-niobate  of  calcium  and  iron,  like  perovskite  with  lime  replaced 
to  some  extent  by  iron,  etc.  Pseudo-isometric,  probably  Orthorhombic.  In  cubic  crystals. 
Color,  iron-black.  From  the  granular  limestone  of  Vogtsburg,  Kaiserstuhl,  Baden,  Ger- 
many. Has  previously  been  called  perovskite,  but  is  in  fact  intermediate  between  the 
titanate,  perovskite,  and  the  niobates,  pyrochlore  and  koppite.  From  Mte.  Somma, 
Vesuvius. 

A  related  mineral,  which  has  also  long  passed  as  perovskite,  occurs  with  magnetite, 
brookite,  rutile,  etc.,  at  Magnet  Cove,  Ark.  It  is  in  octahedrons  or  cubo-octahedrons, 
black  or  brownish  black  in  color  and  submetallic  in  luster. 

See  also  the  allied  titanate,  bixbyite,  mentioned  on  p.  425. 

Geikielite.  Magnesium  iron  titanate,  (Mg,Fe)TiO3.  Hexagonal,  rhombohedral.  Usu- 
ally massive,  as  roUed  pebbles.  H.  =6.  G.  =  4.  Color  bluish  or  brownish  black. 
Index,  very  high.  From  Ceylon. 

Delorenzite.  A  titanate  of  iron,  uranium  and  yttrium  of  uncertain  composition.  Or- 
thorhombic. Prismatic  habit.  Color  black.  Resinous  luster.  Found  in  pegmatite  at 
Graveggia,  Val  Vigezzo,  Piedmont,  Italy. 

Yttrocrasite.  A  hydrous  titanate  of  the  yttrium  earths  and  thorium.  Orthorhombic. 
**•_?  5'5~6;  G-  =  4-8.  Black  color  with  pitchy  to  resinous  luster.  Infusible.  Found 
in  Burnet  Co.,  three  miles  east  of  Barringer  Hill,  Texas. 

Brannerite.  Essentially  (UO,TiO,UO2)TiO3.  Prismatic  crystals  or  granular.  Blank. 
Basin  Idh  greenish  brown>  H<  =  4'5>  G"  "  4'5-5'4-  F°und  in  gold  placers,  Stanley 


NIOBATES,  TANTALATES  587 

Oxygen  Salts 
3.   NIOBATES,   TANTALATES 

The  Niobates  (Columbates)  and  Tantalates  are  chiefly  salts  of  metaniobic 
and  metatantalic  acid,  RNb2O6  and  RTa^A;  also  in  part  Pyroniobates, 
R2Nb2O7,  etc.  Titanium  is  prominent  in  a  number  of  the  species,  which  are 
hence  intermediate  between  the  niobates  and  titanates.  Niobium  and  tanta- 
lum also  enter  into  the  composition  of  a  few  rare  silicates,  as  wohlerite,  laven- 
ite,  etc. 

The  following  groups  may  be  mentioned: 

The  isometric  PYROCHLORE  GROUP,  including  pyrochlore,  microlite,  etc. 
The  tetragonal  FERGUSONITE  GROUP,  including  fergusonite  and  sipylite. 
The  orthorhombic  COLUMBITE  GROUP,  including  columbite  and  tantalite. 
Also  the  orthorhombic  SAMARSKITE  GROUP,  including  yttrotantalite,  samarsk- 
ite,  and  annerodite. 

The  species  belonging  in  this  class  are  for  the  most  part  rare,  and  are 
hence  but  briefly  described. 

PYROCHLORE. 

Isometric.     Commonly  in  octanedrons;  also  in  grains. 

Cleavage :  octahedral,  sometimes  distinct.  Fracture  conchoidal.  Brittle. 
H.  =  5-5-5.  G.  =  4 -2-4 -36.  Luster  vitreous  or  resinous,  the  latter  on  frac- 
ture surfaces.  Color  brown,  dark  reddish  or  blackish  brown.  Streak  light 
brown,  yellowish  brown.  Subtranslucent  to  opaque, 

Comp.  —  Chiefly  a  niobate  of  the  cerium  metals,  calcium  and  other 
bases,  with  also  titanium,  thorium,  fluorine.  Probably  essentially  a  metanio- 
bate  with  a  titanate,  RNb2O6.R(Ti,Th)03;  fluorine  is  also  present. 

Obs.  —  Occurs  in  elseolite-syenite  at  Fredriksvarn  and  Laurvik,  Norway;  on  the  island 
Lovo,  opposite  Brevik,  and  at  several  points  in  the  Langesund  fiord;  near  Miask  in  the  Ural 
Mts.  Named  from  -n-vp,  fire,  and  x^wpos,  green,  because  B.B.  it  becomes  yellowish  green. 
A  variety  of  pyrochlore  from  near  Wausau,  Wis.,  has  been  called  marignadte. 

Neotantalite.     Composition    near    that    of    tantalite.      Isometric,    in    octahedrons. 
H.  =  5-6.     G.  =  5'2.     Color  clear  yellow.     Refractive  index,   1*9.     Found  with  kaolin 
at  Colettes  and  Echassieres,  Dept.  PAllier,  France, 
ii  ii 

Chalcolamprite.  RNb2OeF2.RSiO3.  Isometric.  In  small  octahedrons.  H.  =  5-5. 
G.  =  3 '8.  Color  dark  gray-brown.  Crystal  faces  show  a  copper-red  metallic  iridescence. 
Occurs  sparingly  at  Narsarsuk,  South  Greenland.  Endeiolite  is  a  similar  mineral  from  the 
same  locality  supposed  to  have  the  same  composition  with  the  substitution  of  the  hydroxyl 
group  for  the  fluorine. 

Koppite.  Essentially  a  pyroniobate  of  cerium,  calcium,  etc.,  near  pyrochlore.  In 
minute  brown  dodecahedrons.  G.  =  4'45-4'56.  From  Schelingen,  Kaiserstuhl,  Germany, 
embedded  in  limestone. 

Hatchettolite.  A  tantalo-niobate  of  uranium,  near  pyrochlore.  In  octahedrons  with 
a  (100)  and  m  (311).  G.  =  477-4-90.  Color  yellowish  brown.  Occurs  with  samarskite, 
at  the  mica  mines  of  Mitchell  Co.,  N.  C.;  from  Mesa  Grande,  Cal. 

Samiresite.  A  niobate  of  uranium,  etc.  Isometric.  In  octahedrons.  G.  =  5  24. 
Color  golden-yellow.  From  Antsirabe,  on  Samiresy  Hill,  Madagascar. 

Microlite.  Essentially  a  calcium  pyrotantalate,  CauTa2O7,  but  containing  also  nio- 
bium, fluorine  and  a  variety  of  bases  in  small  amount.  Isometric.  Habit  octa- 
hedral; crystals  often  very  small  and  highly  modified.  H.  =  5'5.  G.  =  5'485-5'562; 
6*13  Virginia.  Color  pale  yellow  to  brown,  rarely  hyacinth-red,  n  =  T94.  From 
Chesterfield,  Mass.,  in  albite;  Branchville,  Conn.;  Rumford,  Me.;  Uto,  Sweden;  Green- 


588  DESCRIPTIVE   MINERALOGY 

land.  Also  in  fine  crystals  up  to  1  in.  in  diameter  at  the  mica  mines  at  Amelia  Court- 
House,  Amelia  Co.,  Va. 

PYRRHITE.  Probably  a  niobate  related  to  pyrochlore,  and  perhaps  identical  with 
microlite.  Occurs  in  minute  orange-yellow  octahedrons.  From  Alabashka,  near  Mursinka 
in  the  Ural  Mts.;  from  Mte.  Somma,  Vesuvius. 

RISORITE.  A  niobate  of  the  yttrium  metals.  Isotropic.  Color  yellow-brown. 
H.  =  5'5.  G.  =  4-18.  In  pegmatite  at  Risor,  Norway. 


FERGUSONITE.     Tyrite.     Bragite 

Tetragonal-pyramidal.  Axis  c  =  T4643.  Crystals  pyramidal  or  pris- 
matic in  habit. 

Cleavage:  s  (111)  in  traces.  Fracture  subconchoidal.  Brittle.  H.  = 
5-5-6.  G.  =  5-8,  diminishing  to  4 -3  when  largely  hydrated.  Luster  exter- 
nally dull,  on  the  fracture  brilliantly  vitreous  and  submetallic.  Color  brown- 
ish black;  in  thin  scales  pale  liver-brown.  Streak  pale  brown.  Subtrans- 
lucent  to  opaque.  Index,  2-19. 

Comp.  —  Essentially  a  metaniobate   (and  tantalate)   of  yttrium  with 

erbium,  cerium,  uranium,  etc.,  in  varying  amounts;   also  iron,  calcium,  etc. 

in  in 

General  formula  R(Nb,Ta)O4  with  R  =  Y,Er,Ce. 

Water  is  usually  present  and  sometimes  in  considerable  amount,  but  probably  not  an 
original  constituent;  the  specific  gravity  falls  as  the  amount  increases. 

Obs.  —  From  Cape  Farewell  in  Greenland,  in  quartz;  also  at  Ytterby  and  Kararfvet, 
Sweden.  From  near  Beforona,  Madagascar;  South  Africa;  Australia;  Ceylon;  Taka- 
yama,  Mino,  Japan.  Tyrite  is  associated  with  euxenite  at  Hampemyr  on  the  island  of 
Tromo,  and  Helle  on  the  mainland,  Norway;  bragite  is  from  Helle,  Naresto,  etc.,  Norway. 

Found  in  the  United  States,  at  Rockport,  Mass.,  in  granite;  in  the  Brindletown  gold 
district,  Burke  Co.,  N.  C.,  in  gold  washings;  with  zircon  in  Anderson  Co.,  S.  C.;  at  the 
gadolinite  locality  in  Llano  Co.,  Texas,  in  considerable  quantity. 

Sipylite.  A  niobate  of  erbium  chiefly,  also  the  cerium  metals,  etc.,  near  fergusonite 
in  form.  Rarely  in  octahedral  crystals.  Usually  in  irregular  masses.  G.  =  4 '89.  Color 
brownish  black  to  brownish  orange.  Occurs  sparingly  with  allanite  in  Amherst  Co.,  Va. 


COLUMBITE-TANTALITE. 

Orthorhombic.     Axes  a  :  b  :  c  =  0'8285  :  1  :  0'8898. 

yy'",    210  A  2lO  =  45°    0'.  ce,       001  A  021  =  60°  40'. 

mm'",  110  A  110  =  79°  17'.  ao,      100  A  111  =  51°  16'. 

gg',       130  A  130  =  43°  50'.  cu,      001  A  133  =  43°  48'. 

cfc,        001  A  103  =  19°  42'.  uu',    133  A  133  =  29°  57'. 

cq,        001  A  023  =  30°  41'.  uu"' ,  133  A  133  =  79°  54'. 

Twins:  tw.  pi.  e  (021)  common,  usually  contact-twins,  heart-shaped  (Fig. 
385,  p.  160),  also  penetration-twins;  further  tw.  pi.  q  (023)  rare  (Fig.  434,  p. 
169).  Crystals  short  prismatic,  often  rectangular  prisms  with  the  three  pina- 
coids  prominent;  also  thin  tabular  ||  a  (100);  the  pyramids  often  but  slightly 
developed,  sometimes,  however,  acutely  terminated  by  u  (133)  alone.  Also  in 
large  groups  of  parallel  crystals,  and  massive. 

Cleavage:  a  (100)  rather  distinct;  6  (010)  less  so.  Fracture  subconchoidal 
to  uneven.  Brittle.  H.  =  6.  G.  =  5 -3-7 -3,  varying  with  the  composition 
(see  below).  Luster  submetallic,  often  very  brilliant,  sub-resinous.  Color 
iron-black,  grayish  and  brownish  black,  opaque;  rarely  reddish  brown  and 


NIOBATES,  TANTALATES 


589 


translucent;  frequently  iridescent.     Streak  dark  red  to  black.     Optically  4- 
«.=  2-26.     0  =  2-20.     7  =  2-34. 


967 


968 


969 


Middletown 


Black  Hills 


Greenland 


Comp.  —  Niobate  and  tantalate  of  iron  and  manganese,  (Fe,Mn)(Nb, 
Ta)206,  passing  by  insensible  gradations  from  normal  COLUMBITE,  the  nearly 
pure  niobate,  to  normal  TANTALITE,  the  nearly  pure  tantalate.  The  iron  and 
manganese  also  vary  widely.  Tin  and  tungsten  are  present  in  small  amount. 
The  percentage  composition  for  FeNb2O6  =  Niobium  pentbxide  82-7,  iron 
protoxide  17  '3  =  100;  for  FeTa^Oe  =  Tantalum  pentoxide  86-1,  iron  protox- 
ide 13-9  =  100. 

In  some  varieties,  manganocolumbite  or  manganotantalite,  the  iron  is  largely  replaced  by 
manganese. 

The  connection  between  the  specific  gravity  and  the  percentage  of  -metallic  acids  is 
shown  in  the  following  table: 

G.  TaaOe 

5  '36  3  '3 

15'8 
13  '8 
13'4 
lO'O 


Greenland 
Acworth,  N.  H. 
Limoges 

Bodenmais  (Dianite) 
Haddam 


5'65 
570 
574 
5'85 


Bodenmais 
Haddam 
Bodenmais 
Haddam 


G. 

5  '92 
6'05 

6  '06 
613 


Ta2O5 
27-1 
30-4 
35-4 
31-5 


Tantalite 


7-03 


65-6 


Diff.  —  Distinguished  (from  black  tourmaline,  etc.)  by  orthorhombic  crystallization, 
rectangular  forms  common;  high  specific  gravity;  submetallic  luster,  often  with  iridescent 
surface;  cleavage  much  less  distinct  than  for  wolframite. 

Pyr.,  etc.  —  For  tantalite,  B.B.  alone  unaltered.  With  salt  of  phosphorus  dissolves 
slowly,  giving  an  iron  glass,  which  in  R.F.  is  pale  yellow  on  cooling;  treated  with  tin  on  char- 
coal it  becomes  green.  Decomposed  on  fusion  with  potassium  bisulphate  in  the  platinum 
spoon,  and  gives  on  treatment  with  dilute  hydrochloric  acid  a  yellow  solution  and  a  heavy 
white  powder,  which,  on  addition  of  metallic  zinc,  assumes  a  smalt-blue  color;  on  dilution 
with  water  the  blue  color  soon  disappears.  Columbite,  when  decomposed  by  fusion  with 
caustic  potash,  and  treated  with  hydrochloric  and  sulphuric  acids,  gives,  on  the  addition  of 
zinc,  a  blue  color  more  lasting  than  with  tantalite.  Partially  decomposed  when  the  powdered 
mineral  is  evaporated  to  dryness  with  concentrated  sulphuric  acid,  its  color  is  changed  to 
white,  light  gray,  or  yellow,  and  when  boiled  with  hydrochloric  acid  and  metallic  zinc  it 
gives  a  beautiful  blue. 

Obs.  —  Columbite  occurs  at  Rabenstein  and  Bodenmais,  Bavaria,  in  granite;  Tam- 
mela,  in  Finland;  Chanteloube,  near  Limoges,  France,  in  pegmatite  with  tantalite;  near 
Miask,  in  the  Ilmen  Mts.,  Russia,  with  samarskite;  in  the  gold-washings  of  the  Sanarka 
region  in  the  Ural  Mts.;  in  Greenland,  in  cryolite,  at  Ivigtut  (or  Evigtok),  in  brilliant 
crystals.  In  crystals  from  Ampangabe  and  Ambatofotsikely,  Madagascar. 

In  the  United  States,  in  Me.,  at  Standish,  in  splendent  crystals  in  granite;  also  at  Stone- 
ham  with  cassiterite,  etc.,  manganotantalite  from  Rumford.  In  N.  H.,  at  Acworth,  at  the 
mica  mine.  In  Mass.,  at  Chesterfield;  Northfield.  In  Conn.,  at  Haddam,  in  a  granite 
vein;  near  Middletown;  at  Branch ville,  Fairfield  Co.,  in  a  vein  of  albitic  granite,  in  large 


590 


DESCRIPTIVE   MINERALOGY 


crystals  and  aggregates  of  crystals,  also  in  minute  translucent  crystals  (manganocolumbite} , 
upon  spodumene.  In  N.  Y.,  at  Greenfield,  with  chrysoberyl.  In  Pa.,  Mineral  Hill,  Dela- 
ware Co.  In  Va.,  Amelia  Co.,  in  fine  splendent  crystals  with  microlite,  monazite,  etc. 
In  N.  C.,  with  samarskite  at  the  mica  mines  of  Mitchell  Co.  In  Col.,  on  microcline  at 
the  Pike's  Peak  region;  Turkey  Creek,  Jefferson  Co.  In  S.  D.  in  the  Black  Hills  region, 
common  in  the  granite  veins.  In  Cal.,  King's  Creek  district,  Fresno  Co.,  from  Rinc.on  and 
manganotantalite  from  Pala. 

Mangantantalite  (Nordenskiold)  from  Uto,  Sweden,  occurs  with  petalite,  lepidolite, 
microlite,  etc.  Manganotantalite  (Arzruni)  is  from  gold-washings  in  the  Sanarka  region  in 
the  Ural  Mts.;  from  Pilbarra  district,  West  Australia. 

Massive  tantalite  occurs  in  Finland,  in  Tammela,  at  Harkasaari  near  Torro;  in  Kimito, 
at  Skogbole;  in  Somero  at  Kaidasuo,  and  in  Kuprtane  at  Katiala,  with  lepidolite,  tourma- 
line, and  beryl;  in  Sweden,  near  Falun,  at  Broddbo  and  Finbo;  in  France,  at  Chanteloube 
near  Limoges,  in  pegmatite.  In  the  United  States,  in  Yancey  Co.,  N.  C.;  Coosa  Co.,  Ala.; 
also  in  the  Black  Hills,  S.  D.;  in  large  masses  near  Canon  City,  Col. 

Use.  —  Source  of  tantalum  used  in  making  filaments  for  incandescent  electric  lights. 

Tapiolite.  Fe(Ta,Nb)aO6.  Like  tantalite,  but  occurring  in  square  tetragonal  octa- 
hedrons. Tapiolite  shows  close  similarities  with  the  minerals  of  the  Rutile  Group,  in 
which  some  authors  place  it.  G.  =  7'496.  Color  pure  black.  From  the  Kulmala  farm, 
Tammela,  Finland.  In  twin  crystals  from  Topsham,  Me.  Mossite,  a  niobium  tapiolite. 
Found  at  Berg  near  Moss,  Norway.  Skogbolite  and  ixiolite  are  twinned  varieties  of  tapio- 
lite. 

Stibio tantalite.  (Sbp)2(Ta,Nb)2Oe.  Orthorhombic,  hemimorphic  in  direction  of  a 
axis.  Polysynthetic  twinning  parallel  to  a  (100).  Cleavage  a  (perfect).  H.  =  5*5. 
G.  =  6'0-7'4  (varying  with  composition).  /S.  =  2'40-2'42.  Fusible.  Color  brown,  reddish 
yellow,  yellow.  Luster  adamantine  to  resinous.  Originally  found  in  tin-bearing  sands  of 
Greenbushes,  Australia.  In  crystals  from  Mesa  Grande,  San  Diego  Co.,  Cal. 


b  :  c  =  0-5412  :   1  :  M330.     Crystals  prismatic, 


YTTROTANTALITE. 

Orthorhombic.     Axes  a 
mm'"  110  A  110  =  56°  50'. 

Cleavage:  b  (010)  very  indistinct.  Fracture  small  conchoidal.  H.  = 
5-5-5.  G.  =  5 '5-5 -9.  Luster  submetallic  to  vitreous  and  greasy.  Color 
black,  brown,  brownish  yellow,  straw-yellow.  Streak  gray  to  colorless. 
Opaque  to  subtranslucent. 

n  m  n  in 

Comp.  —  Essentially  RR2(Ta,Nb)4Oi5.4H2O,  with  R  =  Fe,  Ca,  R  =  Y, 
Er,  Ce,  etc.  The  water  may  be  secondary. 

The  so-called  yellow  yttrotantalite  of  Ytterby  and  Kararfvet  belongs  to  fergusonite. 

Obs.  —  Occurs  in  Sweden  at  Ytterby,  near  Vaxholm,  in  red  feldspar;  at  Finbo  and 
Broddbo,  near  Falun,  in  southern  Norway. 

SAMARSKITE. 

Orthorhombic.     Axes  a  :  b  :  c  =  0*5456 


Crystals  rectangu- 
e  (101)  prominent). 


ee'  101  A  101  =  87°. 
massive,    and    in    flattened 


1  :  0-5178. 

lar    prisms    (a  (100),    b  (010),  with 
Angles,  mm'"  110  A  110  =  57°  14'; 
Faces     rough.       Commonly 
embedded  grains. 

Cleavage:  b  (010)  imperfect.  Fracture  conchoidal. 
Brittle.  H.  =  5-6.  G.  =  5-6-5-8.  Luster  vitreous  to 
resinous,  splendent.  Color  velvet-black.  Streak  dark 
reddish  brown.  Nearly  opaque.  Index,  2*21. 

Comp;  — nRTRs(Nb,Ta)6O2i    with    R  =  Fe,    Ca,   U02, 

m 

etc. ;  R  =  cerium  and  yttrium  metals  chiefly. 

-  In  the  closed  tube  decrepitates,  glows,  cracks  open,  and  turns  black.     B.B, 
edges  to  a  black  glass.     With  salt  of  phosphorus  in  both  flames  an  emerald- 


NIOBATES,    TANTALATES 


591 


green  bead.  With  soda  yields  a  manganese  reaction.  Decomposed  on  fusion  with  potas- 
sium bisulphate,  yielding  a  yellow  mass  which  on  treatment  with  dilute  hydrochloric  acid 
separates  white  tantalic  acid,  and  on  boiling  with  metallic  zinc  gives  a  fine  blue  color.  In 
powder  sufficiently  decomposed  on  boiling  with  concentrated  sulphuric  acid  to  give  the 
blue  reduction  test  when  the  acid  fluid  is  treated  with  metallic  zinc  or  tin. 

Obs.  —  Occurs  in  reddish  brown  feldspar,  with  seschynite  and  columbite  in  the  Ilmen 
mountains,  near  Miask,  Ural  Mts.;  from  Antanamalaza,  Madagascar.  In  the  United 
States  rather  abundant  and  sometimes  in  large  masses  up  to  20  Ibs.  at  the  mica  mines  in 
Mitchell  Co.,  N.  C.,  intimately  associated  with  columbite;  sparingly  elsewhere. 

Ampangabeite.  A  niobate  of  uranium,  etc.  In  rectangular  prisms,  probably  ortho- 
rhombic.  Color  brownish  red.  Luster  greasy.  H.  =  4,  G.  =  3'97-4-29.  Fuses  to  a 
black  slag.  Easily  soluble  in  hydrochloric  acid.  Radioactive.  Found  in  parallel  growth 
with  columbite  at  Ampangabe  and  Ambatofotsikely,  Madagascar. 

Annerodite.  Essentially  a  pyro-niobate  of  uranium  and  yttrium.  In  prismatic  crys- 
tals, often  resembling  columbite.  H.  =6.  G.  =  5'7.  Color  black.  From  the  pegmatite 
vein  at  Annerod,  near  Moss,  Norway. 

Hielmite.  A  stanno-tantalate  (and  niobate)  of  yttrium,  iron,  manganese,  calcium. 
Crystals  (orthorhombic)  usually  rough;  massive.  G.  =  5*82.  Color  pure  black.  From 
the  Kararfvet  mine,  Falun,  Sweden. 


^Eschynite.  A  niobate  and  titanate  (thorate)  of  the  cerium  metals  chiefly,  also  in 
small  amount  iron,  calcium,  etc.  Crystals  prismatic,  orthorhombic.  Fracture  small  con- 
choidal.  Brittle.  H.  =  5-6.  G.  =  4 -93  Hittero;  5 '168  Miask.  Luster  submetallic  to 
resinous,  nearly  dull.  Color  nearly  black,  inclining  to  brownish  yellow  when  translucent. 
From  Miask  in  the  Ilmen  Mts.,  Russia,  in  feldspar  with  mica  and  zircon;  also  with  euclase 
in  the  gold  sands  of  the  Orenburg  District,  Southern  Ural  Mts.  From  Hittero,  Norway. 
Named  from  aurxwh,  shame,  by  Berzelius,  in  allusion  to  the  inability  of  chemical  science, 
at  the  time  of  its  discovery,  to  separate  some  of  its  constituents. 

Polymignite.  A  niobate  and  titanate  (zirconate)  of  the  cerium  metals,  iron,  calcium. 
Crystals  slender  prisms,  vertically  striated.  G.  =  4'77-4'85.  Color  black.  Occurs  at 
Frederiksvarn,  Norway. 

Euxenite.  A  niobate  and  titanate  of  yttrium,  erbium,  cerium  and  uranium.  Crystals 
rare;  commonly  massive.  H.  =  6*5.  G.  =  47-5'0.  Color  brownish  black. 

Occurs  in  Norway,  at  Jolster  near  Tvedestrand;  at  Alve,  etc.,  near  Arendal;  from 
Greenland;  from  various  localities  in  Madagascar. 

Loranskite  and  Wiikite  are  euxenite-like  minerals  from  Impilaks,  Finland.  Usually 
in  irregular  masses  but  orthorhombic  crystals  are  noted.  H.  =6.  G.  =  3'8-4'8.  Color 
black  to  brown  and  yellow. 

Polycrase.  A  niobate  and  titanate  of  yttrium,  erbium,  cerium,  uranium,  like  euxenite. 
Crystals  thin  prismatic,  orthorhombic.  Fracture  conchoidal.  H.  =  5-6.  G.  =  4'97-5'04. 
Luster  vitreous  to  resinous.  Color  black,  brownish  in  splinters. 

From  Hittero,  Norway,  in  granite  with  gadolinite;  at  Slattakra,  Smaland,  Sweden.     In 
the  United  States,  in  N.  C.,  in  the  gold-washings  on  Davis  land,  Henderson 
Co.,  with  zircon,  monazite,  xenotime,  magnetite;   also  in  S.  C.,  four  miles 
from  Marietta   in  Greenville  Co.     Named  from  TTO\US,  many,  and  /cpaais, 
mixture. 

Blomstrandine-Priorite.  Niobates  and  titanates  of  yttrium,  erbium, 
cerium  and  uranium,  similar  to  the  euxenite-poly erase  series.  The  two 
series  may  be  dimorphous.  The  ratio  of  Nb2O6  :  TiO2  ranges  from 
1:2  in  priorite  to  1:6  in  blomstrandine.  Orthohombic.  Crystals 
tabular  parallel  to  b  (010).  Most  prominent  forms  are  6  (010),  c  (001) 
and  n  (130).  G.  =  4'8-4'9.  Color  brownish  black.  Originally  found  in 
a  pegmatite  vein  at  Urstad,  Island  of  Hittero,  Norway.  Also  noted  from 
Arendal  and  elsewhere  in  southern  Norway  and  from  Miask,  Ilmen  Mts., 
Russia. 

Betafite.  A  niobate  and  titanate  of  uranium,  etc.  Isometric  with 
octahedron  and  dodecahedron.  G.  =  3 75-4 '17.  Color,  a  greenish  black. 
Opaque.  Greasy  luster.  Found  in  pegmatites  from  various  localities 
in  Madagascar,  including  Ambolotara,  near  Betafo. 


592 


DESCRIPTIVE   MINERALOGY 


Epistolite.  A  niobate  of  uncertain  composition.  Analysis  shows  chiefly  SiO2,  TiO2, 
Na^O,  H2O.  Monoclinic.  In  rectangular  plates,  also  in  aggregates  of  curved  folia.  Basal 
cleavage  perfect.  H.  =  1-1  '5.  G.  =  2 '9.  Color  white,  grayish,  brownish.  Refractive 
index  1  '67.  Found  in  pegmatite  veins  or  in  massive  albite  from  Julianehaab,  Greenland. 

Plumboniobite.  A  niobate  of  yttrium,  uranium,  lead,  iron,  etc.  Amorphous. 
H.  =  5-5-5.  G.  =  4*81.  Color  dark  brown  to  black.  Found  in  mica  mines  at  Morogoro, 
German  East  Africa. 


Oxygen  Salts 
4.   PHOSPHATES,   ARSENATES,   VANADATES,   ANTIMONATES 

A.   Anhydrous  Phosphates,  Arsenates,  Vanadates,  Antimonates 

Normal  phosphoric  acid  is  H3PO4,  and  consequently  normal  phosphates 

i  n  m 

have  the  formulas  R3P04,  R3(PO4)2  and  RPO4,  and  similarly  for  the  arse- 
nates,  etc.  Only  a  comparatively  small  number  of  species  conform  to  this 
simple  formula.  Most  species  contain  more  than  one  metallic  element,  and  in 
the  prominent  Apatite  Group  the  radical  (CaF),  (CaCl)  or  (PbCl)  enters; 

n 

in  the  Wagnerite  Group  we  have  similarly  (RF)  or  (ROH). 


XENOTIME. 


972 


973 


Tetragonal.     Axisc  =  0-6187,  zz'  (111  A  111)  =  55°  30',  zz"  (111  A  Til) 
82°  22'.     In  crystals  resembling  zircon  in  habit;   sometimes  compounded 
with  zircon  in  parallel  position  (Fig.  462,  p.  173).     In 
rolled  grains. 

Cleavage:  m  (110)  perfect.  Fracture  uneven  and 
splintery.  Brittle.  H.  =  4-5.  G.  =  4-45-4-56. 
Luster  resinous  to  vitreous.  Color  yellowish  brown, 
reddish  brown,  hair-brown,  flesh-red,  grayish  white, 
wine-yellow,  pale  yellow;  streak  pale  brown,  yellow- 
ish or  reddish.  Opaque.  Optically  +  .  o>  =  1  -72. 
e  =  1*81. 

Comp.  —  Essentially  yttrium  phosphate,  YPO4 
or  Y203.P2O5  =  Phosphorus  pentoxide  38 -6,  yttria 
=  100  The  yttrium  metals  may  include  erbium 
m  large  amount;  cerium  is  sometimes  present;  also  silicon  and  thorium  as  in 
monazite. 


nl  u  moi?tene,d  with  sulphuric  acid  colors  the  flame 

Diff       PP  Difficultly  soluble  m  salt  of  phosphorus.     Insoluble  in  acids. 

andDpfrfe7t  '  **  ^^^  f°rm'  but  Distinguished  by  inferior  hardness 


!?  gram'te.veins;  sometimes  in  minute  embedded 

uent  if  tfe  musoovT^Hesof  B±,  6  S™1'  Switzerland:  An  accessory  constit- 
ously  thought  to  ^taKgfaluSf  of  SO  *  ™  &  ™™*™  fr°m  Braz"  errone- 
Hender^n  CIolteMftchten'Co  t^f  d  ™shings  of  Clarksville,  Ga,  in  N.  C.,  Burke  Co., 
tySonite  Ml  Co-  ^  "tile,  etc,  with' 


PHOSPHATES,    ARSENATES,    ETC. 


593 


MONAZITE 

Monoclinic. 

Axes  a  :  b 

mm'", 

110  A  110 

=  86°  34'. 

aw, 

100  A  101 

=  39°  12£'. 

a'x, 

100  A  101 

=  53°  31'. 

ee', 

Oil  A  Oil 

=  83°  56'. 

rr', 

111  A  111 

=  60°  40'. 

vv', 

Til  A  Til 

=  73°  19'. 

Norwich,  Ct. 


Switzerland 


Crystals  commonly  small, 
often  flattened  ||  a  (100)  or 
elongated  ||  axis  6;  some- 
times prismatic  by  extension 
of  v  (111);  also  large  and 
coarse.  In  masses  yielding 
angular  fragments;  in  rolled 
grains. 

Cleavage:  c  (001)  sometimes  perfect  (parting?);  also,  a  (100)  distinct;  6 
(010)  difficult;  sometimes  showing  parting  ||  c  (001),  m  (110).  Fracture  con- 
choidal  to  uneven.  Brittle.  H.  =  5-5 -5.  G.  =  4-9-5-3;  mostly  5*0  to  5-2. 
Luster  inclining  to  resinous.  Color  hyacinth-red,  clove-brown,  reddish  or 
yellowish  brown.  Subtransparent  to  subtranslucent.  Optically  +  .  Ax.  pi. 
±  b  (010)  and  nearly  ||  a  (100).  Bxa  Ac  axis  =  +  1°  to  4°.  Dispersion 
p  <  v  weak;  horizontal  weak.  2V  =  14°.  a  =  1-786.  ft  =  1-788.  7  = 
1-837. 

Comp.  —  Phosphate  of  the  cerium  metals,  essentially  (Ce,La,Di)PO4. 

Most  analyses  show  the  presence  of  ThO2  and  SiO2,  usually,  but  not  always,  in  the 
proper  amount  to  form  thorium  silicate;  that  this  is  mechanically  present  is  not  certain 
but  possible. 

Pyr.,  etc.  —  B.B.  infusible,  turns  gray,  and  when  moistened  with  sulphuric  acid  colors 
the  flame  bluish  green.  With  borax  gives  a  bead  yellow  while  hot  and  colorless  on  cooling; 
a  saturated  bead  becomes  enamel-white  on  flaming.  Difficultly  soluble  in  hydrochloric 
acid. 

Obs.  —  Rather  abundantly  distributed  as  an  accessory  constituent  of  gneissoid  rocks  in 
certain  regions,  thus  in  North  Carolina  and  Brazil.  Occurs  near  Zlatoust  in  the  Ilmen 
Mts.,  Russia,  in  granite.  In  Norway,  near  Arendal,  and  at  Annerod.  In  small  yellow  or 
brown  crystals  (turnerite]  in  Dauphine,  France,  and  Switzerland.  Found  also  in  the  gold 
washings  of  Antioquia,  Colombia;  in  the  diamond  gravels  of  Brazil.  In  crystals  from 
Trundle  near  Condobolin  and  Emmaville,  New  South  Wales;  California  Creek,  Queens- 
land; Olary,  South  Australia.  In  Madagascar  at  various  localities. 

In  the  United  States,  formerly  found  with  the  sillimanite  of  Norwich,  and  at  Portland, 
Conn.;  also  at  Yorktown,  N.  Y.  In  large  coarse  crystals  and  masses  in  albitic  granite  with 
microlite,  etc.,  at  Amelia  Court-House,  Va.  In  Alexander  Co.,  N.  C.,  in  splendent  crystals; 
in  Mitchell,  Madison,  Burke,  and  McDowell  counties,  obtained  in  large  quantities  in 
rolled  grains  by  washing  the  gravels.  In  the  gold  sands  of  southern  Idaho. 

Monazite  is  named  from  nova^iv,  to  be  solitary,  in  allusion  to  its  rare  occurrence. 

Cryptolite  occurs  in  wine-yellow  prisms  and  grains  in  the  green  and  red  apatite  of  Aren- 
dal, Norway,  and  is  discovered  on  putting  the  apatite  in  dilute  nitric  acid.  It  is  probably 
monazite. 

Use.  —  Monazite  is  the  chief  source  of  thorium  oxide  which  is  used  in  the  manufacture 
of  incandescent  gaslight  mantles. 

Berzeliite.  R3As2O8(R  =  Ca,Mg,Mn,Na2).  Isometric,  usually  massive.  G.  =  4-03. 
Color  bright  yellow.  From  Lungban,  Sweden.  Pyrrharsenite  from  the  Sjo  mines,  Sweden, 
contains  also  antimony;  color  yellowish  red.  Caryinite,  associated  with  berzeliite,  is  re- 
lated, but  contains  lead;  massive  (monoclinic). 

Monimolite.  An  antimonate  of  lead,  iron,  and  sometimes  calcium;  in  part,  RsSbaOg. 
Usually  in  octahedrons;  massive,  incrusting.  G.  =  6 '58.  Color  yellowish  or  brownish 
green.  From  the  Harstig  mine,  Pajsberg,  Sweden. 


594  DESCRIPTIVE   MINERALOGY 

Carminite.  Perhaps  Pb3As2O8.10FeAsO4.  In  clusters  of  fine  needles;  also  in  sphe- 
roidal forms.  G.  =  4105.  Color  carmine  to  tile-red.  From  the  Luise  mine  at  Hor- 
hausen,  Nassau,  Germany. 

Georgiadesite.  Pb3(AsO4)2.3PbCl2.  Orthorhombic.  In  small  crystals  with  hexago- 
nal outline.  H.  =  3'5.  G.  =  7'1.  Resinous  luster.  Color  white,  brownish  yellow. 
Found  on  lead  slags  at  Laurium,  Greece. 

Pucherite.  Bismuth  vanadate,  BiVO4.  In  small  orthorhombic  crystals.  H.  =±  4. 
G.  =  6-249.  Color  reddish  brown.  Optically  -.  0  =  2 -50.  From  the  Pucher  Mine, 
Schneeberg,  Saxony;  San  Diego  Co.,  Cal. 

Armangite.  Mn3(AsO3)2.  Hexagonal-rhombohedral.  Prismatic  habit.  H.  =  4. 
G.  =  4-23.  Poor  basal  cleavage.  Color  black,  streak  brown.  Optically  -.  High 
refractive  index.  From  Langban,  Sweden. 


Triphylite  Group.     Orthorhombic 

a  :  b  :  c 

Triphylite  Li(Fe,Mn)P04  0'4348  :  1  :  0'5265 

Lithiophilite  Li(Mn,Fe)PO4 

Natrophilite  NaMnPO4 

Orthophosphates  of  an  alkali  metal,  lithium  or  sodium,  with  iron  and  man- 
ganese. 

TRIPHYLITE-LITHIOPHILITE. 

Orthorhombic.  Axes  a  :  b  :  c  =  0-4348  :  1  :  0'5265.  Crystals  rare,  usu- 
ally coarse  and  faces  uneven.  Commonly  massive,  cleavable  to  compact. 

Cleavage:  c  (001)  perfect;  b  (010)  nearly  perfect;  m  (110)  interrupted. 
Fracture  uneven  to  subconchoidal.  H.  =  4-5-5.  G  =  3-42-3-56.  Luster 
vitreous  to  resinous.  Color  greenish  gray  to  bluish  in  triphylite;  also  pale 
pink  to  yellow  and  clove-brown  in  lithiophilite.  Streak  uncolored  to  grayish 
white.  Transparent  to  translucent.  Axial  angle  variable,  0°-90°.  Mean 
index,  1-68. 

Comp.  —  A  phosphate  of  iron,  manganese  and  lithium,  Li(Fe,Mn)P04, 
varying  from  the  bluish  gray  TRIPHYLITE  with  little  manganese  to  the  salmon- 
pink  or  clove-brown  LITHIOPHILITE  with  but  little  iron. 

Typical  Triphylite  is  LiFePO4  =  Phosphorus  pentoxide  45 '0,  iron  protoxide  45 '5,  lithia 
9'5  =  100.  Typical  Lithiophilite  is  LiMnPO4  =  Phosphorus  pentoxide  45 '3,  manganese 
protoxide  45'1,  lithia  9'6  =  100.  Both  Fe  and  Mn  are  always  present. 

Pyr.,  etc.  —  In  the  closed  tube  sometimes  decrepitates,  turns  to  a  dark  color,  and  gives 
off  traces  of  water.  B.B.  fuses  at  T5,  coloring  the  flame  beautiful  lithia-red  in  streaks, 
with  a  pale  bluish  green  on  the  exterior  of  the  cone  of  flame.  With  the  fluxes  reacts  for 
iron  and  manganese;  the  iron  reaction  is  feeble  in  pure  lithiophilite.  Soluble  in  hydro- 
chloric acid. 

Obs.  —  Triphylite  is  often  associated  with  spodumene;  occurs  at  Rabenstein,  near 
Zwiesel^in  Bavaria;  Keityo,  Finland;  Norwich,  Mass.;  Peru,  Me.;  Grafton,  N.  H.  Named 
from  Tpis,  threefold,  and  <j>v\ri,  family,  in  allusion  to  its  containing  three  phosphates. 

Lithiophilite  occurs  at  Branch ville,  Fairfield  Co.,  Conn.,  in  a  vein  of  albitic  granite,  with 
spodumene,  manganese  phosphates,  etc.;  also  at  Norway,  Me.,  in  crystals  from  Pala,  Cal. 
Named  from  lithium  and  <j>t\6s,  friend. 

Natrophilite.  NaMnPO4.  Near  triphylite  in  form.  Chiefly  massive,  cleavable. 
H.  =  4-5-5.  G.  =  3-41.  Color  deep  wine-yellow.  Occurs  sparingly  at  Branchville,  Conn. 


Graftomte.  (Fe,Mn,Ca)3P2O8.  Monoclinic.  H.  =5.  G.  =  37.  Color  when  fresh 
salmon-pink,  usually  dark  from  alteration.  Fusible.  Occurs  in  laminated  intergrowths 
with  tnphyllite  in  a  pegmatite  from  Grafton,  N.  H. 


PHOSPHATES,-  ARSENATES,    ETC. 


595 


Beryllonite.  A  phosphate  of  sodium  and  beryllium,  NaBePCX.  Crystals  short  pris- 
matic to  tabular,  orthorhombic.  H.  =  5'5-6.  G.  =  2*845.  Luster  vitreous;  on  c  (001) 
pearly.  Colorless  to  white  or  pale  yellowish.  Optically  — .  /3  =  1*558.  From  Stone- 
ham,  Me. 

Apatite  Group 

R5(F,Cl)[(P,As,V)04]3  =  (R(F,Cl))R4[(P,As,V)04]3; 
(CaF)Ca4(PO4)3  Fluor-apatite         c  =  0-7346 

or  (CaCl)Ca4(PO4)3  Chlor-apatite 

(PbCl)Pb4(PO4)3  0-7362 

(PbCl)Pb4(AsO4)3  0-7224 

(PbCl)Pb4(VO4)3  0-7122 


General  formula 
Apatite 

Pyromorphite 

Mimetite 

Vanadinite 


In  addition  to  the  above  species,  there  are  also  certain  intermediate  compounds  contain- 
ing lead  and  calcium;  others  with  phosphorus  and  arsenic,  or  arsenic  and  vanadium,  as 
noted  beyond.  Further  the  rare  calcium  arsenate,  Svabite,  also  seems  to  belong  in  this 
group.  The  radicals  CaO,  Ca.OH,  may  possibly  replace  the  CaF  radical  in  apatite.  A 
probable  member  of  the  group,  wilkeite,  contains  CO3,  SiO2  and  SO4  in  addition  to  usual 
radicals.  Fermorite  contains  strontium. 

The  species  of  the  APATITE  GROUP  crystallize  in  the  hexagonal  system, 
but  all  show,  either  by  the  subordinate  faces,  or  in  .etching-figures,  that  they 
belong  to  the  pyramidal  class  (p.  100).  They  are  chemically  phosphates, 
arsenates,  vanadates  of  calcium  or  lead  (also  manganese),  with  chlorine  or 
fluorine.  The  latter  element  is  probably  present  as  a  univalent  radical 
CaF  (or  CaCl),  etc.,  in  general  RF  (or  RC1),  replacing  one  hydrogen  atom  in 

i  n        n 

the  acid  R9(P04)3,  so  that  the  general  formula  is  (RF)R4(PO4)3,  and  similarly 
for  the  arsenates.  This  is  a  more  correct  way  of  viewing  the  composition  than 
the  other  method  sometimes  adopted,  viz.,  3R3(PO4)2.RF2,  etc. 


APATITE. 

Hexagonal-pyramidal. 
976  977 


Axis  c  =  07346. 
978 


979 


cr,  0001  A  1012  =  22°  59'. 
ex,  0001  A  lOll  =  40°  18'. 
cy,  0001  A  2021  =  59°  29'. 
rr',  1012  A  0112  =  22°  31'. 


xxr,  lOTl  A  1011  =  37 
88',    1121  A  1211  =  48°  50'. 
m^  1010  A  2131  =  30°  20'. 
ms,  1010  A  1121  =  44°  17'. 


Crystals  varying  from  long  prismatic  to  short  prismatic  and  tabular.  Also 
globular  and  reniform,  with  a  fibrous  or  imperfectly  columnar  structure; 
massive,  structure  granular  to  compact. 

Cleavage:    c  (0001)  imperfect;   m  (1010)  more  so.     Fracture  conchoidal 


596  DESCRIPTIVE   MINERALOGY 

and  uneven.  Brittle.  H.  =  5,  sometimes  4-5  when  massive.  G  =  3-17- 
3-23  crystals.  Luster  vitreous,  inclining  to  subresmous.  btreak  white. 
Color  usually  sea-green,  bluish  green;  often  violet-blue;  sometimes  white; 
occasionally  yellow,  gray,  red,  flesh-red  and  brown.  Transparent  to  opaque. 
Optically  -.  Birefringence  low.  co  =  1-6461,  e  =  1-6417. 

Var  —  1  Ordinary  Crystallized,  or  cleavable  and  granular  massive.  Colorless  to 
ereen  blue  yellow,  flesh-red,  (a)  The  asparagus-stone,  originally  from  Murcia  Spain  is 
yellowish  green.  Moroxite,  from  Arendal,  Norway,  is  in  greenish  blue  and  bluish  crystals 
(6)  Lasurapatite  is  a  sky-blue  variety  with  lapis-lazuli  in  Siberia,  (c)  Francohte,  from  Wheal 
Franco,  near  Tavistock,  Devonshire,  England,  occurs  in  small  crystalline  stalactitic  masses 
and  in  minute  curving  crystals.  . 

Ordinary  apatite  is  fluor-apatite,  containing  fluorine  often  with  only  a  trace  of  chlorine, 
up  to  0'5  p.  c.;  rarely  chlorine  preponderates,  and  sometimes  fluorine  is  entirely  absent. 

2.   Manganapatite  contains  manganese  replacing  calcium  to  10'5  p.  c.  MnO;  color  dark 

3    Voelckerite  is  name  given  to  the  possible  isomorphous  molecule,  Ca4(CaO)(PO4)3  and 


. 

4.  Fibrous,  concretionary,  stalactitic.     Phosphorite  includes  the  fibrous  concretionary 
and  partly  scaly  mineral  from  Estremadura,  Spain,  and  elsewhere.     Eupyrchroite,  from 
Crown  Point,  N.  Y.,  belongs  here;  it  is  concentric  in  structure.     Staffelite  occurs  incrust- 
ing  the  phosphorite  of  Staffel,  Germany,  in  botryoidal,  reniform,  or  stalactitic  masses, 
fibrous  and  radiating.     See  p.  597. 

5.  Earthy  apatite;    Osteolite.     Mostly  altered  apatite;    coprolites  are  impure  calcium 
phosphate. 

Comp.  —  For  Fluor-apatite  (CaF)Ca4(PO4)3;  and  for  Chlor-apatite 
(CaCl)Ca4(PO4)3;  also  written  3Ca3P2O8.CaF2  and  SCaaPaOs.CaCl;.  There 
are  also  intermediate  compounds  containing  both  fluorine  and  chlorine.  The 
percentage  composition  for  these  normal  varieties  is  as  follows  : 
Fluor-apatite  P2O542'3  CaO  55'5  F  3'8  =  101'6  or  Ca3PsO8  92'25  CaF2  775  =  100 
Chlor-apatite  P2O541'0  CaO  53  '8  C16'8  =  101-6  or  Ca3P208  89'4  CaCl2  10'6  =  100 

Fluor-apatite  is  much  more  common  than  the  other  variety;  here  belongs  the  apatite  of 
the  Alps,  Spain,  St.  Lawrence  Co.,  N.  Y.,  Canada.  Apatites  in  which  chlorine  is  promi- 
nent are  rare;  this  is  true  of  some  Norwegian  kinds. 

Pyr.,  etc.  —  B.B.  in  the  forceps  fuses  with  difficulty  on  the  edges  (F.  =  4-5-5),  coloring 
the  flame  reddish  yellow;  moistened  with  sulphuric  acid  and  heated  colors  the  flame  pale 
bluish  green  (phosphoric  acid).  Dissolves  in  hydrochloric  and  nitric  acids,  yielding  with 
sulphuric  acid  a  copious  precipitate  of  calcium  sulphate;  the  dilute  nitric  acid  solution  gives 
sometimes  a  precipitate  of  silver  chloride  on  addition  of  silver  nitrate.  Most  varieties  will 
give  a  slight  test  for  fluorine,  when  heat  ed  with  potassium  bisulphate  in  a  closed  tube. 

Diff.  —  Characterized  by  the  common  hexagonal  form,  but  softer  than  beryl,  being 
scratched  by  a  knife;  does  not  effervesce  in  acid  (like  calcite)  ;  difficultly  fusible;  yields  a 
green  flame  B.B.  after  being  moistened  with  sulphuric  acid. 

Micro.  —  Recognized  in  thin  sections  by  its  moderately  high  relief;  extremely  low  bire- 
fringence (hence  not  often  showing  a  disti  net  axial  figure  in  basal  sections),  the  interference 
colors  in  ordinary  sections  scarcely  rising  above  gray  of  the  first  order;  parallel  extinction 
and  negative  extension;  columnar  form;  lack  of  color  and  cleavage;  and  by  the  rude  cross 
parting  seen  as  occasional  cracks  crossing  the  prism. 

Artif.  —  Apatite  may  be  prepared  artificially  by  fusing  sodium  phosphate  with  calcium 
fluoride  or  calcium  chloride. 

Obs.  —  Apatite  occurs  in  rocks  of  various  kinds  and  ages,  but  is  most  common  in  meta- 
morphic  crystalline  rocks,  especially  in  granular  limestone  and  in  many  metalliferous 
veins,  particularly  those  of  tin,  in  gneiss,  syenite,  hornblendic  gneiss,  mica  schist,  beds  of 
iron  ore;  occasionally  in  serpentine.  In  the  form  of  minute  microscopic  crystals  it  has  an 
almost  universal  distribution  as  an  accessory  rock-forming  mineral.  It  is  found  in  all  kinds 
of  igneous  rocks  and  is  one  of  the  earliest  products  of  crystallization.  In  larger  crystals  it  is 
especially  characteristic  of  the  pegmatite  facies  of  igneous  rocks,  particularly  the  granites, 
and  occurs  there  associated  with  quartz,  feldspar,  tourmaline,  muscovite,  beryl,  etc.  It  is 
sometimes  present  in  ordinary  stratified  limestone,  beds  of  sandstone  or  shale  of  the  Silurian, 
Carboniferous,  Jurassic,  Cretaceous,  or  Tertiary.  It  has  been  observed  as  the  petrifying 
matenal  of  wood. 


PHOSPHATES,  ARSENATES,  ETC.  597 

Among  its  localities  are  Ehrenfriedersdorf  in  Saxony;  Schwarzenstein,  the  Knappen- 
wand  in  Untersulzbachtal  and  Zillertal  in  the  Tyrol,  Austria;  St.  Gothard,  Tavetsch,  etc., 
in  Switzerland;  Mussa-Alp  in  Piedmont,  Italy,  white  or  colorless;  Zinnwald  and  Schlacken- 
wald  in  Bohemia;  at  Gellivare,  Sweden;  in  England,  in  Cornwall,  with  tin  ores;  in  Cum- 
berland, at  Carrock  Fells;  in  Devonshire,  cream-colored  at  Bovey  Tracey,  and  at  Wheal 
Franco  (francolite).  The  asparagus-stone  or  spargelstein  of  Jumilla,  in  Murcia,  Spain,  is 
pale  yellowish  green  in  color.  Large  quantities  of  apatite  are  mined  in  Norway  at  Kragero; 
also  at  Odegaard,  near  Bamle,  and  elsewhere. 

In  Me.,  on  Long  Island,  Blue-hill  Bay;  in  fine  purple  crystals  of  gem-quality  from 
Auburn.  In  N.  H.,  Westmoreland.  In  Mass.,  at  Norwich;  at  Bolton  abundant.  In 
Conn.,  at  Branch  ville  (manganapatite) ,  also  greenish  white  and  colorless;  at  Haddam 
Neck.  In  N.  Y.,  common  in  St.  Lawrence  Co.,  in  granular  limestone,  also  Jefferson  Co.; 
Sandford  mine,  East  Moriah,  Essex  Co.,  in  magnetite;  near  Edenville,  Orange  Co.;  at  Tilly 
Foster  iron  mine.  In  Pa.,  at  Leiperville,  Delaware  Co.;  in  Chester  Co.  In  N.  C.,  at 
Stony  Point,  Alexander  Co.,  etc.  In  lavender-colored  crystals  from  Mesa  Grande,  Cal. 

In  extensive  beds  in  the  Laurentian  gneiss  of  Canada,  usually  associated  with  limestone, 
and  accompanied  by  pyroxene,  amphibole,  titanite,  zircon,  garnet,  vesuvianite  and  many 
other  species.  Prominent  mines  are  in  Ottawa  County,  Quebec,  in  the  townships  of  Buck- 
ingham, Templeton,  Portland,  Hull,  and  Wakefield.  Also  in  Renfrew  county,  Ontario, 
and  in  Lanark,  Leeds,  and  Frontenac  counties. 

Apatite  was  named  by  Werner  from  diraTaew,  to  deceive,  older  mineralogists  having 
referred  it  to  aquamarine,  chrysolite,  amethyst,  fluorite,  tourmaline,  etc. 

Besides  the  definite  mineral  phosphates,  including  normal  apatite,  phosphorite,  etc., 
there  are  also  extensive  deposits  of  amorphous  phosphates,  consisting  largely  of  "bone 
phosphate"  (CasPjOs),  of  great  economic  importance,  though  not  having  a  definite  chemi- 
cal composition,  and  hence  not  strictly  belonging  to  pure  mineralogy.  Here  belong  the 
phosphatic  nodules,  coprolites,  bone  beds,  guano,  etc.  Extensive  phosphatic  deposits  also 
occur  in  North  Carolina,  Alabama,  Florida,  Tennessee,  and  in  the  western  states,  Idaho, 
Utah,  and  Wyoming.  Guano  is  bone  phosphate  of  lime,  mixed  with  the  hydrous  phos- 
phates, and  generally  with  some  calcium  carbonate,  and  often  a  little  magnesia,  alumina, 
iron,  silica,  gypsum,  and  other  impurities. 

Use.  —  Apatite  and  phosphate  rock  are  used  chiefly  as  sources  of  mineral  fertilizers. 
Some  clear  finely  colored  varieties  of  apatite  may  be  used  as  gem  stones.  The  mineral  is 
too  soft,  however,  to  permit  of  extensive  use  for  this  purpose. 

STAFFELITE.  A  carbonated  calcium  phosphate.  Occurs  incrusting  the  phosphorite  of 
Staffel,  Germany,  in  botryoidal  or  stalactitic  masses,  fibrous  and  radiating;  it  is  the  result 
of  the  action  of  carbonated  waters.  H.  =4.  G.  =  3 '128.  Color  leek-  to  dark  green, 
greenish  yellow.  Dahllite,  from  Bamle,  Norway,  is  similar. 

Fermorite.  A  member  of  the  Apatite  Group.  (Ca,Sr)4[Ca(OH,F)][(P,As)O4]3. 
H.  =  5.  G.  =  3-52.  Color  pale  pinkish  white  to  white.  Uniaxial,  -  .  Index  =•  1'66. 
Found  with  manganese  ores  at  Sitapar,  Chhindwara  District,  Central  provinces,  India. 

Wilkeite.  3Ca3(PO4)o.CaCO3.3Ca3((SiO4)(SO4)].CaO.  Probably  a  member  of  Apatite 
Group.  Hexagonal.  H.  =5.  G.  =  3*23.  Color  pale  rose-red,  yellow.  Optically  — . 
Index,  1-64.  Fusible  at  5 '5.  Dissolves  in  acids  with  separation  of  silica.  In  crystalline 
limestone  at  Crestmore,  Riverside  Co.,  Cal. 

PYROMORPHITE.     Green  Lead  Ore. 

Hexagonal  pyramidal.     Axis  c  =  07362. 

Crystals  prismatic,  often  in  rounded  barrel-shaped  forms; 
also  in  branching  groups  of  prismatic  crystals  in  nearly  parallel 
position,  tapering  down  to  a  slender  point.  Often  globular, 
reniform,  and  botryoidal  or  in  wart-like  shapes,  with  usually 
a  subcolumnar  structure;  also  jibrous,  and  granular. 

Cleavage:  m  (1010),  x  (1011)  in  traces.  Fracture  subcon- 
choidal,  uneven.  Brittle.  H.  =  3-5-4.  G.  =  6-5-7-1  mostly, 
when  pure;  5-9-6-5,  when  containing  lime.  Luster  resinous. 
Color  green,  yellow,  and  brown,  of  different  shades; 
sometimes  wax-yellow  and  fine  orange-yellow;  also  grayish 
white  to  milk-white.  Streak  white,  sometimes  yellowish. 
Subtransparent  to  subtranslucent.  Optically  — .  co  =  2*050.  e  =  2-042. 


598  DESCRIPTIVE    MINERALOGY 

Var  —  1  Ordinary,  (a)  In  crystals  as  described;  sometimes  yellow  and  in  rounded 
forms  resembling  campylite  (pseudo-campylite) .  (6)  In  acicular  and  moss-like  aggregations. 
(c)  Concretionary  groups  or  masses  of  crystals,  having  the  surface  angular,  (d)  Fibrous, 
(e)  Granular  massive.  (/)  Earthy;  incrusting. 

2  Polysphcerite.  Containing  lime;  color  brown  of  different  shades,  yellowish  gray, 
pale  yellow  to  nearly  white;  streak  white;  G.  =  5'89-6'44.  Rarely  in  separate  crystals; 
usually  in  groups,  globular,  mammillary.  Miesite,  from  Mies  in  Bohemia,  is  a  brown 
variety  Nussierite  is  similar  and  impure,  from  Nussiere,  near  Beaujeu,  Prance;  color 
yellow  greenish  or  grayish;  G.  =  5'042.  3.  Chromiferous;  color  brilliant  red  and  orange. 
4.  Arseniferous;  color  green  to  white;  G.  =  5 '5-6 '6.  5.  Pseudomorphous;  (a)  after 
galena;  (6)  cerussite. 

Comp.  —  (PbCl)Pb4(PO4)3  or  also  written  3Pb3P2O8.PbCl2  =  Phosphorus 
pentoxide  157,  lead  protoxide  82-2,  chlorine  2-6  =  100-5,  or  Lead  phosphate 
897,  lead  chloride  10-3  =  100. 

The  phosphorus  is  often  replaced  by  arsenic,  and  as  the  amount  increases  the  species 
passes  into  mimetite.  Calcium  also  replaces  the  lead  to  a  considerable  extent. 

Pyr.,  etc.  —  In  the  closed  tube  gives  a  white  sublimate  of  lead  chloride.  B.B.  in  the 
forceps  fuses  easily  (F.  =  T5),  coloring  the  flame  bluish  green;  on  charcoal  fuses  without 
reduction  to  a  globule,  which  on  cooling  assumes  a  crystalline  polyhedral  form,  while  the 
coal  is  coated  white  from  lead  chloride  and,  nearer  the  assay,  yellow  from  lead  oxide.  With 
soda  on  charcoal  yields  metallic  lead;  some  varieties  contain  arsenic,  and  give  the  odor  of 
garlic  in  R.F.  on  charcoal.  Soluble  in  nitric  acid. 

Diff.  —  Distinguished  by  its  hexagonal  form;  high  specific  gravity;  resinous  luster; 
blowpipe  characters. 

Obs.  —  Pyromorphite  occurs  principally  in  veins,  and  accompanies  other  ores  of  lead. 
At  Poullaouen  and  Huelgoet  in  Brittany,  France;  at  Zschopau  and  other  places  in  Saxony, 
Germany;  at  Pfibram,  Bleistadt,  in  Bohemia;  in  fine  crystals  at  Ems,  Braubach,  in  Nassau, 
Germany;  also  at  Dernbach  in  Nassau;  in  Siberia  at  Beresov  and  in  the  Nerchinsk  mining 
district;  in  England,  in  Cornwall,  green  and  brown;  Devon,  gray;  Derbyshire,  green  and 
yellow;  Cumberland,  golden  yellow ;  in  Scotland,  Leadhill,  red  and  orange.  From  Broken 
Hill  and  elsewhere,  New  South  Wales. 

In  the  United  States,  has  been  found  very  fine  at  Phenixville,  Pa. ;  also  in  Me.,  at  Lubec 
and  Lenox;  in  N.  Y.,  a  mile  south  of  Sing  Sing;  in  Davidson  Co.,  N.  C.,  also  in  Cabarrus 
and  Caldwell  Cos.;  from  Mullan,  Burke,  Wardner  and  Mace,  Idaho. 

Named  from  irvp,  fire,  vop<f>r),  form,  alluding  to  the  crystalline  form  the  globule  assumes 
on  cooling.  This  species  passes  into  mimetite. 

Use.  —  A  minor  ore  of  lead. 

MIMETITE. 

Hexagonal-pyramidal.     Axis  c  =  07224. 

Habit  of  crystals  like  pyromorphite;  sometimes  rounded  to  globular  forms. 
Also  in  mammillary  crusts. 

Cleavage:  x  (1011)  imperfect.  Fracture  uneven.  Brittle.  H.  =  3-5. 
G.  =  7-0-7-25.  Luster  resinous.  Color  pale  yellow,  passing  into  brown; 
orange-yellow;  white  or  colorless.  Streak  white  or  nearly  so.  Sub  trans- 
parent to  translucent.  Optically—,  co  =  2-135.  €  =  2-118. 

Var-  —  1-  Ordinary,  (a)  In  crystals,  usually  in  rounded  aggregates.  (6)  Capillary  or 
filamentous,  especially  marked  in  a  variety  from  St.  Prix-sous-Beuvray,  France;  somewhat 
like  asbestus,  and  straw-yellow  in  color,  (c)  Concretionary. 

Campylite,  from  Drygill  in  Cumberland,  England,  has  G.  =  7*218,  and  is  in  barrel- 
shaped  crystals  (whence  the  name,  from  Kanirv\os,  curved),  yellowish  to  brown  and  brown- 
ish red;  contains  3  p.  c.  P2O6. 

Comp.  —  (PbCl)Pb4(AsO4)3;  also  written  3Pb3As208.PbCl2  =  Arsenic 
pentoxide  23'2,  lead  protoxide  74-9,  chlorine  2-4  =  100'5,  or  Lead  arsenate 
90-7,  lead  chloride  9-3  =  100. 

Phosphorus  replaces  the  arsenic  in  part,  and  calcium  the  lead.  Endlichite 
(p.  599)  is  intermediate  between  mimetite  and  vanadinite. 


PHOSPHATES,    ARSENATES,    ETC. 


599 


982 


m 


Pyr.,  etc.  —  In  the  closed  tube  like  pyromorphite.  B.B.  fuses  at  1,  and  on  charcoal 
gives  m  R.F.  an  arsenical  odor,  and  is  easily  reduced  to  metallic  lead,  coating  the  coal  at 
first  with  lead  chloride,  and  later  with  arsenic  trioxide  and  lead  oxide.  Soluble  in  nitric 
acid. 

Obs.  —  Occurs  in  England  near  Redruth  and  elsewhere  in  Cornwall;  Beer  Alston  Dev- 
onshire; in  Cumberland;  in  France  near  Pontgibaud,  Puy-de-D6me;  in  Germany  at 
Johanngeorgenstadt,  m  fine  yellow  crystals,  at  Zinnwald;  at  Nerchinsk,  Siberia;  Langban, 
Sweden;  from  Santa  Eulalia,  Chihuahua,  Mexico;  at  the  Brookdale  mine  Phenixville  Pa  • 
Eureka,  Utah. 

Named  from  /it/z^r^s,  imitator,  it  closely  resembling  pyromorphite. 

Use.  —  A  minor  ore  of  lead. 

VANADINITE. 

Hexagonal-pyramidal.     Axis  c  =  07122. 

Crystals  prismatic,  with  smooth  faces  and  sharp  edges;  sometimes  cavern- 
ous, the  crystals  hollow  prisms;  also  in  rounded  forms  and  in  parallel  group- 
ings like  pyromorphite.  In  implanted  globules  or  incrustations. 

Fracture  uneven,  or  flat  conchoidal. 
Brittle.  H.  =  275-3.  G.  '=  6'66- 
7'10.  Luster  of  surface  of  fracture 
resinous.  Color  deep  ruby-red,  light 
brownish  yellow,  straw-yellow,  reddish 
brown.  Streak  white  or  yellowish. 
Subtranslucent  to  opaque.  Opti- 
cally -.  co  =  2-354.  e  =  2-299. 

Comp..  -  -  (PbCl)Pb4(V04)3,  also 
written  3Pb3V2O8.PbCl2  =  Vanadium 
pentoxide  19-4,  lead  protoxide  78-7, 
chlorine  2-5  =  100*6,  or  Lead  vanadate 
90-2,  lead  chloride  9-8  =  100. 

Phosphorus  is  sparingly  present,  also  sometimes  arsenic,  both*  replacing 
vanadium.  In  endlichite  the  ratio  of  V  :  As  =  1  :  1  nearly. 

Pyr.,  etc.  —  In  the  closed  tube  decrepitates  and  yields  a  faint  white  sublimate.  B.B. 
fuses  easily,  and  on  charcoal  to  a  black  lustrous  mass,  which  in  R.F.  yields  metallic  lead 
and  a  coating  of  lead  chloride;  after  completely  oxidizing  the  lead  in  O.F.  the  black  residue 
gives  with  salt  of  phosphorus  an  emerald-green  bead  in  R.F.,  which  becomes  light  yellow 
in  O.F.  Decomposed  by  hydrochloric  acid. 

Obs.  —  First  discovered  at  Zimapan  in  Mexico.  Later  obtained  at  Wanlockhead  in 
Dumfriesshire,  Scotland;  also  at  Berezov  in  the  Ural  Mts.,  with  pyromorphite;  and  near 
Kappel  in  Carinthia,  in  crystals;  at  Undenas,  Bolet,  Sweden.  In  the  Sierra  de  Cordoba, 
Argentine  Republic. 

In  the  United  States,  sparingly  near  Sing  Sing,  N.  Y.  Abundant  in  the  mining  regions 
of  Arizona  and  New  Mexico,  often  associated  with  wulfenite  and  descloizite;  in  Ariz.,  at 
the  mines  in  Yuma  Co.,  in  brilliant  deep  red  crystals;  Vulture,  Phoenix,  etc.,  in  Maricopa 
Co.;  the  Mammoth  gold  mine,  near  Oracle,  Pinal  Co.;  from  Yavapai  Co.  In  N.  M.  at 
Lake  Valley,  Sierra  Co.  (endlichite);  and  the  Mimbres  mines  near  Georgetown;  Hillsboro; 
Magdalena. 

Use.  —  A  source  of  vanadium  and  a  minor  ore  of  lead. 

HEDYPHANE.  From  Langban,  Sweden;  has  ordinarily  been  included  as  a  calcium 
variety  of  mimetite.  Massive,  cleavable.  Color  yellowish  white.  From  Harstig  mine, 
Pajsberg,  Sweden. 

Svabite.  A  calcium  arsenate,  related  to  the  species  of  the  Apatite  Group.  Crystals 
hexagonal  prisms;  colorless;  c  =  07143.  H.  =5.  G.  =  3  -52.  From  the  Harstig  mine, 
Pajsberg,  and  near  Nordmark,  Sweden. 


6QO  DESCRIPTIVE   MINERALOGY 

Wagnerite  Group.     Monoclinic 

a  :b  :  c  ft 

Wagnerite    (MgF)MgP04  1'9145  :  1  :  1'5059;  71°    53' 

Triplite          (RF)RP04,  R  =  Fe  :  Mn  =  2  :  1,  1  :  1,  etc. 
Triploidite      ROH)RP04,  R  =  Mn  :  Fe  =  3  :  1  T8572  : 1  :  1*4925;  71°    46' 
AdSlte          (MgOH)CaAs04  2'1978  :  1  :  1-5642;  73°    15' 

Tilasite         (MgF)CaAs04 
Sarkinite       (MnOH)MnAsO4  2'0017  :  1  :  1  5154;  62°  13*' 

Phosphates  (and  arsenates)  of  magnesium  (calcium),  iron  and  manganese 
containing  fluorine  (also  hydroxyl).  Formula  R2FPO4  or  (RF)RPO4,  etc. 

WAGNERITE. 

Monoclinic.  Axes,  see  above.  Crystals  sometimes  large  and  coarse.  Also 
massive. 

Cleavage:  a  (100),  m  (110)  imperfect;  c  (001)  in  traces.  Fracture  uneven 
and  splintery.  Brittle.  H.  =  5-5*5.  G.  =  3*07-3' 14.  Luster  vitreous. 
Streak  white.  Color  yellow,  of  different  shades;  often  grayish,  also  flesh-red, 
greenish.  Translucent.  Optically  +.  2V  =  26°  (approx.).  a  =  1*569. 
ft  =  1'570.  7  =  1*582. 

Comp.  —  A  fluo-phosphate  of  magnesium,  (MgF)MgPO4  or  Mg3P208. 
MgF2  =  Phosphorus  pentoxide  43 '8,  magnesia  49*3,  fluorine  11*8  =  104*9, 
deduct  (O  =  2F)  4'9  =  100.  A  little  calcium  replaces  part  of  the  magnesium. 

Pyr.,  etc.  —  B.B.  in  the  forceps  fuses  at  4  to  a  greenish  gray  glass;  moistened  with 
sulphuric  acid  colors  the  flame  bluish  green.  With  borax  reacts  for  iron.  On  fusion  with 
soda  effervesces,  but  is  not  completely  dissolved;  gives  a  faint  manganese  reaction.  Re- 
acts for  fluorine.  Soluble  in  nitric  and  hydrochloric  acids.  With  sulphuric  acid  evolves 
fumes  of  hydrofluoric  acid. 

Obs.  —  Wagnerite  (in  small  highly  modified  crystals)  occurs  in  the  valley  of  Hollen- 
graben,  near  Werfen,  in  Salzburg,  Austria.  Kjerulfine  (massive,  cleavable;  also  in  coarse 
crystals)  is  from  Kjorrestad,  near  Bamle,  Norway.  ,  • 

Spodiosite.  A  calcium  fluo-phosphate,  perhaps  (CaF)CaPO4.  In  flattened  prismatic 
orthorhombic  crystals.  G.  =  2 '94.  Color  ash-gray.  From  the  Krangrufva,  Wermland, 
and  Nordmark,  Sweden. 

TRIPLITE. 

Monoclinic.  Massive,  imperfectly  crystalline.  Cleavage:  unequal  in 
two  directions  perpendicular  to  each  other,  one  much  the  more  distinct.  Frac- 
ture small  conchoidal.  H.  =  4-5 -5.  G.  =  3'44-3'S.  Luster  resinous,  inclin- 
ing to  adamantine.  Color  brown  or  blackish  brown.  Streak  yellowish  gray 
or  brown.  Subtranslucent  to  opaque.  Optically  +.  Mean  index  from  1  €66- 
1-68. 

.  Comp.  —  (RF)RP04  or  R3P208.RF2  with  R  =  Fe  and  Mn,  also  Ca  and 
Mg.  The  ratio  varies  widely  from  Fe  :  Mn  =  1  :  1  to  2  :  1  (zwieselite) : 
1:2;  1:7. 

Talktriplite  is  a  variety  from  Horrsjoberg,  Sweden;  contains  magnesium  and  calcium 
in  large  amount. 

Pyr.?  etc.  — B.B.  fuses  easily  at  1*5  to  a  black  magnetic  globule;  moistened  with 
sulphuric  acid  colors  the  flame  bluish  green.  With  borax  in  O.F.  gives  an  amethystine- 
colored  glass  (manganese) ;  in  R.F.  a  strong  reaction  for  iron.  With  soda  reacts  for  man- 
ganese. With  sulphuric  acid  evolves  hydrofluoric  acid.  Soluble  in  hydrochloric  acid. 

D  ~~  UMI  by  Alluaud  at  Limoges  in  France;  Helsingfors,  Finland;  Stoneham, 
Me.;  Branchville,  Conn.;  from  Reagan  mining  district,  White  Pine  Co.,  Nev.  Zwieselite, 
a  clove-brown  variety,  is  from  Rabenstein,  near  Zwiesel  in  Bavaria. 

GRIPHITE.  A  problematical  phosphate  related  to  triplite  occurring  in  embedded  reni- 
form  masses.  From  the  Riverton  lode  near  Harney  City,  Pennington  Co.,  S.  D. 


PHOSPHATES,  ARSENATES,  ETC.  601 

II 

PHOSPHOFERRITE.  H6R9(PO4)3:  R  =  Fe,  Mn,Ca,  Mg.  Columnar.  White  to  yellow  or 
pale  green.  H.  =  4-5.  G.  =  3' 16.  Habendorf,  Bavaria. 

Triploidite.  Like  triplite,  but  with  the  F  replaced  by  (OH).  Monoclinic.  Commonly 
in  crystalline  aggregates.  Fibrous  to  columnar.  H.  =  4'5-5.  G.  =  3*697.  Color  yel- 
lowish to  reddish  brown.  Optically  +  .  0  =  1726.  From  Branchville,  Fair-field  Co., 
Conn. 

Adelite.  (MgOH)CaAsO4.  Monoclinic.  Axes,  see  p.  600;  also  massive.  H.  =  5. 
G.  =  374.  Color  gray  or  grayish  yellow.  Optically +.  Mean  index,  1 '67.  From  Nord- 
mark  and  Langban,  Sweden. 

Tilasite.  Like  adelite,  but  contains  fluorine.  Monoclinic.  Optically  — .  /3  =  1*660. 
From  Langban,  Sweden,  and  Kajlidongri,  Jhabua,  India. 

Sarkinite.  (MnOH)MnAsO4.  In  monoclinic  crystals;  also  in  spherical  forms. 
G.  =  4 '17.  Color  rose-red,  flesh-red,  reddish  yellow.  From  the  iron-manganese  mines 
of  Pajsberg,  Sweden.  Polyarsenite  and  Xantharsenite  from  the  Sjo  mine,  Grythytte 
parish,  Orebro,  Sweden,  and  Chondrasenite  from  Pajsberg,  Sweden,  are  essentially  the 
same. 

Trigonite.  Pb3MnH(AsO3)3.  Monoclinic-clinohedral.  In  small  wedge-shaped  crystals. 
H.  =  2-3.  Perfect  cleavage  ||  (010).  Color  sulphur-yellow,  a.  =  2*08.  7  =  216.  Ax.  pi. 
|  j  (010) .  From  Langban,  Sweden. 

Herderite.  A  fluo-phpsphate  of  beryllium  and  calcium,  Ca[Be(F,OH)]PO4.  In  pris- 
matic crystals,  monoclinic  with  complex  twinning.  H.  =5.  G.  =  2  '99-3  *01.  Luster 
vitreous.  Color  yellowish  and  greenish  white.  Optically—,  ft  =  T612.  From  the  tin 
mines  of  Ehrenfriedersdorf,  Saxony;  from  Epprechtstein,  Bavaria;  also  at  Stoneham, 
Auburn,  Hebron,  and  Paris,  Me. 

Hamlinite.  A  basic  phosphate  of  aluminium,  and  strontium.  In  colorless  rhombo- 
hedral  crystals.  H.  =  4 '5.  G.  =  3*  16-3 '28.  Optically  +.  o>  =  1*620.  Occurs  with 
herderite,  bertrandite,  etc.,  at  Stoneham,  Me.  In  the  diamond  sands  of  Diamantina, 
Brazil.  Found  also  in  Binnental,  Switzerland  (originally  thought  to  be  a  new  species  and 
named  bowmannite) . 

Plumbogummite.  A  basic  phosphate  of  lead  and  aluminium.  In  chemical  group  with 
hamlinite.  Resembles  drops  or  coatings  of  gum;  as  incrustations.  Color  yellowish,  brown- 
ish. From  Roughten  Gill,  Cumberland,  England.  Hitchcockite  from  Canton  mine,  Ga.,  is 
closely  identical.  The  material  from  Huelgoet,  Brittany,  France,  is  a  mixture. 

Florencite.  A  basic  phosphate  of  aluminium  and  the  cerium  metals,  closely  analogous 
to  hamlinite  to  which  it  is  related  in  form.  3Al2O3.Ce2O3.2P2O6.6H2O.  Hexagonal,  rhom- 
bohedral.  Habit  rhombohedral.  Basal  cleavage.  H.  =5.  G.  =  3*58.  Color  pale 
yellow.  Infusible.  Found  in  sands  from  near  Ouro  Preto  and  Diamantina,  Minas 
Geraes,  Brazil. 

Georceixite.  A  basic  phosphate  of  aluminium  and  barium  (with  smaller  amounts  of 
calcium  and  cerium) .  BaO.2Al2p3.P2O5.5H2O.  Microcrystalline,  in  rolled  pebbles.  H.  =  6. 
G.  =  3*1.  Color  brown  and  white.  Refractive  index,  1*63.  From  the  diamond  sands  of 
Minas  Geraes,  Brazil.  Geraesite  is  similar  but  more  acidic  in  composition. 

Crandallite.  2CaO.4Al/)3.2P2O5.10H2O.  In  compact  to  cleavable  masses.  Micro- 
scopically fibrous.  Color  white  to  light  gray.  Indices,  1-58-1*60.  Found  at  Brooklyn 
mine  near  Silver  City,  Utah. 

Harttite.  A  basic  phosphate  and  sulphate  of  aluminium  and  strontium,  (Sr,Ca)O. 
2A12O3.P2O5.SO3.5H2O.  Hexagonal.  Usually  microcrystalline  as  rolled  pebbles. 
H.  =  4'5-5.  G.  =  3*2.  Color  flesh-red.  From  the  diamond  sands  of  Minas  Geraes, 
Brazil. 

Jezekite.  A  fluo-phosphate  of  lime,  soda,  and  alumina,  Na4CaAl(AlO)(F,OH)4(Pp4)2. 
Monoclinic.  H.  =  4*5.  G.  =  2*94.  Cleavage  perfect  (100);  imperfect  (001).  Indices, 
1 '55-1 '59.  Colorless  or  white.  From  Ehrenfriedersdorf,  Saxony. 

Lacroixite.  A  fluo-phosphate  of  soda,  lime,  manganese  oxide,  and  alumina. 
Na4(Ca,Mn)4Al3(F,OH)4P3Oi6.2H2O.  Probably  monoclinic.  Pyramidal  cleavage. 
H.  =  4-1.  G.  =  3*13.  Color  pale  yellow  or  green.  Found  at  Ehrenfriedersdorf, 
Saxony. 

Durangite.  A  fluo-arsenate  of  sodium  and  aluminium,  Na(AlF)AsO4.  In  monoclinic 
crystals.  G.  =  3*94-4*07.  Color  orange-red.  Mean  index,  1*673.  From  Durango, 
Mexico. 


602  DESCRIPTIVE   MINERALOGY 

AMBLYGONITE.    Hebronite. 

Triclinic.  Crystals  large  and  coarse;  forms  rarely  distinct.  Usually 
cleavable  to  columnar  and  compact  massive.  Polysynthetic  twinning  lamellae 
common. 

Cleavage:  c  (001)  perfect,  with  pearly  luster;  a_(100)  somewhat  less  so, 
vitreous;  e  (021)  sometimes  equally  distinct;  M  (110)  difficult;  ca  (001)  A 
(100)  =  75°  30',  ce  (001)  A  (021)  =  74°  40',  cM  (001)  A  (110)  =  92°  20'. 
Fracture  uneven  to  subconchoidal.  Brittle.  H.  =  6.  G.  =  3'01-3'09. 
Luster  vitreous  to  greasy,  on  c  (001)  pearly.  Color  white  to  pale  greenish, 
bluish,  yellowish,  grayish  or  brownish  white.  Streak  white.  Subtrans- 
parent  to  translucent.  Optically  -.  a  =  1'579.  0  =  1*593.  7  =  1'597. 

Comp.  —  A  fluo-phosphate  of  aluminium  and  lithium,  Li(AlF)PO4  or 
AlPO4.LiF  =  Phosphorus  pentoxide  47*9,  alumina  34-4,  lithia  10-1,  fluorine 
12-9  =  105-3,  deduct  (0  =  2F)  5*3  =  100.  Sodium  often  replaces  part  of  the 
lithium,  and  hydroxyl  part  of  the  fluorine. 

Pyr.,  etc.  —  In  the  closed  tube  yields  water,  which  at  a  high  heat  is  acid  and  corrodes 
the  glass.  B.B.  fuses  easily  (at  2)  with  intumescence,  and  becomes  opaque  white  on  cool- 
ing. Colors  the  flame  yellowish  red  with  traces  of  green;  the  Hebron  variety  gives  an  in- 
tense lithia-red;  moistened  with  sulphuric  acid  gives  a  bluish  green  to  the  flame.  With 
borax  and  salt  of  phosphorus  forms  a  transparent  colorless  glass.  In  fine  powder  dissolves 
easily  in  sulphuric  acid,  more  slowly  in  hydrochloric  acid. 

Diff.  —  Distinguished  by  its  easy  fusibility  and  by  yielding  a  red  flame  B.B.,  from  feld- 
spar, barite,  calcite,  etc.;  also  by  the  acid  water  in  the  tube  from  spodumene. 

Obs.  —  Occurs  near  Penig  in  Saxony;  Arendal,  Norway;  Montebras,  Creuze,  France. 
In  the  United  States,  in  Me.,  at  Hebron;  also  at  Paris,  Peru,  etc.;  Branchville,  Conn., 
Pala,  San  Diego  Co.,  Cal. 

The  name  amblygonite  is  from  anftXls,  blunt,  and  yow,  angle. 

Fremontite.  Natramblygonite.  Natromontebrasite.  (Na,Li)Al(OH,F)PO4.  Mono- 
clinic.  Crystals  coarse  with  rough  faces.  Three  cleavages.  Usually  in  cleavage  masses. 
Polysynthetic  twinning  shown  under  microscope.  H.  =  5'5.  G.  =  3 '04.  Luster  vitreous 
to  greasy.  Color,  grayish  white  to  white.  Translucent  to  opaque.  Optically—.  Bisec- 
trix nearly  normal  to  basal  cleavage.  Easily  fusible  to  a  white  enamel  with  strong  sodium 
flame  color.  From  a  pegmatite  near  Canon  City,  Fremont  County,  Col. 

B.  Basic  Phosphates 

This  section  includes  a  series  of  well-characterized  basic  phosphates,  a 
number  of  which  fall  into  the  Olivinite  Group.  Acid  phosphates  are  repre- 
sented by  one  species  only,  the  little  known  monetite,  probably  HCaPO4, 
see  p.  b06. 

Olivenite  Group.     Orthorhombic 

OUvenite  Cu2(OH)AsO4  0-9396  :  1  :  0-6726 

Libethenite  Cu2(OH)PO4  0-9601  :  1  : 0-7019 

Adamite  Zn2(OH)AsO4  0-9733  :  1  :  0-7158 

Descloizite  (Pb,Zn)2(OH)VO4 

a  :  b  :  c  =  0-6368  :  1  :  0-8045  or  fa  :  b  :  c  =  0-9552  :  1  :  0-8045 
Cuprodescloizite  (Pb,Zn,Cu)2(OH)VO4 

The  OLIVENITE  GROUP  includes  several  basic  phosphates,  arsenates,  etc.,  of 

copper,  zinc,  and  lead,  with  the  general  formula  (ROH)RPO4,(ROH)RAsO4, 

1  hey  crystallize  in  the  orthorhombic  system  with  similar  form.     It  is  to 

*™      ,  ?roup  corresP°nds  in  a  measure  to  the  monoclinic  Wagnerite 

Group,  p.  600,  which  also  includes  basic  members. 


PHOSPHATES,   ARSENATES,    ETC. 


603 


\ 


OLIVENITE. 

Orthorhombic.     Axes  a  :  b  :  c  =  0*9396  :  1  :  0-6726. 
mm'",  110  A  110  =  86°  26'.  ee',  Oil  A  Oil  =  67°  51'. 

w'f       101  A  TOl  =  71°  1U'.  ve,   101  A  Oil  =  47°  34'. 

Crystals  prismatic,  often  acicular.  Also  globular  and 
reniform,  indistinctly  fibrous,  fibers  straight  and  divergent, 
rarely  irregular;  also  curved  lamellar  and  granular. 

Cleavage:  m  (110),  6(010),  e  (Oil)  in  traces.  Fracture 
conchoidal'  to  uneven.  Brittle.  H.  =  3.  G.  =  4-1-4-4. 
Luster  adamantine  to  vitreous;  of  some  fibrous  varieties  pearly. 
Color  various  shades  of  olive-green,  passing  into  leek-,  siskin-, 
pistachio-,  and  blackish  green;  also  liver-  and  wood-brown; 
sometimes  straw-yellow  and  grayish  white.  Streak  olive-green  to  brown. 
Subtransparent  to  opaque.  Mean  index,  1-83. 

Var.  —  (a)  Crystallized,  (b)  Fibrous;  finely  and  divergently  fibrous,  of  green,  yellow, 
brown  and  gray,  to  white  colors,  with  the  surface  sometimes  velvety  or  acicular;  found 
investing  the  common  variety  or  passing  into  it;  called  wood-copper  or  wood-arsenate. 
(c)  Earthy;  nodular  or  massive;  sometimes  soft  enough  to  soil  the  fingers. 

Comp.  —  Cu3As2O8Cu(OH)2  or  4CuO.As2O5.H20  =  Arsenic  pentoxide 
407,  cupric  oxide  56-1,  water  3-2  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  gives  water.  B.B.  fuses  at  2,  coloring  the  flame  bluish 
green,  and  on  cooling  the  fused  mass  appears  crystalline.  B.B.  on  charcoal  fuses  with 
deflagration,  gives  off  arsenical  fumes,  and  yields  a  metallic  arsenide  which  with  soda  yields 
a  globule  of  copper.  With  the  fluxes  reacts  for  copper.  Soluble  in  nitric  acid. 

Obs.  —  The  crystallized  varieties  occur  in  Cornwall,  at  various  mines;  Tavistock,  in 
Devonshire;  in  Tyrol,  Austria;  the  Banat,  Hungary;  Nizhni  Tagilsk  in  the  Ural  Mts.; 
Chile.  In  the  United  States,  in  Utah,  at  the  American  Eagle  and  Mammoth  mines,  Tintic 
district,  both  in  crystals  and  wood-copper.  The  name  olivenite  alludes  to  the  olive-green 
color. 


LIBETHENITE. 
Orthorhombic. 


Axes  a  :  b  :  c  =  0-9601  :  1 
mm"',  110  A  110  =  87°  40'. 
ee',       Oil  A  Oil  =  70°    8'. 


0-7019. 


Ill  A  111  =  59°   4£'. 
Ill  A  111  =  61°  47|'. 


In  crystals  usually  small,  short  prismatic  in  habit ;  often 
united  in  druses.  Also  globular  or  reniform  and  compact. 

Cleavage:  a  (100),  b  (010)  very  indistinct.  Fracture 
subconchoidal  to  uneven.  Brittle.  H.  =  4.  G.  =  3-6- 
3*8.  Luster  resinous.  Color  olive-green,  generally  dark. 
Streak  olive-green.  Translucent  to  subtranslucent.  Mean 
index,  1'72. 

Comp.  —  Cu3P2O8.Cu(OH)2  or  4CuO.P2O5.H2O  = 
Phosphorus  pentoxide  29'8,  cupric  oxide  66*4,  water 
3'8  =  100. 


Pyr.,  etc.  —  In  the  closed  tube  yields  water  and  turns  black, 
the  flame  emerald-green. 


B.B.  fuses  at  2  and  colors 

On  charcoal  with  soda  gives  metallic  copper,  sometimes  also  an 

arsenical  odor.  Fused  with  metallic  lead  on  charcoal  is  reduced  to  metallic  copper,  with 
the  formation  of  lead  phosphate,  which  treated  in  R.F.  gives  a  crystalline  polyhedral  bead 
on  cooling.  With  the  fluxes  reacts  for  copper.  Soluble  in  nitric  acid. 

Obs.  —  Occurs  with  chalcopyrite  at  Libethen,  near  Neusohl,  Hungary;  at  Rhein- 
breitenbach  and  Ehl  on  the  Rhine,  Germany;  at  Nizhni  Tagilsk  in  the  Ural  Mts.;  from 
Viel-Salm,  Belgium;  in  small  quantities  in  Cornwall,  England.  In  Clifton-Morenci  dis- 
trict, Ariz. 


604  DESCRIPTIVE   MINERALOGY 

Tarbuttite,  Zn3P2O8  Zn(OH)2.  Triclinic.  Crystals  striated  and  rounded,  frequently 
in  sheaf-like  aggregates.  Perfect  basal  cleavage.  H.  =  37.  G.  =  4'1.  Colorless  to  pale 
yellow,  brown,  red,  or  green.  Fusible.  From  Broken  Hill,  N.  W.  Rhodesia. 

Adamite.  Zn3As->O8.Zn(OH)2.  In  small  orthorhombic  crystals,  often  grouped  in  crusts 
and  granular  aggregations.  H.  =  3'5.  G.  =  4'34-4'35.  Color  honey-yellow,  violet,  rose- 
red,  green,  colorless.  Mean  index,  173.  From  Chanarcillo,  Chile;  Cap  Garonne,  France; 
from  Mte.  Valerio,  Campiglia  Marittima,  Italy;  at  the  ancient  zinc  mines  of  Laurion, 
Greece.  From  Island  of  Thasos,  Turkey.  Varieties  from  Cap  Garonne,  Var,  France,  con- 
taining cobalt  and  copper  have  been  called  cobaltoadamiie  and  cuproadamite. 

Descloizite.  R2V2O8.R(OH)2  or  4RO.V2O6.H2O;  R  =  Pb,  Zn  chiefly,  and  usually  in 
the  ratio  1  :  1  approx.  In  small  orthorhombic  crystals,  often  drusy;  also  massive,  fibrous 
radiated  with  mammillary  surface.  H.  =  3 '5.  G.  =  5'9-6'2.  Color  cherry-red  and 
brownish  red,  to  light  or  dark  brown,  black.  Streak  orange  to  brownish  red  or  yellowish 
gray.  Mean  index,  1'83. 

From  the  Sierra  de  Cordoba,  Argentina;  Kappel  in  Carinthia.  Abundant  at  Lake 
Valley,  Sierra  Co.,  N.  M.,  also  near  Georgetown  and  at  Magdalena;  in  Ariz,  near  Tomb- 
stone; in  Yavapai  Co.;  at  the  Mammoth  Gold  mine,  near  Oracle,  Final  Co. 

A  massive  variety,  containing  copper  (6'5  to  9  p.  c.),  in  crusts,  and  reniform  masses  with 
radiated  structure,  occurs  in  San  Luis  Potosi,  also  in  a  vein  of  argentiferous  galena  in 
Zacatecas,  Mexico;  it  has  been  variously  named  cuprodescloizite,  tritochorite,  ramirite.  A 
similar  variety  (11  p.  c.  CuO)  occurs  as  an  incrustation  on  quartz  at  the  Lucky  Cuss  mine, 
Tombstone,  Cochise  Co.,  and  in  stalactites  at  Shattuck  Arizona  mine,  Bisbee,  Ariz.  From 
Camp  Signal,  San  Bernardino  Co.,  Cal. 

EUSYNCHITE  may  be  identical  with  descloizite.  Massive:  in  nodular,  stalactitic  forms. 
G.  =  5 '596.  Color  yellowish  red,  reddish  brown,  greenish.  From  Hofsgrund  near  Frei- 
burg in  Baden,  Germany.  The  same  may  be  true  of  arceoxene  from  Dahn  near  Nieder- 
Schlettenbach,  Rhenish  Bavaria,  Germany. 

Pyrobelonite.  4PbO.7MnO.2V2O5.3H2O.  Orthorhombic.  In  small  acicular  crystals. 
Fire-red  color.  H.  =  3'5.  G.  =  5'377.  High  index.  Probably  related  crystallographic- 
ally  to  descloizite.  From  Langban,  Sweden. 

DECHENITE.  Composition  usually  accepted  as  PbV2O6.  Massive,  botryoidal,  nodular. 
G.  =  5'6-5'81.  Color  deep  red  to  yellowish  red  and  brownish  red.  From  Nieder-Schlet- 
tenbach  in  the  Lautertal,  Rhenish  Bavaria,  Germany. 

Calciovolborthite.  Probably  (Cu,Ca)sVXMChi,Ca)(OH)8.  In  thin  green  tables;  also 
gray,  fine  crystalline  granular.  Mean  index,  2 '05.  From  Friedrichsrode,  Thuringia,  Ger- 
many. Minerals  from  Richardson,  southeastern  Utah,  and  from  near  Baker  City,  Oregon, 
probably  belong  here. 

Higginsite.  CuCa(OH)AsO4.  Orthorhombic.  Small  prismatic  crystals.  H.  =  4'5. 
G.  =  4 '33.  n  =  1745.  Pleochroic,  green,  yellow-green,  blue-green.  From  Higgins  mine, 
Bisbee,  Ariz. 

Brackebuschite.  Near  descloizite  (monoclinic?).  From  the  State  of  Cordoba,  Ar- 
gentina. 

TURANITE.  A  copper  vanadate,  5CuO.V2O5.2H2O.  Radiating  fibrous.  From  Tyuya- 
Muyun,  south  of  Andidjan,  Alai  Mts.,  Turkestan. 

Psittacinite.  A  vanadate  of  lead  and  copper,  from  the  Silver  Star  District,  Mon  In 
thin  coatings;  also  pulverulent.  Color  siskin-  to  olive-green. 

MOTTRAMITE.  A  vanadate  of  lead  and  copper;  possibly  identical  with  psittacinite; 
in  velvety  black  incrustations.  From  Mottram  St.  Andrew's,  Cheshire,  England. 

Furnacite.  A  basic  chrom-arsenate  of  lead  and  copper.  In  dark  olive-green  small 
.prismatic  crystals.  From  Djocie,  French  Equatorial  Africa. 

Tsumebite.  Preslite.  A  basic  lead  and  copper  phosphate.  Orthorhombic?  In 
small  tabular  crystals.  H  =  3'5.  G.  =  6'1.  Index,  >  178.  Color  emerald-green. 
Pleochroic,  blue-green  to  yellow-green.  Easily  fusible.  From  Tsumeb,  Otavi,  German 
o.  W .  Alrica. 


CLINOCLASITE.     Aphanese. 

Monoclinic.     Axes  a  :  b  :  c  =  1-9069  :  1  :  3-8507;  0  =  80°  30' 

Crystals  prismatic  (TO  (110));    also  elongated  ||  6  axis;   of  ten*  grouped  in 


PHOSPHATES,    ARSENATES,    ETC.  605 

nearly  spherical  forms.  Also  massive,  hemispherical  or  reniform;  structure 
radiated  fibrous. 

Cleavage:  c  (001)  highly  perfect.  Brittle.  H.  =  2'5-3.  G.  =  4'19-4'37. 
Luster:  c  pearly;  elsewhere  vitreous  to  resinous.  Color  internally  dark  verdi- 
gris-green; externally  blackish  blue-green.  Streak  bluish  green.  Subtrans- 
parent  to  translucent. 

Comp.  —  Cu3As2O8.3Cu(OH)2  or  6CuO.As2O5.3H20  =  Arsenic  pentoxide 
30'3,  cupric  oxide  62'6,  water  71  =  100. 

Pyr.,  etc.  —  Same  as  for  olivenite. 

Obs.  —  Occurs  in  Cornwall,  with  other  ores  of  copper.  In  Utah,  Tintic  district,  at  the 
Mammoth  mine.  From  Collahurasi,  Tarapaca,  Chile.  Named  in  allusion  to  the  basal 
cleavage  being  oblique  to  the  sides  of  the  prism. 

Erinite.  Cu3As2O8.2Cu(OH)2.  In  mammillated  crystalline  groups.  Color  fine  emer- 
ald-green. From  Cornwall;  also  the  Tintic  district,  Utah. 

Dihydrite.  Cu3P2Og.2Cu(OH)2.  In  dark  emerald-green  crystals  (monoclinic). 
H.  =  4'5-5.  G.=  4-4'4.  From  Ehl  near  Linz  on  the  Rhine,  Germany ;  the  Ural  Mts.,  etc. 

Pseudomalachite.  In  part  Cu3P2O8.3Cu(OH)2.  Massive,  resembling  malachite  in 
color  and  structure.  Indices,  1*83-1*93.  From  Rheinbreitenbach,  Germany;  Nizhni 
Tagilsk,  Russia,  etc.  Ehlite  is  closely  allied. 

DUFRENITE.     Kraurite. 

Orthorhombic.  Crystals  rare,  small,  and  indistinct.  Usually  massive,  in 
nodules;  radiated  fibrous  with  drusy  surface. 

Cleavage:  a  (100),  probably  also  b  (010),  but  indistinct.  H.  =  3*5-4. 
G.  =  3'2-3'4.  Luster  silky,  weak.  Color  dull  leek-green,  olive-green,  or 
blackish  green;  alters  on  exposure  to  yellow  and  brown.  Streak  siskin-green. 
Subtranslucent  to  nearly  opaque.  Strongly  pleochroic.  Indices,  1'83-1'93. 

Comp.  —  Doubtful;  in  part  FeP04.Fe(OH)3  =  2Fe2O3.P2O5.3H2O  = 
Phosphorus  pentoxide  27  -5,  iron  sesquioxide  62'0,  water  10*5  =  100. 

Pyr.,  etc.  —  Same  as  for  vivianite,  but  less  water  is  given  out  in  the  closed  tube.  B.B. 
fuses  easily  to  a  slag. 

Obs.  —  Occurs  near  Anglar,  Dept.  of  Haute  Vienne,  France;  in  Germany  at  Hirsch- 
berg  in  Westphalia  and  from  the  Rothlaufchen  mine  near  Waldgirmes;  St.  Benigna, 
Bohemia;  East  Cornwall,  England. 

In  the  United  States,  at  Allentown,  N.  J.;  in  Rockbridge  Co.,  Va.,  in  radiated  coarsely 
fibrous  masses;  from  Graf  ton,  N.  H.  Dufreniberaunite  is  a  variety  intermediate  in  com- 
position between  dufrenite  and  beraunite  from  Hellertown,  Pa. 

LAZULITE. 

Monoclinic:  Axes  a  :  b  :  c  =  0-9750  :  1  :_  1-6483;  0  =  89°  14'. 

at,     100  A  101  =  30°  24'.  ee',  Til  A  111  =  80°  20'.  986 

ppf,  111  A  111  =  79°  40'.  pe,   111  A  111  =  82°  30'. 

Crystals  usually  acute  pyramidal  in  habit.  Also 
massive,  granular  to  compact. 

Cleavage:  prismatic,  indistinct.  Fracture  uneven. 
Brittle.  H.  =  5-6.  G.  =  3-057-3-122.  Luster  vitreous. 
Color  azure-blue;  commonly  a  fine  deep  blue  viewed 
along  one  axis,  and  a  pale  greenish  blue  along  another. 
Streak  white.  Subtranslucent  to  opaque.  Optically  — . 
2V  =  69°.  a  =  1-603.  (3  =  1'632.  7  =  1-639. 

Comp.  — RAL(OH)2P2O8  or  2AlPO4.(Fe,Mg)(OH)2  with 
Fe  :  Mg(Ca)  =  1  :  12,  1  :  6,  1  :  2,  2  :  3.     For  1  :  2  the  for- 
mula requires:   Phosphorus  pentoxide  45*4,  alumina  32*6,  iron  protoxide  7*7, 
magnesia  8'5,  water  5*8  =  100. 


506  DESCRIPTIVE   MINERALOGY 

Pyr  etc  —  In  the  closed  tube  whitens  and  yields  water.  In  the  forceps  whitens,  cracks 
open  swells  up,  and  without  fusion  falls  to  pieces,  coloring  the  flame  bluish  green.  B.B. 
with  cobalt  solution  the  blue  color  of  the  mineral  is  restored.  The  green  color  of  the  flame 
is  made  more  intense  by  moistening  the  assay  with  sulphuric  acid.  With  the  fluxes  gives  an 
iron  glass;  with  soda  on  charcoal  an  infusible  mass.  Unacted  upon  by  acids,  retaining 
perfectly  its  blue  color. 

Obs.  —  Occurs  near  Werfen  in  Salzburg,  Austria;  Kneglach,  in  Styna;  also  Horrs- 
joberg,  Sweden;  from  Madagascar. 

Abundant  with  corundum  at  Crowder's  Mt.,  Gaston  Co.,  N.  C.;  and  on  Graves  Mt., 
Lincoln  Co.,  Ga.,  with  cyanite,  rutile,  etc. 

The  name  lazulite  is  derived  from  an  Arabic  word,  azw,  meaning  heaven,  and  alludes  to 
the  color  of  the  mineral. 

Tavistockite.  Ca3P2O8.2Al(OH)2.  In  microscopic  acicular  crystals,  sometimes  stellate 
groups.  Color  white.  From  Tavistock,  Devonshire. 

Cirrolite.  Perhaps  Ca3Al(PO4)3.Al(OH)3.  Compact.  G.  =  3'OS.  Color  pale  yellow. 
Occurs  at  the  iron  mine  at  Westana,  in  Scania,  Sweden. 

Arseniosiderite.  Ca3Fe(AsO4)3.3Fe(OH)3.  In  yellowish  brown  fibrous  concretions. 
G.  =  3'520.  Index,  3'83.  From  Romaneche,  near  Macon,  France;  also  at  Schneeberg, 
Saxony. 

Allactite.  Mn3As2O8.4Mn(OH)2.  Monoclinic.  In  small  brownish  red  prismatic  crys- 
stals.  Mean  index,  1786.  From  the  Moss  mine,  Nordmark,  and  at  Langban,  Sweden. 

Synadelphite.  2(Al,Mn)AsO4.5Mn(OH)2.  In  prismatic  crystals;  also  in  grains.  G.= 
3 '45-3 -50.  Color  brownish  black  to  black.  From  the  Moss  mine,  Nordmark,  Sweden. 

Flinkite.  MnAsO4.2Mn(OH)2.  In  minute  orthorhombic  crystals,  tabular  ||  c  (001); 
grouped  in  feather-like  aggregates.  G.  =  3 '87.  Color  greenish  brown.  From  the  Harstig 
mine,  Pajsberg,  Sweden. 

Hematolite.  Perhaps  (Al,Mn)AsO4.4Mn(OH)2.  In  rhombohedral  crystals.  G.  = 
3 -30-3 '40.  Color  brownish  red,  black  on  the  surface.  Mean  Index,  1730.  From  the 
Moss  mine,  Nordmark,  Sweden. 

Retzian.  A  basic  arsenate  of  the  yttrium  earths,  manganese  and  calcium.  In  ortho- 
rhombic  crystals.  H.  =4.  G.  =  415.  Color  chocolate-  to  chestnut-brown.  From  the 
Moss  mine,  Nordmark,  Sweden. 

n  m  ii  ni 

Arseniopleite.  Perhaps  RgR^OH^AsO^e;  R  =  Mn,  Ca,  also  Pb,  Mg;  R  =  Mn, 
also  Fe.  Massive,  cleavable.  Color  brownish  red.  Occurs  at  the  Sjo  mine,  Grythytte 
parish,  Sweden,  with  rhodonite  in  crystalline  limestone. 


Manganostibiite.  Hematostibiite.  Highly  basic  manganese  antimonates.  In  em- 
bedded grains.  Color  black.  Manganostibiite  occurs  at  Nordmark,  Sweden;  hematostibiite 
is  from  the  Sjo  mine,  Grythytte  parish,  Sweden. 

Atelestite.  Basic  bismuth  arsenate,  H2Bi3AsO8.  In  minute  tabular  crystals  G  = 
6'4.  Color  sulphur-yellow.  From  Schneeberg,  Saxony. 

C.   Normal  Hydrous  Phosphates,  etc. 

The  only  important  group  among  the  normal  hydrous  phosphates  is  the 
monoclinic  VIVIANITE  GROUP. 

Struvite.     Hydrous  ammonium-magnesium  phosphate.     In  orthorhombic-hemimorphic 
Sanod  P'  6  °r  yeUowish;    sli8htly  soluble.     Index,  1'502.     From 

Collophanite.     Ca3P2O8.H2O.     In  layers  resembling  gymnite   or  opal.     Colorless   or 
r*k    •  i'    A    ™L59'     From  the  island  of  Sombrero,  West  Indies.     Monile  is  similar, 
•  Mona  and  Moneta  in  the  West  Indies,  where  it  is  associated  with  monetite, 
4  occurring  in  yellowish  white  triclinic  crystals. 


PHOSPHATES,  ARSENATES,  ETC.  607 

Hopeite.  Hydrous  zinc  phosphate,  Zn3P2O8.4H2O.  Orthorhombic.  In  minute  pris- 
matic crystals.  Also  in  reniform  masses.  Three  cleavages:  a  (100),  perfect;  6  (010),  good; 
c  (001),  poor.  Crystals  from  Broken  Hill  show  interbanding  of  two  modifications,  a-  and 
/3-hopeite  which  have  the  same  composition  but  differ  in  their  optical  characters.  H.  = 
3'2.  G.  =  3-0-3'  1.  Color  grayish  white.  Optically-,  ft  =  1'59.  Found  in  cavities  in 
calamine  at  the  zinc  mines  of  Moresnet,  Belgium;  at  the  Broken  Hill  mines,  Rhodesia. 

Parahopeite.  Zn3P2O8.4H2O.  Same  as  for  hopeite.  Triclinic.  In  tabular  crystals 
with  deep  striations.  Good  cleavage.  H.  =  37.  G.  =  3'3.  Colorless.  Found  at 
Broken  Hill,  Rhodesia. 

Dickinsonite.  3R3P2O8.H2O  with  R  =  Mn,  Fe,  Na2  chiefly,  also  Ca,  K2,  Li2.  In 
tabular,  pseudo-rhombohedral  crystals;  commonly  foliated  to  micaceous.  G.  =  3 '338- 
3-343.  Color  olive-  to  oil-green,  grass-green.  ft  =  1-662.  From  Branchville,  Fairneld 
Co.,  Conn. 

Fillowite.  Formula  as  for  dickinsonite  and  also  from  Branchville,  Conn.,  but  differing 
in  angle.  In  granular  crystalline  masses.  G.  =  3'43.  Color  wax-yellow,  yellowish  to 
reddish  brown,  colorless.  ft  =  T672. 


The  three  following  triclinic  species  are  related  in  composition  and  may  be  in  crystalline 
form. 

Roselite.  (Ca,Co,Mg)3As2O8.2H2O.  In  small  crystals;  often  in  druses  and  spherical 
aggregates.  G.  =  3'5-3*6.  Color  light  to  dark  rose-red.  From  Schneeberg,  Saxony. 

Brandtite.  Ca2MnAs2Os.2H2O.  In  prismatic  crystals;  crystals  often  united  in  radi- 
ated groups.  G.  =  3'671-3'672.  Colorless  to  white.  From  the  Harstig  mine,  near  Pajs- 
berg,  Sweden. 

Fairfieldite.  A  hydrous  phosphate  of  calcium  and  manganese,  Ca2MnP2O8.2H2O. 
Triclinic.  In  prismatic  crystals;  usually  in  foliated  or  fibrous  crystalline  aggregates. 
G.  =  3'07-3'15.  Color  white  or  greenish  white  to  pale  straw-yellow,  ft  =  T644.  From 
Branchville,  Fairfield  Co.,  Conn.;  Rabenstein,  Bavaria  (leucomanganite) . 


Messelite.  (Ca,Fe)3P2O8.2^H2O.  In  minute  tabular  crystals.  Colorless  to  brownish. 
ft  =  1'653.  From  near.Messel  in  Hesse,  Germany.  Perhaps  an  alteration  of  Anapaite 
through  loss  of  water. 

Anapaite.  Tamanite.  (Ca,Fe)3P2O8.4H2O.  Triclinic.  In  tabular  crystals.  One  per- 
fect cleavage.  H.  =  3 '5.  G.  =  2 '8.  Color  greenish  white.  From  the  limonite  mines 
near  Anapa  on  the  Taman  peninsula,  Russia. 

Reddingite.  Mn3P2O8.3H2O.  In  orthorhombic  crystals  near  scorodite  in  angle;  also 
granular.  G.  =  3'102.  Color  pinkish  white  to  yellowish  white.  Optically +.  ft  =  1'656 . 
From  Branchville,  Conn. 

Palaite.  Hydrous  manganese  phosphate,  5MnO.2P2O6.4H2O.  Monoclinic?  In  crys- 
talline masses.  G.  =  3'2.  Color,  flesh-pink.  Indices  1 '65-1  "66.  From  Pala,  San  Diego 
Co.,  Cal.  Derived  by  alteration  from  lithiophilite  and  alters  into  hureaulite. 

Stewartite.  Hydrous  manganese  phosphate,  3MnO.P2O5.4H2O.  Triclinic?  In  fibers 
or  minute  crystals.  G.  =  2 '94.  Indices,  1  '63-1  '69.  Pleochroic,  colorless  to  yellow. 
Found  as  an  alteration  product  of  lithiophilite  from  Pala,  Cal. 

Picropharmaoolite.  R3As2O8.6H2O,  with  R  =  Ca  :  Mg  =  5  :  1.  In  small  spherical 
forms.  Color  white.  From  Riechelsdorf  and  Freiberg,  Germany;  Joplin,  Mo. 

Trichalcite.  CusAs^s.SH^O.  In  radiated  groups,  columnar;  dendritic.  Color  verdi- 
gris-green. From  the  Turginsk  copper  mine  near  Bogoslovsk,  Ural  Mts. 

Vivianite  Group.     Monoclinic 

Vivianite  Fe3P2O8.8H2O    a  :  b  :  c  =  0-7498  :  1  :  0-7015      ft  =  75°  34' 

Symplesite  Fe3As208.8H2O  0-7806  :  1  : 0-6812  72°  43' 

Bobierrite  Mg3P2O8.8H20 

Hoernesite  Mg3As2O8.8H2O 

Erythrite  Co3As2O8.8H2O  0-75      :  1  : 0-70  75° 

Annabergite  Ni3As2O8.8H2O 

Cabrerite  (Ni,Mg)3As2O8.8H2O 

Kbttigite  Zn3As2O8.8H20 


608  DESCRIPTIVE   MINERALOGY 

The  VIVIANITE  GROUP  includes  hydrous  phosphates  of  iron,  magnesium, 
cobalt,  nickel  and  zinc,  all  with  eight  molecules  of  water.  The  crystallization 
is  monoclinic,  and  the  angles,  so  far  as  known,  correspond  closely. 

VIVIANITE. 

Monoclinic.  Crystals  prismatic  (mm'"  110  A  110  =  71°  58');  often  in 
stellate  groups.  Also  reniform  and  globular;  structure  divergent,  fibrous,  or 
earthy;  also  incrusting. 

Cleavage:  b  (010)  highly  perfect;  a  (100)  in  traces;  also  fracture  fibrous 
nearly  _L  c  axis.  Flexible  in  thin  laminae;  sectile.  H.  =  1'5  —  2.  G  =  2'58 
-  2*68.  Luster,  b  (010)  pearly  or  metallic  pearly;  other  faces  vitreous. 
Colorless  when  unaltered,  blue  to  green,  deepening  on  exposure.  Streak 
colorless  to  bluish  white,  changing  to  indigo-blue  and  to  liver-brown. 
Transparent  to  translucent;  opaque  after  exposure.  Pleochroism  strong; 
X  =  cobalt-blue,  Y  and  Z  =  pale  greenish  yellow.  Optically  -f.  a  =  1*581. 
ft  =  1'604.  7  =  1-636. 

Comp.  —  Hydrous  ferrous  phosphate,  Fe3P208.8H20  =  Phosphorus  pent- 
oxide  28'3,  iron  protoxide  43'0,  water  287  =  100. 

Many  analyses  show  the  presence  of  iron  sesquioxide  due  to  alteration. 

Pyr.,  etc.  —  In  the  closed  tube  yields  neutral  water,  whitens,  and  exfoliates.  B.B. 
fuses  at  1  "5, .  coloring  the  flame  bluish  green,  to  a  grayish  black  magnetic  globule.  With 
the  fluxes  reacts  for  iron.  Soluble  in  hydrochloric  acid. 

Obs.  —  Occurs  associated  with  pyrrhotite  and  pyrite  in  copper  and  tin  veins;  some- 
times in  narrow  veins  with  gold,  traversing  graywacke;  both  friable  and  crystallized  in  beds 
of  clay,  and  sometimes  associated  with  limonite,  or  bog  iron  ore;  often  in  cavities  of  fossils 
or  buried  bones. 

Occurs  at  St.  Agnes  and  elsewhere  in  Cornwall,  England;  at  Bodenmais,  Germany;  the 
gold  mines  of  Verespatak  in  Transylvania.  From  Ashio,  Shimotsuke,  Japan.  A  variety 
from  the  Kertsch  and  Taman  peninsulas,  South  Russia,  that  contains  small  quantities  of 
manganese  and  magnesium  has  been  called  paravivianite.  The  earthy  variety,  sometimes 
called  blue  iron-earth  or  native  Prussian  blue  (Fer  azure),  occurs  in  Greenland,  Carinthia, 
Guatemala,  Bolivia,  Victoria,  Australia,  etc. 

In  North  America,  in  N.  J.,  at  Allentown,  Monmouth  Co.,  both  crystallized,  in  nodules, 
and  earthy;  at  Mullica  Hill,  Gloucester  Co.  (mullicite},  in  cylindrical  masses.  In  Va.,  in 
Stafford  Co.  In  Ky.,  near  Eddyville.  In  Col.  at  Leadville;  in  Idaho,  at  Silver  City.  In 
Canada,  with  limonite  at  Vaudreuil. 

Symplesite.  Probably  Fe3As2O8.8H2O.  In  small  prismatic  crystals  and  in  radiated 
spherical  aggregates.  G.  =  2 '957.  Color  pale  indigo,  inclined  to  celandine-green.  From 
Lobenstein,  Germany;  Hiittenberg,  Carinthia. 

Bobierrite.  Mg3P2O8.8H2O.  In  aggregates  of  minute  crystals;  also  massive.  Color- 
less to  white.  From  the  guano  of  Mexillones,  on  the  Chilian  coast.  Hautefeuillite 
is  like  bobierrite,  but  contains  calcium.  Monoclinic.  Index  1*52.  From  Bamle, 
Norway. 

Hoernesite.  Mg3As2p8.8H2O.  In  crystals  resembling  gypsum;  also  columnar;  stellar- 
foliated.  Color  snow-white.  From  the  Banat,  Hungary. 

ERYTHRITE.     Cobalt  bloom. 

Monoclinic.  Crystals  prismatic  and  vertically  striated.  Also  in  globular 
and  reniform  shapes,  having  a  drusy  surface  and  a  columnar  structure;  some- 
times stellate.  Also  pulverulent  and  earthy,  incrusting. 

Cleavage:  b  (010)  highly  perfect.  Sectile.  H.  =  T5-2'5;  least  on  b. 
G.  =  2'948.  Luster  of  6  pearly;  other  faces  adamantine  to  vitreous;  also 
dull,  earthy.  Color  crimson-  and  peach-red,  sometimes  gray.  Streak  a  little 
paler  than  the  color.  Transparent  to  subtranslucent.  Strongly  pleochroic. 
Optically  -.  a  =  1'626.  ft  =  1'661.  7  =  1'699. 


PHOSPHATES,  ARSENATES,  ETC.  609 

Comp.  —  Hydrous  cobalt  arsenate,  Co3As208.8H2O  =  Arsenic  pentoxide 
38*4,  cobalt  protoxide  37'5,  water  24' 1  =  100.  The  cobalt  is  sometimes  re- 
placed by  nickel,  iron,  and  calcium. 

Pyr.,  etc.  —  In  the  closed  tube  yields  water  at  a  gentle  heat  and  turns  bluish;  at  a 
higher  heat  gives  off  arsenic  trioxide  which  condenses  in  crystals  on  the  cool  glass,  and  the 
residue  has  a  dark  gray  or  black  color.  B.B.  in  the  forceps  fuses  at  2  to  a  gray  bead,  and 
colors  the  flame  light  blue  (arsenic).  B.B.  on  charcoal  gives  an  arsenical  odor,  and  fuses 
to  a  dark  gray  arsenide,  which  with  borax  gives  the  deep  blue  color  characteristic  of  cobalt. 
Soluble  in  hydrochloric  acid,  giving  a  rose-red  solution. 

Obs.  —  Occurs  at  Schneeberg  in  Saxony,  in  micaceous  scales;  Wolfach  in  Baden; 
Modum  in  Norway.  From  the  Veta  Rica  mine,  Sierra  Mojada,  Coahuila,  Mexico;  Chile. 

In  the  United  States,  in  Pa.,  sparingly  near  Philadelphia;  in  Nev.,  at  Lovelock's  station. 
In  Cal.  In  crystals  from  Cobalt,  Canada.  Named  from  epi>0p6s,  red. 

Annabergite.  NiaAsaOs.SH^O.  Monoclinic.  In  capillary  crystals;  also  massive  and 
disseminated.  Color  fine  apple-green.  Optically  — .  Mean  index,  1'68.  From  Alle- 
mont  in  Dauphine,  France;  Annaberg,  Schneeberg  and  Riechelsdorf,  Germany;  in  Col.; 
Nev.;  Cobalt,  Ontario,  Canada. 

Cabrerite.  (Ni,Mg)3As2O8.8H2O.  Like  erythrite  in  habit.  Also  fibrous,  radiated; 
reniform,  granular.  Color  apple-green.  From  the  Sierra  Cabrera,  Spain;  at  Laurion, 
Greece. 

Kottigite.  Hydrous  zinc  arsenate,  ZnsAs2O8.8H2O.  Massive,  or  in  crusts.  Color 
light  carmine-  and  peach-blossom-red.  Occurs  with  smaltite  at  the  cobalt  mine  Daniel, 
near  Schneeberg,  Germany. 

Rhabdophanite.  Scovillite.  A  hydrous  phosphate  of  the  cerium  and  yttrium  metals. 
Massive,  small  mamillaryj  as  an  incrustation.  G.  =  3'94-4'OL  Color  brown,  pinkish  or 
yellowish  white.  Rhabdophanite  is  from  Cornwall;  Scovillite  is  from  the  Scoville  (limonite) 
ore  bed  in  Salisbury,  Conn. 

Churchite.  A  hydrous  phosphate  of  cerium  and  calcium.  As  a  thin  coating  of  minute 
crystals.  G.  =  3'14.  Color  pale  smoke-gray  tinged  with  flesh-red.  From  Cornwall,  Eng- 
land.   

Uvanite.  2UO3.3V2O6.15H2O.  Orthorhombic.  Fine  granular.  Two  pinacoidal  cleav- 
ages. Color  brownish  yellow.  Indices,  1 '82-2 '06.  Found  disseminated  in  rocks  near 
Temple  Rock,  45  miles  southwest  of  Greenriver,  Utah. 

Ferganite.  U3(VO4)2.6H2O.  In  scales.  Color  sulphur-yellow.  From  province  of 
Fergana,  Russian  Turkestan. 

Fernandinite.  CaO.V^O^SVaOe.MHaO.  Massive.  Color  dull  green.  Readily  soluble 
in  acids,  partly  soluble  in  water.  Found  at  Minasragra,  Peru. 

Pascoite.  Hydrous  calcium  vanadate,  possibly  2CaO.3V2O6.11H2O.  Monoclinic.  In 
grains.  H.  =  2'5.  G.  =  2'46.  Color  orange.  Streak  yellow.  Indices,  177-1 '83. 
Easily  fusible.  Soluble  in  water.  Found  at  Minasragra,  Province  of  Pasco,  Peru. 

Pintadoite.  Hydrous  calcium  vanadate,  2CaO.V2O6.9H2O.  As  an  efflorescence.  Color 
green.  Found  coating  surfaces  of  sandstone  in  Canyon  Pintado,  Utah. 


SCORODITE.  987 

Orthorhombic.     Axes  a  :  b  :  c  =  0*8658  :  1  :  0-9541. 

dd',   120  A  120  =  60°  1'.       .  pp",    111  A  111  =  111°    6'. 

pp',  111  A  111  =  77°  8'.  pp'",  111  A  111  =    65°  20'. 

Habit  octahedral,  also  prismatic.     Also  earthy,  amorphous. 

Cleavage:  d (120)  imperfect;  a  (100),  6(010)  in  traces.  Frac- 
ture uneven.  Brittle.  H.  =  3'5-4.  G.  =  3'l-3'3.  Luster  vit- 
reous to  subadamantine  and  subresinous.  Color  pale  leek-green 
or  liver-brown.  Streak  white.  Subtransparent  to  translucent. 
Mean  index,  1'84. 

Comp.  —  Hydrous    ferric    arsenate,    FeAsO4.2H20  =  Arsenic    pentoxide 
49'8,  iron  sesquioxide  34'6,  water  15'6  =  100. 


610  DESCRIPTIVE   MINERALOGY 

Pyr.,  etc.  —  In  the  closed  tube  yields  neutral  water  and  turns  yellow.  B.B.  fuses 
easily,  coloring  the  flame  blue.  B.B.  on  charcoal  gives  arsenical  fumes,  and  with  soda  a 
black  magnetic  scoria.  Wit^h  the  fluxes  reacts  for  iron.  Soluble  in  hydrochloric  acid. 

Obs.  —  Often  associated  with  arsenopyrite.  From  Schwarzenberg,  Saxony;  Dern- 
bach,  Nassau,  Germany;  Lolling,  Carinthia;  Schlaggenwald,  Bohemia;  Nerchinsk,  Siberia, 
in  fine  crystals;  leek-green,  in  the  Cornish  mines.  From  Congo  Free  State.  From  Obira, 
Japan. 

Occurs  near  Edenville,  N.  Y.,  with  arsenopyrite;  in  Utah,  Tintic  district,,  at  the  Mam- 
moth mine  on  enargite.  As  an  incrustation  on  siliceous  sinter  of  the  Yellowstone  geysers. 
From  Cobalt,  Ontario,  Canada. 

Named  from  anopodov,  garlic,  alluding  to  the  odor  before  the  blowpipe. 

Vilateite.  Hydrous  iron  phosphate  with  a  little  manganese.  Monoclinic.  H.  =  3-4. 
G.  =  275.  Color  violet.  Index,  174.  Found  in  pegmatite  at  La  Vilate  near  Chante- 
loube,  Haute  Vienne,  France. 

Purpurite.  2(Fe,Mn)PO4.H2O.  Orthorhombic(?).  In  small  irregular  masses.  Two 
cleavages  at  right  angles.  H.  =  4-4*5.  G.  =  3  '4.  Color  deep  red  or  reddish  purple 
Refractive  index,  1*66-1*65,  Fusible.  Found  at  Kings  Mt.,  Gaston  Co.,  N.  C.,  sparingly 
from  Pala,  San  Diego  Co.,  Cal.,  Hill  City,  S.  D.,  and  Branchville,  Conn. 

Strengite.  FePO4.2H2O.  Crystals  rare;  in  habit  and  angle  near  scorodite;  generally 
in  spherical  and  botryoidal  forms.  G.  =  2  '87.  Color  pale  red.  Optically  +.  0  =  172'. 
From  iron  mines  near  Giessen,  Germany;  also  in  Rockbridge  Co.,  Va.,  with  dufrenite;  irom 
Pala,  Cal. 

Phosphosiderite.  2FePO4.3£H2O.  An  iron  phosphate  near  strengite,  but  with  3|H2O. 
Color  red.  Index  173.  From  the  Siegen  mining  district,  Germany;  from  Sardinia. 

Barrandite.  (Al,Fe)PO4.2H2O.  In  spheroidal  concretions,  color  pale  shades  of  gray. 
Index,  1-57.  From  Bohemia. 

Variscite.  A1PO4.2H2O.  Orthorhombic.  Commonly  in  crystalline  aggregates  and 
incrustations  with  reniform  surface.  Color  green.  Optically  -.  0  =  1'556.  Strongly 
pleochroic.  From  Messbach  in  Saxon  Voigtland;  Montgomery  Co.,  Ark.,  on  quartz  in 
nodular  masses  from  Tooele  Co.,  Utah  (Utahlite);  crystalized  from  Lucin,  Utah. 

Lucinite.  Comp.  same  as  for  varisdte,  A1PO4.2H2O.  Orthorhombic.  Octahedral 
habit.  Also  compact,  massive.  H.  =  5.  G.  =  2*52.  Color  green.  Indices,  1  -56-1  '59 
Found  with  varisdte  at  Utahlite  Hill,  near  Lucin,  Boxelder  Co.,  Utah. 

Callainite.  A1PO4.2£H2O.  Massive;  wax-like.  Color  apple-  to  emerald-green  From 
a  Celtic  grave  in  Lockmariaquer,  Brittany. 

Zepharovichite.  A1PO4.3H2O.  Crystalline  to  compact.  Color  yellowish  or  grayish 
white.  From  Trenic  in  Bohemia. 

Palmerite.  HK2A12(PO4)3.7H2O.  Amorphous,  pulverulent.  Color  white.  Occurs  as 
a  stratum  in  a  guano  deposit  on  Mte.  Alburno,  Salerno,  Italy. 

Rosieresite.    A  hydrous  phosphate  of  aluminium  with  lead  and  copper.     In  stalao- 
u68^  GJ=  2'2'      C.olor  yellow  to  brown.     Index,  1*5.     Isotropic.     Infusible.     Found  in 
abandoned  copper  mine  at  Rosieres,  Tarn,  France. 

yelbw™m  R^Su       ^  ^^  *******  °f  ^^  needles'    Color 


•>rr  •5w^Arite;      ^  hydrous  iron-manganese  phosphate  with  lithia,   Fe2O3.6MnO.4P2O6 
3  Li,H)20.     In  cleavable  masses.     G.  =  3*45.      Color  dark  brown.     Indices,   171-175 

flamf  Trom  piTa°C°aiange"red'     ^  perpendicular  to  cleavaSe-     Fusible>  giving  lithium 


SaLmonsite.    A  hydrous  iron-manganese  phosphate,  Fe2O3.9MnO.4P2O5  14H,O     Cleav- 

COl0rbUff'     ^4,1-65-1.67.     Fou^d 


Acid  Hydrous  Phosphates,  etc. 
PHARMACOLITE. 


"    C°mmonly  in  delicate  si 
Cleavage:   6  (010)  perfect.     Fracture  uneven.     Flexible  in  thin  laminse. 


PHOSPHATES,    ARSENATES,    ETC.  611 

H.  =  2-2;5.  G.  =  2'64-273.  Luster  vitreous;  on  6  (010)  inclining  to  pearly. 
Color  white  or  grayish;  frequently  tinged  red.  Streak  white.  Translucent 
to  opaque.  Optically  -.  a  =  1'583.  0  =  1'589.  7  =  1'594. 

Comp.  —  Probably  HCaAsO4.2H2O  =  Arsenic  pentoxide  53*3,  lime  25'9, 
water  20'8  =  100. 

Obs.  —  Found  with  arsenical  ores  of  cobalt  and  silver,  also  with  arsenopyrite;  at 
Andreasberg  in  the  Harz  Mts.,  Germany;  Riechelsdorf  in  Hesse,  Germany;  Joachimstal  in 
Bohemia,  Markirch,  Alsace,  etc.  Named  from  ^ap/za/cop,  poison. 


Haidingerite.  HCaAsO4.H2O.  In  minute  crystal  aggregates,  botryoidal  and  drusy. 
G.  =  2  -848.  Color  white.  Index,  1  '67.  From  Joachimstal,  Bohemia,  with  pharmacolite. 

Wapplerite.  HCaAsO4.3£H2O.  In  minute  crystals;  also  in  incrustations.  Colorless 
to  white.  Found  with  pharmacolite  at  Joachimstal,  Bohemia. 

Brushite.  HCaPO4.2H2O.  In  small  slender  monoclinic  prisms:  concretionary  massive. 
Colorless  to  pale  yellowish.  £  =  1*545.  Occurs  in  guano.  Metabrushite,  similarly  asso- 
ciated, is  2HCaPO4.3H2O.  Stoffertite  is  a  mineral  similar  to  brushite  but  said  to  contain  a 
little  more  water.  From  guano  deposits  on  the  island  of  Mona,  West  Indies. 

Martinite.  H2Ca5(PO4)4.|H2O.  From  phosphorite  deposits  (from  guano)  in  the  island 
of  Curacoa,  West  Indies. 

Hewettite.  CaO.3V2O5.9H2O.  In  microscopic  needles.  G.  =  2'5-2'6.  Color  deep 
red.  Pleochroic,  light  orange-yellow  to  red.  On  heating  loses  water  changing  color  through 
shades  of  brown  to  a  bronze.  Easily  fusible.  Found  as  an  alteration  of  patronite  at  Minas- 
ragra,  Peru.  Also  observed  from  Paradox  Valley,  Col. 

Metahewettite.  Comp.  same  as  for  hewetlite.  In  minute  tabular  orthorhombic  crys- 
tals. On  heating  loses  water  changing  from  dark  red  to  yellow-brown.  From  Paradox 
Valley,  Col.,  and  at  Thompson's,  Utah. 

Newberyite.  HMgPO4.3H2O.  In  white  orthorhombic  crystals.  Index,  1'52.  From 
guano  of  Skipton  Caves,  Victoria.  Hannayite,  from  same  locality,  is  a  hydrous  phosphate 
of  ammonium  and  magnesium.  Schertelite,  Mg(NH4)2H2(PO4)2.4H2O.  Occurs  in  small 
tabular  crystals  in  hot  guano  deposits  near  Skipton,  southwest  of  Ballarat,  Australia. 

Stercorite.  Microcosmic  salt.  HNa(NH4)PO4.4H2O.  In  white  crystalline  masses  and 
nodules  in  guano. 

Hureaulite.  H2Mn6(PO4)4.4H2O.  In  short  prismatic  crystals  (monoclinic).  Also 
massive,  compact,  or  imperfectly  fibrous.  Color  yellowish,  orange-red,  rose,  grayish. 
Optically  —  .  (3  =  T654.  From  Limoges,  commune  of  Bureaux,  France.  In  the  United 
States,  at  Branchville,  Conn.;  Pala,  Cal. 

Forbesite.  H2(Ni,Co)2As2O8.SH2O.  Structure  fibro-crystalline.  Color  grayish  white. 
From  Atacama,  Chile. 

FERRAZITE.  3(Ba,Pb)O.2P2O6.8H2O.  A  "fava"  found  in  the  diamond  sands  of  Brazil. 
Color  dark  yellowish  white.  G.  =  3  '0-3  '3. 

Basic  Hydrous  Phosphates,  etc. 

Isoclasite.  Ca3P2O8.Ca(OH)2.4H2O.  In  minute  white  crystals;  also  columnar.  From 
Joachimstal,  Bohemia. 

Hemafibrite.  Mn3As2O8.3Mn(OH)2.2H2O.  Commonly  in  spherical  radiated  groups. 
Color  brownish  red  to  garnet-red,  becoming  black.  From  the  Moss  mine,  Nordmark, 
Sweden. 

EUCHROITE. 

Orthorhombic.  Habit  prismatic  mm'"  110  A  110  =  62°  40'.  Cleavage: 
m  (110),  n  (Oil)  in  traces.  Fracture  small  conchoidal  to  uneven.  Rather 
brittle.  H.  =  3  -5-4.  G.  =  3-389.  Luster  vitreous.  Color  bright  emerald- 
or  leek-green.  Transparent  to  translucent.  Mean  index,  1-70. 

Comp.  —  Cu3As2Os.Cu(OH)2.6H2O  =  Arsenic  pentoxide  34'2,  cupric 
oxide  47-1,  water  187  =  100. 

Obs.  —  Occurs  in  quartzose  mica  slate  at  Libethen  in  Hungary,  in  crystals  of  consider- 
able size,  having  much  resemblance  to  dioptase.  Named  from  evxpoa,  beautiful  color. 


612  DESCRIPTIVE   MINERALOGY 

Conichalcite.  Perhaps  (Cu,Ca)3As2O8.(Cu,Ca)(OH)2.|H2O.  Orthorhombic.  Usually 
reniform  and  massive,  resembling  malachite.  Color  pistachio-green  to  emerald-green 
From  Andalusia,  Spain;  Maya-Tass,  Akmolinsk,  Siberia  (crystals);  Tintic  district,  Utah. 

Bayldonite.  (Pb,Cu)3As2O8.(Pb,Cu)(OH)2.H2O.  In  mamillary  concretions,  drusy. 
Color  green.  From  Cornwall,  England. 

Tagilite.  Cu3P2O8.Cu(OH)2.2H2.O.  In  reniform  or  spheroidal  concretions;  earthy. 
Color  verdigris-  to  emerald-green.  From  the  Ural  Mts. 

Leucochalcite.  Probably  Cu3As2O8.Cu(OH)2.2H2O.  In  white,  silky  acicular  crystals. 
From  the  Wilhelmine  mine  in  the  Spessart,  Germany. 

Barthite.  3ZnO.CuO.3As2O6.2H2O.  In  small  monoclinic  (?)  crystals.  H.  =  3. 
G.  =  419.  Color  grass-green.  Found  in  druses  of  a  dolomite  at  Guchab,  Otavi,  German 
Southwest  Africa. 

Volbprthite.  A  hydrous  vanadate  of  copper,  barium,  and  calcium.  In  small  six-sided 
tables;  in  globular  forms.  .  Color  olive-green,  citron-yellow.  Index,  1 '90.  From  the  Ural 
Mts. 

Hiigelite.  A  hydrous  lead-zinc  vanadate.  Monoclinic.  In  microscopic  hair-like 
crystals.  Color  orange-yellow  to  yellow-brown.  From  Reichenbach  near  Lahr,  Baden, 
Germany. 

Cornwallite.  Cu3As2O8.2Cu(OH)2.H2O.  Massive,  resembling  malachite.  Color  emer- 
ald-green. From  Cornwall;  England. 

Tyrolite.  Tirolit.  Perhaps  Cu3As2O8.2Cu(OH)2.7H2O.  Usually  in  fan-shaped  crystal- 
line groups;  in  foliated  aggregates;  also  massive.  Cleavage  perfect,  yielding  soft  thin 
flexible  laminae.  Color  pale  green  inclining  to  sky-blue.  Index,  T70.  From  Libethen, 
Hungary;  Nerchinsk,  Siberia;  Falkenstein,  Tyrol;  etc.  In  the  United  States,  in  the  Tin- 
tic  district,  "Utah.  Some  analyses  yield  CaCO3,  usually  regarded  as  an  impurity,  but  it 
may  be  essential. 

Spencerite.  Zn3(PO4)2.Zn(OH)2.3H2p.  Monoclinic.  In  radiating  and  reticulated 
crystals.  Cleavages  parallel  to  three  pinacoids.  Color  white.  G.  =  3*12.  H.  =  2*7. 
0  =  1-61.  Optically  -.  From  Hudson  Bay  Mine,  Salmo,  B.  C. 

Hibbenite.  2Zn3(PO4)2.Zn(OH)2.6fH2O.  Orthorhombic.  Tabular  parallel  to  a  (100). 
Cleavages  parallel  to  three  pinacoids.  Color  white.  G.  =  3 '21.  H.  =  3 7.  Optically  — . 
From  Hudson  Bay  Mine,  Salmo,  British  Columbia. 

CHALCOPHYLLITE. 

Rhombohedral.     Axis  c  =  2761.     cr  0001  A  1011  =  72°  2'. 

In  tabular  crystals;     also  foliated    massive;     in 
druses. 

Cleavage:     c  (0001)  highly  perfect;     r  (lOll)   in 
traces.     H.  =  2.     G.  =  2'4-2'66.     Luster  of  c  pearly; 
______^__  of  other   faces   vitreous   or   subadamantine.      Color 

emerald-  or  grass-green  to   verdigris-green.     Streak 
somewhat  paler  than   the   color.     Transparent  to  translucent.     Opticallv  - 
1-632.     €  =  1-575. 

(??I!lp"  7"  A  highly  basic  arsenate  of  copper;  formula  uncertain,  perhaps 
uO.  As2O5. 14H20. 

Pyr.,  etc.  — -  In  the  closed  tube  decrepitates,  yields  much  water,  and  gives  a  residue  of 
olive-green  scales.  In  other  respects  like  olivenite.  Soluble  in  nitric  acid,  and  in  ammonia. 

Ubs.  —  *rom  the  copper  mines  near  Redruth  in  Cornwall;  at  Sayda,  Saxony;  Moldawa 
Bisbi  Ariz  gary;  from  ChUe-  In  the  United  States,  in  the  Tintic  district,  Utah; 

Veszelyite.     A   hydrous   phospho-arsenate   of    copper   and   zinc,   formula   uncertain. 
a  greenish  blue  crystalline  incrustation  at  Morawitza,  in  the  Banat,  Hungary. 

WAVELLITE. 

Orthorhombic.     Axes  a  :  b  :  c  =  0*5049  :  1  :  0-3751.     Crystals  rare     Usu- 
hemispherical  or  Slobular  with  crystalline  surface,  and 


PHOSPHATES,  ARSENATES,  ETC.  613 

Cleavage:  p  (101)  and  b  (010)  rather  perfect.  Fracture  uneven  to  sub- 
conchoidal.  Brittle.  H.  =  3-25-4.  G.  =  2-316-2-337.  Luster  vitreous, 
inclining  to  pearly  and  resinous.  Color  white,  passing  into  yellow,  green' 
gray,  brown,  and  black.  Streak  white.  Translucent.  Mean  index,  T526 

Comp.  —  4A1PO4.2A1(OH)3.9H2O  =  Phosphorus  pentoxide  35'2,  alu- 
mina 38'0,  water  26-8  =  100.  Fluorine  is  sometimes  present,  up  to  2  p.  c. 

Pyr.,  etc.  —  In  the  closed  tube  gives  off  much  water,  the  last  portions  of  which  may 
react  acid  (fluorine).  B.B.  in  the  forceps  swells  up  and  splits  into  fine  infusible  particles 
coloring  the  flame  pale  green.  Gives  a  blue  on  ignition  with  cobalt  solution.  Soluble  in 
hydrochloric  acid,  and  also  in  caustic  potash. 

Obs.  —  From  Barnstaple  in  Devonshire,  England;  at  Zbirow  in  Bohemia:  at  Franken- 
berg,  Saxony;  Arbrefontaine,  Belgium;  Montebras,  France;  Minas  Geraes,  Brazil,  etc. 

In  the  United  States  at  the  slate  quarries  of  York  Co.,  Pa.;  White  Horse  Station  Ches- 
ter Valley  R.  R.,  Pa.;  Magnet  Cove,  Ark. 

Fischerite.  AlPO4.Al(OH)3.2^H2p.  In  small  prismatic  crystals  and  in  drusy  crusts. 
Color  green.  Index,  1'55.  From  Nizhni  Tagilsk  in  the  Ural  Mts. 

Peganite.  A1(PO4).A1(OH)3.UH2O.  Occurs  in  green  crusts,  of  small  prismatic  crys- 
tals, at  Striegis,  near  Freiberg,  Saxony. 

TURQUOIS.     Turquoise. 

Triclinic.  Crystals  minute  and  in  angle  near  those  of  chakosiderite  with 
which  it  may  be  isomorphous.  Usually  massive;  amorphous  or  cryptocrystal- 
line.  Reniform,  stalactitic,  or  incrusting.  In  thin  seams  and  disseminated 
grains.  Also  in  rolled  masses. 

Cleavage  in  two  directions  in  crystals ;  none  in  massive  material.  Fracture 
small  conchoidal.  Rather  brittle.  H.  =  5-6.  G.  =  2-6-2-83.  Luster  some- 
what waxy,  feeble.  Color  sky-blue,  bluish  green  to  apple-green,  and  greenish 
gray.  Streak  white  or  greenish.  Feebly  subtranslucent  to  opaque.  Opti- 
cally +  .  a  =  1-61.  j8  =  1-62.  7  =  1-65. 

Comp.  —  A  hydrous  phosphate  of  aluminium  and  copper  CuO.3Al203. 
2P205.9H2O  or  perhaps  H6(CuOH)[Al(OH)2]6(PO4)4  =  Phosphorus  pentox- 
ide 34-12,  alumina  36-84,  cupric  oxide  9-57,  water  19-47  =  100. 

Penfield  considers  that  the  H,(CuOH)  and  A1(OH)2  mutually  replace  each  other  in  the 
orthophosphoric  molecule. 

Pyr.,  etc.  —  In  the  closed  tube  decrepitates,  yields  water,  and  turns  brown  or  black. 
B.B.  in  the  forceps  becomes  brown  and  assumes  a  glassy  appearance,  but  does  not  fuse; 
colors  the  flame  green;  moistened  with  hydrochloric  acid  the  color' is  at  first  blue  (copper 
chloride).  With  the  fluxes  reacts  for  copper.  Soluble  in  hydrochloric  acid. 

Obs.  —  The  highly  prized  oriental  turquois  occurs  in  narrow  seams  (2  to  4  or  even  6  mm. 
in  thickness)  or  in  irregular  patches  in  the  brecciated  portions  of  a  porphyritic  trachyte 
and  the  surrounding  clay  slate  in  Persia,  not  far  from  Nishapur,  Khorassan;  in  the  Megara 
Valley,  Sinai;  in  the  Kara-Tube  Mts.  in  Turkestan,  50  versts  from  Samarkand. 

In  the  United  States,  occurs  in  the  Los  Cerillos  Mts.,  20  m.  S.E.  of  Santa  Fe,  New 
Mexico,  in  a  trachytic  rock,  a  locality  long  mined  by  the  Mexicans  and  in  recent  years  re- 
opened and  extensively  worked;  in  the  Burro  Mts.,  Grant  Co.,  N.  M.;  pale  green  variety 
near  Columbus,  and  in  Lincoln  Co.,  Nevada.  In  crystals  near  Lynch  Station,  Campbell 
Co.,  Va. 

Natural  turquois  of  inferior  color  is  often  artificially  treated  to  give  it  the  tint  desired. 
Mor-ovrr,  many  ctcncs  vrhich  are  of  a  fine  blue  when  first  found  retain  the  color  only  so 
long  as  they  arc  kept  moist,  and  when  dry  they  fade,  become  a  dirty  green,  and  are  of  littlo 
value.  Much  of  the  turquois  (not  artificial)  used  in  jewelry  in  former  centuries,  as  well 
as  the  present,  and  that  described  in  the  early  works  on  minerals,  was  bone-turquois  (called 
also  odontolite,  from  o*oy~,  tooth),  which  is  fossil  bone,  or  tooth,  colored  by  a  phosphate  of 
iron.  Its  organic  origin  becomes  manifest  under  a  microscope.  Moreover,  true  turquois. 
when  decomposed  by  hydrochloric  acid,  gives  a  fine  blue  color  with  ammonia,  which  is  not 
true  of  the  odontolite. 

Use.  —  As  an  ornamental  material. 


614  DESCRIPTIVE   MINERALOGY 

Wardite.  2A12O3.P2O6.4H2O.  Forms  light  green  or  bluish  green  concretionary  incrus- 
tations in  cavities  of  nodular  masses  of  variscite  from  Cedar  Valley,  Utah.  H.  =  5. 
G.  =  277. 

Sphserite.  Perhaps  4A1PO4.6A1(OH)3.  In  globular  drusy  concretions.  Color  light 
gray,  bluish.  From  near  St.  Benigna,  Bohemia. 

Liskeardite.  (Al,Fe)AsO4.2(Al,Fe)(OH)3.5H2O.  In  thin  incrusting  layers,  white  or 
bluish.  From  Liskeard,  Cornwall,  England. 

Evansite.  2A1PO4.4A1(OH)3.12H2O.  Massive;  reniform  or  botryoidal.  Colorless,  or 
milk-white,  n  -  1'485.  From  Zsetcznik,  Hungary;  Gross-Tresny,  Moravia;  Tasmania; 
Coosa  coalfield,  Ala.;  Goldburg,  Idaho. 

CCERULEOLACTITE.  Perhaps  3A12O3.2P2O6.10H2O.  Crypto-crystalline;  milk-white  to 
light  copper-blue.  From  near  Katzenellnbogen,  Nassau,  Germany;  also  East  Whiteland 
Township,  Chester  Co.,  Pa. 

Augelite.  2A12O3.P2O5.3H2O.  In  tabular  monoclinic  crystals  and  massive.  G.  =  27. 
Colorless  to  white.  Optically  +.  0  =  T576.  From  Bolivia;  from  the  iron  mine  of 
Westana,  Sweden.  The  same  locality  has  also  yielded  the  three  following  aluminium 
phosphates. 

BERLINITE.  2A12O3.2P2O5.H20.  Compact,  massive.  G.  =  2 '64.  Colorless  to  grayish 
or  rose-red. 

TROLLEITE.  4Al2O3.3P206.3H2O.  Compact,  indistinctly  cleavable.  G.  =  310.  Color 
pale  green. 

ATTACOLITE.  P2O5,Al203,MnO,CaO,H2O,  etc.;  formula  doubtful.  Massive.  G.=3'09. 
Color  salmon-red. 

MINASITE.    An  aluminium  phosphate.     In  rolled  pebbles  from  Brazil. 

VASHEGYITE.  4A1203.3P206.30H20.  Massive.  H.=  2-3.  G.  =  1'96.  Color  white 
or  yellow  to  rust-brown  when  colored  by  iron  oxide.  From  iron  mine  at  Vashegy  in  Comi- 
tat  Gomor,  Hungary. 

Soumansite.  A  fluo-phosphate  of  aluminium  and  sodium  with  water.  Tetragonal. 
Pyramidal  habit.  H.  =  4'5.  G.  =  2«87.  Colorless.  Indices,  1 '55-1 '56.  Optically  +. 
Fusible  with  intumescence.  From  Montebras  in  Soumans,  Creuse,  France. 


PHARMACOSIDERITE. 

Isometric-tetrahedral.     Commonly  in  cubes;    also  tetrahedral.     Rarely 
granular. 

Cleavage:  a  (100)  imperfect.     Fracture  uneven.     Rather  sectile.     H.  = 
989  2 -5.     G.  =  2*9-3.     Luster  adamantine  to  greasy,  not 

very  distinct.  Color  olive-,  grass-  or  emerald-green, 
yellowish  brown,  honey-yellow.  Streak  green  to 
brown,  yellow,  pale.  Subtransparent  to  subtranslu- 
cent.  n  =  1-676.  Pyroelectric. 

Comp.  —  Perhaps   6FeAs04.2Fe(OH)3.12H2O   = 
Arsenic  pent  oxide  43%  iron  sesquioxide  40 '0,  water 
16 -9  =  100.     Some  varieties  contain  K2O. 
Pyr.,  etc.  —  Same  as  for  scorodite. 

Obs.  —  Obtained  at  the  mines  in  Cornwall.  England,  with 
v..   .    ,  .    ores  of  copper;  at  Schneeberg  and  Schwarzenberg,  Saxony;  at 

Konigsberg,  near  Schemmtz,  Hungary.     In  Utah,  at  the  Mammoth  mine,  Tintic  district, 
from  QapucxKov,  poison,  and  aidrjpos,  iron. 

*£     2F^pA.Fe(OH)2.8H2O.     Occurs  in  small  green  tabular  crystals  (mono- 
Iruro,  Cornwall,  England. 


.-     In  radiated  tufts  of  a  yellow  or  brownish  color. 
From  near  St.  Benigna  in  Bohemia;  Lancaster  Co    Pa 


rnnnl  ii  with  FeO,  MnO,  CaO,  MgO,  A12O3.     Mono- 

stem   Bavaria     P  W'    Pleochroic-    G-  =  2'^-    From  Hiihnerkobel,  Raben- 


PHOSPHATES,  ARSENATES,  ETC.  615 

Beraunite.  Perhaps  2FePO4.Fe(OH)3.2£H2O.  Commonly  in  druses  and  in  radiated 
globules  and  crusts.  Color  reddish  brown  to  dark  hyacinth-red.  From  St.  Benigna  near 
Beraun,  in  Bohemia.  From  Hellertown,  Pa.  Eleonorite,  in  tabular  crystals,  is  the' same 
mineral.  From  the  Eleonore  mine  near  Giessen,  Germany. 

GLOBOSITE,  PICITE,  DELVAUXITE,  KERTSCHENITE,  OXYKERTSCHENITE,  are  other 
hydrated  ferric  phosphates. 

CHILDRENITE. 

Orthorhombic.     Axes  a  :  b  :  c  =  07780  :  1  :  0-52575. 

mm'",  110  A  110  =  75°  46'.  rr'",  131  A  131  =  105°    9' 

rr',        131  A  131  =  39°  47'.  ss',     121  A  121  =    49°  56£'. 

Only  known  in  crystals.  Cleavage:  a  (100)  imperfect.  Fracture  uneven. 
H.  =  4-5-5.  G.  =  3-18-3-24.  Luster  vitreous  to  resinous.  Color  yellowish 
white,  pale  yellowish  brown,  brownish  black.  Streak  white  to  yellowish. 
Translucent.  2E  =  74°.  Optically  -.  a  =  1-631.  ft  =  1-660.  7  =  1*664! 
Comp.  —  In  general  2AlPO4.2Fe(OH)2.2H2O.  Phosphorus  pentoxide 
30'9,  alumina  22-2,  iron  protoxide  31-3,  water  15-6  =  100.  Manganese 
replaces  part  of  the  iron  and  it  hence  graduates  into  eosphorite. 

Pyr.,  etc.  —  In  the  closed  tube  gives  off  neutral  water.  B.B.  swells  up  into  ramifica- 
tions, and  fuses  on  the  edges 'to  a  black  mass,  coloring  the  flame  pale  green.  Heated  on 
charcoal  turns  black  and  becomes  magnetic.  With  soda  gives  a  reaction  for  manganese. 
With  borax  and  salt  of  phosphorus  reacts  for  iron  and  manganese.  Soluble  in  hydro- 
chloric acid. 

Obs.  —  From  Tavistock,  Devonshire,  England;  from  Greifenstein,  Germany.  In 
United  States,  at  Hebron,  Me. 

KREUZBERGITE.  Aluminium  phosphate  with  Fe,Mn,H2O.  Orthorhombic.  White  to 
yellow.  From  the  Kreuzberg,  Pleystein,  Bavaria. 

Eosphorite.  Form  and  composition  as  for  childrenite,  but  containing  chiefly  man- 
ganese instead  of  iron.  In  prismatic  crystals;  also  massive.  Color  rose-pink,  yellowish, 
etc.  |8  =  1*65.  From  Branchvi  lie,  Conn. 

Mazapilite.  Ca3Fe2(AsO4)4.2FeO(OH).5H2O.  In  slender  prismatic  crystals.  G.  = 
3-567-3-582.  Color  black.  From  Mazapil,  Mexico. 

YUKONITE.  (Ca3,Fe2'")(AsO4)2.2Fe(OH)3.5H2O.  Amorphous.  In  irregular  concre- 
tions. H.  —  2-3.  G.  =  2*8.  Color  nearly  black  with  brown  tinge.  Decrepitates  at  low 
heat,  also  when  immersed  in  water.  Easily  fusible  with  intumescence.  From  Tagish  Lake, 
Yukon  Territory. 

Calcioferrite.  Ca3Fe2(PO4)4.Fe(OH)3.8H2O.  Occurs  in  yellow  to  green  nodules  in  clay 
at  Battenberg,  Rhenish  Bavaria,  Germany. 

Borickite.  Perhaps  Ca3Fe2(PO4)4.12Fe(OH)3.6H2O.  Reniform  massive;  compact. 
Color  reddish  brown.  From  Leoben  in  Styria;  Bohemia.  Foucherite,  possibly  same  as 
borichite  from  Foucheres,  Aube,  France. 

Egueiite.  A  hydrous  basic  phosphate  of  ferric  iron  with  calcium  and  aluminium. 
Amorphous.  In  small  nodules  with  fibrous-lamellar  structure.  Index,  1  '65.  Fusibility  1. 
Easily  soluble  in  hydrochloric  acid.  Found  embedded  in  clay  from  Egue'i,  Sudan. 

RICHELLITE.  Perhaps  4FeP2O8.Fe2OF2(OH)2.36H2O.  Massive,  compact  or  foliated. 
Color  yellow.  From  Richelle,  Belgium. 

990 

LIROCONITE. 

Monoclinic.   Axes  a  :  b  :  c  =  1-3191  :  1  :  1-6808;  ft  = 
88°  33'. 

mm"'    110  A  110  =  105°  39'.         me,    110  A  Oil  =  46°  10'. 
ee',        Oil  A  Oil  =  118°  29'.         m'e,  IlO  A  Oil  =  47°  24'. 

Crystals  resembling   rhombic  octahedrons.     Rarely 
granular.     Cleavage:    m (1 10),  e  (Oil)  indistinct.     Frac- 
ture   subconchoidal    to  uneven.      Imperfectly    sectile. 
H.  =  2-2-5.    G.  =  2-882-2-985.     Luster  vitreous,  inclining  to  resinous.     Color 
and  streak  sky-blue  to  verdigris-green. 


615  DESCRIPTIVE   MINERALOGY 

Tomn  -  -  A  hvdrous  arsenate  of  aluminium  and  copper,  formula  uncertain; 
analysSP'correspond  nearly  to  CueAl(As04)5  3CuAl(OH),20H2O  =  Arsenic 
pentoxide  28-9,  alumina  10-3,  cupric  oxide  35-9,  water  24-9  =  100.  Phos- 
phorus replaces  part  of  the  arsenic. 

Pvr  etc  —  In  the  closed  tube  gives  much  water  and  turns  olive-green.  B.B  cracks 
open  but  does  not  decrepitate;  fuses  less  readily  than  olivenite  to  a  dark  gray  slag;  on 
charcoal  cracks  open,  deflagrates,  and  gives  reactions  like  olivenite.  Soluble  in  nitric  acid. 

Obs.  —  From  Cornwall;  Herrengrund  m  Hungary. 

Chenevixite.  Perhaps  Cu2(FeO)2As2O8.3H2O.  Massive  to  compact.  Color  dark  green 
to  greenish  yellow.  From  Cornwall;  Utah. 

HENWOODITE.  A  hydrated  phosphate  of  aluminium  and  copper.  In  botryoidal  globu- 
lar masses.  Color  turquois-blue.  From  Cornwall. 

Ceruleite.  CuO.2Al2O3.As2O5.8H2O.  Compact,  made  up  of  very  minute  crystals. 
G.  =  2-8.  Color,  turquois-blue.  Soluble  in  acids.  From  Huanaco,  Taltal  province, 
Chile. 

Chalcosiderite.  CuO.3Fe2O3.2P2O5.8H2O.  Probably  isomorphous  with  turquois  and 
should  have  9H2O.  In  sheaf-Jike  crystalline  groups,  as  incrustations.  Color  light  siskin- 
green.  Indices,  1  '83-1  '93.  From  Cornwall. 

ANDREWSITE,  also  from  Cornwall,  is  near  chalcosiderite. 

Kehoeite.  A  hydrated  phosphate  of  aluminium,  zinc,  etc.  Massive.  G.  =  2'34. 
From  Galena,  S.  D. 

Goyazite.  Perhaps  Ca3AljoP2O23.9H2O.  Strontia  has  been  found  in  the  mineral  and 
it  is  possible  that  it  is  identical  with  hamlinite.  In  small  rounded  grains.  Color  yellowish 
white.  From  Minas  Geraes,  Brazil. 

Roscherite.  (Mn,Fe,Ca)2Al(OH)(PO4)2.2H2O.  Monoclinic.  From  Ehrensfriedersdorf , 
Saxony. 

Uranite  Group  ^ 

TORBERNITE.    Copper  Uranite. 

Tetragonal.  Axis  c  —  2*9361.  Crystals  usually  square  tables,  sometimes 
very  thin,  again  thick;  less  often  pyramidal.  Also  foliated,  micaceous. 

Cleavage:  c  (001)  perfect,  micaceous.  Laminae  brittle.  H.  =  2-2-5. 
G.  =  !3'4-3'6.  Luster  of  c  pearly,  other  faces  subadamantine.  Color  emerald- 
and  grass-green,  and  sometimes  leek-,  apple-,  and  siskin-green.  Streak  paler 
than  the  color.  Transparent  to  subtranslucent.  Optically  uniaxial;  negative, 
w  =  1-61. 

Comp.  —  A  hydrous  phosphate  of  uranium  and  copper,  Cu(UO2)2P2O8. 
12H2O  =  Phosphorus  pentoxide  14-1,  uranium  trioxide  56*6,  copper  7'9,  water 
21*4  =  100.  Arsenic  may  replace  part'  of  the  phosphorus. 

Pyr.,  etc.  —  In  the  closed  tube  yields  water.  Fuses  at  2*5  to  a  blackish  mass,  and 
colors  the  flame  green.  With  salt  of  phosphorus  gives  a  green  bead,  which  with  tin  on  char- 
coal becomes  on  cooling  opaque  red  (copper).  With  soda  on  charcoal  gives  a  globule  of 
copper.  .Soluble  in  nitric  acid. 

Obs. —  From  Germany  at  Schneeberg,  etc.,  Saxony;  Reichenbach,  Baden;  at 
Joachimstal,  Bohemia;  Ambert,  Puy-de-D6me;  France.  From  Mt.  Painter,  South 
Australia.  The  material  from  Gunnis  Lake,  Cornwall  corresponds  to  Cu(UO2)2P2O8.8H2O 
and  is  the  same  as  the  first  dehydration  product  of  torbernite,  which  has  been  called 
meta-torbernite  I.  G.  =  3'68.  o>  =  T623.  e=l'625. 

Zeimerite.  Cu(UO>);A>,O8.SH2O.  In  tabular  crystals  resembling  torbernite  in  form 
and  color.  G.  =  3'2.  co  =  1-64.  From  Schneeberg,  Saxony;  near  Joachimstal,  Bohemia; 
Cornwall. 

AUTUNITE.     Lime  Uranite. 

Orthorhombic.  In  thin  tabular  crystals,  nearly  tetragonal  in  form  and 
deviating  but  slightly  from  torbernite  in  angle;  also  foliated,  micaceous. 


PHOSPHATES,    ARSENATES,    ETC.  617 

Cleavage:  basal,  eminent.  Laminae  brittle.  H.  =  2-2'5.  G.  =  3-05- 
3*19.  Luster  of  c  (001)  pearly,  elsewhere  subadamantine.  Color  lemon-  to 
sulphur-yellow.  Streak  yellowish.  Transparent  to  translucent.  Optically 
-.  Ax.  pi.  ||  6  (010).  Bx  _L  c  (001).  a  =  1-553.  0  =  1-575.  7  =  1-577. 

Comp.  —  A  hydrous  phosphate  of  uranium  and  calcium,  probably  analo- 
gous to  torbernite,  Ca(UO2)2P2O8.8H2O  or  CaO.2UO3.P2O5.8H2O  =  Phos- 
phorus pentoxide  15*5,  uranium  trioxide  62-7,  lime  6-1,  water  15-7  =  100. 

Some  analyses  give  10  and  others  12  molecules  of  water,  but  it  is  not  certain  that  the 
additional  amount  is  essential. 

Pyr.,  etc.  —  Same  as  for  torbernite,  but  no  reaction  for  copper. 

Obs.  —  With  uraninite,  as  in  Germany  at  Johanngeorgenstadt  and  Falkenstein;  in  Italy 
at  Lurisia,  Cuneo;  in  Madagascar;  at  Tinh-Tuc,  Tongking,  China;  from  Mt.  Painter, 
South  Australia.  In  the  United  States,  at  Middletown  and  Branchville,  Conn.  In  N.  C., 
at  mica  mines  in  Mitchell  Co.;  in  Alexander  Co.;  Black  Hills,  S.  D. 

Bassetite.  Composition  probably  the  same  as  autunite.  Monoclinic.  /3  =  89°  17'. 
Twinned;  tw.  pi.  6  (010).  Cleavage  parallel  to  three  pinacoids.  G.  =  3'10.  Color  yel- 
low. Transparent.  Indices,  1 '57-1 '58.  From  the  Basset  mines,  Cornwall.  Previously 
considered  to  be  autunite. 

Uranospinite.  Probably  Ca(UO2)2As2O8.8H2O.  In  thin  tabular  orthorhombic  crystals 
rectangular  in  outline.  Color  siskin-green.  /3  =  T63.  From  near  Schneeberg,  Saxony. 

Uranocircite.  Ba(UO2)2P2O8.8H2O.  In  crystals  similar  to  autunite.  Color  yellow- 
green.  j8-=  1'62.  From  Falkenstein,  Saxon  Voigtland,  Germany. 

Carnotite.  Approximately,  K2O.2U2O3.V2O6.3H2O.  Orthorhombic.  In  the  form  of 
powder,  sometimes  in  crystalline  plates  |  j  c  (001) .  Basal  cleavage.  Color  yellow.  /3  =  1  '86. 
Occurs  as  a  yellow  crystalline  powder,  or  in  loosely  cohering  masses,  intimately  mixed  with 
quartzose  material.  It  is  found  in  large  quantities  in  western  Colorado  and  eastern  Utah. 
Is  mined  there  not  only  for  its  uranium  and  vanadium  content  but  also  for  the  small  amount 
of  radium  it  contains.  Noted  also  from  Radium  Hill,  near  Olary,  South  Australia,  and  from 
near  Mauch  Chunk,  Pa. 

TYUYAMUNITE.     CaO.2UO3.y2O5.4H2O.     Perhaps     a     calcium     carnotite.     Found     at 
Tyuya-Muyun,  Fergana,  Russian  Central  Asia. 

Uranospathite.  A  hydrated  uranyl  phosphate.  Orthorhombic,  pseudo- tetragonal.  In 
elongated  tabular  crystals.  Cleavages  parallel  to  the  three  pinacoids.  Color  yellow  to 
pale  green.  From  Redruth,  Cornwall.  Previously  considered  to  be  autunite. 

Phosphuranylite.  (yO-2)3P2O8.6H2O.  As  a  pulverulent  incrustation.  Color  deep 
4emon-yellow.  From  Mitchell  Co.,  N.  C. 

Trogerite.  (UO2)3As2O8.12H2O.  In  thin  druses  of  tabular  crystals.  Probably  tetrago- 
nal. Color  lemon-yellow.  From  near  Schneeberg,  Saxony. 

Walpurgite.  Probably  Biio(UO2)3(OH)24(AsO4)4.  In  thin  yellow  crystals  resembling 
gypsum.  G.  =  5'76.  Color  yellow.  Index,  2 '00.  From  near  Schneeberg,  Saxony. 

Rhagite.  Perhaps  2BiAsO4.3Bi(OH)3.  In  crystalline  aggregates.  Color  yellowish 
green,  wax-yellow.  From  near  Schneeberg,  Saxony. 

ARSENO-BISMITE.  A  hydrous  bismuth  arsenate.  In  cryptocrystalline  aggregates. 
Color  yellowish  green  with  tinge  of  brown.  G.  =  5'7.  Index,  1-6.  Found  at  Mammoth 
mine,  Tintic  district,  Utah. 

Mixite.  A  hydrated  basic  arsenate  of  copper  and  bismuth,  formula  doubtful.  In 
acicular  crystals;  as  an  incrustation.  Color  green  to  whitish.  From  Joachimstal,  Bo- 
hemia; Wittichen,  Baden;  Tintic  district,  Utah. 

Antimonates ;   also  Antimonites,  Arsenites. 

A  number  of  antimonates  have  been  included  in  the  preceding  pages 
among  the  phosphates,  arsenates,  etc. 

Bindheimite.  A  hydrous  antimonate  of  lead.  Amorphous,  reniform;  also  earthy  or 
incrusting.  Color  gray,  brownish,  yellowish.  Index,  2'0.  A  result  of  the  decomposition 


518  DESCRIPTIVE   MINERALOGY 

of  other  antimonial  ores;   thus  at  Horhausen,  Germany;   in  Cornwall,  England;    Sevier 


meite.'  An  antimonite  of  calcium,  perhaps  CaSb2O4  In  groups  of  minute  square 
octahedrons  H.  above  5'5.  G.  =  4713.'  Color  hyacinth-  or  honey-yellow,  n  =  183- 
1  87  From  St.  Marcel,  Piedmont;  Miguel  Burnier,  Mmas  Geraes.  Atopite  from  Lang- 
ban,  Sweden,  is  probably  the  same  species. 

Nadorite  PbClSbO2.  In  orthorhombic  crystals.  H.  =  3'5-4.  G.  =  7'02.  Color 
brownish  yellow.  0  =  2  '35.  From  Djebel-Nador,  Constantme.  Algeria. 

Ecdemite.  Heliophyllite.  Perhaps  Pb4As2O7.2PbCl2.  In  crystals,  massive,  and  as  an 
incrustation.  G.  =  6'89-7'14.  Color  bright  yellow  to  green.  From  Langban,  Sweden; 
also  Pajsberg  (heliophyllite)  . 

Ochrolite.  Probably  Pb4Sb2O7.2PbCl2.  In  small  crystals,  united  in  diverging  groups. 
Color  sulphur-yellow.  From  Pajsberg,  Sweden. 

Trippkeite.  nCuO.As2O3.  In  small  bluish  green,  tetragonal  crystals.  From  Copiapo, 
Chile. 

Schafarzikite  is  described  as  isomorphous  with  trippkeite  with  the  formula,  nFeO.P2O3. 
From  Pernek,  Comitat  Pozsony,  Hungary. 

Tripuhyite.  An  iron  antimonate.  2FeO.Sb2O5.  In  microcrystalline  aggregates  of  a 
dull  greenish  yellow  color.  From  Tripuhy,  Brazil. 

Flajolotite.  4FeSbO4.3H2O.  Compact  or  earthy.  Color  lemon-yellow.  In  nodular 
masses.  From  Hammam  N'Bail,  Constantine,  Algiers. 

Catoptrite.  14(Mn,Fe)O.2(Al,Fe)2O3.2SiO2.Sb2O5.  Monoclinic.  Crystals  minute  tab- 
ular parallel  to  6  (010).  Perfect  basal  cleavage.  H.  =  5  '5.  G.  =  4  '5.  Color  black.  In 
thin  splinters,  red.  Pleochroic,  red-brown  to  red-yellow.  From  Brattsfor  mine,  Nord- 
marken,  Sweden. 

Derbylite.  An  antimo-titanate  of  iron.  In  prismatic,  orthorhombic  crystals.  H.  =  5. 
G.  =  4-53.  Color  black.  Tripuhy,  Brazil. 

Lewisite.  5CaO.2TiO2.3Sb2O6.  In  minute  yellow  to  brown  isometric  octahedrons. 
Tripuhy,  Brazil. 

Mauzeliite.  A  titano-antimonate  of  lead  and  calcium,  related  to  lewisite.  In  dark 
brown  isometric  octahedrons.  Jakobsberg,  Sweden. 

AMMIOLITE.     A  doubtful  antimonite  of  mercury;  forming  a  scarlet  earthy  mass.     Chile. 


Phosphates  or  Arsenates  with  Carbonates,  Sulphates,  Borates 

Podolite.  3Ca3(PO4)2.CaCO3.  Hexagonal.  In  microscopic  prismatic  crystals,  also  in 
spherulites.  G.  =  3'1.  Color  yellow,  ft  =  1'64.  Occurs  in  cavities  in  the  phosphorite 
nodules  from  near  the  Uschitza  River,  Podolien,  southern  Russia.  See  also  staff  elite  and 
dahllite,  p.  597. 

Diadochite.  A  hydrated  phosphate  and  sulphate  of  ferric  iron.  Index,  1*606.  From 
Thuringia.  Destinezite  is  similar;  from  Belgium. 

Pitticite.  A  hydrated  arsenate  and  sulphate  of  ferric  iron.  Reniform  and  massive. 
Yellowish  and  reddish  brown.  Index,  1  -63.  From  Saxony,  Cornwall,  etc. 

Svanbergite.  A  hydrated  phosphate  and  sulphate  of  aluminium  and  calcium.  In 
rhombohedral  crystals.  Color  yellow  to  yellowish  brown,  rose-red,  co  =  T64.  From 
Horrsjoberg,  Sweden. 

Beudantite.  A  phosphate  or  arsenate  with  sulphate  of  ferric  iron  and  lead;  formula 
perhaps,  3Fe2O3.2PbO.2SO3.As2O5.6H2O.  In  rhombohedral  crystals.  Color  green  to  brown 
and  black.  Indices,  175-1  '94.  From  Dernbach  and  Horhausen,  Nassau.  Corkite  is  same 
mineral  from  Cork,  Ireland;  Beaver  Co.,  Utah. 

Phosphophyllite.  3Fe3P2O8.2Al(OH)SO4.9H2O,  with  Ca,Ba,Mg,Mn,K2  Monoclinic. 
Colorless  to  pale  blue-green.  3  pinacoidal  cleavages.  H.  =  3-4.  G.  =  3 '08.  n  =  T65. 
From  Habendorf,  Bavaria. 

Hinsdalite.  2PbO.3Fe2O3.2SO3.P2O5.6H2O.  Pseudo-rhombohedral.  In  coarse,  dull 
crystals.  Cleavage,  basal  perfect.  H.  =  4'5.  G.  =  4'65.  Colorless  with  greenish  tone. 
Indices  1 -67-1 -69.  Found  at  Golden  Fleece  mine,  Hinsdale  Co.,  Col. 

Lindackerite.  Perhaps  3NiO.6CuO.SO3.2As2O5.7H2O.  In  rosettes,  and  in  reniform 
masses.  Color  verdigris-  to  apple-green.  From  Joachimstal,  Bohemia. 


BO  RATES  619 

Liineburgite.  3MgO.B2O3.P2O5.8H2O.  Monoclinic?  In  flattened  masses,  fibrous  to 
earthy  structure.  Biaxial,  — .  Index,  T53.  From  Ltineburg,  Hannover. 

Lossenite.     A  hydrous  iron  arsenate  and  lead  sulphate  from  Laurion,  Greece. 

Nitrates 

The  Nitrates  being  largely  soluble  in  water  play  but  an  unimportant  role 
in  Mineralogy. 

SODA   NITER. 

Rhombohedral.  Axis  c  =  0-8276;  rr"  1011  A  1101  =  73°  30'.  Homceo- 
morphous  with  calcite.  Usually  massive  form,  as  an  incrustation  or  in  beds. 

Cleavage:  r  (1011)  perfect.  Fracture  conchoidal,  seldom  observable. 
Rather  sectile.  H.  =  T5-2.  G.  =  2'24-2'29.  Luster  vitreous.  Color 
white;  also  reddish  brown,  gray  and  lemon-yellow.  Transparent.  Taste 
cooling.  Optically  -.  co  =  T5874,  e  =  1'3361. 

Comp.  —  Sodium  nitrate,  NaNO3  =  Nitrogen  pentoxide  63'5,  soda  36'5 
=  100. 

Pyr.,  etc.  —  Deflagrates  on  charcoal  with  less  violence  than  niter,  causing  a  yellow 
light,  and  also  deliquesces.  Colors  the  flame  intensely  yellow.  Dissolves  in  three  parts  of 
water  at  60°  F. 

Obs.  —  From  Tarapaca,  northern  Chile,  and  also  the  neighboring  parts  of  Bolivia;  also 
in  Humboldt  Co.,  Nev.;  near  Calico,  San  Bernardino  Co.,  Cal. 

Use.  —  A  source  of  nitrates.     The  deposits  in  Chile  are  of  great  importance. 

Niter.  Potassium  nitrate,  KNO3.  Orthorhombic.  0  =  T505.  In  thin  white  crusts 
and  silky  tufts. 

Nitrocalcite.  Hydrous  calcium  nitrate,  Ca(NO3)2.nH2O.  In  efflorescent  silky  tufts 
and  masses.  In  many  limestone  caverns,  as  those  of  Kentucky. 

Nitromagnesite.     Mg(NO3)2.nH2O.     In  efflorescences  in  limestone  caves. 

Nitrobarite.  Barium  nitrate,  Ba(NO3)2.  Isometric-tetartohedral.  n  =  1'57.  From 
Chile. 

Gerhardtite.  Basic  cupric  nitrate,  Cu(NO3)2.3Cu(OH)2.  In  pyramidal  orthorhombic 
crystals.  G.  =  3 '426.  Color  emerald-green.  /3  =  1713.  From  the  copper  mines  at 
Jerome,  Ariz. 

Darapskite.  NaNOs.Na2SO4.H2O.  Monoclinic.  In  square  tabular  crystals.  Color- 
less. From  Atacama,  Chile. 

Nitroglauberite.     6NaNO3.2Na2SO4.3H2O.     From  Atacama,  Chile. 


Lautarite.  Calcium  iodate,  Ca(IO3)2.  In  prismatic,  monoclinic  crystals,  colorless  to 
yellowish.  From  the  sodium  nitrate  deposits  of  Atacama,  Chile. 

Dietzeite.  -A  calcium  iodo-chromate.  Monoclinic;  commonly  fibrous  or  columnar. 
H.  =  3-4.  G.  =  370.  Color  dark  gold-yellow.  From  the  same  region  as  lautarite. 

Oxygen  Salts 

5.   BORAXES 

The  aluminates,  ferrates,  etc.,  allied  chemically  to  the  borates,  have  been  already  intro- 
duced among  the  oxides.  They  include  the  species  of  the  Spinel  Group,  pp.  418-423,  also 
Chrysoberyl,  p.  423,  etc. 

SUSSEXITE. 

In  fibrous  seams  or  veins.  H.  =  3.  G.  =  3 -42.  Luster  silky  to  pearly. 
Color  white  with  a  tinge  of  pink  or  yellow.  Translucent.  Index,  T59. 


620 


DESCRIPTIVE    MINERALOGY 


Comp.  —  HRB03,  where  R  =  Mn,  Zn  and  Mg  =  Boron  trioxide  34  1, 
manganese  protoxide,  41 '5,  magnesia  15'6,  water  8'8  =  100.  Here  Mn 
(+  Zn)  :  Mg  =  3  :  2. 

Pyr.,  etc. In  the  closed  tube  darkens  in  color  and  yields  neutral  water.  If  turmeric 

paper  is  moistened  with  this  water,  and  then  with  dilute  hydrochloric  acid,  it  assumes  a 
red  color  (boric  acid).  In  the  forceps  fuses  in  the  flame  of  a  candle  (F.  =  2),  and  B.B.  in 
O  F.  yields  a  black  crystalline  mass,  coloring  the  flame  intensely  yellowish  green.  With 
the  fluxes  reacts  for  manganese.  Soluble  in  hydrochloric  acid. 

Obs. Found  on  Mine  Hill,  Franklin  Furnace,  Sussex  Co.,  N.  J.,  with  franklinite, 

zincite  willemite,  etc.  An  intimate  mixture  of  zincite  and  calcite,  not  uncommon  at  Min? 
Hill,  is  often  mistaken  for  sussexite,  but  the  ready  fusibility  of  the  genuine  mineral  is  dis- 
tinctive. 

Ludwigite.  Perhaps  3MgO.B2O3.FeO.Fe2O3.  Orthorhombic.  In  finely  fibrous  masses. 
G.  =  3-91-4-02.  Color  blackish  green  to  nearly  black.  Index,  T86.  Strongly  pleochroic. 
From  Morawitza,  Hungary.  Collbranite  from  Korea  is  ludwigite. 

VONSENITE.  3(Fe,Mg)O.B2O3.FeO.Fe2O3.  Similar  to  ludwigite  with  more  ferrous  iron. 
Riverside;  Cal. 

Magnesioludwigite.  3MgO.B2O3.MgO.Fe2O3.  From  Mountain  Lake  mine,  south  of 
Brighton,  Utah. 

Pinakiolite.  3MgO.B2O3.MnO.Mn2O3.  In  small  rectangular  crystals.  H.  =  6. 
G.=  3-881.  Luster  metallic.  Color  black.  From  Langban,  Sweden. 

Nordenskioldine.  A  calcium-tin  borate,  CaSn(BOi)2.  In  tabular  rhombohedral 
crystals.  H.  =  5*5-6.  G.  =  4'20.  Color  sulphur-yellow.  From  the  Langesund  fiord, 
Norway. 

Jeremejevite.  Eichwaldite.  Aluminium  borate,  A1BO3.  In  prismatic  hexagonal 
crystals.  H.  =  6'5.  G.  =  3/28.  Colorless  to  pale  yellow.  Index,  1'64.  From  Mt. 
Soktuj,  Adun-Chalon  range  in  Eastern  Siberia. 

Hambergite.  Be2(OH)BO3.  In  grayish  white  orthorhombic  prismatic  crystals. 
H.  =  7-5.  G.  =  2-347.  Optically  +.  0  =  1'588.  From  Langesund  fiord,  southern  Nor- 
way; various  localities  in  Madagascar. 

Szaibelyite.  2Mg5B4Ou.3H2O.  In  small  nodules;  white  outside,  yellow  within.  From 
Rezbdnya,  Hungary. 

BORACITE. 

Isometric  and  retrahedral  in  external  form  under  ordinary  conditions,  but 
in  molecular  structure  orthorhombic  and  pseudo-isometric;  the  structure 
becomes  isotropic,  as  required  by  the  form,  only  when  heated  to  265°.  (See 
Art.  429.) 


991 


\7 


993 


Habit  cubic  and  tetrahedral  or  octahedral;  also  dodecahedral.  Crystals 
usually  isolated,  embedded;  less  often  in  groups.  Faces  o  (111)  bright  and 
smooth,  o,  (111)  dull  or  uneven. 

Cleavage:  o,oy  in  traces.  Fracture  conchoidal,  uneven.  Brittle  H  =7 
in  crystals.  G.  =  2-9-3.  Luster  vitreous,  inclining  to  adamantine.  Color 
white,  inclining  to  gray,  yellow  and  green.  Streak  white.  Subtransparent  to 


BORATES  621 

translucent.  Commonly  shows  double  refraction,  which,  however,  disappears 
upon  heating  to  265°,  when  a  section  becomes  isotropic.  Refractive  index, 
n  =  1-667;  7  -  a  =  0-0107. 

Strongly  pyroelectric,  the  opposite  polarity  corresponding  to  the  position 
of  the  +  and  -  tetrahedral  faces  (see  pp.  306,  307).  The  faces  of  the  dull 
tetrahedron  o/  (111)  form  the  analogous  pole,  those  of  the  polished  form  o 
(111)  the  antilogous  pole. 

Comp.  —  Mg7Cl2B16O3o  or  6MgO.MgCl2.8B2O3  =  Boron  trioxide  62*5, 
magnesia  31'4,  chlorine  7'9  =  101'8,  deduct  (O=  Cl)  1'8  =  100. 

Var.  —  1.  Ordinary.  In  crystals  of  varied  habit.  2.  Massive,  with  sometimes  a  sub- 
columnar  structure;  stassfurtite  of  Rose.  It  resembles  a  fine-grained  white  marble  or 
granular  limestone.  Parasite  of  Volger  is  the  plumose  interior  of  some  crystals  of  boracite. 
3.  Eisenstassfurtite  contains  some  Fe. 

Pyr.,  etc.  —  The  massive  variety  gives  water  in  the  closed  tube.  B.B.  both  varieties 
fuse  at  2  with  intumescence  to  a  white  crystalline  pearl,  coloring  the  flame  green;  heated 
after  moistening  with  cobalt  solution  assumes  a  deep  pink  color.  Mixed  with  oxide  of 
copper  and  heated  on  charcoal  colors  the  flame  deep  azure-blue  (copper  chloride).  Soluble 
in  hydrochloric  acid. 

Alters  very  slowly  on  exposure,  owing  to  the  magnesium  chloride  present,  which  takes 
up  water.  It  is  the  frequent  presence  of  this  deliquescent  chloride  in  the  massive  mineral, 
thus  originating,  that  led  to  the  view  that  there  was  a  hydrous  boracite  (stassfurtite). 
Parasite  of  Volger  is  a  result  of  the  same  kind  of  alteration  in  the  interior  of  crystals  of 
boracite;  this  alteration  giving  it  its  somewhat  plumose  character,  and  introducing  water. 

Obs.  —  Observed  in  beds  of  anhydrite,  gypsum  or  salt.  In  crystals  in  Germany  at 
Kalkberg  and  Schildstein  in  Llineburg,  Hannover;  at  Segeberg,  near  Kiel,  in  Holstein; 
massive,  or  as  part  of  the  rock,  also  in  crystals,  at  Stassfurt,  Prussia;  at  Luneville,  La 
Meurthe,  France. 

Ascharite.  A  hydrous  magnesium  borate.  In  white  lumps  with  boracite.  G.  =  2'7. 
Index,  1*54.  From  Aschersleben  and  Neustassfurt,  Germany.  Paternoite.  A  similar 
mineral  from  Sicily. 

Rhodizite.  A  borate  of  aluminium  and  potassium,  with  caesium  and  rubidium.  Iso- 
metric-tetrahedral;  in  white,  translucent  dodecahedrons.  H.  =  8.  G.  =  3 '41.  n  =  T69. 
Found  on  red  tourmaline  from  near  Ekaterinburg,  Ural  Mts.;  from  Madagascar. 

Warwickite.  (Mg,  Fe)3TiB2O8.  In  elongated  prismatic  crystals.  G.  =  3'36.  Color 
dark  brown  to  dull  black.  From  Edenville,  N.  Y. 

Howlite.  A  silico-borate  of  calcium,  H5  Ca2B6SiOi4.  In  small  white  rounded  nodules; 
also  earthy.  From  Nova  Scotia;  Lang,  Los  Angeles  Co.,  and  in  San  Bernardino  Co.,  Cal. 

Lagonite.     Fe2O3.3B2O3.3H2O.     An  incrustation  at  the  Tuscan  lagoons,  Italy. 

Larderellite.     (NH4)2Bi0O16.5H2O.     From  the  Tuscan  lagoons,  Italy. 

COLEMANITE. 

Monoclinic.     Axes  a  :  b  :  c  =  07748  :  1  :  0'5410;j3  =  69°  51'. 

Crystals  usually  short  prismatic  (mm'"  110  A  110  =  72°  4').  Massive 
cleavable  to  granular  and  compact. 

Cleavable:  b  (010)  highly  perfect;  c  (001)  distinct.  Fracture  uneven  to 
subconchoidal.  H.  =  4-4'5.  G.  =  2*42.  Luster  vitreous  to  adamantine, 
brilliant.  Colorless  to  milky  white,  yellowish  white,  gray.  Transparent  to 
translucent.  Optically  +  .  a  =  1'586.  0  =  1'592.  7  =  1'614. 

Comp.  —  Ca2B6On.5H2O,  perhaps  HCa(BO2)3.2H20  =  Boron  trioxide 
50'9,  lime  27*2,  water  21*9  =  100. 

Pyr.  —  B.B.  decrepitates,  exfoliates,  sinters,  and  fuses  imperfectly,  coloring  the  flame 
yellowish  green.  Soluble  in  hot  hydrochloric  acid  with  separation  of  boric  acid  on  cooling. 

Obs.  —  First  discovered  in  Death  Valley,  Inyo  Co.,  Cal.;  later  in  Calico  district,  San 
Bernardino  Co.  Neocolemanite  from  Lang,  Los  Angeles  Co.,  Cal.,  is  identical  with  cole- 
manite. 

PRICEITE.  Near  colemanite.  Massive,  friable  and  chalky.  Color  snow-white.  From 
Curry  Co.,  Oregon.  Pandermite  is  •  similar;  in  compact  nodules  from  Asia  Minor; 
Argentina. 


622 


DESCRIPTIVE   MINERALOGY 


Inyoite.  2CaO.3B2O3.13H2O.  Monoclinic.  In  large  tabular  crystals.  Cleavage, 
c  (001).  H.  =2.  G.  =  1-87.  Indices,  1 '49-1*52.  Decrepitates  and  fuses  with  intu- 
mescence, giving  green  flame.  Largely  altered  into  meyerhofferite.  From  Mt.  Blanco  dis- 
trict, on  Furnace  Creek,  near  Death  Valley,  Inyo  Co.,  Cal.  Associated  with  colemanite. 

Meyerhofferite.  2CaO.3B2O3.7H2O.  Triclinic  crystals  prismatic,  often  tabular  parallel 
to  a  (100).  Fibrous.  Cleavage,  b  (010).  H.  =  2.  G.  =  2*12.  Colorless  to  white.  In- 
dices, 1  '50-1  '56.  Fuses  without  decrepitation  but  with  intumescence.  Found  with  inyoite 
(which  see)  as  an  alteration  product. 

Pinnoite.  MgB2O4.3H2O.  Tetragonal-pyramidal.  Usually  in  nodules,  radiated  fibrous. 
G.  =  2 '29.  Color  sulphur-  or  straw-yellow,  co  =  1'56.  From  Stassfurt,  Germany. 

Heintzite.  Hintzeite.  Kaliborite.  A  hydrous  borate  of  magnesium  and  potassium. 
In  small  monoclinic  crystals,  sometimes  aggregated  together.  H.  =  4-5.  G.  =  2*13. 
Colorless  to  white,  ft  =  T525.  From  Leopoldshall,  Stassfurt,  Germany. 

Hulsite.     12(Fe,Mg)O.2Fe2O3.lSnO2.3B2O«.2H2O.     Orthorhombic  (?)  as  small  crystals 
or  tabular  masses.     H.  =  3.     G.  =  4 '3.     Color  and  streak  black.     Fusible.     Found  in 
metamorphosed  limestone  at  a  granite  contact  at  Brooks  mountain,  Seward  Peninsula, 
Alaska.     Paigeile  is  a  similar  mineral   from   the  same  locality   with   the   composition 
30FeO.5Fe2O3.lSnO2.6B2O3.5H2O. 


BORAX. 

Monoclinic. 
994 


Axes  a  :  b  :  c  =  1-0995  :  1  :  0-5632;  0  =  73°  25'. 

ca,         001  A  100  =  73°  25'.  cz,  001  A  221  =  64°    8'. 

mm'",  110  A  110  =  93°    0'.  oo',  III  A  Til  =  57°  27'. 

co,         001  A  111  =  40°  31'.  zz',  221  A  221  =  83°  28'. 

Crystals     prismatic,      sometimes     large;      resembling 
pyroxene  in  habit  and  angles. 

Cleavage:  a  (100)  perfect;  m  (110)  less  so;  6](010)  in 
traces.  Fracture  conchoidal.  Rather  brittle.  H.  =  2-2*5. 
G.  =  T69-172.  Luster  vitreous  to  resinous;  sometimes 
earthy.  Color  white;  sometimes  grayish,  bluish  or  green- 
ish. Streak  white.  Translucent  to  opaque.  Taste  sweet- 
ish alkaline,  feeble.  Optically  -  .  Ax.  pi.  ±  b  (010). 
Bxa  _L  6  (010).  Bxo.r  A  c  axis  =  -  56°  50'.  2V  =  39°. 
T470.  7  =  1-472. 

Comp.  —  Na2B4O7.10H2O  or  Na2O.2B2O3.10H2O 
soda  16-2,  water  47-2  =  100. 


a  =  1-447.     0  = 
Boron  trioxide  36'6. 


of  bomx 


F,~^  ?  'B:fEUflS  Up.and  afterward  fuses  to  a  transparent  globule,  called  the  glass 
and  P°t*?*um  bisulphate,  it  colors  the  flame  around  the 
a  «  alkaline  soMon-     Boi^g  water 


the  i 


°f  Tibet;   the  crude  mineral  is  called  . 

two  small  alkaline  lakes  in 


t 
inolderin^  gold 


Co-;  at 

,  which  included  also  the  niter  (sodium  carbonate) 
Called  <=h^o-»-  by  Agricola 

a  sclent  t^^^^^^^^^^  ^  preservative;  „ 
tJLEXITE.    Boronatrocalcite.    Natronborocalcite. 

are  acTcu&r,Tned  massf  ',  Ioose  m  texture,  consisting  of  fine  fibers,  which 
Color  S      ^  "f^ycrystas.     H.  =  1.    G.  -  1'65.    Luster  silky  within. 
r  white.     Tasteless. 


H.  = 
Ophcally  +. 


1.    G.  -  1'65. 
«  =  1'500.    (3 


1-508.    7  =  T520. 


BORATES,    URANATES  623 

Comp.  —  A  hydrous  borate  of  sodium  and  calcium,  probably  NaCaB5O9. 
8H2O  =  Boron  trioxide  43'0,  lime  13'8,  soda  77,  water  35'5  =  100. 

Pyr.,  etc.  —  Yields  water.  B.B.  fuses  at  1  with  intumescence  to  a  clear  blebby  glass, 
coloring  the  flame  deep  yellow.  Moistened  with  sulphuric  acid  the  color  of  the  flame  is 
momentarily  changed  to  deep  green.  Not  soluble  in  cold  water,  and  but  little  so  in  hot; 
the  solution  alkaline  in  its  reactions. 

Obs.  —  From  the  dry  plains  of  Iquique,  Chile.  In  Nev.,  in  large  quantities  in  the  salt 
marshes  of  the  Columbus  Mining  District,  Esmeralda  Co. 

Named  after  the  German  chemist,  G.  L.  Ulex. 

Bechilite.     CaB4O7.4H2O.     In  crusts,  as  a  deposit  from  springs  in  Tuscany,  Italy. 

Hydroboracite.  CaMgB6On.6H2O.  Resembles  fibrous  and  foliated  gypsum;  color 
white.  /3  =  T587.  From  the  Caucasus  Mts. 

Sulphoborite.  2MgSO4.4MgHBO3.7H2O.  In  colorless  prismatic  orthorhombic  crys- 
tals. H.  =  4.  G.  =  2-38-2-45.  Optically  -.  ft  =  1'540.  From  Westeregeln,  and 
Wittmar,  Germany. 


Uranates 
URANINITE.     Cleveite.     Broggerite.     Nivenite.     Pitchblende. 

Isometric.  In  octahedrons  (o),  also  with  dodecahedral  faces  (d) ;  less  often 
in  cubes  with  o  and  d.  Crystals  rare.  Usually  massive  and  botryoidal;  also 
in  grains;  structure  sometimes  columnar,  or  curved  lamellar. 

Fracture  conchoidal  to  uneven.  Brittle.  H.  =  5'5.  G.  =  9'0  to  97  of 
crystals;  of  massive  altered  forms  from  6*4  upwards.  Luster  submetallic,  to 
greasy  or  pitch-like,  and  dull.  Color  grayish,  greenish,  brownish,  velvet- 
black.  Streak  brownish  black,  grayish,  olive-green,  a  little  shining.  Opaque. 

Comp.  —  A  uranate  of  uranyl,  lead,  usually  thorium  (or  zirconium), 
often  the  metals  of  the  lanthanum  and  yttrium  groups;  also  containing  the 
gases  nitrogen,  helium  and  argon,  in  varying  amounts  up  to  2'6  p.  c.  Calcium 
and  water  (essential?)  are  present  in  small  quantities;  iron  also,  but  only  as  an 
impurity.  The  relation  between  the  bases  varies  widely  and  no  definite  for- 
mula can  be  given.  Radium  was  first  discovered  in  this  mineral  and  it  has  been 
shown  that  it  and  the  helium  present  are  products  of  the  breaking  down  of 
the  uranium. 

Var.  —  The  minerals  provisionally  included  under  the  name  uraninite  are  as  follows: 

1.  Crystallized.     Uranniobite  from  Norway.     In  crystals,  usually  octahedral,  with  G. 
varying  for  the  most  part  from  9'0  to  9 '7;  occurs  as  an  original  constituent  of  coarse  granites. 
The  variety  from  Branchville,  Conn.,  which  is  as  free  from  alteration  as  any  yet  examined, 
contains  chiefly  UO2  with  a  relatively  small  amount  of  UO3.     Thoria  is  prominent,  while 
the  earths  of  the  lanthanum  and  yttrium  groups  are  only  sparingly  represented. 

Broggerite,  as  analyzed  by  Hillebrand,  gives  the  oxygen  ratio  of  tlOs  to  other  bases  of 
about  1:1;  it  occurs  in  octahedral  crystals,  also  with  d  (110)  and  a  (100).  G.  =  9'03. 

Cleveite  and  nivenite  contain  UO3  in  larger  amount  than  the  other  varieties  mentioned, 
and  are  characterized  by  containing  about  10  p.  c.  of  the  yttrium  earths.  Cleveite  is  a 
variety  from  the  Arendal,  Norway,  region  occurring  in  cubic  crystals  modified  by  the  dodeca- 
hedron and  octahedron.  G.  =  7'49.  It  is  particularly  rich  in  the  gas  helium.  Nivenite 
occurs  massive,  with  indistinct  crystallization.  Color  velvet-black.  H.  =  5'5.  G.  =  8'01. 
It  is  more  soluble  than  other  kinds  of  uraninite,  being  completely  decomposed  by  the  action 
for  one  hour  of  very  dilute  sulphuric  acid  at  100°. 

2.  Massive,  probably  amorphous.     Pitchblende.     Contains  no  thoria;   the  rare  earths 
also  absent.     Water  is  prominent  and  the  specific  gravity  is  much  lower,  in  some  cases  not 
above  6'5;    these  last  differences  are  doubtless  largely  due  to   alteration.     Here  belong 
the  kinds  of  pitchblende  which  occur  in  metalliferous  veins,  with  sulphides  of  silver,  lead, 
cobalt,  nickel,  iron,  zinc,  copper,  as  that  from  Johanngeorgenstadt,  Germany;   Pfibram, 
Bohemia,  etc.;  probably  also  that  from  Black  Hawk,  Col. 


624  DESCRIPTIVE   MINERALOGY 

Pyr.,  etc.  —  B.B.  infusible,  or  only  slightly  rounded  on  the  edges,  sometimes  coloring 
the  outer  flame  green  (copper).  With  borax  and  salt  of  phosphorus  gives  a  yellow  bead  in 
O.F.,  becoming  green  in  R.F.  (uranium).  With  soda  on  charcoal  gives  a  coating  of  lead 
oxide,  and  frequently  the  odor  of  arsenic.  Many  specimens  give  reactions  for  sulphur  and 
arsenic  in  the  open  tube.  Soluble  in  nitric  and  sulphuric  acids;  the  solubility  differs  widely 
in  different  varieties,  being  greater  in  those  kinds  containing  the  rare  earths.  Not  attract- 
able by  the  magnet.  Strongly  radioactive. 

Obs.  —  As  noted  above,  uraninite  occurs  either  as  a  primary  constituent  of  granitic  rocks 
or  as  a  secondary  mineral  with  ores  of  silver,  lead,  copper,  etc.  Under  the  latter  condition 
it  is  found  in  Germany  at  Johanngeorgenstadt,  Marienberg,  and  Schneeberg  in  Saxony; 
in  Bohemia  at  Joachimstal  and  Pfibram;  in  Hungary  at  Rezbanya.  Occurs  in  Norway  in 
pegmatitic  veins  at  several  points  near  Moss,  viz.:  Annerod  (broggerite),  Elvestad,  etc., 
also  near  Arendal  at  the  Garta  feldspar  quarry  (deveite),  associated  with  orthite,  fergusonite, 
thorite,  etc. 

In  the  United  States,  at  the  Middletown  feldspar  quarry,  Conn.,  in  large  octahedrons, 
rare;  at  Hale's  quarry  in  Glastonbury,  a  few  miles  N.E.  of  Middletown.  At  Branchville, 
Conn.,  in  a  pegmatite  vein,  as  small  octahedral  crystals,  embedded  in  albite.  In  N.  C.,  at 
the  Flat  Rock  mine  and  other  mica  mines  in  Mitchell  Co.,  rather  abundant,  but  usually 
altered,  in  part  or  entirely,  to  gummite  and  uranophane;  the  crystals  are  sometimes  an  inch 
or  more  across  and  cubic  in  habit.  In  S.  C.,  at  Marietta.  In  Texas,  at  the  gadolinite 
locality  in  Llano  Co.  (nivenite).  In  large  quantities  at  Black  Hawk,  near  Central  City, 
Col.  Rather  abundant  in  the  Bald  Mountain  district,  Black  Hills,  S.  D.  Also  with 
monazite,  etc.,  at  the  Villeneuye  mica  veins,  Ottawa  Co.,  Quebec,  Canada. 

Use.  —  As  a  source  of  uranium  and  of  radium  salts. 

Gummite.  An  alteration-product  of  uraninite  of  doubtful  composition.  In  rounded 
or  flattened  pieces,  looking  much  like  gum.  G.  =  3'9-4'20.  Luster  greasy.  Color  red- 
dish yellow  to  orange-red,  reddish  brown,  n  =  1'61.  From  Johanngeorgenstadt,  Ger- 
many, also  Mitchell  Co.,  N.  C. 

YTTROGUMMITE.     Occurs  with  cleveite  as  a  decomposition-product. 
THOROGUMMITE.     Occurs  with  fergusonite,  cyrtolite,  and  other  species  at  the  gadolinite 
locality  in  Llano  Co.,  Texas. 

Thorianite.  Chiefly  thorium  and  uranium  oxides.  Isometric,  cubic  habit.  G.  =  9'3. 
Color  black.  Radioactive.  Obtained  from  gem  gravels  of  Balangoda,  Ceylon.  Also  noted 
from  Province  of  Betroka,  Madagascar. 

Uranosphaerite.  (BiO)2U2O7.3H2O.  In  half-globular  aggregated  forms.  Color  orange- 
yellow,  brick-red.  From  near  Schneeberg,  Saxony. 

Oxygen  Salts 

6.   SULPHATES,   CHROMATES,   TELLURATES 
A.   Anhydrous   Sulphates,  etc. 

The  important  BARITE  GROUP  is  the  only  one  among  the  anhydrous  sul- 
phates and  chromates. 


ipg£ite*     A™mo™™  sulphate,  (NH4)2SO4.     Orthorhombic.     Usually  in  crusts  and 
forms,    ft  =  1'523.     Occurs  about  volcanoes,  as  at  Etna,  Vesuvius,  etc. 

0r  80*'     ^  ^  C°m 


dal     hTrf  nr^m  ^^T*  s?diu™  sulphate,  Na2S04.     In  orthorhombic  crystals,  pyrami- 

Opticanv    £    T     i°/77      ^ti^  aS  twlnS  (Fig>  384'  p-  160)'     White  to  brownish. 

n  thp   vT         /V    ,Sol£b  f  m  water"     Often  ob^rved  in  connection  with  salt 

AnSfof  ?n  Ta™n°reS  nJf  ke  TBalk,hash>  Central  Asia;  similarly  elsewhere;   also  in  South 

vSde  An"  TaTrnaPrT'  ^     Ir?  t,he  ynited  States>  f°rms  extensive  deposits  on  the  Rio 

erae  Ariz.     In  Cal.,  at  Borax  Lake,  San  Bernardino  Co. 

cruste      Co^wh^^6-     £laSerite"     (K'Na)^O4.     Rhombohedral;     also    massive,    in 
many3,'  in'  k  U 


SULPHATES,    CHROMATES,    ETC. 


625 


67°  49'. 


995 


GLAUBERITE. 

Monoclinic.     Axes  a  :  b  •  c  =  i'2200  :  1  :  T0275;  /3 
ca,        001  A  100  =  67°  49'.      cs,    001  A  111  =  43°    2' 
mm'",  110  A  110  =  96°  58'.      cm,  001  A  110  =  75°  30f. 

In  crystals  tabular  ||  c  (001);  also  prismatic. 

Cleavage:  c  perfect.  Fracture  conchoidal.  Brittle. 
H.  =  2-5-3.  G.  =  2-7-2-85.  Luster  vitreous.  Color 
pale  yellow  or  gray;  sometimes  brick-red.  Streak 
white.  Taste  slightly  saline.  Optically—.  2V  = 
7°.  a  =  1-515.  j8  =  1-532.  y  =  1'536.  Optical 
characters  change  on  heating,  see  p.  297. 

Comp.  —  Na2SO4.CaSO4  =  Sulphur  trioxide  57'6, 
lime  20'1,  soda  22'3  =  100;  or,  Sodium  sulphate 
51'1,  calcium  sulphate  48  "9  =  100. 

Pyr.,  etc.  —  B.B.  decrepitates,  turns  white,  and  fuses  at  1'5  to  a  white  enamel,  coloring 
the  flame  intensely  yellow.  On  charcoal  fuses  in  O.F.  to  a  clear  bead;  in  R.F.  a  portion 
is  absorbed  by  the  charcoal,  leaving  an  infusible  hepatic  residue.  Soluble  in  hydrochloric 
acid.  In  water  it  loses  its  transparency,  is  partially  dissolved,  leaving  a  residue  of  calcium 
sulphate,  and  in  a  large  excess  this  is  completely  dissolved. 

Obs.  —  In  crystals  in  rock  salt  at  Villa  Rubia,  in  New  Castile,  Spain;  also  at  Aussee  and 
Hallstatt,  Upper  Austria;  in  Germany  at  Berchtesgaden,  Bavaria;  Westeregeln;  Stassfurt. 
In  crystals  in  the  Rio  Verde  Valley,  Ariz.,  with  thenardite,  mirabilite,  etc.;  Borax  lake,  San 
Bernardino  Co.,  Cal. 

Langbeinite.  K2Mg2(SO4)3.  Isometric-tetartohedral.  In  highly  modified  colorless 
crystals.  G.  =  2'83.  n  =  1'533.  From  Westeregeln  and  Stassfurt,  Germany;  Hall, 
Tyrol;  Punjab,  India. 

Vanthoffite.  3Na2SO4.MgSO4.  Almost  colorless  crystalline  material  found  at  Wil- 
helmshall,  near  Stassfurt,  Prussia. 

Barite  Group.     RS04.     Orthorhombic 

m  A  m'"         dd'_ 
110  A  110    102  A  102 
77°  43' 
78°  49' 
78°  47' 
(58°  31') 


Barite  BaSO4 

Celestite  SrSO4 

Anglesite  PbSO4 

Anhydrite  CaS04 


78°  22J' 

75°  50' 

76°  16J' 

(83°  33') 


00' 

Oil  A  .011 

a 

b  : 

c 

105°  26' 

0-8152 

1 

1-3136 

104°  0' 

0-7790 

1 

1-2801 

104°  24i' 

0-7852 

1 

1-2894 

(90°  3') 

0-8933 

1 

1-0008 

The  BARITE  GROUP  includes  the  sulphates  of  barium,  strontium,  and  lead, 
three  species  which  are  closely  isomorphous,  agreeing  not  only  in  axial  ratio 
but  also  in  crystalline  habit  and  cleavage.  With  these  is  also  included  cal- 
cium sulphate,  anhydrite,  which  has  a  related  but  not  closely  similar  form;  it 
differs  from  the  others  conspicuously  in  cleavage.  It  is  to  be  noted  that  the 
carbonates  of  the  same  metals  form  the  isomorphous  ARAGONITE  GROUP,  p.  437. 


BARITE.     Heavy  Spar.     Barytes. 

Orthorhombic.     Axes  a  :  b  :  c 
mm'",  110  A  110  =  78°  22|'. 
cd,         001  A  102  =  38°  51  i'. 
co,         001  A  Oil  =  52°  43'. 

Crystals  commonly  tabular 


G'8152  :  1  :  1-3136. 

dd"f,  102  A  102  =  102°  17'. 
oo'",  Oil  A  Oil  =  74°  34'. 
cz,  001  A  111  =  64°  19'. 

c  (001),  and  united  in  diverging  groups  having 

the  axis  b  in  common;  also  prismatic,  most  frequently  ||  axis  b,  d  (102)  predomi- 
nating; also  ||  axis  c,  m  (110)  prominent;  again  ||  axis  a,  with  o  (Oil)  promi- 
nent. Also  in  globular  forms,  fibrous  or  lamellar,  crested;  coarsely  laminated, 


626 


DESCRIPTIVE    MINERALOGY 


laminae  convergent  and  often  curved;  granular,  resembling  white  marble,  and 
earthy;  colors  sometimes  banded  as  in  stalagmite. 

Cleavage:  c  (001)  perfect;  m  (110)  also  perfect,  Fig.  996  the  form  yielded 

996  997  998  999 


1000 


1001 


1002 


1003 


1004 


37°  30'.    a  =  1.636. 


by  cleavage;  also  6  (010)  imperfect.  Fracture  un- 
even. Brittle.  H.  =  2'5-3;5.  G.  =  4'3-4'6.  Lus- 
ter vitreous,  inclining  to  resinous;  sometimes  pearly 
on  c  (001),  less  often  on  m  (110).  Streak  white. 
Color  white;  also  inclining  to  yellow,  gray,  blue,  red, 
or  brown,  dark  brown.  Transparent  to  translucent 
to  opaque.  Sometimes  fetid,  when  rubbed.  Opti- 
cally +.  Ax.  pi.  ||  6(010).  Bx  J_  a (100).  2V  = 
=  1-637.  7  =  1-648. 


Var.  —  Ordinary,  (a)  Crystals  usually  broad  or  stout;  sometimes  very  large;  again  in 
slender  needles.  (6)  Crested;  massive  aggregations  of  tabular  crystals,  the  crystals  project- 
ing at  surface  into  crest-like  forms,  (c)  Columnar;  the  columns  often  coarse  and  loosely 
aggregated,  and  either  radiated  or  parallel;  rarely  fine  fibrous,  (d)  In  globular  or  nodular 
concretions,  subfibrous  or  columnar  within.  Bologna  Stone  (from  near  Bologna)  is  here 
included;  it  was  early  a  source  of  wonder  because  of  the  phosphorescence  it  exhibited  after 
heating  with  charcoal.  "Bologna  phosphorus"  was  made  from  it.  (e)  Lamellar,  either 
straight  or  curved;  the  latter  sometimes  as  aggregations  of  curved  scale-like  plates. 
(/)  Granular,  (g)  Compact  or  cryptocrystalline.  (h)  Earthy,  (i)  Stalactitic  and  stalag- 
mitic;  similar  in  structure  and  origin  to  calcareous  stalactites  and  stalagmites  and  of  much 
beauty  when  polished,  (h)  Fetid;  so  called  from  the  odor  given  off  when  struck  or  when 
two  pieces  are  rubbed  together,  which  odor  may  be  due  to  carbonaceous  matters  present. 

The  barite  of  Muzsaj  and  of  Betler,  near  Rosenau,  Hungary,  was  early  called  Wolnyn. 
Cawk  is  the  ordinary  barite  of  the  Derbyshire  lead  mines.  Dreelite,  supposed  to  be  rhom- 
bohedral,  is  simply  barite.  Michel-levyte  from  Perkin's  Mill,  Templeton,  Quebec  (described 
as  monoclinic),  is  peculiar  in  its  pearly  luster  on  m,  twinning  striations,  etc. 

Comp.  —  Barium  sulphate,  BaSO4  =  Sulphur  trioxide  34'3,  baryta  657 
=  100. 

Strontium  sulphate  is  often  present,  also  calcium  sulphate;  further,  as  impurities,  silica, 
clay,  bituminous  or  carbonaceous  substances. 

Pyr,  etc.  —  B.B.  decrepitates  and  fuses  at  3,  coloring  the  flame  yellowish  green;   the, 
fused  mass  reacts  alkaline  with  test  paper.     On  charcoal-  reduced  to  a  sulphide.     With  soda 
gives  at  first  a  clear  pearl,  but  on  continued  blowing  yields  a  hepatic  mass,  which  spreads 
out  and  soaks  into  the  coal.     This  reacts  for  sulphur  (p.  340).     Insoluble  in  acids. 

DifE.  —  Characterized  by  high  specific  gravity  (higher  than  celestite,  aragonite,  albite, 
calcite,  gypsum,  etc.);  cleavage;  insolubility;  green  coloration  of  the  blowpipe  flame. 
Albite  is  harder  and  calcite  effervesces  with  acid. 

Obs.  —  Occurs  commonly  in  connection  with  beds  or  veins  of  metallic  ores,  especially  of 
lead,  also  copper,  silver,  cobalt,  manganese,  as  part  of  the  gangue  of  the  ore;  also  often 
accompanies  stibmte.  Sometimes  present  in  massive  forms  with  hematite  deposits.  It  is 
met  with  m  secondary  limestones  and  sandstones,  sometimes  forming  distinct  veins,  and  in 


SULPHATES,    CHROMATES,    ETC.  627 

the  former  often  in  crystals  along  with  calcite  and  celestite;  in  the  latter  often  with  coooer 
ores.  Sometimes  occupies  the  cavities  of  amygdaloidal  basalt,  porphyry,  etc  •  forms  earthv 
masses  in  beds  of  marl.  Occurs  as  the  petrifying  material  of  fossils  and  occupying  cavities 
in  them. 

Fine  crystals  are  obtained  in  England  at  the  Dufton  lead  mines,  Westmoreland-  also  in 
Cumberland  and  Lancashire;  in  Derbyshire,  Staffordshire,  etc.;  Cleator  Moor-'  Alston 
Moor.  In  Scotland,  in  Argyleshire,  at  Strontian,  Some  of  the  most  important  of  the 
many  European  localities  are  Felsobanya,  Nagybanya.  Schemnitz,  and  Kremnitz  in 
Hungary,  and Jlef eld,  often  with  stibnite;  Huttenberg,  Carinthia;  Freiberg,  Marienberg  in 
Saxony;  Claustal  in  the  Harz  Mts.;  Pribram,  Bohemia;  Auvergne,  France. 

In  the  United  States,  formerly  in  Conn.,  at  Cheshire^intersecting  the  red  sandstone  in 
veins  with  chalcocite  and  malachite.  In  N.  Y.,  at  Pillar  Point,  opposite  Sackett's  Harbor 
massive;  at  Scoharie,  fibrous;  in  St.  Lawrence  Co.,  crystals  at  DeKalb;  the  crested  variety 
at  Hammond.  In  Pa.,  in  crystals  at  Perkiomen  lea^mine.  In  Va.,  at  Eldridge's  gold 
mine  in  Buckingham  Co.  In  N.  C.,  white  ma^sw^aTCrowders  Mt.,  Gaston  Co.,  etc  In 
Tenn.,  on  Brown's  Creek;  at  Haysboro'  near  Nashville;  in  large  veins  in  sandstone  on 
the  west  end  of  Isle  Roy  ale,  Lake  Superior,  and  on  Spar  Island,  north  shore.  In  Mo. 
not  uncommon  with  the  lead  ores;  in  concretionary  forms  at  Salina,  Saline  Co.,  Kan  In 
Col.,  at  Sterling,  Weld  Co.;  Apishapa  Creek;  also  in  El  Paso  and  Fremont  Cos.  In  fine 
crystals,  near  Fort  Wallace,  N.  M.  Crystals  enclosing  quartz  sand,  "sand  barite,"  from 
Norman,  Oklahoma.  In  distorted  crystals  from  the  Bad  Islands,  S.  D. 

In  Ontario,  in  Bathurst,  and  North  Burgess,  Lanark  Co.;  Malway,  Peterborough  Co.' 
as  large  veins  on  Jarvis,  McKellars,  and  Pie  islands,  in  Lake  Superior,  and  near  Fort  William' 
Thunder  Bay.  In  Nova  Scotia,  in  veins  in  the  slates  of  East  River  of  the  Five  Islands) 
Colchester  Co. 

Named  from  papvs,  heavy. 

Use.  —  Source  of  barium  hydroxide  used  in  the  refining  of  sugar;  ground  and  used  as  a 
pigment,  to  give  weight  to  paper,  cloth,  etc. 

CELESTITE.     Coelestine. 

Orthorhombic.     Axes  a  :  b  :  c  =  07790  :  1  :  1-2800. 

1005  1006 


mm"',  110  A  110  =  75°  50'.  cd,  001  A  102  =  39°  24£'. 

d,          001  A  104  =  22°  20'.  co,  001  A  Oil  =  52°  0'. 

Crystals  resembling  those  of  barite  in  habit;  commonly  tabular  1 1  c  (001)  or 
prismatic  ||  axis  a  or  6;  also  more  rarely  pyramidal  by  the  prominence  of  the 
forms  \j/  (133)  or  x  (144).  Also  fibrous  and  radiated;  sometimes  globular; 
occasionally  granular. 

Cleavage:  c  (001)  perfect;  ra  (110)  nearly  perfect;  b  (010)  less  distinct. 
Fracture  uneven.  H.  =  3-3'5.  G.  =  3'95-3'97.  Luster  vitreous,  sometimes 
inclining  to  pearly.  Streak  white.  Color  white,  often  faint  bluish,  and  some- 
times reddish.  Transparent  to  subtranslucent.  Optically  +.  Ax.  pi.  ||  b  (010). 
Bx  _L  a  (100).  2V  =  51°.  a  =  1'622.  ft  =  1'624.  7  =  1'631. 

Var.  —  1.  Ordinary,  (a)  In  crystals  of  varied  habit  as  noted  above;  a  tinge  of  a  deli- 
cate blue  is  very  common  and  sometimes  belongs  to  only  a  part  of  a  crystal.  The  variety 
from  Montmartre,  near  Paris,  France,  called  apotome,  is  prismatic  by  extension  of  o  (Oil) 
and  doubly  terminated  by  the  pyramid  ^  (133).  (6)  Fibrous,  either  parallel  or  radiated. 
(c)  Lamellar;  of  rare  occurrence,  (d)  Granular,  (e)  Concretionary.  (/)  Earthy;  impure 
usually  with  carbonate  of  lime  or  clay. 


628 


DESCRIPTIVE   MINERALOGY 


Comp.  —  Strontium  sulphate,  SrSO4  =  Sulphur  trioxide  43'6,  stron- 
tia  56'4  =  100.  Calcium  and  barium  are  sometimes  present. 

Pyr.j  etc.  —  B.B.  frequently  decrepitates,  fuses  at  3  to  a  white  pearl,  coloring  the  flame 
strontia-red;  the  fused  mass  reacts  alkaline.  On  charcoal  fuses,  and  in  R.F.  is  converted 
into  a  difficultly  fusible  hepatic  mass;  this  treated  with  hydrochloric  acid  and  alcohol  gives 
an  intensely  red  flame.  With  soda  on  charcoal  reacts  like  barite.  Insoluble  in  acids. 

Diff.  — Characterized  by  form,'  cleavage,  high  specific  gravity,  red  coloration  of  the 
blowpipe  flame.  Does  not  effervesce  with  acids  like  the  carbonates  (e.g.,- strontianite); 
specific  gravity  lower  than  that  of  barite. 

Obs. — Usually  associated  with  limestone,  or  sandstone  of  various  ages;  occasionally 
with  metalliferous  ores,  as  with  galena  and  sphalerite  at  Condorcet,  France;  at  Rezbanya, 
Hungary;  also  in  beds  of  gypsum,  rock  salt,  as  at  Bex,  Switzerland;  Ischl,  Austria;  Liine- 
berg,  Hannover;  sometimes  fills  cavities  in  fossils,  e.g.,  ammonites;  with  sulphur  in  some 
volcanic  regions  as  at  Girgenti,  Sicily.  From  Yate,  Gloucester,  England. 

Specimens,  finely  crystallized,  of  a  bluish  tint,  are  found  in  limestone  about  Lake  Huron, 
particularly  on  Drummond  Island,  also  on  Strontian  Island,  Put-in-Bay,  Lake  Erie,  and 
at  Kingston  in  Ontario,  Canada;  Chaumont  Bay,  Lake  Ontario,  Schoharie,  and  Lockport, 
N.  Y.  From  near  Syracuse,  N.  Y.  A  blue  fibrous  celestite  occurs  at  Bell's  Mills,  Blair 
Co.,  Pa.  From  near  Cumberland,  Md.  In  Mineral  Co.,  W.  Va.,  a  few  miles  south  of  Cum- 
berland, Md.,  in  pyramidal  blue  crystals.  At  Tifflin,  Ohio.  In  Texas,  at  Lampasas,  large 
crystals.  With  colemanite  at  Death  Valley,  San  Bernardino  Co.,  Cal.  In  Canada,  in 
crystalline  masses  at  Kingston,  Frontenac  Co.;  Lansdowne,  Leeds  Co.;  in  radiating  fibrous 
masses  in  the  Laurentian  of  Renfrew  Co. 

Named  from  ccelestis,  celestial,  in  allusion  to  the  faint  shades  of  blue  often  present. 

Use.  —  Used  in  the  preparation  of  strontium  nitrate  for  fireworks;  other  salts  used  in 
the  refining  of  sugar, 

ANGLESITE. 
Orthorhombic.     Axes  a  :  b  :  c  =  07852  :  1  :  1*2894. 


1007 


1008 


1009 


d, 


110  A  110  =  76° 
001  A  104  =  22° 


16*'. 
19'. 


cd,  001  A  102  =  39°  23'. 
co,  001  A  Oil  =  52°  12'. 


n  Some1times  tabular  1 1  c  (001) ;  more  often  prismatic  in  habit,  and  in 

all  the  three  axial  directions,  m  (110),  d  (102),  o  (Oil),  predominating  in  the 

ifferent  cases;  pyramidal  of  varied  types.  Also  massive,  granular  to  com- 
pact;  stalactitic;  nodular. 

di.1  C1vJrageh  -Ctt^°\m  (1,1Sl  oisti?,ct'  but  interrupted.     Fracture  conchoi- 

&«  in  tny       6;  H'  =  ^t8-  -G;-=  6'3~6'39-  Luster  WBUy  adaman- 

tme :  in  some  specimens,  m  others  inclining  to  resinous  and  vitreous.     Color 
white,  tinged  yellow,  gray,  green,  and  sometimes  blue.     Streak  uncolored 
Transparent  to  opaque.     Optically +.     Ax.  pi.  ||  6  (010)      Bx      T  100) 
B^persion   strong,   P  <„.     2V  =  60°-75°.     a  =  1-877,    >  -1-882 L    T= 


SULPHATES,    CHROMATES,    ETC. 


629 


Comp.  —  Lead  sulphate,  PbSO4  =  Sulphur  trioxide  26*4,  lead  oxide  73*6 
=  100. 

Pyr.,  etc.  —  B.B.  decrepitates,  fuses  in  the  flame  of  a  candle  (F.  =  1*5).  On  charcoal 
in  O.F.  fuses  to  a  clear  pearl,  which  on  cooling  becomes  milk-white;  in  R.F.  is  reduced 
with  effervescence  to  metallic  lead.  With  soda  on  charcoal  in  R.F.  gives  metallic  lead, 
and  the  soda  is  absorbed  by  the  coal.  Difficultly  soluble  in  nitric  acid. 

Diff. —  Characterized  by  high  specific  gravity;  adamantine  luster;  cleavage;  and  by 
yielding  lead  B.B.  Cerussite  effervesces  in  nitric  acid. 

Obs.  —  A  result  of  the  decomposition  of  galena,  and  often  found  in  its  cavities;  also 
surrounds  a  nucleus  of  galena  in  concentric  layers.  First  found  in  England  at  Pary's  mine 
in  Anglesea;  in  Derbyshire  and  in  Cumberland  in  crystals;  at  Leadhill,  Scotland;  in  Ger- 
many at  Claustal,  in  the  Harz  Mts.;  near  Siegen  in  Prussia;  Schapbach  and  Badenweiler 
in  Baden;  in  Hungary  at  Felsobanya  and  elsewhere;  Nerchinsk,  Siberia;  and  at  Monte 
Poni,  Sardinia;  Granada  and  Andalusia,  Spain;  massive  in  Siberia;  in  Australia,  whence 
it  is  exported  to  England.  At  Broken  Hill,  New  South  Wales.  In  the  Sierra  Mojada, 
Mexico,  in  immense  quantities,  mostly  massive. 

In  the  United  States  in  crystals  at  Wheatley's  mine,  Phenixville,  Pa. ;  in  Missouri  lead 
mines;  in  crystals  of  varied  habit  at  the  Mountain  View  mine,  Carroll  Co.,  Md.  In  Col.  at 
various  points,  but  less  common  than  cerussite.  At  the  Cerro  Gordo  mines  of  Cal.  (argen- 
tiferous galena),  with  other  lead  minerals.  In  Ariz.,  in  the  mines  of  the  Castle'Dome  dis- 
trict, Yuma  Co.,  and  elsewhere.  In  fine  crystals  from  Kingston  and  Wardner,  Idaho; 
Eureka,  Utah. 

Named  from  the  locality,  Anglesea,  where  it  was  first  found. 

Use.  —  An  ore  of  lead. 

ANHYDRITE. 

Orthorhombic.     Axes  a  :  b  :  c  =  0'8933  :  1  :  1'OOOS. 

mm'",  110  A  1TO  =  83°  33'  ss',  Oil  A  Oil  =  90°    3' 

rr\        101  A  TOl  =  96°  30'  bo,   010  A  111  =  56°  19' 

Twins:  1,  tw.  pi.  d  (012);  2,  r  (101)  occasionally  as  tw.  lamellae.  Crystals 
not  common,  thick  tabular,  also 
prismatic  ||  axis  6.  Usually 
massive,  cleavable,  fibrous, 
lamellar,  granular,  and  some- 
times impalpable. 

Cleavage :  in  the  three  pinac- 
oidal  directions  yielding  rec- 
tangular fragments  but  with 
varying  ease,  thus,  c  (001)  very 
perfect;  b  (010)  also  perfect; 
a  (100)  somewhat  less  so. 
Fracture  uneven,  sometimes 
splintery.  Brittle.  H.  =  3-3' 5. 


1010 


1012 


1010,  1011,  'Stassfurt 


1012,  Aussee 
Luster:    c  pearly, 


_      G.  =  2-899-2-985. 

especially  after  heating  in  a  closed  tube;  a  somewhat  greasy;  6  vitreous;  in 
massive  varieties,  vitreous  inclining  to  pearly.  Color  white,  sometimes  a 
grayish,  bluish,  or  reddish  tinge;  also  brick-red.  Streak  grayish  white. 
Optically  +  .  Ax.  pi.  ||  b  (010).  Bx  J_  a  (100).  2V  =  42°.  a  =  1-571. 
(3  =  1-576.  7  =  1'614. 

Var.  —  1.  Ordinary,  (a)  Crystallized;  crystals  rare,  more  commonly  massive  and 
cleavable  in  its  three  rectangular  directions.  (6)  Fibrous;  either  parallel,  radiated  or 
plumose,  (c)  Fine  granular,  (d)  Scaly  granular.  Vulpinite  is  a  scaly  granular  kind  from 
Vulpino  in  Lombardy,  Italy;  it  is  cut  and  polished  for  ornamental  purposes.  A  kind  in 
contorted  concretionary  forms  is  the  tripestone. 

2.    Pseudomorphous;  in  cubes  after  rock-salt. 

Comp.  —  Anhydrous  calcium  sulphate,  CaS04  =  Sulphur  trioxide,  58'8, 
lime  41-2  =  100. 


630  DESCRIPTIVE   MINERALOGY 

Pyr.,  etc.  —  B.B.  fuses  at  3,  coloring  the  flame  reddish  yellow,  and  yielding  an  enamel- 
like  bead  which  reacts  alkaline.  On  charcoal  in  R.F.  reduced  to  a  sulphide;  with  soda 
does  not  fuse  to  a  clear  globule,  and  is  not  absorbed  by  the  coal  like  barite;  is,  however, 
decomposed,  and  yields  a  mass  which  blackens  silver.  Soluble  in  hydrochloric  acid. 

Diff.  —  Characterized  by  its  cleavage  in  three  rectangular  directions  (pseudo-cubic  in 
aspect);  harder  than  gypsum;  does  not  effervesce  with  acids  like  the  carbonates. 

Obs.  —  Occurs  in  rocks  of  various  ages,  especially  in  limestone  strata,  and  often  the  same 
that  contain  ordinary  gypsum,  and  also  very  commonly  in  beds  of  rock-salt;  at  the  salt 
mine  near  Hall  in  Tyrol,  Austria;  of  Bex,  Switzerland;  at  Aussee,  upper  Austria,  crystal- 
lized and  massive;  Liineburg,  Hannover,  Germany;  Kapnik  in  Hungary;  Wieliczka  in 
Poland;  Ischl  in  Upper  Austria;  Berchtesgaden  in  Bavaria;  Stassfurt,  Germany,  in  fine 
crystals,  embedded  in  kieserite;  in  cavities  in  lava  at  Santorin  Island. 

"  In  the  United  States,  at  Meriden,  Conn.;  at  Lockport,  N.  Y.,  fine  blue,  in  geodes  of 
black  limestone,  with  calcite  and  gypsum;  at  West  Paterson,  N.  J.;  in  limestone  at  Nash- 
ville, Tenn.,  etc.  In  the  salt  beds  of  central  Kansas.  In  Nova  Scotia  it  forms  extensive  beds. 

Anhydrite  by  absorption  of  moisture  changes  to  gypsum.  Extensive  beds  are  some- 
times thus  altered  in  part  or  throughout,  as  at  Bex,  in  Switzerland,  where,  by  digging  down 
60  to  100  ft.,  the  unaltered  anhydrite  may  be  found.  Sometimes  specimens  of  anhydrite 
are  altered  between  the  folia  or  over  the  exterior. 

Bassanite.  CaSO4.  In  white  opaque  crystals  having  form  of  gypsum  but.  composed 
of  slender  needles  in  parallel  arrangement.  These  show  parallel  extinction  and  positive 
elongation.  G.  =  2  '69-2  76.  Transformed  into  anhydrite  at  red  heat.  Found  in  blocks 
ejected  from  Vesuvius. 

Zinkosite.     ZnSO4.     Reported  as  occurring  at  a  mine  in  the  Sierra  Almagrera,  Spain. 

Hydrocyanite.  CuSO4.  Found  at  Vesuvius  as  a  pale  green  to  blue  incrustation  after 
the  eruption  of  1868. 

HOKUTOLITE.  A  mixture  in  variable  proportions  of  lead  and  barium  sulphates.  A 
radioactive  crystalline  crust  deposited  by  hot  springs  at  Hokuto,  Formosa. 

Millosevichite.  Normal  ferric  and  aluminium  sulphate.  As  a  violet  incrustation,  Alum 
Grotto,  Island  of  Vulcano,  Lipari  Islands. 

CROCOITE. 

Monoclinic.    Axes  a  :  b  :  c  =  0*9603  :  1  :  0*9159;  0  =  77°  33'. 
1n1Q  mm'",  110  A  1TO  =  86°  19'.  «',  111  A  111  =  60°  50'. 

ck,        001  A  101  =  49°  32'.  ct,   001  A  111  =  46°  58'. 

Crystals  usually  prismatic,  habit  varied.  Also  imperfectly 
columnar  and  granular. 

Cleavage:  m  (110)  rather  distinct;  c  (001),  a  (100)  less  so. 
Fracture  small  conchoidal  to  uneven.  Sectile.  H.  =  2*5-3.  G.  = 
5*9-6*1.  Luster  adamantine  to  vitreous.  Color  various  shades 
Of  bright  hyacinth-red.  Streak  orange-yellow.  Translucent. 
p  —  £  4<£. 

Comp.  —  Lead  chromate,  PbCrO4  =  Chromium  trioxide 
3rl,  lead  protoxide  68*9  =  100. 

With 


_ 

and  nea'r  NiT.rfH,*'         rTi  ^  ^tSVn  crystals  in  I™**  veins;  ali»  at  Mursinka 
Tn  HuSLrv  Molrf^   TT      Ura'  Mt?';  m  BraZl1'  at  ConS°^^  do  Campo;  at  Rezbanya 

infineCryStal8fr0m 

°^i^ 


SULPHATES,    CHROMATES,    ETC.  631 

Bellite.     Lead  chromate  containing  arsenious  oxide.     Hexagonal.  In  aggregates  of 

delicate  tuffs.     H.  =  2' 5.     G.  =  5'5.     Color   crimson  red,   yellow  to  orange.     Fusible. 
From  Magnet,  Tasmania. 


Sulphates  with  Chlorides,  Carbonates,  etc.  —  In  part  hydrous 
LEADHILLITE. 

Monoclinic.     Axes  a  :  b  :  c  =  17476  :  1  :  2'2154;  0  =  89°  48'. 

mm'",  110  A  110  =  120°  27'.  ex,    001  A  111  =  68°  31'. 

cw,        001  A  101  =    51°  36'.  cm,  001  A  110  =  89°  54'. 

Twins:  tw.  pi.  m  (110),  analogous  to  aragonite.  Crystals  commonly  tabu- 
lar ||  c  (001). 

Cleavage:  c  (001)  very  perfect;  a  (100)  in  traces.  Fracture  conchoidal, 
scarcely  observable.  Rather  sectile.  H.  =  2'5.  G.  =  6'26-6'44.  Luster  of 
c  pearly,  other  parts  resinous,  somewhat  adamantine.  Color  white,  passing 
into  yellow,  green,  or  gray.  Streak  uncolored.  Transparent  to  translucent. 
Optically  -.  0  =  1*93. 

Comp.  —  Sulphato-carbonate  of  lead,  4PbO.S03.2C02.H20  or  PbSO4. 
2PbCO3.Pb(OH)2  =  Sulphur  trioxide  7'4,  carbon  dioxide  8'2,  lead  oxide  827, 
water  17  =  100. 

Pyr.,  etc.  —  B.B.  intumesces,  fuses  at  1'5,  and  turns  yellow;  but  becomes  white  on 
cooling.  Easily  reduced  on  charcoal.  With  soda  affords  the  reaction  for  sulphuric  acid. 
Effervesces  briskly  in  nitric  acid,  and  leaves  white  lead  sulphate  undissolved.  Yields  water 
in  the  closed  tube. 

Obs.  —  Found  at  Leadhill,  Scotland,  with  other  ores  of  lead;  in  England  at  Red  Gill, 
Cumberland,  and  at  Matlock,  Derbyshire.  -From  the  Mala-Calzetta  lead  mine  near 
Iglesias,  Sardinia  (maxite).  Observed  from  Arizona,  at  the  Schulz  gold  mine  with  wul- 
fenite,  yanadinite,  cerussite;  partly  altered  to  cerussite.  From  Tintic  district,  Utah;  from 
Searchlight,  Nev.,  from  Granby,  Mo. 

SUSANNITE.  Regarded  at  one  time  as  rhombohedral  and  dimorphous  with  leadhillite, 
but  probably  only  a  modification  of  that  species.  From  the  Susanna  mine,  Leadhill,  in 
Scotland. 

Sulphohalite.  3Na2SO4NaCl.NaF.  In  pale  greenish  yellow  octahedrons  and  dodeca- 
hedrons, n  =  T455.  From  Borax  lake,  and  Searles  lake,  San  Bernardino  Co.,  Cal. 

Caracolite.  Perhaps  Pb(OH)Cl.Na2SO4.  As  a  crystalline  incrustation.  Colorless. 
From  Atacama,  Chile. 

Kainite.  MgSO4.KC1.3H2O.  Usually  granular  massive  and  in  crusts.  Color  white 
to  dark  flesh-red.  Optically  — .  0  =  1'509.  From  Stassfurt,  Germany,  and  Wolfenbrittel, 
Brunswick;  Kalusz,  Galicia. 

Connellite.  Probably  CuSO4.2CuCl2.19Cu(OH)2.H2O.  Crystals  slender,  hexagonal 
prisms.  Color  fine  blue.  Optically  +.  co  =  1724.  From  Cornwall,  England;  from 
Eureka,  Utah;  Bisbee,  Ariz.  Footeite,  originally  described  as  a  hydrous  oxy chloride  of 
copper  from  Bisbee,  Ariz.,  is  identical  with  connellite. 

Spangolite.  A  highly  basic  sulphate  of  aluminium  and  copper,  Cu6AlClSOio.9H2p.  In 
dark  green  hexagonal  crystals  (hemimorphic),  tabular  or  short  prismatic.  Usually  in  very 
small  crystals.  From  the  neighborhood  of  Tombstone,  Ariz.;  Clifton  and  Bisbee,  Ariz.; 
Tintic  district;  Utah;  from  Cornwall,  England;  Sardinia. 

Hanksite.  9Na2SO4.2Na2CO3.KCl.  In  hexagonal  prisms,  short  prismatic  to  tabular; 
also  in  quartzoids.  Color  white  to  yellow.  Optically—.  o>  =  T481.  From  Borax  Lake, 
San  Bernardino  Co.,  Cal.;  also  from  Death  Valley,  Inyo  Co 


B.   Acid  and  Basic  Sulphates 

Misenite.     Probably  acid  potassium  sulphate,  HKSO4.     In  silky  fibers  of  a  white  color. 
From  Cape  Misene,  near  Naples,  Italy. 


DESCRIPTIVE   MINERALOGY 

BROCHANTITE. 

Orthorhombic.     Axes  a  :  b  :  c  =  07739  :  1  :  0'4871.       _ 

In  groups  of  prismatic  acicular  crystals  (mm"'  110  A  110  =  75°  28')  and 
drusy  crusts;  massive  with  reniform  structure. 

Cleavage:  6(010)  very  perfect ;  m  (110)  in  traces.  Fracture  uneven.  H.= 
3'5-4.  G.  =  3'907.  Luster  vitreous;  a  little  pearly  on  the  cleavage-face 
6(101).  Color  emerald-green,  blackish  green.  Streak  paler  green.  Trans- 
parent to  translucent. 

Comp.  —  A  basic  sulphate  of.  copper,  CuSO4.3Cu(OH)2  or  4CuO.S03. 
3H2O  =  Sulphur  trioxide  17'7,  cupric  oxide  70'3,  water  12'0  =  100. 

Pyr.,  etc.  —  Yields  water,  and  at  a  higher  temperature  sulphuric  acid,  in  the  closed  tube, 
and  becomes  black.  B.B.  fuses,  and  on  charcoal  affords  metallic  copper.  With  soda  gives 
the  reaction  for  sulphuric  acid. 

Obs.  —  Occurs  in  the  Ural  Mts. ;  the  konigme  (or  komgite)  was  from  Gumeshevsk, 
Ural  Mts.;  in  England  near  Roughten  Gill,  in  Cumberland  and  in  Cornwall  (in  part  waring- 
tonite);  at  Rezbanya,  Hungary;  in  small  beds  at  Krisuvig  in  Iceland  (krisuvigite) ;  in 
Mexico  (brongnartine);  Atacama  and  Tarapaca,  Chile.  In  the  United  States,  at  Monarch 
mine,  Chaffee  Co.,  Col.;  in  Utah,  at  Frisco,  in  Tintic  district,  at  the  Mammoth  mine;  in 
Ch'fton-Morenci  district,  and  Bisbee,  Ariz. 

Lanarkite.  Basic  lead  sulphate,  Pb2SO6.  In  monoclinic  crystals.  Color  greenish 
white,  pale  yellow  or  gray.  From  Leadhill,  Scotland;  Siberia;  the  Harz  Mts.,  Germany. 

Dolerophanite.  A  basic  cupric  sulphate,  Cu2SOs(?).  In  small  brown  monoclinic 
crystals.  From  Vesuvius  (eruption  of  1868). 

Caledonite.  A  basic  sulphate  of  lead  and  copper,  perhaps  2(Pb,Cu)O.SO3.H2O.  Said 
at  times  to  contain  CO2.  In  small  prismatic  orthorhombic  crystals.  Color  deep  verdigris- 
green  or  bluish  green.  Index,  1'85.  From  Leadhill,  Scotland;  Red  Gill,  Cumberland, 
etc.,  England;  Inyo  Co.,  Cal.;  Organ  Mts.,  N.  M.;  Butte,  Mon.;  Atacama,  Chile;  New 
Caledonia. 

Linarite.  A  basic  sulphate  of  lead  and  copper,  (Pb,Cu)SO4.(Pb,Cu)(OH)2.  In  deep 
blue  monoclinic  crystals.  Optically  — .  0  =  T838.  From  Leadhill,  Scotland;  Cumber- 
land, England;  the  Ural  Mts.;  Broken  Hill,  New  South  Wales;  Sardinia.  Also  Inyo  Co., 
Cal.;  Eureka,  Utah;  Schiilz,  Ariz.;  Slocan,  British  Columbia. 

Antlerite.  Perhaps  CuSO4.2Cu(OH)2.  In  light  green  soft  lumps.  From  the  Antler 
mine,  Mohave  Co.,  Ariz.  Stelznerite  from  Remolinos,  Vallinar,  Chile,  is  probably  the  same 
as  antlerite.  In  prismatic  crystals.  G.  =  3 '9. 

Alumian.     Perhaps   A12O3.2SO3.     White    crystalline    or   massive.     Sierra    Almagrera, 


C.    Normal  Hydrous  Sulphates 

Three  well-characterized  groups  are  included  here.  Two  of  these,  the 
EPSOMITE  GROUP  and  the  MELANTERITE  GROUP,  have  the  same  general 
formula,  RS04.7H20,  but  in  the  first  the  crystallization  is  orthorhombic, 
in  the  second  monoclinic.  The  species  are  best  known  from  the  artificial 
crystals  of  the  laboratory;  the  native  minerals  are  rarely  crystallized.  There 
is  also  the  isometric  ALUM  GROUP,  to  which  the  same  remark  is  applicable. 


Lecontite.     (Na,NH4,K)2SO4.2H2O.     From  bat  guano  in  the  cave  of  Las  Piedras,  near 
Comayagua,  Central  America. 

MIRABILITE.    Glauber  Salt. 

Monoclinic.  Crystals  like  pyroxene  in  habit  and  angle.  Usually  in 
efflorescent  crusts. 

Cleavage:  a  (100),  perfect;  e  (001),  b  (010)  in  traces.  H.  =  I' 5-2.  G.  = 
1*481.  Luster  vitreous.  Color  white.  Transparent  to  opaque.  Taste  cool, 


SULPHATES,    CHROMATES,    ETC. 


633 


then  feebly  saline  and  bitter.     Optically  — .     2V  =  76°.     a  =  1-396     6  = 
T410.     7  =  1-419. 

Comp.  —  Hydrous  sodium  sulphate,  Na2SO4.10H2O  =  Sulphur  trioxide 
24'8,  soda  19'3,  water  55'9  =  100. 


Very 


Pyr.,  etc.  —  In  the  closed  tube  much  water;  gives  an  intense  yellow  to  the  flame, 
soluble  in  water.     Loses  its  water  on  exposure  to  dry  air  and  falls  to  powder. 

Obs.  —  Occurs  at  Ischl,  Hallstadt,  and  Aussee  in  Upper  Austria;  also  in  Hungary, 
Switzerland,  Italy;  at  the  hot  springs  at  Carlsbad,  Bohemia,  etc.  Large  quantities  of  this 
sodium  sulphate  are  obtained  from  the  waters  of  Great  Salt  Lake,  Utah. 

Kieserite.  MgSO4.H2O.  Monoclinic.  Usually  massive,  granular  to  compact.  Color 
white,  grayish,  yellowish.  Optically  +.  ft  =  1'535.  From  Stassfurt,  Germany;  Hall- 
stadt, Austria;  India. 

Szomolnokite.  FeSO4.H2O.  Monoclinic.  Isomorphous  with  kieserite.  In  pyramids. 
G.  =  3 '08.  Color  yellow  or  brown.  Found  with  other  iron  sulphates  from  Szomolnok, 
Hungary.  Apparently  identical  with  ferropallidite  from  near  Copiapo,  Chile. 

Szmikite.     MnSO4.H2O.     Stalactitic.     Whitish,  reddish.     From  Felsobdnya,  Hungary. 


GYPSUM. 
Monoclinic. 


mm' 

cd, 

ct, 

ce, 
vv', 

1014 


Axes  a  :  b  :  c  =  0'6899 

110  A  110  =  68°  30'. 
001  A  101  =  28°  17'. 
001  A  101  =  33°    8*'. 
001  A  103  =  11°  29'. 
Oil  A  Oil  =  44°  17|'. 


0-4124;  0  =  _80°  42'. 

«',  111  A  111  =  36°  12'. 
nn',  111  A  Til  =  41°  20'. 
ml,  110  A  111  =  49°  9'. 
mn,  110  A  111  =  59°  15'. 


1015 


1016 


1017 


1018 


Crystals  usually  simple  in  habit,  common  form  flattened  ||  6  (010)  or  pris- 
matic to  acicular  1 1  c  axis;  again  prismatic  by  extension  o{l  (111).  Also  lentic- 
ular by  rounding  of  I  (111)  and  e  (103).  The  form  e  (103),  whose  faces  are 
usually  rough  and  convex,  is  nearly  at  right  angles  to  the  vertical  axis  (edge 
m  (110)/w'"  (110),  hence  the  apparent  hemimorphic  character  of  the  twin 
(Fig.  1018).  Simple  crystals  often  with  warped  as  well  as  curved  surfaces. 
Also  foliated  massive;  lamellar-stellate;  often  granular  massive;  and  some- 
times nearly  impalpable.  Twins:  tw.  pi.  a  (100),  very  common,  often  the 
familiar  swallow-tail  twins. 

Cleavage:  6(010)  eminent,  yielding  easily  thin  polished  folia;  a  (100), 
giving  a  surface  with  conchoidal  fracture;  n(lll),  with  a  fibrous  fracture  || 
£(101);  a  cleavage  fragment  has  the  rhombic  form  of  Fig.  1019,  with  plane 
angles  of  66°  and  114°.  H.  =  l'5-2.  G.  =  2*3 14-2'328,  when  in  pure  crystals. 
Luster  of  b  (010)  pearly  and  shining,  other  faces  sub  vitreous.  Massive 
varieties  often  glistening,  sometimes  dull  earthy.  Color  usually  white;  some- 
times gray,  flesh-red,  honey-yellow,  ocher-yellow,  blue;  impure  varieties  often 
black,  brown,  red,  or  reddish  brown.  Streak  white.  Transparent  to  opaque. 


634 


DESCRIPTIVE   MINERALOGY 


Optically  +  .  Ax.  pi.  ||  6  (010),  and  Bx  A  c  axis  =  4 
(cf.  Fig.  1019).  Dispersion  p  >  v;  also  inclined  strong. 
30'.  2V  =  58°.  < 


1019 


•  52i°  (at  9*4°  C.), 
Bxr  A  Bxw  =  Q° 

1-520.      |8  =  1?523.     7  =  1-530.      On  the   effect  of 
heat  on  the  optical  properties,  see  p.  297. 

Var.  —  1.  Crystallized,  or  Selenite;  colorless,  transpar- 
ent; in  distinct  crystals,  or  broad  folia,  often  large.  Us- 
ually flexible  and  yielding  a  fibrous  fracture  ||  t  (101),  but 
the  variety  from  Montmartre  near  Paris,  France,  rather 
brittle. 

2.  Fibrous;   coarse  or  fine.     Called  Satin  spar,  when 
fine-fibrous,  with  pearly  opalescence. 

3.  Massive;  Alabaster,  a  fine-grained  variety,  white  or 
delicately  shaded;  earthy  or  rock-gypsum,  a   dull-colored 
rock,  often  impure  with  clay,  calcium  carbonate  or  silica. 

Also,  in  caves,  curious  curved  forms,  often  grouped  in 
rosettes  and  other  shapes. 

Comp.  —  Hydrous  calcium  sulphate, 
CaS04.2H2O  =  Sulphur  trioxide  46-6,  lime  32-5, 
water  20'9  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  gives  off  water  and  becomes  opaque.  Fuses  at  2 '5-3, 
coloring  the  flame  reddish  yellow.  For  other  reactions  see  ANHYDRITE,  p.  629.  Ignited 
at  a  temperature  not  exceeding  260°  C.,  it  again  combines  with  water  when  moistened,  and 
becomes  firmly  solid.  Soluble  in  hydrochloric  acid,  and  also  in  400  to  500  parts  of  water. 

Diff.  —  Characterized  by  its  softness  in  all  varieties,  and  by  cleavages  in  crystallized 
kinds;  it  does  not  effervesce  with  acids  like  calcite,  nor  gelatinize  like  the  zeolites;  harder 
than  talc  and  yields  much  water  in  the  closed  tube. 

Obs.  —  Gypsum  often  forms  extensive  beds  in  connection  with  various  stratified  rocks, 
especially  limestones,  and  marlites  or  clay  beds.  It  occurs  occasionally  in  crystalline 
rocks.  It  is  also  a  product  of  volcanoes,  occurring  about  fumaroles,  or  where  sulphur 
gases  are  escaping,  being  formed  from  the  sulphuric  acid  generated,  and  the  lime  afforded 
by  the  decomposing  lavas.  It  is  also  produced  by  the  decomposition  of  pyrite  when  lime 
is  present.  Gypsum  is  also  deposited  on  the  evaporation  of  sea-water  and  brines,  in  which 
it  exists  in  solution. 

Fine  specimens  are  found  in  the  salt  mines  of  Bex  in  Switzerland;  Hall  in  Tyrol,  Austria; 
the  sulphur  mines  of  Sicily;  in  the  clay  of  Shotover  Hill,  near  Oxford,  England;  and  large 
lenticular  crystals  at  Montmartre,  near  Paris,  France.  A  noted  locality  of  alabaster  occurs 
at  Castelino,  35  m.  from  Leghorn,  Italy,  whence  it  is  taken  to  Florence  for  the  manufacture 
of  vases,  figures,  etc. 

Occurs  in  extensive  beds  in  several  of  the  United  States,  and  more  particularly  N.  Y., 
Iowa,  Mich.,  Okla.,  Texas,  Ohio,  and  Ark.,  and  is  usually  associated  with  salt  springs,  also 
with  rock  salt.  Also  on  a  large  scale  in  Nova  Scotia,  etc. 

Handsome  selenite  and  snowy  gypsum  occur  in  N.  Y.,  near  Lockport  in  limestone. 
In  Md.,  large  grouped  crystals  on  the  St.  Mary's  in  clay.  In  Ohio,  large  transparent 
crystals  have  been  found  at  Ellsworth  and  Canfield,  Trumbull  Co.  In  Tenn.,  selenite  and 
alabaster  in  Davidson  Co.  In  Ky.,  in  Mammoth  Cave,  it  has  the  forms  of  rosettes,  or 
flowers,  vines,  and  shrubbery.  Also  common  in  isolated  crystals  and  masses,  in  the  Cre- 
taceous clays  in  the  western  United  States.  In  enormous  crystals,  several  feet  in  length,  in 
Wayne  Co.,  Utah.  In  Nova  Scotia,  in  Sussex,  Kings  Co.,  large  single  and  grouped  crystals, 
which  mostly  contain  much  symmetrically  disseminated  sand. 

Named  from  yy^os,  the  Greek  for  the  mineral,  but  more  especially  for  the  calcined 
mineral.  The  derivation'  ordinarily  suggested,  from  777,  earth,  and  tyeiv,  to  cook,  corre- 
sponds with  this,  the  most  common  use  of  the  word  among  the  Greeks. 

Burnt  gypsum  is  called  Plaster-of-Paris,  because  the  Montmartre  gypsum  quarries,  near 
Pans,  are,  and  have  long  been,  famous  for  affording  it. 

Use.  —  In  the  manufacture  of  plaster-of-Paris  used  for  molds  and  casts  and  as  "staff  " 
in  erection  of  temporary  buildings;  in  making  adamant  plaster  for  interior  use;  as  land 
plaster  for  fertilizer;  as  alabaster  for  ornamental  purposes. 

Hesite.  (Mn,Zn,Fe)SO4.4H2O.  In  loosely  adherent  aggregates.  Color  clear  green, 
from  Colorado. 


SULPHATES,    CHROMATES,    ETC.  635 

Epsomite  Group.     RS04.7H20.     Orthorhombic 

Epsomite  MgS04.7H2O  a  :  b  :  c  =  0-9902  :  1  :  0-5709 

(Fe,Mg)S04.7H20 
Goslarite  ZnSO4.7H2O  0-9807  :  1  : 0-5631 

Ferro-goslarite  (Zn,Fe)SO4.7H2O 

Morenosite  NiSO4.7H2O  0-9816  :  1  : 0-5655 

EPSOMITE.    Epsom  Salt. 

Orthorhombic.  Usually  in  botryoidal  masses  and  delicately  fibrous  crusts. 
Cleavage:  6  (010)  very  perfect.  Fracture  conchoidal.  H.  =  2-0-2-5.  G.  = 
=  1*751.  Luster  vitreous  to  earthy.  Streak  and  color  white.  Transparent 
to  translucent.  Taste  bitter  and  saline.  Optically  — .  2V  =  52°.  a  = 
1-433.  ft  =  1-455.  T  =  1-461. 

Comp.  —  Hydrous  magnesium  sulphate,  MgSO4.7H2O  =  Sulphur  triox- 
ide  32-5,  magnesia  16-3,  water  51-2  =  100. 

Obs.  —  Common  in  mineral  waters,  and  as  a  delicate  fibrous  or  capillary  efflorescence  on 
rocks,  in  the  galleries  of  mines,  and  elsewhere.  In  the  former  state  it  exists  at  Epsom, 
England,  and  at  Sedlitz  and  Saidschitz  (or  Saidschiitz)  in  Bohemia.  At  Idria  in  Carniola, 
Austria,  it  occurs  in  silky  fibers,  and  is  hence  called  hair  salt  by  the  workmen.  Also  ob- 
tained at  the  gypsum  quarries  of  Montmartre,  near  Paris.  Also  found  at  Vesuvius,  at 
the  eruptions  of  1850  and  1855. 

The  floors  of  the  limestone  caves  of  Kentucky,  Tennessee,  and  Indiana,  are  in  many 
instances  covered  with  epsomite,  in  minute  crystals,  mingled  with  the  earth.  In  the 
Mammoth  Cave,  Ky.,  it  adheres  to  the  roof  in  loose  masses  like  snowballs.  From  Laramie 
Basin,  Wy.;  near  Leona  Heights,  Alameda  Co.,  Cal.;  Cripple  Creek,  Col. 

Goslarite.  ZnSO4.7H2O.  Commonly  massive.  Color  white,  reddish,  yellowish. 
Optically  — .  0  =  1'480.  Formed  by  the  decomposition  of  sphalerite,  and  found  in  the 
passages  of  mines,  as  at  the  Rammelsberg  mine  near  Goslar,  in  the  Harz  Mts.,  Germany, 
etc.  In  Mon.  at  the  Gagnon  mine,  Butte.  Ferro-goslarite  (4*9  p.  c.  FeSO4)  occurs  with 
sphalerite  at  Webb  City,  Jasper  Co.,  Mo.  Cuprogoslarite  (13 '4  p.  c.  CuSO-j)  occurs  as  a 
light  greenish  blue  incrustation  on  the  wall  of  an  abandoned  zinc  mine  at  Galena,  Kan. 

Morenosite.  NiSO4.7H2O.  In  acicular  crystals;  also  fibrous,  as  an  efflorescence. 
Color  apple-green  to  greenish  white.  0  =  1  '489.  A  result  of  the  alteration  of  nickel  ores, 
as  near  Cape  Hortegal,  in  Galicia;  Riechelsdorf,  in  Hesse,  Germany;  Zermatt,  Switzerland, 
containing  magnesium. 

Melanterite  Group.     RS04.7H2O.     Monoclinic 

a  :  b  :  c 
Melanterite  FeSO4.7H20  1  -1828  :  1  :  1  -5427    ft  =  75°  44' 

Luckite  (Fe,Mn)SO4.7H2O 

Mallardite  MnSO4.7H2O 

Pisanite  (Fe,Cu)SO4.7H2O  1-1609  :  1  :  1-5110  74°  38' 

Bieberite  CoSO4.7H20  1-1815  :  1  :  1-5325  75°  20' 

Cupromagnesite  (Cu,Mg)SO4.7H2O 

Boothite  CuSO4.7H2O  1-1622  :  1  ;  1-500  74°  24' 

Chalcanthite  CuSO4.5H2O  Triclinic 

a  :  b  :  c  =  0-5656  :  1  :  0-5507;  a  =  82°  21',  ft  =  73°  11',  7  =  77°  37'. 

The  species  here  included  are  the  ordinary  vitriols.  They  are  identical  in 
general  formula  with  the  species  of  the  Epsomite  group,  and  are  regarded  as 
the  same  compound  essentially  under  oblique  crystallization.  The  copper 
sulphate,  chalcanthite,  diverges  from  the  others  in  crystallization,  and  con- 
tains but  5  molecules  of  water. 


636  DESCRIPTIVE   MINERALOGY 

MELANTERITE.    Copperas. 

Monoclinic.  Usually  capillary,  fibrous,  stalactitic,  and  concretionary; 
also  massive,  pulverulent.  Cleavage:  c  (001)  perfect;  m  (110)  less  so.  Frao- 
turernchoidal.  Brittle.  H.  =  2.  G.  =  1-89-1-90.  Luster  vitreous.  Color, 
various  shades  of -green,  passing  into  white;  becoming  yellowish  on  exposure. 
Streak  uncolored.  Subtransparent  to  translucent.  Taste  sweetish  astrin- 
gent, and  metallic.  Optically  +  .  2V  =  86°.  a  =  1-471.  ft  =  1-478.  7  = 

1  *486 

Comp  —  Hydrous  ferrous  sulphate,  FeSO4.7H2O  =  Sulphur  trioxide 
28-8,  iron  protoxide  25-9,  water  45*3  =  100.  Manganese  and  magnesium 
sometimes  replace  part  of  the  iron. 

Obs  Proceeds  from  the  decomposition  of  pyrite  or  marcasite;  thus  near  Goslar  in  the 
Harz  Mts  Germany;  Bodenmais  in  Bavaria;  Falun,  Sweden,  and  e sewhere.  Usually 
accompanies  pyrite  in  the  United  States,  as  an  efflorescence.  In  crystals  from  near  Leona 
Heights,  Alameda  Co.,  Cal.  Luckite  (1'9  p.  c.  MnO)  is  from  the  "Lucky  Boy  mine, 
Butterfield  Canon,  Utah. 

Mallardite.  MnSO4.7H2O.  Fibrous,  massive;  colorless.  From  the  mine  Lucky 
Boy,"  south  of  Salt  Lake,  Utah. 

Pisanite.  (Fe,Cu)SO4.7H2O.  CuO  10  to  15  p.  c.  In  concretionary  and  stalactitic 
forms.  Color  blue.  From  Turkey.  From  Bingham,  Utah;  Ducktown,  Tenn.«  near 
Leona  Heights,  Cal. 

SALVADORITE.  A  copper-iron  vitriol  near  pisanite.  From  the  Salvador  mine  Quetena, 
Chile. 

Bieberite.  CoSO4.7H2O.  Usually  in  stalactites  and  crusts.  Color  flesh-  and  rose-red. 
From  Bieber,  in  Hesse,  Germany,  etc. 

Boothite.  CuSO4.7H2O.  Usually  massive.  H.  =  2-2'5.  G.  =  1'94.  Color  blue, 
paler  than  chalcanthite.  Found  at  Alma  pyrite  mine,  near  Leona  Heights,  Alameda  Co., 
and  at  a  copper  mine  near  Campo  Seco,  Calaveras  Co.,  Cal. 

CUPROMAGNESITE.     (Cu,Mg)SO4.7H2O.     From  Vesuvius. 


CHALCANTHITE.    Blue  Vitriol. 

Triclinic.  Crystals  commonly  flattened  ||  p  (111).  Occurs  also  massive, 
stalactitic,  reniform,_sometimes  with  fibrous  structure. 

Cleavage:  M  (110),  m  (110),  p  (111)  imperfect.  Fracture  conchoidal. 
Brittle.  H.  =  2-5.  G.  =  212-2 -30.  Luster  vitreous.  Color  Berlin-blue 
to  sky-blue,  of  different  shades ;  sometimes  a  little  greenish.  Streak  uncolored. 
Subtransparent  to  translucent.  Taste  metallic  and  nauseous.  Optically  — . 
2V  =  56°.  a  =  1-516.  ft  =  1-539.  7  =  1'546. 

Comp.  —  Hydrous  cupric  sulphate,  CuSO4.5H20  =  Sulphur  trioxide 
32-1,  cupric  oxide  31-8,  water  361  =  100. 

Pyr.,  etc.  —  In  the  closed  tube  yields  water,  and  at  a  higher  temperature  sulphur  tri- 
oxide. B.B.  with  soda  on  charcoal  yields  metallic  copper.  With  the  fluxes  reacts  for 
copper.  Soluble  in  water;  a  drop  of  the  solution  placed  on  a  surface  of  iron  coats  it  with 
metallic  copper. 

Obs.  —  Found  in  waters  issuing  from  mines  and  in  connection  with  rocks  containing 
chalcopyrite,  by  the  alteration  of  which  it  is  formed;  thus  at  the  Rammelsberg  mine  near 
Goslar  in  the  Harz  Mts.,  Germany;  Falun  in  Sweden;  Parys  mine,  Anglesea,  England;  at 
various  mines  in  County  Wicklow,  Ireland;  Rio  Tinto  mine,  Spain;  Zajecar,  Servia.  From 
the  Hiwassee  copper  mine,  also  in  large  quantities  at  other  mines,  in  Polk  Co.,  Tenn.  In 
Ariz.,  near  Clifton,  Graham  Co.,  and  Jerome,  Yavapai  Co.;  in  Cal.  near  Leona  Heights, 
Alameda  Co.;  from  Ely  and  Reno,  Nev. 

Syngenite.  Kaluzite.  CaSO4.K2SO4.H2O.  In  prismatic  (monoclinic)  crystals.  Color- 
less or  milky-white.  0  =  1  '517.  From  Kalusz,  Galicia. 


SULPHATES.    CHROMATES,    ETC.  637 

Loweite.  MgSO4.Na2SO4.2|H2O.  Tetragonal.  Massive,  cleavable.  Color  pale  yel- 
low. Index,  1'49.  From  Ischl,  Austria. 

Blodite.  MgSO4.Na2SO4.4H2O.  Crystals  short  prismatic,  monoclinic;  also  massive 
granular  or  compact.  Colorless  to  greenish,  yellowish,  red.  Optically  — .  ft  =  1/488. 
From  the  salt  mines  of  Ischl  and  at  Hallstadt  (simonyite),  Austria;  at  Stassfurt,  Germany; 
the  salt  lakes  of  Astrakhan  (astrakanite),  Asia;  India;  Chile,  etc.  From  Soda  Lake,  San 
Luis  Obispo  Co.,  Cal 

Leonite.  MgSO4.K2SO4.4H2O.  In  monoclinic  crystals  from  Westeregeln  and  Leo- 
poldshall,  Germany.  0  =  1-487. 

Boussingaultite.  (NH4)2SO4.MgSO4.6H2O.  From  the  boric  acid  lagoons,  Tuscany. 
Italy.  Index,  1-474. 

Picromerite.  MgSO4.K2SO4.6H2.O.  As  a  white  crystalline  incrustation.  Monoclinic. 
Optically  +.  /3  =  1'463.  From  Vesuvius  with  cyanochroite,  an  isomorphous  species  in 
which  copper  replaces  the  magnesium.  Also  at  Stassfurt  (schoenite)  and  Aschersleben, 
Germany;  Galusz  in  East  Galicia. 

Polyhalite.  2CaSO4.MgSO4.K2SO4.2H2O.  Triclinic.  Usually  in  compact  fibrous  or 
lamellar  masses.  Color  flesh-  or  brick-red.  Optically  — .  ft  =  1'562.  Occurs  at  the 
mines  of  Ischl,  Hallstadt,  etc.,  in  Austria;  in  Germany  at  Berchtesgaden,  Bavaria; 
Stassfurt,  Prussia. 

Hexahydrite.  MgSO4.6H2O.  Columnar  to  fibrous  structure.  Cleavage  prismatic. 
G.  =  1"76.  Color,  white  with  light  green  tone.  Pearly  luster.  Opaque.  Salty,  bitter 
taste.  B.B.  exfoliates  and  yields  water  but  does  not  fuse.  Found  in  Lillooet  district, 
British  Columbia. 


Alum  Group.     Isometric 

RA1(SO4)2.12H2O  or  R2SO4.A12(SO4)3.24H2O. 

Kalinite  Potash  Alum  KA1(SO4)2.12H20 

Tschermigite  Ammonia  Alum  (NH4)A1(S04)2.12H2O 

Mendozite  Soda  Alum  NaAl(SO4)2.12H2O 

The  ALUMS  proper  are  isometric  in  crystallization  and,  chemically,  are 
hydrous  sulphates  of  aluminium  with  an  alkali  metal  and  12  (i.e.,  if  the  for- 
mula is  doubled,  24)  molecules  of  water.  The  species  listed  above  occur  very 
sparingly  in  nature,  and  are  best  known  in  artificial  form  in  the  laboratory. 

The  HALOTRICHITES  are  oblique  in  crystallization,  very  commonly  fibrous 
in  structure,  and  are  hydrous  sulphates  of  aluminium  with  magnesium,  man- 
ganese, etc. ;  the  amount  of  water  in  some  cases  is  given  as  22  molecules,  and  in 
others  24,  but  it  is  not  always  easy  to  decide  between  the  two.  Here  belong: 

Pickeringit«.     Magnesia  Alum.      MgSO4.Al2(SO4)3.22H2O.      In  long  fibrous  masses; 
and  in  efflorescences. 

Halotrichite.     Iron  Alum.    FeSO4.Al2(SO4)3.24H2O.     In  yellowish  silky  fibrous  forms. 
Index,  1.48. 

Bilinite.     FeSO4.Fe2(SO4)3.24H2O.    Radiating  fibrous.    Color  white  to  yellow.     From 
Schwaz,  near  Bilin,  Bohemia. 

Apjohnite.  Manganese  Alum.  MnSO4.Al2(SO4)3.24H2O.  Bushmanite  contains  MgO. 
In  fibrous  or  asbestiform  masses;  also  as  crusts  and  efflorescences. 

Dietrichite.     (Zn,Fe,Mn)SO4.Al2(SO4)3.22H2O. 


Coquimbite.  Fe2(SO4)3.9H2O.  Rhombohedral.  Granular  massive.  Color  white,  yel- 
lowish, brownish.  Optically  +.  «  =  1-550.  From  the  Tierra  Amarilla  near  Copiapo, 
Chile  (not  from  Coquimbo). 

Quenstedtite.  Fe2(SO4)3.10H2O.  In  reddish  tabular  crystals.  With  coquimbite, 
Chile. 


638  DESCRIPTIVE   MINERALOGY 

Ihleite.  Fe2(SO4)3.12H2O?  An  orange  yellow  efflorescence  on  graphite.  From  Mu- 
grau,  Bohemia.  Perhaps  identical  with  copiapite. 

Alunogen.  A12(SO4)3.18H2O.  Usually  in  delicate  fibrous  masses  or  crusts;  massive. 
Color  white,  or  tinged  with  yellow  or  red.  From  near  Bilm,  Bohemia;  Bodenmais,  Ger- 
many; Pusterthal,  Tyrol,  Austria;  from  Vesuvius;  Elba.  Fjom  Cripple  Creek,  Doughty 
Springs,  and  Alum  Gulch,  Col. 

DOUGHTYITE.  A  hydrated  aluminium  sulphate  deposited  by  the  alkaline  waters  of  the 
Doughty  Springs  in  Col. 

Krohnkite.  CuSO4.Na2SO4.2H2O.  Monoclinic  crystalline;  massive,  coarsely  fibrous. 
Color  azure-blue.  Optically  — .  /3  =  1'577.  From  Calama,  Atacama,  Chuquicamata, 
Autofagasta,  and  Collahurasi,  Tarapaca,  Chile. 

Natrochalcite.  Cu4(OH)2(SO4)2.Na2SO4.2H2O.  Monoclinic.  Habit  pyramidal.  Per- 
fect basal  cleavage.  H.  =  4 -5.  G.  =  2 '3.  Color  bright  emerald-green.  0  =  1-65. 
Found  at  Chuquicamata,  Autofagasta,  Chile. 

PHILLIPITE.  Perhaps  CuSO4.Fe2(SO4)3.nH2O.  In  blue  fibrous  masses.  Found  at  the 
copper  mines  in  the  Cordilleras  of  Condes,  province  of  Santiago,  Chile. 

Ferronatrite.  3Na2SO4.Fe2(SO4)3.6H2O.  Rhombohedral.  Rarely  in  acicular  crystals; 
usually  in  spherical  forms.  Color  greenish  or  gray  to  white.  Optically  +•  eo  =  1-558. 
From  Sierra  Gorda  near  Caracoles,  Chile. 

Romerite.  FeSO4.Fe2(SO4)3.14H2O.  In  tabular  triclinic  crystals;  granular,  massive. 
Color  chesnut-brown.  From  Goslar  in  the  Harz  Mts.,  Germany;  Persia;  Chile. 


Basic  Hydrous  Sulphates 

Langite.  Near  brochantite.  CuSO4.3Cu(OH)2.H2O.  Usually  in  fibre-lamellar,  con- 
cretionary crusts.  Color  blue  to  greenish  blue.  From  Cornwall. 

Herrengrundite.  2(CuOH)2SO4.Cu(OH)2.3H2O  with  one-fifth  of  the  copper  replaced 
by  calcium.  In  thin  tabular  monoclinic  crystals;  usually  in  spherical  groups.  Color 
emerald-green,  bluish  green.  From  Herrengrund,  Hungary. 

Vernadskite.  3CuSO4.Cu(OH)2.4H2O.  In  aggregates  of  minute  crystals.  H.  =  3'5. 
Occurs  as  an  alteration  of  dolerophanite  at  Vesuvius. 

Kamarezite.     A  hydrous  basic  copper  sulphate  from  Laurion,  Greece. 

Cyanotrichite.  Lettsomite.  Perhaps  4CuO.Al2O3.SO3.8H2O.  In  velvet-like  druses;  in 
spherical  forms.  Color  bright  blue.  From  Moldawa  in  the  Banat,  Hungary;  Cap  Ga- 
ronne, France.  In  Utah  and  Arizona. 

Serpierite.  A  basic  sulphate  of  copper  and  zinc.  In  minute  crystals,  tabular,  in  tufts. 
Color  bluish  green.  From  Laurion,  Greece. 

Beaverite.  CuO.PbO.Fe2O3.2SO3.4H2O.  Hexagonal  ?  In  microscopic  plates  Color 
canary-yellow.  Refractive  index  >  174.  From  Horn  Silver  mine,  Frisco,  Beaver  Co 
Utah. 

Vegasite.  PbO.3Fe2O3.3SO3.6H2O.  Hexagonal.  In  microscopic  fibrous  crystals  some- 
times showing  hexagonal  plates.  Optically  - .  Indices,  1 75-1  '82.  Found  in  Yellow  Pine 
district,  near  Las  Vegas,  Nev. 


COPIAPITE. 


Monoclinic.  Usually  in  loose  aggregations  of  crystalline  scales,  or  granular 
massive;  mcrusting. 

Cleavage:  b  (010)..  H.  =  2-5.  G.  =  2-103.  Luster  pearly.  Color  sul- 
phur-yellow, citron-yellow.  Translucent.  Optically  -.  a  =  1-527.  0  =' 

l'O4/.      y  =   1'572. 

Comp.—A  basic  ferric  sulphate,  perhaps  2Fe2O3.5SO3.18H2O  =  Sul- 
phur tnoxide  38  -3,  iron  sesquioxide  30-6,  water  31-1  =  100. 

•arSe^nrl  fnl^l  Wh/Ch  !l?S  been.83mew^t  vaguely  applied.     It  seems  to  belong  in 
t  here  and  in  part  also  to  other  related  species.     Janosite  is  identical  with  copiapit?. 


SULPHATES,    CHROMATES,    ETC.  639 

Pyr.,  etc.  —  Yields  water,  and  at  a  higher  temperature  sulphuric  acid.  On  charcoal 
becomes  magnetic,  and  with  soda  affords  the  reaction  for  sulphuric  acid.  With  the  fluxes 
reacts  for  iron.  Soluble  in  water,  and  decomposed  by  boiling  water. 

Obs.  —  The  original  copiapite  was  from  Copiapo,  Chile.  Also  from  Elba  and  from 
near  Leona  Heights,  Alameda  Co.,  Cal. 

Other  hydrated  ferric  sulphates: 

Castanite.-    Fe2O3.2SO3.8H2O.     Color  chestnut-brown.     From  Sierra  Gorda,  Chile. 
Utahite.     3Fe2O3.2SO3.7H2O.     In    aggregates    of    fine    scales.     Color    orange-yellow 
From  the  Tintic  district,  Utah;  Guanaco,  '  Taltal,  Chile.     Perhaps  identical  with  carpho- 

siderite. 

Amarantite.  Fe2O3.2SO3.7H2O.  Triclinic.  Usually  in  columnar  or  bladed  masses,  also 
radiated.  Color  amaranth-red.  From  near  Caracoles,  Chile.  Hohmannite  is  the  same 
partially  altered;  this  is  probably  also  true  of  paposite. 


Fibroferrite.  Fe^Os^SO-j-lOHaO.  Orthorhombic.  In  delicately  fibrous  aggregates. 
Color  pale  yellow,  nearly  white.  From  the  Tierra  Amarilla  near  Copiapo,  Chile. 

Raimondite.  2Fe2O3.3SO3.7H2O.  In  thin  six-sided  tables.  Color  between  honey-  arid 
ocher-yellow.  From  the  tin  mines  of  Ehrenfriedersdorf  ;  mines  of  Bolivia.  Perhaps  iden- 
tical with  carphosiderite. 

Carphosiderite.  3Fe2O3.4SO3.7H2O.  In  reniform  masses,  and  incrustations;  also  in 
micaceous  lamellae.  Color  straw-yellow.  From  Greenland.  Utahite,  apatelite,  raimon- 
dite  and  cyprusite  are  probably  identical  with  carphosiderite. 

Planoferrite.  Fe2O3.SO3.15H2O.  Orthorhombic?  In  rhombic  or  hexagonal  plates. 
Yellowish  green  to  brown.  From  near  Morro  Moreno,  Autofagasta,  Chile. 

Glockerite.  2Fe2O3.SO3.6H2O.  Massive,  sparry  or  earthy;  stalactitic.  Color  brown 
to  ocher-yellow  to  pitch-black;  dull  green.  From  Goslar,  Harz  Mts.,  Germany. 

Knoxvillite.  A  hydrous  basic  sulphate  of  chromium,  ferric  iron,  and  aluminium.  In 
rhombic  plates.  Color  greenish  yellow.  From  the  Redington  mercury  mine,  Knoxville, 
Cal. 

REDINGTONITE.  A  hydrous  chromium  sulphate,  in  finely  fibrous  masses  of  a  pale 
purple  color.  From  Redington  mercury  mine,  Knoxville,  Cal. 

Cyprusite.  Perhaps  7Fe2O3.Al2O3.10SO3.14H2O.  An  aggregation  of  microscopic 
crystals.  Color  yellowish.  From  the  island  of  Cyprus.  Perhaps  identical  with  carpho- 
siderite. 

Aluminite  (  Websterite)  .  A12O3.SO3.9H2O.  Usually  in  white  earthy  reniform  masses, 
compact.  Index,  1'48.  From  near  Halle,  Germany,  in  clay;  also  at  Newhaven,  Sussex, 
England,  and  elsewhere. 

Paraluminite.     Near  aluminite,  but  supposed  to  be  2A12O3.SO3.15H2O. 

Felsobanyite.  2A12O3.SO3.10H2O.  Massive;  in  scaly  concretions.  Color  snow-white. 
From  near  Felsobanya,  Hungary. 

Botryogen.  Perhaps  MgO.FeO.Fe2O3.4SO3.18H2O.  Monoclinic.  Usually  in  reniform 
and  botryoidal  shapes.  Color  deep  hyacinth-red,  ocher-yellow.  13  =  1*548.  From  Falun, 
Sweden;  also  from  Persia;  from  Lake  and  Napa  Cos.,  Cal. 

Sideronatrite.  2Na2O.Fe2O3.4SO3.7H2O.  Fibrous,  massive.  Color  yellow.  From  the 
province  of  Tarapaca,  Chile.  Also  on  the  Urus  plateau,  near  Sarakaya,  on  the  island, 
Cheleken,  in  the  Caspian  Sea  (urusite). 

Voltaite.  Perhaps  3(K2,Fe)O.2(Al,Fe)2O3.6SO3.9H2O.  In  octahedrons,  etc.  Color 
dull  oil-green  to  brown  or  black.  From  the  solfatara  near  Naples;  Schmolnitz,  Hungary; 
also  Persia. 

Metavoltine.  Perhaps  5(K2,Na2,Fe)O.3Fe2O3.12SO3.18H2O.  In  aggregates  of  minute 
yellow  scales.  Occurs  with  voltaite  in  Persia.  From  Vesuvius;  found  in  fumeroles  on 
islands  of  Milo  and  Vulcano;  from  Miseno,  Italy. 

ALUNITE.     Alumstone. 

Rhombohedral.  Axis  c  =  1-2520.  In  rhombohedrons,  resembling  cubes 
(rr'  1011  A  1101  =  90°  50').  Also  massive,  having  a  fibrous,  granular,  or 
impalpable  texture. 


640  DESCRIPTIVE    MINERALOGY 

Cleavage:  c  (0001)  distinct;  r  (lOll)  in  traces.  Fracture  flat  conchoidal, 
uneven;  of  massive  varieties  splintery;  and  sometimes  earthy.  Brittle.  H.  = 
3-5-4.  G.  =  2-58-2:752.  Luster  of  r  vitreous,  basal  plane  somewhat  pearly. 
Color  white,  sometimes  grayish  or  reddish.  Streak  white.  Transparent  to 
subtranslucent.  Optically  +  .  co  =  1-572.  e  =  1'592. 

Comp.  —  Basic  hydrous  sulphate  of  aluminium  and  potassium,  K2A16 
(OH)i2(SO4)4  =  Sulphur  trioxide  38'6,  alumina  37'0,  potash  11-4,  water  13  -0  = 
100.  Sometimes  contains  considerable  soda,  natroalunite. 

Pyr.,  etc.  —  B.B.  decrepitates,  and  is  infusible.  In  the  closed  tube  yields  water,  some- 
times also  ammonium  sulphate,  and  at  a  higher  temperature  sulphurous  and  sulphuric 
oxides.  Heated  with  cobalt  solution  affords  a  fine  blue  color.  With  soda  and  charcoal 
infusible,  but  yields  a  hepatic  mass.  Soluble  in  sulphuric  acid. 

Obs.  —  Forms  seams  in  trachytic  and  allied  rocks,  where  it  has  been  formed  as  a  result 
of  the  alteration  of  the  rock  by  means  of  sulphurous  vapors;  as  at  Tolfa,  near  Civitavecchia, 
Italy;  in  Hungary;  on  Milo,  Grecian  Archipelago;  at  Mt.  Dore,  France;  Kinkwaseki, 
Formosa.  In  the  United  States,  associated  with  diaspore,  in  rhombohedral  crystals,  tabu- 
lar through  the  presence  of  c  (0001)  at  the  Rosita  Hills,  Custer  Co.,  and  from  Red  Mt.,  Col.; 
Marysvale,  Utah;  Goldfield  and  near  Sulphur,  Nev. 

JAROSITE. 

_Rhombohedral.  Axis  c  =  1-2492;  rr'  lOll  A  TlOl  =  90°  45',  cr  0001  A 
1011  =  55°  16'.  Often  in  druses  of  minute  crystals;  also  fibrous,  granular 
massive;  in  nodules,  or  as  an  incrustation. 

Cleavage:  c  (0001)  distinct.  Fracture  uneven.  Brittle.  H.  =  2-5-3-5. 
G.  =  3-15-3-26.  Luster  vitreous  to  subadamantine  :  brilliant,  also  dull. 
Color  ocher-yellow,  yellowish  brown,  clove-brown.  Streak  yellow,  shining. 
Optically  +.  co  =  1-74.  e  =  177. 

Comp.  —  K2Fe6(OH)i2(SO4)4  =  Sulphur  trioxide  31*9,  iron  sesquixoide 
47-9,  potash  9-4,  water  10'8  =  100. 

Obs.  —  The  original  Gelbeisenerz  was  from  Luschitz,  between  Kolosoruk  and  Bilin, 
Bohemia,  in  brown  coal;  and  later  from  Modum,  Norway,  in  alum  slate.  The  jarosite  was 
from  Barranco  Jaroso,  in  the  Sierra  Almagrera,  Spain;  Schlaggenwald,  Bohemia;  Elba; 
Chocaya,  Potosi,  Bolivia.  In  the  United  States  on  quartz  in  the  Vulture  mine,  Ariz.;  in 
Chaffee  County,  Col.;  Tintic  district,  Utah;  Lawrence  Co.,  S.  D.;  Dona  Ana  Co.  N.  M  • 
Bisbee,  Ariz.;  Brewster  Co.,  Texas. 

^    Natrojarosite.     Na*Fe6(OH)12(SO4)4.     Rhombohedral.     In    minute    tabular    crvstals. 
Color  yellow-brown.     From  Soda  Springs  Valley,  Esmeralda  Co.,  Nev. 

Plumbojarosite.  PbFe6(OH)12(SO4)4.  Rhombohedral.  In  minute  tabular  crystals. 
Color  dark  brown.  From  Cook's  Peak,  N.  M.,  and  in  Beaver  County,  Utah. 

Palmierite.  3(K,Na)2SO4.4PbSO4?  In  microscopic  plates,  often  hexagonal  in  outline. 
Colorless.  Fusible.  Found  in  fumerole  deposits  at  Vesuvius. 

K20.3A1203.4SO  9H20.     In  rounded  masses,  similar  to  compact 


N^S°4-Al2(S°4)3-5A1(OH)3.H20.       Compact.      White.      From  Almeria, 

From^m^6*     ?erihapS  6?a9-A1^3.3S03.33H20.     In  minute  colorless  acicular  crystals. 
From  limestone-inclusions  m  lava,  near  Mayen,  Rhenish  Prussia;   Tombstone,  An/ 


of 


TUNGSTATES,    MOLYBDATES 


641 


canary-yellow.     H.  =2.     G.  >  3 '3.     Indices,   1  '57-1  -61.     Infusible.     Readily  soluble  in 
acids.     From  Gilpin  Co.,  Col. 

Uranopilite.  Perhaps  CaUgSaOai^SH^O.  In  velvety  incrustations;  yellow.  From 
Johanngeorgenstadt,  Germany. 

Zippeite,  voglianite,  uraconite  are  uncertain  uranium  sulphates,  from  Joachimstal, 
Bohemia. 

Minasragrite.  An  acid  hydrous  vanadyl  sulphate  (V2O2)H2(SO4)».15HjO.  Probably 
monoclinic.  In  granular  aggregates,  small  mammillary  masses,  or  in  spherulites.  Two 
cleavages.  Color  blue.  Indices  1-5 1-1 '54.  Strongly  pleochroic,  deep  blue  to  colorless. 
Easily  fusible.  Soluble  in  cold  water.  Found  as  an  efflorescence  on  patronite  from  Minas- 
ragra,  Peru. 

Rhomboclase.  A  hydrated  acid  ferric  sulphate.  Fe2O3.4SO3.9H2O.  In  rhombic  plates. 
Basal  cleavage.  Colorless.  Occurs  at  Szomolnok,  Hungary. 


Tellurates;  also  Tellurites,  Selenites 

In  earthy  incrustations;    yellowish  to  white.     From 


Montanite. 
Highland,  Mon.,  with  tetradymite. 

Emmonsite.  Probably  a  hydrated  ferric  tellurite.  In  thin  yellow-green  scales.  From 
near  Tombstone,  Ariz. 

Durdenite.  Hydrous  ferric  tellurite,  Fe2(TeOs)3.4H2O.  In  small  mammillary  forms; 
greenish  yellow.  Honduras. 

Chalcomenite.  Hydrous  cupric  selenite,  CuSeO3.2H2O.  In  small  blue  monoclinic 
crystals.  From  the  Cerro  de  Cacheuta,  Argentina,  with  silver,  copper  selenides. 

MOLYBDOMENITE  is  lead  selenite  and  COBALTOMENITE  probably  cobalt  selenite,  from 
the  same  locality  as  chalcomenite. 

Oxygen  Salts 
7.   TUNGSTATES,   MOLYBDATES 

The  monoclinic  Wolframite  Group  and  the  tetragonal  Scheelite  Group  are 
included  here. 

Wolframite  Group 

Wolframite         (Fe,Mn)WO4    a  :  b  :  c  =  0-8300  :  1  :  0-8678 
Hiibnerite  MnWO4  0-8362  :  1  :  0-8668 


89° 
89° 


22' 


WOLFRAMITE. 

Monoclimc.     Axes   a  : 

mm'",  110  A  110  =  79°  23'. 
at,    100  A  102  =  61°  54'. 


c  =  0-8300  :  1   :  0-8678; 
ay',  100  A  102  =  62°  54' 
ff',    Oil  A  Oil  =  81°  54'. 


89°    22' 
1020 


Twins:  (1)  tw.  axis  c  with  a  (100)  as  comp.-face;  (2) 
tw.  pi.  k  (023),  Fig.  449,  p.  171.  Crystals  commonly 
tabular  ||  a  (100);  also  prismatic.  Faces  in  prismatic 
zone  vertically  striated.  Often  bladed,  lamellar,  coarse 
divergent  columnar,  granular. 

Cleavage:  b  (010)  very  perfect;  also  parting  || 
a  (100),  and  ||  t  (102).  Fracture  uneven.  Brittle.  H.  = 
5-5-5.  G.  =  7-2-7-5.  Luster  submetallic.  Color  dark 
grayish  or  brownish  black.  Streak  nearly  black.  Opaque, 
magnetic.  0  =  1*93. 


Sometimes  weakly 


642 


DESCRIPTIVE   MINERALOGY 


Comp.  —  Tungstate  of  iron  and  manganese  (Fe,Mn)W04.  Fe  :  Mn  = 
chiefly  4  :  1  (FeO  18-9,  MnO  47  p.  c.)  and  2  :  3  (FeO  9'5,  MnO  14-0). 

Pyr.,  etc.  —  Fuses  B.B.  easily  (F.  =  2-5-3)  to  a  globule,  which  has  a  crystalline  surface 
and  is  magnetic.  With  salt  of  phosphorus  gives  a  clear  reddish  yellow  glass  while  hot 
which  is  paler  on  cooling;  in  R.F.  becomes  dark  red;  on  charcoal  with  tin,  if  not  too  satu- 
rated, the  bead  assumes  on  cooling  a  green  color,  which  continued  treatment  in  R.F.  changes 
to  reddish  yellow.  With  soda  and  niter  on  platinum  foil  fuses  to  a  bluish  green  manganate. 
Decomposed  by  aqua  regia  with  separation  of  tungstic  acid  as  a  yellow  powder.  Suffi- 
ciently decomposed  by  concentrated  sulphuric  acid,  or  even  hydrochloric  acid,  to  give  a 
colorless  solution,  which,  treated  with  metallic  zinc,  becomes  intensely  blue,  but  soon 
bleaches  on  dilution. 

Obs.  —  Wolframite  is  often  associated  with  tin  ores;  also  in  quartz,  with  native  bismuth, 
scheelite,  pyrite,  galena,  sphalerite,  etc.  In  Bohemia  in  fine  crystals  at  Schlackenwald, 
Zinnwald,  Bohemia;  in  Germany  at  Schneeberg,  Freiberg,  Altenberg,  Neudorf;  at  Ner- 
chinsk, Siberia;  Chanteloup,  near  Limoges,  France;  near  Redruth  and  elsewhere  in  Corn- 
wall with  tin  ores.  From  Sardinia;  Greenland;  Central  Provinces,  India.  In  South 
America,  at  Oruro  in  Bolivia.  With  tin  stone  at  various  points  in  New  South  Wales. 

In  the  United  States  at  Lane's  mine,  Monroe,  Conn.;  Flowe  mine,  Mecklenburg  Co., 
N.  C.,  with  scheelite;  in  Mo.,  near  Mine  la  Motte;  Laurence  Co.,  S.  D.;  Boulder  Co.] 
Col.;  Ariz. 

Use.  —  An  ore  of  tungsten. 

Hiibnerite.  Near  wolframite,  but  containing  20  to  25  p.  c.  MnO.  Usually  in  bladed 
forms,  rarely  in  distinct  terminated  crystals.  Color  brownish  red  to  hair-brown  to  nearly 
black.  Streak  yellowish  brown,  greenish  gray.  Often  translucent,  ft  =  2 '24.  Mammoth 
district,  Nev.;  Ouray  County,  Col.,  and  near  Silyerton,  San  Juan  Co.;  Black  Hills,  S.  D.; 
Dragoon,  Ariz.  Also  in  Peru,  and  in  rhodochrosite  at  Adervielle  in  the  Pyrenees. 


Scheelite 
Cuprotungstite 

Cuproscheelite 
Powellite 
Stolzite 
Wulfenite 


Scheelite  Group.  Tetragonal-pyramidal 

CaW04  pp'  (111  A  111)  =  79°  55J'     c  =  1-5360 

CuWO4 

(Ca,Cu)W04 

Ca(Mo,W)04  80°     1'      c  =  1-5445 

PbW04  80°  15'      c  =  T5667 

PbMo04  80°  22'      c  =  1-5771 


The  SCHEELITE  GROUP  includes  the  tungstates  and  molybdates  of  calcium 
and  lead;  also  copper.     In  crystallization  they  belong  to  the  Pyramidal  class 
of  the  Tetragonal  System.     Wulfenite  is  probably  hemimorphic. 
SCHEELITE. 
Tetragonal-pyramidal.     Axis  c  =  1-5356. 

ee',  101  A  Oil  =  72°  40*'.  pp',  111  A  ill  =  79°  55*' 

cp,    001  A  111  =  65°  16|'. 


ce,    001  A  101  =  56°  56'. 


1021 


1022 


1023 


1024 


Forms:    0  (102),    e  (101).    ft  (113),    p  (111),     k  (515),    ft  (313),    ,,(131) 


TUNGSTATES,  MOLYBDATES  643 

Twins:  (1)  tw.  pi.  a  (100),  both  contact-  and  penetration-twins  (Fig.  416, 
p.  167).  Habit  octahedral,  also  tabular.  Symmetry  shown  by  faces  k,  h,  s 
(Fig.  1023).  Also  reniform  with  columnar  structure;  massive  granular. 

Cleavage:  p  (111)  most  distinct;  e  (101)  interrupted.  Fracture  uneven. 
Brittle.  H.  =  4-5-5.  G.  =  5-9-6-1.  Luster  vitreous,  inclining  to  adaman- 
tine. Color  white,  yellowish  white,  pale  yellow,  brownish,  greenish,  reddish. 
Streak  white.  Transparent  to  translucent.  Optically  -f.  Indices:  w  = 
1-918.  e  =  1-934. 

Comp.  —  Calcium  tungstate,  CaWO4  =  Tungsten  trioxide  80-6,  lime 
19-4  =  100. 

Molybdenum  is  usually  present  (to  8  p.  c.).  Copper  may  replace  calcium,  see  cupro- 
scheelite. 

Pyr.,  etc.  —  B.B.  in  the  forceps  fuses  at  5  to  a  semi-transparent  glass.  Soluble  with 
borax  to  a  transparent  glass,  which  afterward  becomes  opaque  and  crystalline.  With  salt 
of  phosphorus  forms  a  glass,  colorless  in  outer  flame,  in  inner  green  when  hot,  and  fine 
blue  when  cold;  varieties  containing  iron  require  to  be  treated  on  charcoal  with  tin  before 
the  blue  color  appears.  In  hydrochloric  or  nitric  acid  decomposed,  leaving  a  yellow  powder 
soluble  in  ammonia.  The  hydrochloric  acid  solution  treated  with  tin  and  boiled  assumes 
a  blue  color,  later  changing  to  brown. 

Obs.  —  Scheelite  is  usually  associated  with  crystalline  rocks,  and  is  commonly  found  in 
connection  with  cassiterite,  topaz,  fluorite,  apatite,  molybdenite,  or  wolframite,  in  quartz; 
also  associated  with  gold.  Thus  at  Schlackenwald  and  Zinnwald,  Bohemia;  Altenberg, 
Saxony;  Riesengrund  in  the  Riesengebirge,  Germany;  the  Knappenwand  in  the  Unter- 
sulzbachtal,  Tyrol,  Austria;  Carrock  Fells  in  Cumberland,  England;  Traversella  in  Pied- 
mont, Italy;  Meymac,  Correze,  France  (containing  Ta2O5);  Sweden;  Pitkaranta  in  Fin- 
land. In  New  South  Wales,  at  Adelong,  from  a  gold  mine;  New  Zealand,  massive;  Mt. 
Ramsay,  Tasmania,  with  cassiterite.  From  Sonora,  Mexico. 

In  the  United  States,  at  Lane's  Mine,  Monroe,  and  at  Trumbull,  Conn.;  Flowe  mine, 
Mecklenburg  Co.,  N.  C.;  the  Mammoth  mining  district,  Nev.;  with  gold  at  the  Charity 
mine,  Warren's,  Idaho;  Lake  Co.,  Col.;  Atolia  mining  field,  Cal.;  White  Pine  Co.,  Nev.; 
Dragoon,  Ariz.  In  quartz  veins  in  Risborough  and  Marlow,  Beauce  county,  Quebec. 

Use.  —  An  ore  of  tungsten. 

Cuprotungstite.  Cupric  tungstate,  CuWO4.  From  the  copper  mines  of  Llamuco,  near 
Santiago,  Chile.  CUPROSCHEELITE,  from  the  vicinity  of  La  Paz,  Lower  California,  is 
(Ca,Cu)WO4,  with  6'8  p.  c.  CuO;  color  green.  From  Montoro,  Spain;  from  Yeoral,  New 
South  Wales. 

Powellite.  Calciuni  molybdate  with  calcium  tungstate  (10  p.  c.  WO3),  Ca(Mo,W)O4. 
In  minute  yellow  tetragonal  pyramids.  G.  =  4'349.  w  =  2 '00.  From  western  Idaho; 
Houghton  Co.,  Mich.;  from  Llano  Co.,  Texas,  and  Nye  Co.,  Nev. 

Stolzite.  Lead  tungstate,  PbWO4.  In  pyramidal  tetragonal  crystals.  H.  =  2-75-3. 
G.  =  7-87-8-13.  Color  green  to  gray  or  brown.  Optically  -.  <o  =  2'269.  Zinnwald, 
Bohemia;  Sardinia;  Minas  Geraes,  Brazil;  Broken  Hill,  New  South  Wales.  From  Loud- 
ville,  Mass. 

Raspite.  Has  the  same  composition  as  stolzite,  but  is  referred  to  the  monoclinic 
system.  In  small  tabular  crystals.  Color  brownish  yellow.  Index,  2*60.  From  the 
Broken  Hill  mines,  New  South  Wales;.  Minas  Geraes,  Brazil. 

Chillagite.  3PbWO4.PbMoO4.  In  tabular  tetragonal  crystals,  apparently  hemimorphic. 
Color  yellow  to  brownish.  H.  =  3 -5.  G.  =  7'5.  From  Chillagoe,  Queensland. 

WULFENITE. 

Tetragonal-pyramidal;  hemimorphic.  Axis  c  =  1-5771. 

cu,  001  A  102  =  38°  15'.  uu',  102  A  012  =  51°  56'. 

ce,   001  A  101  =  57°  37'.  ee',    101  A  Oil  =  73°  20'. 

en,  001  A  111  =  65°  51'.  nn't  111  A  Til  =  80°  22'. 

Crystals  commonly  square  tabular,  sometimes  extremely  thin;  less  fre- 
quently octahedral;  also  prismatic.  Hemimorphism  sometimes  distinct. 
Also  granularly  massive,  coarse  or  fine,  firmly  cohesive. 


644 


DESCRIPTIVE   MINERALOGY 


Cleavage-  n  (111)  very  smooth;  c  (001),  s  (113)  less  distinct.  Fracture 
subconchoidal.  Brittle.  H.  =  275-3.  G.  =  67-7-0.  Luster  resinous  or 
adamantine.  Color  wax-  to  orange-yellow,  siskin-  and  olive-green,  yellowish 


1028 


1027 


gray,  grayish  white  to  nearly  colorless,  brown;  also  orange  to  bright  red. 
Streak  white.  Subtransparent  to  subtranslucent.  Optically  negative. 
Indices:  <*  =  2-402,  er  =  2-304. 

Comp.  —  Lead  molybdate,  PbMo04  =  Molybdenum  trioxide  39'3,  lead 
oxide  607  =  100.  Calcium  sometimes  replaces  the  lead. 

Pyr.,  etc.  —  B.B.  decrepitates  and  fuses  below  2.  With  salt  9f  phosphorus  in  O.F.  gives 
a  yellowish  green  glass,  which  in  R.F.  becomes  dark  green.  With  soda  on  charcoal  yields 
metallic  lead.  Decomposed  on  evaporation  with  hydrochloric  acid,  with  the  formation  of 
lead  chloride  and  molybdic  oxide;  on  moistening  the  residue  with  water  and  adding  metallic 
zinc,  it  gives  an  intense  blue  color,  which  does  not  fade  on  dilution  of  the  liquid. 

Obs. -^Occurs  in  veins  with  other  ores  of  lead.  At  Bleiberg,  Carinthia;  Rezbanya, 
Hungary;  Pfibram,  Austria;  Moldawa  in  the  Banat,  Hungary;  Annaberg,  Schneeberg, 
Germany;  Sardinia;  Broken  Hill,  New  South  Wales. 

In  the  United  States,  sparingly  at  the  Southampton  lead  mine,  and  at  Quincy,  Mass., 
and  near  Sing  Sing,  N.  Y.;  near  Phenixville,  Pa.;  at  the  Comstock  lode  and  at  Eureka  in 
Nev. ;  in  large  thin  orange-yellow  tables  at  the  Tecomah  mine,  Utah.  In  N.  M.,  pale  yellow 
crystals  in  the  Organ  Mts.  In  Ariz.,  large  deep  red  crystals  at  the  Hamburg  and*  other 
mines,  Yuma  Co.,  often  with  red  vanadinite;  also  at  the  Castle  Dome  district,  30  miles 
distant;  at  the  Mammoth  gold  mine  near  Oracle,  Pinal  Co.,  with  vanadinite  and  descloizite. 

Named  after  the  Austrian  mineralogist  Wulfen  (1728-1805). 

Use.  —  An  ore  of  molybdenum. 


Reinite.  Ferrous  tungstate,  FeWO4.  In  blackish  brown  tetragonal  pyramids,  perhaps 
pseudomorphous.  H.  =  4.  G.  =  6*64.  Kimbosan,  Japan. 

Koechlinite.  A  molybdate  of  bismuth,  Bi2O3.MoO3.  Orthorhombic.  In  minute  tabu- 
lar crystals.  Cleavage,  a  (100).  Color,  greenish  yellow.  Index,  2'55.  Easily  fusible. 
From  Schneeberg,  Saxony,  Germany. 

Ferritungstite.  Fe2O3.WO3.6H2O.  In  microscopic  hexagonal  plates.  Color  pale  yel- 
low to  brownish  yellow.  Decomposed  by  acids  leaving  yellow  tungstic  oxide.  Product  of 
oxidation  of  Wolframite  from  Germania  Tungsten  mine.  Deer  Trail  district,  Wash. 


VII. 


SALTS   OF   ORGANIC   ACIDS 
Oxalates,  Mellates 

Calcium  oxalate,  CaC2O4.H2O.     In  sfmall  colorless  monoclinic  crystals. 
•555.     From  Saxony,  with  coal;  also  from  Bohemia  and  Alsace. 

From  the  guano  of  the  Guanape 


Whewellite. 
Optically  +.     0 

Oxammite.    Ammonium  oxalate,  (NH4)2C2O4.2H2O. 
Islands,  Peru. 


HYDROCARBON   COMPOUNDS  645 

Humboldtine.  Hydrous  ferrous  oxalate,  FeC2O4.2H2O.  Orthorhombic.  Color  yellow. 
/5  =  1-561.  From  near  Bilin,  Bohemia;  Capo  d'Arco,  Elba. 

Mellite.  Hydrous  aluminium  mellate,  Al2Ci2Oi2.1SH2O.  In  square  tetragonal  pyra- 
mids; also  massive,  granular.  G.  =  1 -55^-1 '65.  Color  honey-yellow.  Optically  — . 
w  =  T539.  Occurs  in  brown  coal  in  Thuringia,  Bohemia,  etc. 


VIII.  HYDROCARBON   COMPOUNDS 

The  Hydrocarbon  compounds  in  general,  with  few  exceptions,  are  not  homogeneous  sub- 
stances, but  mixtures,  which  by  the  action  of  solvents  or  by  fractional  distillation  may  be 
separated  into  two  or  more  component  parts.  They  are  hence  not  definite  mineral  species 
and  do  not  strictly  belong  to  pure  Mineralogy,  rather,  with  the  recent  gums  and  resins,  to 
Chemistry  or,  so  far  as  they  are  of  practical  value,  to  Economic  Geology.  In  the  following 
pages  they  are  treated  for  the  most  part  with  great  brevity. 


1.    Simple  Hydrocarbons.     Chiefly  members  of  the  Paraffin  Series  CraH2n+2. 

SCHEERERITE.  In  whitish  monoclinic  crystals.  Perhaps  a  polymer  of  marsh-gas 
(CH4).  Found  in  brown  coal  at  Uznach,  Switzerland. 

HATCHETTITE.  Mountain  Tallow.  In  thin  plates,  or  massive.  Like  soft  wax.  Color 
yellowish.  Indices,  1 '47-1 '50.  Ratio  of  C  to  H  =  nearly  1:1.  From  the  Coal-measures 
near  Merthyr-Tydvil  in  Glamorganshire,  England;  from  Galicia. 

PARAFFIN.  A  native  crystallized  paraffin  has  been  described  as  occurring  in  cavities 
in  basaltic  lava  near  Paterno,  Sicily.  Indices,  1*49-1 '52. 

OZOCERITE.  Mineral  wax  in  part.  Like  wax  or  spermaceti  in  appearance  and  consis- 
tency. Colorless  to  white  when  pure;  often  leek-green,  yellowish,  brownish  yellow,  brown. 
Indices,  1  '51-1 "54.  Essentially  a  paraffin,  and  consisting  chiefly  of  one  of  the  higher  mem- 
bers of  the  series.  Occurs  in  beds  of  coal,  or  associated  bituminous  deposits,  as  at  Slanik, 
Moldavia;  Roumania;  Boryslaw  in  the  Carpathians.  Also  occurs  in  southern  Utah  on  a 
large  scale. 

Zietrisikite,  Chrismatite,  Urpethite  are  near  ozocerite. 

FICHTELITE.  In  white  monoclinic  tabular  crystals.  Perhaps  CsHg.  Occurs  in  thin 
layers  of  pine  wood  from  peat-beds,  near  Redwitz,  in  the  Fichtelgebirge,  Bavaria;  from 
Borkovic,  Bohemia.  Hartite  has  a  similar  occurrence. 

NAPALITE.  A  yellow  bituminous  substance  of  the  consistency  of  shoemaker's  wax. 
C3H4.  From  the  Phoenix  mercury  mine  in  Pope  Valley,  Napa  county,  Cal. 


2.   Oxygenated  Hydrocarbons 

AMBER.  In  irregular  masses,  with  conchoidal  fracture.  H.  =  2-2 '5.  G.  =  1'096. 
Luster  resinous.  Color  yellow,  sometimes  reddish,  brownish,  and  whitish,  often  clouded, 
sometimes  fluorescent.  Transparent  to  translucent.  Heated  to  150°  begins  to  soften, 
and  finally  melts  at  250°-300°.  Ratio  for  C  :  H  :  O  =  40  :  64  :  4. 

Part  of  the  so-called  amber  is  separated  mineralogicatly  as  succinite  (yielding  succinic 
acid).  Other  related  fossil  resins  from  many  other  regions  (e.g.,  the  Atlantic  coast  of  the 
United  States)  have  been  noted.  Some  of  them  have  been  called  retinite,  gedanite,  glessite, 
rumanite,  simetite,  krantzite,  chemawinite,  delatynite,  etc. 

Amber  occurs  abundantly  on  the  Prussian  coast  of  the  Baltic  from  Dantzig  to  Memel; 
also  on  the  coasts  of  Denmark,  Sweden,  and  the  Russian  Baltic  provinces.  It  is  mined 
extensively,  and  is  also  found  on  the  shores  cast  up  by  the  waves  after  a  heavy  storm. 
Amber  and  the  similar  fossil  resins  are  of  vegetable  origin,  altered  by  fossilization;  this  is 
inferred  both  from  its  native  situation  with  coal,  or  fossil  wood,  and  from  the  occurrence  of 
insects  incased  in  it.  Amber  was  early  known  to  the  ancients,  and  called  yXtxTpov, 
electrum,  whence,  on  account  of  its  electrical  susceptibilities,  has  been  derived  the  word 
electricity. 

COPALITE,  or  Highgate  resin,  is  from  the  London  blue  clay.  It  is  like  the  resin  copal  in 
hardness,  color,  luster,  transparency,  and  difficult  solubility  in  alcohol.  Color  clear  pale 
yellow  to  dirty  gray  and  dirty  brown.  Emits  a  resinous  aromatic  odor  when  broken. 


DESCRIPTIVE   MINERALOGY 

The  following  are  oxygenated  hydrocarbons  occurring  with  coal  and  peat  deposits  etc  : 
BATHVILLITE      Occurs  in  dull,  brown,  porous  lumps  in  the  torbamte  or  Boghead  coal 

fnf  the  Crrbonfferous  formation)  adjoining  the  lands  of  Torbane  Hill,  Bathville,  Scotland. 

I?  may  be an ^atoed  riin,  or  else  material  which  has  filtrated  into  the  cavity  from  the 

surrounding  torbanite. 

TASMANITE      In  minute  reddish  brown  scales  disseminated  through  a  laminated  shale; 

average  diameter  of  scales  about  0'03  in.     Not  dissolved  at  all  by  alcohol,  ether,  benzene. 

turpentine  Tcarbon  disulphide,  even  when  heated.     Remarkable  as  yielding  5 '3  p.  c, 

sufpto!  Vom  the  river  Mersey,  north  side  of  Tasmania;   the  rock  is  called  combustible 

DYSODILE  In  very  thin  folia,  flexible,  slightly  elastic ;  yellow  or  greenish  gray.  Analy- 
sis gave  2  3  p.  c.  sulphur  and  1 7  p.  c.  nitrogen.  From  lignite  deposits  at  Melili,  Sicily,  and 
elsewhere. 

GEOCERITE  A  white,  wax-like  substance,  separated  from  the  brown  coal  ot  Gesterwitz, 
near  Weissenfels.  Geomyricite  and  geocerellite  are  other  products  from  the  same  source. 

LEUCOPETRITE.  Also  from  the  Gesterwitz  brown  coal.  Between  a  resin  and  wax  in 
physical  characters. 

PYRORETINITE.     From  brown  coal  near  Aussig,  Bohemia. 

DOPPLERITE.  In  elastic  or  partly  jelly-like  masses;  brownish  black.  An  acid  sub- 
stance or  mixture  of  different  acids,  related  to  humic  acid.  Ratio  for  C,  H,  O,  nearly 
10  :  12  :  5.  From  peat  beds  near  Aussee  in  Styria;  Fichtelgebirge,  Bavaria. 

IDRIALITE.  Occurs  with  the  cinnabar  of  Idria.  In  the  pure  state  white  and  crystalline 
in  structure.  In  nature  found  only  impure,  being  mixed  with  cinnabar,  clay,  and  some 
pyrite  and  gypsum  in  a  brownish  black  earthy  material,  called,  from  its  combustibility 
and  the  presence  of  mercury,  inflammable  cinnabar. 

POSEPNYTE.  Occurs  in  hard,  brittle  plates  or  nodules,  light  green  in  color.  From  the 
Great  Western  mercury  mine,  Lake  Co.,  Cal.  See  also  napalite,  p.  645. 

FLAGSTAFFITE.  Ci2H24O3.  Orthorhombic.  In  minute  prisms.  Colorless,  n  =  T51. 
G.  =  1'092.  Found  in  cracks  of  buried  tree  trunks,  near  Flagstaff.  Ariz. 

The  following  are  still  more  complex  native  hydrocarbon  compounds  of  great  importance 
from  an  economic  standpoint. 

Petroleum.     NAPHTHA;  PETROLEUM.     Mineral  oil.     Kerosene. 

PITT  ASPHALT:  Maltha.     Mineral  Tar. 

Liquids  or  oils,  in  the  crude  state  of  disagreeable  odor;  varying  widely  in  color,  from 
colorless  to  dark  yellow  or  brown  and  nearly  black,  the  greenish  brown  color  the  most 
common;  also  in  consistency  from  thin  flowing  kinds  to  those  that  are  thick  and  viscous; 
and  in  specific  gravity  from  0'6  to  0*9.  Petroleum,  proper,  passes  by  insensible  gradations 
into  pittasphalt  or  maltha  (viscid  bitumen) ;  and  the  latter  as  insensibly  into  asphalt  or  solid 
bitumen. 

Chemically,  petroleum  consists  for  the  most  part  of  members  of  the  paraffin  series, 
CnH2n+2,  varying  from  marsh  gas,  CH4,  to  the  solid  forms.  The  olefines,  CreH2w,  are 
also  present  in  smaller  amount.  This  is  especially  true  of  the  American  oils.  Those  of  the" 
Caucasus  have  a  higher  density,  the  volatile  constituents  are  less  prominent,  they  distill  at 
about  150°  and  contain  the  benzenes,  CnH2n-6,  in  considerable  amount.  There  are  present 
also  members  of  the  series  CnH2n-8.  The  German  petroleum  is  intermediate  between  the 
American  and  the  Caucasian.  The  Canadian  petroleum  is  especially  rich  in  the  solid 
paraffins. 

Petroleum  occurs  in  rocks  or  deposits  of  nearly  all  geological  ages,  from  the  Lower 
Silurian  to  the  present  epoch.  It  is  associated  most  abundantly  with  argillaceous  shales, 
sands,  and  sandstones,  but  is  found  also  permeating  limestones,  giving  them  a  bituminous 
odor,  and  rendering  them  sometimes  a  considerable  source  of  oil.  From  these  oleiferous 
shales,  sands  and  limestones  the  oil  often  exudes,  and  appears  floating  on  the  streams  or 
lakes  of  the  region,  or  rises  in  oil  springs.  It  also  exists  collected  in  subterranean  cavities 
in  certain  rocks,  whence  it  issues  in  jets  or  fountains  whenever  an  outlet  is  made  by  Coring. 
The  oil  which  fills  the  cavities  has  ordinarily  been  derived  from  the  subjacent  rocks;  for 
the  strata  in  which  the  cavities  exist  are  frequently  barren  sandstones.  The  conditions 
required  for  the  production  of  such  subterranean  accumulations  would  be  therefore  a  bitu- 
minous oil-bearing  or  else  oil-producing  stratum  at  a  greater  or  less  depth  below;  cavities 
to  receive  the  oil;  an  overlying  stratum  of  close-grained  shale  or  limestone,  not  allowing  of 
the  easy  escape  of  the  naphtha  vapors. 


HYDROCARBON   COMPOUNDS  647 

The  important  petroleum  districts  in  the  United  States  are:  (1)  The  Appalachian  in- 
cluding fields  in  N.  Y.,  Pa.,  Ohio,  W.  Va.,  Ky.,  Tenn.,  (2)  The  Ohio-Indiana,  (3)  Illinois 
(4). Kansas-Oklahoma,  (5)  Louisiana-Texas,  (6)  California,  (7)  Wyoming.  In  Canada  oil 
chiefly  produced  in  Ontario.  Important  fields  in  Mexico  from  Tampico  to  Tuxpam.  The 
chief  foreign  districts  are  in  the  Baku  region,  Russia,  in  Galicia  and  Roumania,  also  in 
Borneo. 

Asphaltum.     Mineral  Pitch.     Asphalt. 

Asphaltum,  or  mineral  pitch,  is  a  mixture  of  different  hydrocarbons,  part  of  which  are 
oxygenated.  Its  ordinary  characters  are  as  follows:  Amorphous.  G.  =  1-1-8;  some- 
times higher  from  impurities.  Luster  like  that  of  black  pitch.  Color  brownish  black 
and  black.  Odor  bituminous.  Melts  ordinarily  at  90°  to  100°,  and  burns  with  a  bright 
flame.  Soluble  mostly  or  wholly  in  oil  of  turpentine,  and  partly  or  wholly  in  ether;  com- 
monly partly  in  alcohol.  The  more  solid  kinds  graduate  into  the  pittasphalts  or  mineral 
tar,  and  through  these  there  is  a  gradation  to  petroleum.  The  fluid  kinds  change  into  the 
solid  by  the  loss  of  a  vaporizable  portion  on  exposure,  and  also  by  a  process  of  oxidation, 
which  consists  first  in  a  loss  of  hydrogen,  and  finally  in  the  oxygenation  of  a  portion  of  the 
mass.  The  action  of  heat,  alcohol,  ether,  naphtha  and  oil  of  turpentine,  as  well  as  direct 
analyses,  show  that  the  so-called  asphaltum  from  different  localities  is  very  various  in  com- 
position. 

Asphaltum  belongs  to  rocks  of  no  particular  age.  The  most  abundant  deposits  are 
superficial.  But  these  are  generally,  if  not  always,  connected  with  rock  deposits  contain- 
ing some  kind  of  bituminous  material  or  vegetable  remains.  Some  of  the  noted  localities 
of  asphaltum  are  the  region  of  the  Dead  Sea,  or  Lake  Asphaltites,  whence  the  most  of  the 
asphaltum  of  ancient  writers;  a  lake  on  Trinidad,  1|  m.  in  circuit,  which  is  hot  at  the 
center,  but  is  solid  and  cold  toward  the  shores,  and  has  its  borders  over  a  breadth  of  f  m. 
covered  with  the  hardened  pitch  with  trees  flourishing  over  it;  at  various  places  in  South 
America;  in  California,  near  the  coast  of  St.  Barbara;  also  in  smaller  quantities,  elsewhere. 

ELATERITE.  Elastic  Bitumen.  Mineral  Caoutchouc.  Soft,  elastic,  sometimes  much 
like  india-rubber;  occasionally  hard  and  brittle.  Color  usually  dark  brown.  Found  at 
Castleton  in  Derbyshire,  and  elsewhere. 

ALBERTITE.  Differs  from  ordinary  asphaltum  in  being  only  partially  soluble  in  oil  of 
turpentine,  and  in  its  very  imperfect  fusion  when  heated.  H.  =  1-2.  G.  =  T097.  Luster 
brilliant,  pitch-like;  color  jet-black.  Occurs  filling  an  irregular  fissure  in  rocks  of  the 
Lower  Carboniferous  in  Nova  Scotia.  Impsonite  from  Impson  valley,  Indian  Territory,  is 
like  albertite  except  that  it  is  almost  insoluble  in  turpentine. 

GRAHAMITE.  Resembles  albertite  in  its  pitch-black,  lustrous  appearance.  H.  =  2. 
G.  =  1'145.  Soluble  mostly  in  oil  of  turpentine;  partly  in  ether,  naphtha  or  benzene;  not 
at  all  in  alcohol;  wholly  in  chloroform  and  carbon  disulphide.  Melts  only  imperfectly,  and 
with  a  decomposition  of  the  surface.  Occurs  in  W.  Va.,  about  20  m.  S.  of  Parkersburg, 
filling  a  fissure  in  a  Carboniferous  sandstone;  from  Kunda,  Esthonia,  Russia. 

GILSONITE,  also  called  Uintahite  or  Uintaite.  A  variety  of  asphalt  from  near  Ft.  Du- 
chesne,  Utah,  which  has  found  many  applications  in  the  arts.  Occurs  in  masses  several 
inches  in  diameter,  with  conchoidal  fracture;  very  brittle.  H.  =  2-2'5;  G.  =  1  '065-1  '070. 
Color  black,  brilliant  and  lustrous;  streak  and  powder  a  rich  brown.  Fuses  easily  in  the 
flame  of  a  car  idle  and  burns  with  a  brilliant  flame,  much  like  sealing-wax.  Named  after 
Mr.  S.  H.  Gilson  of  Salt  Lake  City. 

NIGRITE  is  a  variety  of  asphaltum  from  Utah. 

Mineral  Coal.  Compact  massive,  without  crystalline  structure  or  cleavage;  sometimes 
breaking  with  a  degree  of  regularity,  but  from  a  jointed  rather  than  a  cleavage  structure. 
Sometimes  laminated;  often  faintly  and  delicately  banded,  successive  layers  differing 
slightly  in  luster.  Fracture  conchoidal  to  uneven.  Brittle;  rarely  somewhat  sectile. 
H.  =  0-5-2-5.  G.  =  1-1  '80.  Luster  dull  to  brilliant,  and  either  earthy,  resinous  or  sub- 
metallic.  Color  black,  grayish  black,  brownish  black,  and  occasionally  iridescent;  also 
sometimes  dark  brown.  Opaque.  Infusible  to  subfusible;  but  often  becoming  a  soft, 
pliant  or  paste-like  mass  when  heated.  On  distillation  most  kinds  afford  more  or  less  of 
oily  and  tarry  substances,  which  are  mixtures  of  hydrocarbons  and  paraffin. 

The  varieties  recognized  depend  partly  (1)  on  the  amount  of  the  volatile  ingredients 
afforded  on  destructive  distillation;  or  (2)  on  the  nature  of  these  volatile  compounds,  for 
ingredients  of  similar  composition  may  differ  widely  in  volatility,  etc.;  (3)  on  structure, 
luster  and  other  physical  characters. 

Coal  is  in  general  the  result  of  the  gradual  change  which  has  taken  place  in  geological 
history  in  organic  deposits,  chiefly  vegetable,  and  its  form  and  composition  depend  upon 


548  DESCRIPTIVE   MINERALOGY 

the  extent  to  which  this  change  has  gone  on.     Thus  it  passes  from  forms  which  still  retain 
he  origmal  structure  of  the  wood  (peat,  lignite)  and  through  those  with  less  of  volatile  or 
bituni  S  matter  to  anthracite  and  further  to  kinds  which  approach  graphite. 

1  ANTHRACITE      H    =  2-2 '5.     G.  =  1'32-1'7.     Luster  bright,  often  submetalhc,  iron- 
black   and  frequently  iridescent.     Fracture  conchoidal.     Volatile  matter  after  drying  3^6 
p.  c.  '  Burns  with  a  feeble  flame  of  a  pale  color      The  anthracites  of  Pennsylvania  contain 
ordinarily  85-93  per  cent  of  carbon;   those  of  South  Wales   88-95;   of  France   80-83;   of 
Saxony   81;    of  southern  Russia,  sometimes  94  per  cent.     Anthracite  graduates  through 
semi-anthracite  into  bituminous  coal,  becoming  less  hard  and  containing  more  volatile 
matter;  and  an  intermediate  variety  is  called  free-burning  anthracite. 

2  BITUMINOUS  COAL.     Burns  in  the  fire  with  a  yellow,  smoky  flame,  and  gives  out  on 
distillation  hydrocarbon  oils  or  tar;  hence  the  name  bituminous.     The  ordinary  bituminous 
coals  contain  from  5-15  p.  c.  (rarely  16  or  17)  of  oxygen  (ash  excluded);  while  the  so-called 
brown  coal  or  lignite  contains  from  20-36  p.  c.,  after  the  expulsion,  at  100  ,  of  15-36  p.  c.  of 
water.     The  amount  of  hydrogen  in  each  is  from  4-7  p.  c.     Both  have  usually  a  bright, 
pitchy,  greasy  luster,  a  firm  compact  texture,  are  rather  fragile  compared  with  anthracite, 
and  have  G.  =  1  '14-1  '40.     The  brown  coals  have  often  a  brownish  black  color,  whence  the 
name,  and  more  oxygen,  but  in  these  respects  and  others  they  shade  into  ordinary  bitumin- 
ous coals.     The  ordinary  bituminous  coal  of  Pennsylvania  has  G.  =  1  '26-1  '37;    of  New- 
castle, England,  1'27;  of  Scotland,  1  '27-1  '32;  of  France,  1  "2-1  "33;  of  Belgium,  1'27-1'3. 
The  most  prominent  kinds  are  the  following: 

(a)  Caking  or  Coking  Coal.  A  bituminous  coal  which  softens  and  becomes  pasty  or  semi- 
viscid  in  the  fire.  This  softening  takes  place  at  the  temperature  of  incipient  decomposition, 
and  is  attended  with  the  escape  of  bubbles  of  gas.  On  increasing  the  heat,  the  volatile 
products  which-  result  from  the  ultimate  decomposition  of  the  softened  mass  are  driven  off, 
and  a  coherent,  grayish  black,  cellular  or  fritted  mass  (coke)  is  left.  Amount  of  coke  left 
(or  part  not  volatile)  varies  from  50-85  p.  c. 

(6)  Non-Caking  Coal.  Like  the  preceding  in  all  external  characters,  and  often  in  ulti- 
mate composition;  but  burning  freely  without  softening  or  any  appearance  of  incipient 
fusion.  There  are  all  gradations  between  caking  and  non-caking  bituminous  coals. 

(c)  Cannel  Coal  (Parrot  Coal).     A  variety  of  bituminous  coal,  and  often  caking;    but 
differing  from  the  preceding  in  texture,  and  to  some  extent  in  composition,  as  shown  by  its 
products  on  distillation.     It  is  compact,  with  little  or  no  luster,  and  without  any  appearance 
of  a  banded  structure;  and  it  breaks  with  a  conchoidal  fracture  and  smooth  surface;  color 
dull  black  or  grayish  black.     On  distillation  it  affords,  after  drying,  40  to  66  p.  c.  of  vola- 
tile matter,  and  the  material  volatilized,  includes  a  large  proportion  of  burning  and  lubri- 
cating oils,  much  larger  than  the  above  kinds  of  bituminous  coal;  whence  it  is  extensively 
used  for  the  manufacture  of  such  oils.     It  graduates  into  oil-producing  coaly  shales,  the 
more  compact  of  which  it  much  resembles.     Torbanite  is  a  variety  of  cannel  coal  of  a  dark 
brown  color,  from  Torbane  Hill,  near  Bathgate,  Scotland;    also  called  Boghead  Cannel. 

(d)  Brown  Coal  (Lignite).     The  prominent  characteristics  of  brown  coal  have  already 
been  mentioned.     They  are  non-caking,  but  afford  a  large  proportion  of  volatile  matter; 
sometimes  pitch-black,  but  often  rather  dull  and  brownish  black.     G.  =  1  '15-1  '3.     Brown 
coal  is  often  called  lignite.     But  this  term  is  sometimes  restricted  to  masses  of  coal  which 
still  retain  the  form  of  the  original  wood.     Jet  is  a  black  variety  of  brown  coal,  compact  in 
texture,  and  taking  a  good  polish,  whence  its  use  in  jewelry. 

Coal  occurs  in  beds,  interstratified  with  shales,  sandstones,  and  conglomerates,  and 
sometimes  limestones,  forming  distinct  layers,  which  vary  from  a  fraction  of  an  inch  to  30 
feet  or  more  in  thickness.  In  the  United  States,  the  anthracites  occur  east  of  the  Alleghany 
range,  in  rocks  that  have  undergone  great  contortions  and  fracturings,  while  the  bitumin- 
ous coals  are  found  extensively  in  many  States  farther  west,  in  rocks  that  have  been  less 
disturbed;  and  this  fact  and  other  observations  have  led  geologists  to  the  view  that  the 
anthracites  have  lost  their  bitumen  by  the  action  of  heat.  The  origin  of  coal  is  mainly 
vegetable,  though  animal  life  has  contributed  somewhat  to  the  result.  The  beds  were  once 
beds  of  vegetation,  analogous,  in  most  respects,  in  mode  of  formation  to  the  peat  beds  of 
modern  times,  yet  in  mode  of  burial  often  of  a  very  different  character.  This  vegetable 
origin  is  proved  not  only  by  the  occurrence  of  the  leaves,  stems  and  logs  of  plants  in  the  coal, 
but  also  by  the  presence  throughout  its  texture,  in  many  cases,  of  the  forms  of  the  original 
resi  also  by  the  direct  observation  that  peat  is  a  transition  state  between  unaltered  vege- 

i  £  s  *  brown  coal»  being  sometimes  found  passing  completely  into  true  brown 
coal.  Peat  differs  from  true  coal  in  want  of  homogeneity,  it  visibly  containing  vegetable 
fibers  only  partially  altered;  and  wherever  changed  to  a  fine-textured  homogeneous  ma- 
terial, even  though  hardly  consolidated,  it  may  be  true  brown  coal. 

.bor  an  account  of  the  chief  coal  fields,  as  also  of  the  geological  relations  of  the  different 
coal  deposits,  reference  is  made  to  works  on  Economic  Geology. 


APPENDIX  A. 
ON  THE  DRAWING  OF  CRYSTAL  FIGURES 


IN  the  representation  of  crystals  by  figures  it  is  customary  to  draw  their  edges  as  if  they 
were  projected  upon  some  definite  plane.  Two  sorts  of  projection  are  used;  the  ortho- 
graphic in  which  the  lines  of  projection  fall  at  right  angles  and  the  clinographic  where  they 
fall  at  oblique  angles  upon  the  plane  of  projection.  The  second  of  these  projections  is  the 
more  important,  and  must  be  treated  here  in  some  detail.  Two  points  are  to  be  noted  in 
regard  to  it.  In  the  first  place,  in  the  drawings  of  crystals  the  point  of  view  is  supposed  to 
be  at  an  infinite  distance,  and  it  follows  from  this  that  all  lines  which  are  parallel  on  the 
crystal  appear  parallel  in  the  drawing. 

In  the  second  place,  in  all  ordinary  cases,  it  is  the  complete  ideal  crystal  which  is  repre- 
sented, that  is,  the  crystal  with  its  full  geometrical  symmetry  as  explained  on  pp.  10  to 
13  (cf.  note  on  p.  13). 

In  general,  drawings  of  crystals  are  made,  either  by  constructing  the  figure  upon  a 
projection  of  its  crystal  axes,  using  the  intercepts  of  the  different  faces  upon  the  axes  in  order 
to  determine  the  directions  of  the  edges  or  by  constructing  the  figure  from  the  gnomonic 
(or  stereographic)  projection  of  the  crystal  forms.  Both  of  these  methods  have  their 
advantages  and  disadvantages.  By  drawing  the  crystal  figure  by  the  aid  of  a  projection 
of  its  crystal  axes  the  symmetry  of  the  crystal  and  the  relations  of  its  faces  to  the  axes  are 
emphasized.  In  many  cases,  however,  drawing  from  a  projection  of  the  poles  of  the 
crystal  faces  is  simpler  and  takes  less  time.  The  student  should  be  able  to  use  both  methods 
and  consequently  both  are  described  below. 

DRAWING  OF   CRYSTALS  UPON   PROJECTIONS  OF  THEIR 
CRYSTAL   AXES 

PROJECTION   OF  THE   AXES    .    / 

The  projection  of  the  particular  axes  required  is  obviously  the  first  step  in  the  process. 
These  axes  can  be  most  easily  obtained  by  making  use  of  the  Penfield  Axial  Protractor, 
illustrated  in  Fig.  1030.  *  The  customary  directions  of  the  axes  for  the  isometric,  tetragonal, 
orthorhombic  and  hexagonal  systems  are  given  on  the  protractor  and  it  is  a  simple  matter, 
as  explained  below,  to  determine  the  directions  of  the  inclined  axes  of  the  monoclinic  and 
tri clinic  systems.  Penfield  drawing  charts  giving  the  projection  of  the  isometric  axes, 
which  are  easily  modified  for  the  tetragonal  and  orthorhombic  systems,  and  of  the  hexag- 
onal axes,  (see  Figs.  1031,  1032)  are  also  quite  convenient. 

Isometric  System.  —  The  following  explanation  of  the  making  of  the  projection  of  the 
isometric  axes  has  been  taken  largely  from  Penfield's  description,  f 

Figure  1033  will  make  clear  the  principles  upon  which  the  projection  of  the  isometric 
axes  are  based.  Figure  1033A  is  an  orthographic  projection  (a  plan,  as  seen  from  above) 
of  a  cube  in  two  positions,  one,  a  b  c  d,  in  what  may  be  called  normal  position,  the  other, 
A  B  C  D,  after  a  revolution  of  18°  26'  to  the  left  about  its  vertical  axis.  The  broken- 
dashed  lines  throughout  represent  the  axes.  Figure  1033B  is  likewise  an  orthographic 
projection  of  a  cube  in  the  position  A  B  C  D  of  A,  when  viewed  from  in  front,  the  eye 
or  point  of  vision  being  on  a  level  with  the  crystal.  In  the  position  chosen,  the  ap- 
parent width  of  the  side  face  B  C  B'  C'  is  one-third  that  of  the  front  face  ABA'  Bf,  this 
being  dependent  upon  the  angle  of  revolution  18°  26',  the  tangent  of  which  is  equal  to  f. 
To  construct  the  angle  18°  26',  draw  a  perpendicular  at  any  point  on  the  horizontal  line, 
X  —  Y,  figure  1033A  as  at  o,  make  op  equal  one-third  Oo,  and  join  O  and  p.  The  next 
step  in  the  construction  is  to  change  from  orthographic  to  clinographic  projection.  In 
order  to  give  crystal  figures  the  appearance  of  solidity  it  is  supposed  that  the  eye  or  point 

*  The  various  Penfield  crystal  drawing  apparatus  may  be  obtained  from  the  Mineralogical.  Laboratory  of  the 
Sheffield  Scientific  School  of  Yale  University,  New  Haven,  Conn, 
t  On  Crystal  Drawing;  Am.  J.  Sc.,  19,  39,  1905. 

649 


650 


APPENDIX   A 
1030 


Protractor  for  plotting  crystallographic  axes;   one-third  natural  size  (after  Penfield) 
1031  1032 


Scheme  of  the  engraved  axes  of  the  isometric  and  hexagonal  systems,  one-sixth  natural 

size  (after  Penfield) 


APPENDIX   A 


651 


1033 


of  vision  is  raiseji,  so  that  one  looks  down  at  an  angle  upon  the  crystal;  thus,  in  the  case 
under  consideration,  figure  1033C,  the  top  face  of  the  cube  comes  into  view.  The  position 
of  the  crystal,  however,  is  not  changed,  and  the  plane  upon  which  the  projection  is  made 
remains  vertical.  From  A  it  may  be  seen  that  the 
positive  ends  of  the  axes  a\  and  a2  are  forward  of  the 
ImeXY,  the  distances  a\x  and  «2  y  being  as  3  :  1.  In 
B  it  must  be  imagined,  and  by  the  aid  of  a  model  it 
may  easily  be  seen,  that  the  extremities  of  these  same 
axes  are  to  the  front  of  an  imaginary  vertical  plane  (the 
projection  of  XY  above)  passing  through  the  center  of 
the  crystal,  the  distance  being  the  same  as  ai  x  and  a2 
y  of  the  plan.  In  D  the  distance  ax  is  drawn  the 
same  length  as  a\x  of  the  plan,  and  the  amount  to 
which  it  is  supposed  that  the  eye  is  raised,  indicated 
by  the  arrow,  is  such  that  a,  instead  of  being  projected 
horizontally  to  x,  is  projected  at  an  inclination  of  9° 
28'  from  the  horizontal  to  w,  the  distance  xw  being  one- 
sixth  of  ax;  hence  the  angle  9°  28'  is  such  that  its 
tangent  is  |.  Looking  down  upon  a  solid  at  an  angle, 
and  still  making  the  projection  on  a  vertical  plane,  may 
be  designated  as  clinographic  projection;  accordingly, 
to  plot  the  axes  of  a  cube  in  clinographic  projection 
in  conformity  with  figures  A,  B  and  D  draw  the 
horizontal  construction  line  hk,  figure  C,  and  cross  it 
by  four  perpendiculars  in  vertical  alignment  with  the 
points  «i,  —  «i  and  a2,  —  a2  of  figures  A  and  B.  Then 
determine  the  extremities  of  the  first,  a\,  —  a\  axis  by 
laying  off  distances  equal  to  xw  of  figure  D,  or  one- 
sixth  ai  x  of  figure  A,  locating  them  below  and  above 
the  horizontal  line  hk.  The  line  ai,  —  a\  is  thus  the 
projection  of  the  first,  or  front-to-back  axis.  In  like 
manner  determine  the  extremities  of  the  second  axis, 
«2,  —  02,  by  laying  off  distances  equal  to  one-thircUcw 
of  figure  D,  or  one-sixth  a2y  of  figure  A,  plotted  below 
and  above  the  line  hk.  The  line  a2,  —  a2  is  thus~tKe~ 
projection  of  the  second,  or  right-tp-left  axis.  It  is 
important  to  keep  in  mind  that  in  clinographic  projec- 
tion there  is  no  foreshortening  of  vertical  distances. 
In  figure  C  the  axis  a2,  —  a2  is  somewhat,  and  a\,  —  «i 
much  foreshortened,  yet  both  represent  axes  of  the' 
same  length  as  the  vertical,  a3,  —  a3. 

It  is  wholly  a  matter  of  choice  that  the  angle  of 
revolution  shown  in  figure  1033A  is  18°  26',  and  that 
the  eye  is  raised  so  as  to  look  down  upon  a  crystal  at  Development  of  the  axes  of  the 
an  angle  of  9°  28'  from  the  horizontal,  as  indicated  by      isometric  system  in  orthographic 
figure  1033D.     Also  it  is  evident  that  these  angles  may      and      clinographic      projection 
be  varied  to  suit  any  special  requirement.     As  a  mat-      (after  Penfield) 
ter  of  fact,  however,  the  angles  18°  26'  and  9°  28'  have 

been  well  chosen  and  are  established  by  long  usage,  and  practically  all  the  figures  in  clin- 
ographic projection,  found  in  modern  treatises  on  crystallography  and  mineralogy,  have 
been  drawn  in  accordance  with  them. 

Tetragonal  and  Orthorhombic  Systems.  —  The  projection  of  tetragonal  and  orthor- 
hombic axes  can  be  easily  obtained  from  the  isometric  axes  by  modifying  the  lengths  of  the 
various  axes  to  conform  to  the  axial  ratio  of  the  desired  crystal.  For  instance  with  zircon 
the  vertical  axis  has  a  relative  length  of  c  =  0.64  in  respect  to  the  equal  lengths  of  the  hori- 
zontal axes.  By  taking  0.64  of  the  unit  length  of  the  vertical  axis  of  the  isometric  projec- 
tion the  crystal  axes  for  a  zircon  figure  are  obtained.  The  Penfield  axial  charts  all  give 
decimal  parts  of  the  unit  length  of  the  isometric  vertical  axis,  so  that  any  proportion  of 
this  length  can  be  found  at  once.  In  the  orthorhombic  system  the  lengths  of  both  the  a 
and  c  axes  must  be  modified.  The  desired  point  upon  the  c  axis  can  be  obtained  as  de- 
scribed above.  In  the  case  of  the  a  axis  the  required  point  can  be  found  by  some  simple 
method  of  construction.  If,  as  is  the  case  in  the  Penfield  charts,  a  plan  of  the  unforeshort- 
ened  horizontal  axes  is  given  in  a  top  view,  the  desired  length  can  be  laid  off  directly  upon 


652 


APPENDIX   A 


1034 


the  a  axis  in  this  orthographic  projection  by  means  of  the  decimal  scale  and  then  projected 

vertically  down  upon  its  clinographic  projection.     Or  the  proper  distance  can  be  laid  oft 

on  the  vertical  axis  and  then  by  means  of  a  line  drawn  from  this  point  parallel  to  a  line 

ioinine  the  extremities  of  the  c  and  a  axes  of  the  isometric  projection  the  proper  proportional 

part  of  the  a  axis  can  be  determined  by  intersection. 

Hexagonal  System.  —  For  projecting  the  hexagonal  axes 
exactly  the  same  principles  may  be  made  use  of  as  were 
employed  in  the  construction  of  the  isometric  axes.  Figure 
1034A  is  an  orthographic  projection,  a  plan,  of  a  hexagonal 
prism  in  two  positions,  one  of  them,  ai,  02,  etc.,  after  a 
revolution  of  18°  26'  from  what  may  be  called  normal  posi- 
tion. In  figure  1034B  the  extremities  of  the  horizontal  axes 
of  A  have  been  projected  down  upon  the  horizontal  construc- 
tion line  hk,  and  a\,  a2  and  —  a3  which  are  forward  of  the 
line  XY  in  A  are  located  below  the  line  hk  in  the  clin- 
ographic projection,  the  distances  from  hk  being  one-sixth 
of  dix,  (hy  and  —  asz  of  A.  Figure  1034C  is  a  scheme  for 
getting  the  distances  which  the  extremities  of  the  axes  are 
dropped.  The  vertical  axis  in  1034B  has  been  given  the 
same  length  as  the  axes  of  the  plan. 

Monoclinic  System.  —  In  the  case  of  the  monoclinic 
axes  the  inclination  and  length  of  the  a  axis  must  be 
determined  in  each  case.  The  axial  chart,  Fig.  1030,  can 
be  most  conveniently  used  for  this  purpose.  The  ellipse 
in  the  figure,  lettered  A,  C,  —  A,  —  C  gives  the  trace  of 
the  ends  of  the  a  and  c  axes  as  they  are  revolved  in  the 
A  —  C  plane.  To  find,  therefore,  the  inclination  of  the  a 
axis  it  is  only  necessary  to  lay  off  the  angle  /8  by  means 
of  the  graduation  given  on  this  ellipse.  The  unit  length  of 
the  a  axis  may  be  determined  in  various  ways.  The  plan  of 
the  axes  given  at  the  top  of  the  chart  may  be  used  for  this 
purpose.  Fig.  1035  will  illustrate  the  method  of  procedure 
as  applied  in  the  case  of  orthoclase,  where  0  =  64°  and 
a  =  0.66.  The  foreshortened  length  of  the  a  axis  is  de- 
termined as  indicated  and  then  this  length  can  be  projected 
vertically  downward  upon  the  inclined  a  axis,  the  direction 
of  which  has  been  previously  determined  as  described  above. 
Triclinic  System.  —  In  the  construction  of  triclinic  axes  the  inclination  of  the  a  axis 

and  its  length  are  determined  in  exactly  the  same  manner  as  described  in  the  preceding 

paragraph  in  the  case  of  the  monoclinic  system.     The  direction  of  the  6  axis  is  determined 

as  follows.     The  vertical  plane  of  the  6  and  c  axes  is 

revolved  about  the  c  axis  through  such  an  angle  as 

will  conform  to  the  angle  between  the  pinacoids 

100  and  010.     Care  must  be  taken  to  note  whether 

this  plane  is  to  be  revolved  toward  the  front  or 

toward  the  back.    If  the  angle  between  the  normals 

to  100  and  010  is  greater  than  90°  the  right  hand 

end  of  this  plane  is  to  be  revolved  toward  the  front. 

Figure  1036,  which  is  a  simplified  portion  of  the 

axial  chart,  shows  the  necessary   construction  in 

order  to  obtain  the  direction  of  the  6  axis  in  the 

case  of  rhodonite  in  which  100  A  010  =  94°  26'  and 

a  =  103°  18'.     The  plane  of  the  b-c  axes  will  pass 

through  the  point  p  which  is  94°  26'  from  -a.     To 

locate  the  point  6',  which  is  the  point  where  the  6 

axis  would  emerge  from  the  sphere,  draw  through 

the  point  p  two  or  more  chords  from  points  where 

the  vertical  ellipses  of  the  chart  cross  the  horizontal 

ellipse,   as   lines  a-p.  -a-p.  b-p,   in  figure    1036. 

Ihen  from  points  on  these  same  vertical  ellipses 

which  are  13°  18'  below  the  horizontal  plane  draw 

chords  parallel  to  the  first  series  as  x-x',  y-y',  z-z'.     The  point  where  these  three  chords 

meet  determines  the  position  of  6'  and  a  line  from  this  point  drawn  through  the  center  of  the 


Development  of  the  axes  of 
the  hexagonal  system  in 
orthographic  and  clin- 
ographic projection  (after 
Penfield) 


10£5 


APPENDIX   A 


653 


chart  determines  the  direction  of  the  b  axis,  since  it  Ues  in  the  proper  vertical  plane  and 
makes  the  angle  a,  103°  18',  with  the  c  axis.  The  foreshortened  length  of  the  6  axis  can 
be  determined  by  the  use  of  the  orthographic  projection  of  the  a  and  b  axes  at  the  top  of 
the  chart  in  exactly  the  same  manner  as  described  under  the  monoclinic  system  and  the 
point  thus  determined  may  be  projected  vertically  downward  upon  the  line  of  the  b  axis 
of  the  clinographic  projection  as 

already  determined.     It  must  be  1036 

remembered,  however,  that  the 
position  of  the  b  axis  in  the  ortho- 
graphic projection  must  conform 
to  the  position  of  the  plane  of 
the  b  and  c  axes  or  in  the  case  of 
rhodonite  have  its  right  hand  end 
at  an  angle  of  94°  26'  with  the 
negative  end  of  the  projection  of 
the  a  axis. 

Drawing  of  Crystal  Figures  by 
Aid  of  Projections  of  their 
Axes.  —  In  order  to  determine  in 
the  drawing  the  direction  of  any 
edge  between  two  crystal  faces  it 

is  necessary  to  establish  two  points,  both  of  which  shall  be  common  to  these  two  faces. 
A  line  connecting  two  such  points  will  obviously  have  the  desired  direction.  The  posi- 
tions of  these  points  is  commonly  established  by  use  of  the  linear  or  Quendstedt  projec- 
tion as  explained  in  the  following  paragraphs,  which  have  been  taken  almost  verbatim 
from  Penfield's  description  of  the  process. 

The  principle  upon  which  the  linear  projection  is  based  is  very  simple:  Every  face  of  a 
crystal  (shifted  if  necessary,  but  without  change  of  direction)  is  made  to  intersect  the  vertical 
axis  at  UNITY,  and  then  its  intersection  with  the  horizontal  plane,  or  the  plane  of  the  a  and  b 
axis  is  indicated  by  a  line.  For  instance  if  a  given  face  has  the  indices  111  it  is  clear  that 
its  linear  projection  would  be  a  line  passing  through  la  and  16,  since  the  face  under  these 
conditions  will  also  pass  through  Ic.  If,  however,  the  indices  of  the  face  are  112  it  will 
only  pass  through  1/2  c  when  it  passes  through  la  and  15.  In 
order  to  fulfill,  therefore,  the  requirements  of  the  linear  projec- 
tion that  the  plane  should  pass  through  Ic  the  indices  must 
be  multiplied  by  two  and  then  under  these  conditions  the  line 
in  which  the  plane  intercepts  the  horizontal  plane,  or  in  other 
words  the  linear  projection  of  the  face,  will  pass  through  2a  and 
26.  In  the  case  of  a  prism  face  with  the  indices  110,  its  linear 
projection  will  be  a  line  having  the  same  direction  as  a  line  join- 
ing la  and  16  but  passing  through  the  point  of  intersection  of 
these  axes,  since  a  vertical  plane  such  as  a  prism  can  only 
pass  through  Ic  when  it  also  includes  the  c  axis  and  so  must 
have  its  linear  projection  pass  through  the  point  of  intersection 
of  the  three  axes.  •- 

When  it  is  desired  to  find  the  direction  of  an  edge  made  by  the 
meeting  of  any  two  faces,  the  lines  representing  the  linear  projec- 
tion of  the  faces  are  first  drawn,  and  the  point  where  they  inter- 
sect is  noted.  Thus  a  point  common  to  both  faces  is  deter- 
mined, which  is  located  in  the  plane  of  the  a  and  6  axes.  A 
second  point  common  to  the  two  faces  is  unity  on  the  vertical 
axis,  and  a  line  from  this  point  to  where  the  lines  of  the  linear 
projection  intersect  gives  the  desired  direction. 

A  simple  illustration,  chosen  from  the  orthorhombic  system, 
will  serve  to  show  how  the  linear  projection  may  be  employed 
in  drawing.  The  example  is  a  combination  of  barite,  such  as 
is  shown  in  figure  1037.  The  axial  ratio  of  barite  is  as  follows: 

a  :  b  :  c  =  0'8152  :  1  :  1'3136 

The  forms  shown  in  the  figure  and  the  symbols  are,  base  c  (001), 
prism  m  (110),  brachydome  o  (Oil)  and  macrodome  d  (102). 

Figure   1038  represents  the   details    of  construction  of  the 
orthographic  and  clinographic  projections  shown  in  figure  1037. 
On  the  orthographic  axes  the  axial  lengths  a  and  6  are  located,  the  vertical  axis  c  being 


1037 


654 


APPENDIX  A 


1038 


(2a  :  oo  6  ;  c),  the  lines  xy  and  x'y',  through  2a  parallel  to  the  6  axis:  The  prism  m  (110) 
is  parallel  to  the  vertical  axis,  hence  in  order  that  such  a  plane  shall  satisfy  the  con- 
ditions of  the  linear  projection  and  pass  through  unity  on  the  vertical  axis,  it  must  be 
considered  as  shifted  (without  change  of  direction)  until  it  passes  through  the  center: 
Its  linear  projection  therefore  is  represented  by  the  lines  yz  and  y'z',  parallel  to  the 
directions  la  to  16  on  the  two  sets  of  axes.  Since  a  linear  projection  is  made  on  the 
plane  of  the  a  and  6  axes,  the  intersection  of  any  face  with  the  base  (001)  has  the  same 
direction  as  the  line  representing  its  linear  projection.  It  is  well  to  note  that  the  inter- 
sections x,  y  and  z  and  x',  y'  and  z'  are  in  vertical  alignment  with  one  another. 

Concerning  the  drawing  of  figure  1038,  it  is  a  simple  matter  to  proportion  the  general 
outline  of  the  barite  crystal  in  orthographic  projection.  The  direction  of  the  edge  between 
d,  102,  and  o,  Oil,  is  determined  by  finding  the  point  x,  where  the  lines  of  the  linear  pro- 
jection of  d  and  o  intersect,  and  drawing  the  edge  parallel  to  the  direction  from  x  to  the 
center  c.  The  intersection  of  the  prism  m,  110,  with  d  and  o  is  a  straight  line,  parallel  to 
the  direction  la  to  16  or  y  to  z.  To  construct  the  clinorraphic  figure,  at  some  convenient 
point  beneath,  the  axes  the  horizontal  middle  edges  of  the  crystal  may  be  drawn  parallel 
to  the  a  and  6  axes,  their  lengths  and  intersections  being  determined  by  carrying  down 
perpendiculars  from  the  orthographic  projection  above.  The  intersection  between  d, 


APPENDIX  A 


655 


1039 


102,  and  o,  Oil,  is  determined  by  finding  the  point  x'  of  the  linear  projection  and  drawing 
the  edge  parallel  to  the  direction  from  x'  to  1  (unity]  on  the  vertical  axis,  while  the  corre- 
sponding direction  below  is  parallel  to  the  direction  x'  to  -  1,  The  size  of  the  prism  m 
110,  and  its  intersections  with  d  and  o  may  all  be  determined  by  carrying  down  perpendicu- 
lars from  the  orthographic  projection  above,  but  it  is  well  to  control  the  directions  by 
means  of  the  linear  projection:  The  edges  between  m,  110,  and  d,  102;  and  m,  110,  and 
o,  Oil,  are  parallel  respectively  to  the  directions  y'  to  1  and  z'  to  1.  Having  completed 
a  figure,  a  copy  free  from  construction  lines  may  be  had  by  placing  the  .drawing  over  a 
clean  sheet  of  paper  and  puncturing  the  intersections  of  all  edges  with  a  needle-point: 
An  accurate  tracing  may  then  be  made  on  the  lower  paper. 

Should  it  happen  that  the  linear  projection  made  on  the  plane  of  the  a  and  b  axes  gives 
intersections  far  removed  from  the  center  of  the  figure,  a  linear  projection  may  be  made  on 
the  clinographic  axes  either  on  the  plane  of  the  a  and  c  or  b  and  c  axes,  supposing  that  the 
faces  pass,  respectively,  through  unity  on  the  b  or  the  a  axes. 

Importance  of  an  Orthographic  in  connection  with  a  Clinpgraphic  Projection.  —  Many 
students,  on  commencing  the  study  of  crystallography,  fail  to  derive  the  benefit  they  should 
from  the  figures  given  in  text-books.  Generally 
clinographic  projections  are  given  almost  exclus- 
ively, with  perhaps  occasional  basal  or  ortho- 
graphic projections,  and  beginners  find  it  hard 
to  reconcile  many  of  the  figures  with  the  ap- 
pearance of  the  models  and  crystals  which  they 
are  intended  to  represent.  For  example,  given 
only  the  clinographic  projection  of  barite,  figure 
1037,  it  takes  considerable  training  and  knowledge 
of  the  projection  employed  to  gain  from  the  figure 
a  correct  idea  of  the  proportions  of  the  crystal 
which  it  actually  represents.  This  may  be  shown 
by  comparing  figures  1037  and  1039,  which  rep- 
resent the  same  crystal,  drawn  one  with  the  a, 
the  other  with  the  6  axis  to  the  front.  It  is 

seen  from  figure  1039  that  the  crystal  is  far  longer  in  the  direction  of  the  a  axis  than  one 
would  imagine  from  'inspection  of  only  the  clinographic  projection  of  figure  1037.  The 
front  or  a  axis  is  much  foreshortened  in  clinographic  projection, 
consequently  by  the  use  of  only  this  one  kind  of  projection  there 
is  a  two-fold  tendency  to  err;  on  the  one  hand,  in  drawing,  one 
is  inclined  to  represent  those  edges  running  parallel  to  the  a 
axis  by  lines  which  are  considerably  too  long,  while,  on  the 
other  hand,  in  studying  figures  there  is  a  tendency  to  regard 
them  as  representing  crystals  which  are  too  much  compressed 
in  the  direction  of  the  a  axis.  By  using  orthographic  in  con- 
nection with  clinographic  projections  these  tendencies  are  over- 
come. Having  in  mind  the  proportions  of  a  certain  crystal,  or 
having  at  hand  a  model,  it  is  easy  to  construct  an  orthographic 
projection  in  which  the  a  and  b  axes  are  represented  with  their 
true  proportions;  then  the  construction  of  a  clinographic  projec- 
tion of  correct  proportions  follows  as  a  comparatively  simple 
matter.  Without  an  orthographic  projection  it  would  have  been 
a  difficult  task  to  have  constructed  the  clinographic  projection 
of  figure  1039  wth  the  proportions  of  the  intercepts  upon  the 
a  and  6  axes  the  same  as  in  figure  1037,  while  with  the  ortho- 
graphic projection  orientated  as  in  figure  1039  it  was  an  easy 
matter.  A  combination  of  the  two  projections  is  preferable  in 
many  cases  and  from  the  two  figures  a  proper  conception  of 
the  development  of  the  crystal  may  be  had. 

Drawing  of  Twin  Crystals.  —  The  axial  protractor  furnishes  a 
convenient  means  for  plotting  the  axes  of  twin  crystals.  The 
actual  operation  will  differ  with  different  problems  but  the  gen- 
eral methods  are  the  same.  The  two  examples  given  will  illus- 
trate these  methods. 

(1).    To  plot  the  axes  for  the  staurolite  twin  shown  in  Fig.  1040. 
In  this  _  case    the   twinning    plane    is   parallel    to    the  crystal 
face  232  which  has  the   axial   intercepts   of  -3/2a,  b,  -3/2c. 
For  staurolite,  a  :  b  :  c  =  0'473  :  1  :  0'683,  while  the  #  and  p  angles  of  the  twinning  plane 


1040 


656 


APPENDIX   A 


are  A  =  010  A  230  =  54°  37'  and  P  =  001  A  232  =  60°  31'.  To  insure  accuracy  in  plot- 
ting the  full  lengths  of  the  axes  of  the  protractor  have  been  regarded  as  unity.  The  first 
steD  is  to  locate  on  the  clinographic  projection  the  position  of  the  twinning  plane,  232. 

This  is   shown   in  Fig.  1041  as  the  triangle 


1041 


1042 


from  -  3/2a  to  b  to  -  3/2c.  The  next  step  is 
to  find  the  position  of  the  twinning  axis 
which  will  be  normal  to  this  plane.  The 
coordinates  of  this  twinning  axis  are  given 
by  the  <f>  and  p  angles  quoted  abov«.  The 
point  p  which  is  54°  37'  back  from  the  pole 
to  010  or  b  marks  _the  place  where  the  normal 
to  the  prism  face  230  would  ejnerge  from  the 
sphere.  The  normal  to  232,  which  is  the 
twinning  axis  will  emerge  on  the  meridian 
that  runs  through  the  point  p  and  at  such  a 
distance  below  it  that  it  will  make  the  angle 
60°  31'  with  the  negative  end  of  the  c  axis. 
Chords  are  drawn  to  p  from  the  points  where 
the  a  and  b  axes  meet  the  equator  of  the 
sphere  and  then  chords  parallel  to  these  are 
drawn  from  the  points  x,  y  and  z  which  are  in 
each  case  60°  31'  from  the  point  where  the 
negative  end  of  the  c  axis  cuts  the  spherical 
surface.  The  common  meeting  point  of 

these  chords  T  marks  the  place  where  the  twinning  axis  pierces  the  spherical  surface. 

The  next  step  is    to   determine   the  point    t  at  which    the    twinning    axis    cuts    the 

twinning  plane.     The  line  OPp  is  by  construction  at  right  angles  to  the  line  connecting 

-3/2a  and  16.     Therefore  a  vertical  plane  which  is  normal  to  the  twinning  plane  would 

intersect  that  plane  in  the  line  connecting— 3 /2c  and  P.     The  twinning  axis  OT  would  He 

in  this  plane  also.     Consequently  the  point  t,  where  OT  and  -3/2c-P  intersect  would  Ke 

both  on  the  twinning  axis  and  in 

the  twinning  plane.     In  order  to 

make  the  method  of  construction 

clearer  Fig.  1042  is  given.     Here 

the    twinning    axis    is    repeated 

from  Fig.  1041.     The  twin  posi- 
tion of  the  crystal  is  to  be  found 

by  revolving  it  from  its  normal 

position  through  an  arc  of  180°, 

using  the  twinning  axis  as    the 

axis    of    revolution.      This    will 

turn  the  twinning   plane    about 

upon  the  point  t  as  a  pivot  and 

so  transpos3  the  points  -3/2a,  6 

and  -3/2c  to  points   equidistant 

from  it  in  an   opposite  position. 

By  drawing  lines  through  t  and 

laying  off  equal  distances  beyond 

that  point  the  new  points  -3/2 A, 

B  and  -3/2C  will  be  obtained. 

These  points  lie  upon  the  three 

axes  in  their  twin  position  and  so 

determine  their  directions. 
The  plotting  of  the  twin   axes 

in  the  top  view  follows  similar 

methods.     In  order  to  make  the 

construction     learer  a    separate 

figure.  Fig.  1043,  is  given.     The 

line  0-t  is  laid  off  at  an  angle  of 
4°  37'  to  the  6  axis.     Upon  this 

ith*  th^  £  1S  founlby  Projection  upward  from  the  clinographic  view  below.     This 
meS      6    0"?1  a,r°Uud  which  the  axes  are  ^olved  180°  to  their  twin 
Y         methods  of  construction  and  the  directions  of 


APPENDIX   A 


657 


1043 


Upon  the  twin  axes  found  in  this  way  the  portion  of  the  crystal  in  twin  position  is  drawn 
in  exactly  the  same  manner  as  if  it  was  in  the  normal  position. 

(2).  To  plot  the  axes  for  the  calcite  twin  shown  in  Fig.  1044.  In  this  case  it  was  desired 
to  represent  a  scalenohedron 
twinned  upon  the  rhombohedron 
/  (0221)  and  so  drawn  that  the 
twinning  plane  should  be  vertical 
and  have  the  position  of  6  (010)  of 
an  orthorhombic  crystal.  The 
angle  from  c  (001)  to  /  (0221) 

equals   63°  7'.     In   order  to  make  \ 

the  face  /  vertical,  the  vertical  axis  \ 

must  be  inclined  at  an  angle  of 
26°  53',  or  the  angle  between  the 
c  axes  of  the  two  individuals  com- 
posing the  twin  would  be  double 
this  or  53°  46'.  These  relations  are 
shown  in  Fig  1045.  As  indicated 
in  Fig.  1046  the  position  of  these 
axes,  c  and  C  in  the  figure,  are  easily 
obtained  at  inclinations  of  26°  53* 
by  use  of  the  graduation  of  the 
vertical  ellipse  that  passes  through 
B  and  -B.  The  points  X,X'  and 
Y,  Y'  indicate  the  intersections  with 
this  same  eclipse  of  the  two  planes 
containing  the  a\,  a-2  and  a3  axes  in 
their  respective  inclined  positions, 
the  angles  -BX,  BX',  and  BY  and 

-BY'  being  in  each  case  equal  to  26°  53'.     In  order  to  have  the  twinning  plane  occupy  a  posi- 
tion parallel  to  the  010  plane  of  an  orthorhombic  crystal  it  is  necessary  to  revolve  the  axes  so 


1044 


1045 


1045 


that  one  of  the  a  hexagonal  axes  shall  coincide  with  the  position  of  the  a  axis  of  the  orthor- 
hombic system,  as  -a3,  a3  in  Fig.  1046.  The  two  other  hexagonal  axes  corresponding  to  the 
axis  c  must  therefore  lie  in  a  plane  which  includes  -a3,  as  and  the  points  X  and  X'  and  have 
such  positions  that  they  will  make  angles  of  60°  with  -o3,  a3.  The  construction  necessary 


APPENDIX  A 

to  determine  the  ends  of  these  axes  is  as  follows:  Draw  the  two  chords  lettered  x-x' 
SrouKh^Snte  that  are  60°  from  -as  and  a3  and  parallel  to  the  direction  of  a  chord  that 
would ^Hhrough  -B  and  X.  In  a  similar  way  draw  the  two  chords  y-y  through  the 
second  ™r  of  Sts  that  are  60°  from  -a,  and  a,,  parallel  to  the  direction  of  a  chord  that 
wou?d  pis  through  the  points  B  and  X.  The  intersections  of  these  two  sets  of  chords 
determfnTthe  points  *  and  -a*  which  are  the  ends  of  these  respective  axes.  The  hexagon 
shown  in  the  figure  connects  the  ends  of  the  fll,  «2  and  as  axes  that  lie  in  a  plane  perpendicular 
to  the  axis  c.  The  set  of  axes  that  belong  to  the  axis  C  are  to  be  found  m  a  similar  way. 
The  length  of  the  vertical  axis  is  to  be  obtained  by  multiplying  that  of  calcite  c  =  0'854 
by  three  and  laying  off  on  the  vertical  line  the  length  obtained  or  2'562  This  is  transferred 
to  the  twin  axis  c  by  drawing  the  line  p'-p'  parallel  to  the  line  p-p.  The  desired  figure  of 
the  calcite  twin  is  to  be  drawn  upon  these  two  sets  of  inclined  axes. 

DRAWING  CRYSTALS  BY  USE  OF  THE  STEREOGRAPHIC  AND  GNOMONIC 
PROJECTIONS 

The  following  explanation  of  the  methods  of  drawing  crystals  from  the  projections  of 
their  forms  has  been  taken  with  only  minor  modifications  from  Penfield's  description.* 

1.  USE  OF  THE  STEREOGRAPHIC  PROJECTION 

In  explaining  the  method,  a  general  example  has  been  chosen;  the  construction  of  a 
drawing  of  a  crystal  of  axinite,  of  the  triclinic  system.  Figure  1047A  represents  a  steno- 
graphic projection  of  the  ordinary  forms  of  axinite,  m  (110),  a  (100),  M  (110),  p  (111), 
r  (111)  and  s  (201).  As  shown  by  the  figure,  theirs*  meridian,  locating  the  position  of  010, 
has  been  chosen  at  20°  from  the  horizontal  direction  SS'. 

Figure  1047B  is  a  plan,  or  an  orthographic  projection  of  an  axinite  crystal,  as  it  appears 
when  looked  at  in  the  direction  of  the  vertical  axis.  It  may  be  derived  from  the  stereo- 
graphic  projection  in  a  simple  manner,  as  follows:  —  The  direction  of  the  parallel  edges 
made  by  the  intersections  of  the  faces  in  the  zone  m,  s,  r,  m',  A,  is  parallel  to  a  tangent  at 
either  m  or  m',  and  this  direction  may  be  had  most  easily  by  laying  a  straight  edge  from 
m  to  m'  and,  by  means  of  a  90°  triangle,  transposing  the  direction  to  B,  as  shown  by  the 
construction. 

The  construction  of  C,  which  may  be  called  a  parallel-perspective  view,  may  next  be 
explained:  It  is  not  a  clinographic  projection  like  the  usual  crystal  drawings  from  axes, 
but  an  orthographic  projection,  made  on  a  plane  intersecting  the  sphere,  represented  by 
the  stereographic  projection,  A,  along  the  great  circle  SES';  the  distance  EC  being  10°. 
The  plane  on  which  a  drawing  is  to  be  made  may,  of  course,  have  any  desired  inclination 
or  position,  but  by  making  the  distance  CE  equal  10°  and  taking  the  first  meridian  at  20° 
from  S,  almost  the  same  effects  of  plan  and  parallel  perspective  are  produced  as  in  the 
conventional  method  of  drawing  from  axes^  where  the  eye  is  raised  9°  28'  and  the  crystal 
turned  18°  26'. 

The  easiest  way  to  explain  the  construction  of  C  from  A  is  to  imagine  the  sphere,  repre- 
sented by  the  stereographic  projection,  as  revolved  80°  about  an  axis  joining  S  and  S',  or 
until  the  great  circle  SES'  becomes  horizontal.  After  such  a  revolution,  the  stereographic 
projection  shown  in  A  would  appear  as  in  D,  and  the  parallel-perspective  drawing,  E, 
could  then  be  derived  from  D  in  exactly  the  same  manner  as  B  was  derived  from  A.  This 
is,  for  example,  because  the  great  circle  through  m,  s  and  r,  D,  intersects  the  graduated 
circle  at  x,  where  the  pole  of  a  vertical  plane  in  the  same  zone  would  fall,  provided  one 
were  present;  hence  the  intersection  of  such  a  surface  with  the  horizontal  plane,  and,  con- 
sequently, the  direction  of  the  edges  of  the  zone,  would  be  parallel  to  a  tangent  at  z:  In 
other  words,  E  is  a  plan  of  a  crystal  in  the  position  represented  by  the  stereographic  pro- 
jection, D.  Although  not  a  difficult  matter  to  transpose  the  poles  of  a  stereographic 
projection  so  as  to  derive  D  from  A,  it  takes  both  time  and  skill  to  do  the  work  with  ac- 
curacy, and  it  is  not  at  all  necessary  to  go  through  the  operation.  To  find  the  direction 
of  the  edges  of  any  zone  in  C,  for  example  m  s  r,  note  first  in  A  the  point  x,  where  the  great 
circles  m  s  r  and  SES'  cross.  During  the  supposed  revolution  of  80°  about  the  axis  SS', 
the  pole  x  follows  the  arc  of  a  small  circle  and  falls  finally  at  x'  (the  same  position  as  x  of 
D)  and  a  line  at  right  angles  to  a  diameter  through  x',  as  shown  by  the  construction,  is 
the  desired  direction  for  C.  Similarly  for  the  zones  pr,  MrM'  and  MspM',  their  inter- 
sections with  SES'  at  w,  y  and  z  are  transposed  by  the  revolution  of  80°  to  w',  y'  and  z'. 
The  transposition  of  the  poles  w,  x,  y  and  z,  A,  to  w',  x',  y'  and  z'  may  easily  be  accomplished 

*  Am.  J.  Sc.,  21,  206,  1906. 


APPENDIX  A 


659 


in  the  following  ways:  —  (1)  By  means  of  the  Penfield  transparent,  small-circle  pro- 
tractor (*ig-  68,  p.  39)  the  distances  of  w,  x,  y  and  z  from  either  S  or  S'  may  be  deter- 
mined and  the  corresponding  number  of  degrees  counted  off  on  the  graduated  circle.  (2) 

1047 


Development  of  a  plan  and  parallel-perspective  figure  of  axinite,  triclinic  system 
from  a  stereographic  projection  (after  Penfield) 

Find  first  the  pole  P  of  the  great  circle  SES',  where  P  is  90°  from  E  or  80°  from  C,  and 
is  located  by  means  of  a  stereographic  scale  or  protractor  (Fig.  62,  p.  35) :  A  straight  line 
drawn  through  P  and  x  will  so  intersect  the  graduated  circle  at  x',  that  S'x  and  S'x'  are 
equal  in  degrees.  The  reason  for  this  is  not  easily  comprehended  from  A,  but  if  it  is  im- 
agined that  the  projection  is  revolved  90°  about  an  axis  A  A',  so  as  to  bring  S'  at  the  center, 
the  important  poles  and  great  circles  to  be  considered  will  appear  as  in  figure  1048,  where 
P  and  C'  are  the  poles,  respectively,  of  the  great  circles  ES'E'  and  AS' A',  and  x  is  41  £° 
from  S'  as  in  figure  1047 A.  It  is  evident  from  the  symmetry  of  figure  1048  that  a  plane 
surface  touching  at  C',  P  and  x  will  so  intersect  the  great  circle  AS' A'  that  the  distances 
S'x  and  S'x'  are  equal.  Now  a  plane  passing  through  C",  P,  x  and  x',  if  extended,  would 
intersect  the  sphere  as  a  small  circle,  shown  in  the  figure,  but  since  this  circle  passes  through 
C',  which  in  figure  1047A  is  the  pole  of  the  stereographic  projection  (antipodal  to  C),  it 
will  be  projected  in  figure  A  as  a  straight  line,  drawn  through  P  and  x,  since  the  intersec- 
tions upon  the  plane  of  projection  of  all  planes  that  pass  through  the  point  of  vision  of  the 
projection  will  appear  as  straight  lines.  (3)  In  figure  1048  B  is  located  midway  between  E 


660 


APPENDIX  A 


and  A'  BS'B'  is  a  great  circle,  and  W,  40°  from  C,  is  its  pole:  It  is  now  evident  from  the 
symmetry  of  the  figure  that  a  great  circle  through  W  and  x  so  intersects  the  great  circle 
A&A'  that  the  distances  S'x  and  S'x'  are  equal.  Transferring  the  foregoing  relations 

to  figure  1047A,  W,  40°  from  C,  is  the  pole  of  the 
great  circle  SBS',  and  a  great  circle  drawn 
through  W  and  x  falls  at  x'.  However,  it  is  not 
necessary  to  draw  the  great  circle  through  W 
and  x  to  locate  the  point  x'  on  the  graduated 
circle:  By  centering  the  Penfield  transparent 
great  circle  protractor,  (Fig.  67,  p.  39)  at  C,  and 
turning  it  so  that  W  and  x  fall  on  the  same  great 
circle,  the  point  x  may  be  transposed  to  x',  and 
other  points,  wf,  y'  and  z',  would  be  found  in 
like  manner. 

The  three  foregoing  methods  of  transposing  x 
tox',z  to  z',  etc.,  are  about  equally  simple,  and 
it  may  be  pointed  out  that,  supplied  with 
transparent  stereographic  protractors,  and 
having  the  poles  of  a  crystal  plotted  in  stereo- 
graphic  projection,  it  is  only  necessary  to  draw 
the  great  circle  SES'  and  to  locate  one  point, 
either  W  or  P,  in  order  to  find  the  directions 
needed  for  a  parallel-perspective  drawing,  cor- 
responding to  figure  1047C.  Thus,  with  only  a 
great  circle  protractor,  the  great  circle  through 
the  poles  of  any  zone  may  be  traced,  and  its 

intersection  with  SES'  noted  and  spaced  off  with  dividers  from  either  S  or  S';  then 
the  great  circle  through  the  intersection  just  found  and  W  is  determined,  and  where 
it  falls  on  the  divided  circle  noted,  when  the  desired  direction  may  be  had  by  means  of 
a  straight  edge  and  90°  triangle,  as  already  explained. 

2.   DRAWING  OF  TWIN  CRYSTALS  BY  USE  OF  THE  STEREOGRAPHIC  PROJECTION 

In  the  great  majority  of  cases  the  drawing  of  twin  crystals  can  be  most  advantageously 
accomplished  by  the  use  of  a  stereographic  projection  of  their  forms.  It  is  only  necessary 
first  to  prepare  a  projection  showing  the  poles  of  the  faces  in  the  normal  and  twin  po- 
sitions and  then  follow  the  methods  outlined  above.  The  preparation  of  the  desired  pro- 
jection may,  however,  need  some  explanation.  An  illustrative  example  is  given  below 
taken  from  an  article  by  Ford  and  Tillotson  on  some  Bavenno  twins  of  orthoclase.* 

According  to  the  Baveno  law  of  twinning  the  n  (021)  face  becomes  the  twinning  plane 
and  as  the  angle  c  A  n  =  44°  56  1/2'  the  angle  between  c  and  c'  (twin  position)  becomes 
89°  53'.  For  the  purposes  of  drawing  it  is  quite  accurate  enough  to  assume  that  this 
angle  is  exactly  90°  and  that  accordingly  the  r.  face  of  the  twin  will  occupy  a  position  paral- 
lel to  that  of  the  b  face  of  the  normal  individual. 

Fig.  1049  shows  the  forms  observed  of  the  crystals  both  in  normal  and  in  twin  positions, 
the  faces  in  twin  position  being  indicated  by  open  circles  and  a  prime  mark  (')  after  their 
respective  letters,  while  the  zones  in  twin  position  are  drawn  in  dashed  lines.  Starting 
out  with  the  forms  in  normal  position,  the  first  face  to  transp9se  is  the  base  c.  This  form, 
from  the  law  of  the  twinning,  will  be  transposed  to  c'  where  it  occupies  the  same  position 
as  6  of  the  normal  individual,  and  it  necessarily  follows  that  6  itself  in  being  transposed  will 
come  to  b'  at  the  point  where  the  normal  c  is  located. 

In  turning  therefore  the  crystal  to  the  left  from  normal  to  twin  position,  the  fades  c 
and  6  travel  along  the  great  circle  I  through  an  arc  of  90°  until  they  reach  their  respective 
twin  positions.  We  have,  in  other  words,  revolved  the  crystal  90°  to  the  left  about  an  axis 
which  is  parallel  to  the  faces  of  the  zone  I.  The  pole  of  this  axis  is  located  on  the  stereo- 
graphic  projection  at  90°  from  the  great  circle  I  and  falls  on  the  straight  line  II,  another 
great  circle  which  intersects  zone  I  at  right  angles.  This  pole  P  is  readily  located  by  the 
stereographic  protractor  on  the  great  circle  II  at  90°  from  c.  The  problem  then  is  to  re- 
volve the  poles  of  the  faces  from  their  normal  positions  about  the  point  P  to  the  left  and 
through  an  arc  of  90°  in  each  case. 

During  the  revolution  the  poles  of  the  n  faces  remain  on  the  great  circle  I  and  as  the 
angle  n  A  n  =  K)  ,  the  location  of  their  poles  when  in  twin  position  is  identical  with  that  of 


Am.  J.  Sc.,  26,  149,  1908. 


APPENDIX  A 


661 


the  normal  position  and  n'  falls  on  top  of  n.  We  can  now  transpose  the  great  circle  II  from 
its  normal  to  its  twin  position,  since  P  remains  stationary  during  the  revolution  and  we 
have  determined  the  twin  position  of  c.  The  dashed  arc  II'  gives  the  twin  position  of  the 

1049 


great  circle  II.  The  twin  position  of  y  must  lie  on  arc  II'  and  can  be  readily  located  at  y', 
the  intersection  of  arc  II'  with  a  small  circle  about  P  having  the  radius  P  Ay.  It  is  now 
possible  to  construct  the  arc  of  the  zone  III  in  its  transposed  position  III',  for  we  have  two 
of  the  points,  y'  and  n'  of  the  latter,  already  located.  By  the  aid  of  the  Penfield  transparent 
great  circle  protractor  the  position  of  the  arc  of  the  great  circle  on  which  these  two  points 
lie  can  be  determined.  On  this  arc,  III',  o'  and  m'  must  also  lie.  Their  positions  are  most 
easily  determined  by  drawing  arcs  of  small  circles  about  b'  with  the  required  radii,  6  A  o 
=  63°  8',  b  A  //*  =  59°  22  1/2'  and  the  points  at  which  they  intersect  arc  III'  locate  the 
position  of  the  poles  o'  and  mf.  At  the  same  time  the  corresponding  points  on  IV  may  be 
Jocated,  it  being  noted  that  IV  and  III  are  the  same  arc.  But  one  other  form  remains 
to  be  transposed,  the  prism  z.  We  have  already  6'  and  m'  located  and  it  is  a  simple  matter 
with  the  aid  of  the  great  circle  protractor  to  determine  the  position  of  the  great  circle 
upon  which  they  lie.  Then  a  small  circle  about  6'  with  the  proper  radius,  b/\z  =  29°  24', 
determines  at  once  by  its  intersections  with  this  arc  the  position  of  the  poles  of  the  z  faces. 
It  may  be  pointed  out  that  if  it  should  be  desired  to  make  use  of  the  methods  of  the 
gnonomic  projection  for  the  drawing  of  the  figures  as  described  below,  the  stereographic 
projection  of  the  forms  may  be  readily  transformed  into  a  gnomonic  projection  by  doubling 
the  angular  distance  from  the  center  of  the  projection  to  each  pole  by  the  use  of  the  stereo- 
graphic  protractor,  Fig.  62,  p.  35. 

3.   USE  OF  THE  GNOMONIC  PROJECTION 

As  an  illustration,  the  method  of  drawing  a  simple  combination  of  barite  has  been  chosen. 
The  forms  shown  in  figure  1050  are  c  (001),  m  (110),  o  (Oil)  and  d  (102).  The  location 
of  the  poles  in  the  gnomonic  projection  is  shown  in  A,  where,  as  in  figure  1047A.  the  first 


662 


APPENDIX   A 


meridian  is  taken  at  20°  from  the  horizontal  direction  SS  .  The  poles  of  the  prism  m  and 
locations  of  S  and  S'  (compare  figure  1047A)  fall  in  the  gnomonic  projection  at  infinity. 
In  any  plan  such  as  figure  1050B,  the  direction  of  an  edge  made  by  the  meeting  of  two  faces 


1050 


A  at  oo 


tfatoo 


y  at  oo 


is  at  right  angles  to  a  line  joining  the  poles  of  the  faces,  shown  in  figures  A  and  B  by  the  di- 
rection at  90°  to  the  line  joining  m"  and  c. 

The  parallel-perspective  view,  1050C,  is  an  orthographic  projection  (compare  figures 
1047  A  and  C)  drawn  on  a  plane  passing  through  S  and  S',  and  intersecting  the  sphere  on 
which  the  gnomonic  projection  is  based  as  a  great  circle  passing  through  E,  figure  1050A, 
and  drawn  parallel  to  SS',  the  distance  cE  being  10°:  This  great  circle  is  called  by  Gold- 
schmidt  the  Leitlinie.  To  find  such  intersections  as  between  m"'  and  c,  and  m  and  d, 
figure  C,  note,  as  in  figure  1047A,  where  the  great  circles  through  the  poles  of  the  faces 
intersect  the  Leitlinie;  thus,  the  one  through  m'"  and  c  at  x,  and  that  through  m  and  d 
(through  d  parallel  to  m  m",  since  m  and  m"  are  at  infinity)  at  y.  Next  imagine  the  points 
x  and  y  transposed  as  in  figure  1047  A  to  x'  and  y',  which  latter  pomts,  however,  are  located 
at  infinity:  This  transposition  is  done  by  locating  first  the  so-called  Winkelpunkt,  W,  of 
Goldschmidt,  40°  from  c  in  figure  1050A,  and  as  in  figure  1047A,  90°  from  a  point  B,  which 
is  an  equal  number  of  degrees  from  E  and  A'  (compare  figure  1048).  Of  the  three  methods 
given  above  for  transposing  x  and  y  to  x'  and  y',  the  third  may  be  easily  applied  in  the  gnom- 
onic projection.  Great  circles,  or  straight  lines,  through  W  and  x  and  W  and  y,  figure 
1050A,  if  continued  to  infinity,  would  determine  x'  and  y',  which  is  accomplished  by  draw- 
ing lines  parallel  to  Wx  and  Wy  through  the  center.  It  is  not  necessary,  however,  to 
draw  the  lines  Wx  and  Wy,  nor  the  parallel  lines  through  the  center;  all  that  is  needed  to 
find  the  directions  of  the  edges  m'"  A  c  and  m  A  d  is  to  lay  a  straight  edge  from  W  to  x,  re- 
spectively W  to  y,  and  with  a  90°  triangle  transpose  the  directions  to  C,  as  indicated  in 
the  drawings.  The  principles  are  exactly  the  same  as  worked  put  for  the  interrelations 
of  figures  1047A  and  C.  As  in  the  case  of  the  stereographic  projection,  it  is  evident  that, 
given  the  poles  of  a  crystal  plotted  in  the  gnomonic  projection,  it  would  be  necessary  to 
draw  only  one  line,  the  Leitlinie,  and  to  locate  one  point,  the  Winkelpunkt,  W,  in  order  to 
find  all  possible  directions  for  a  plan  and  parallel-perspective  views,  corresponding  to 
figures  1050B  and  C. 


APPENDIX  B 


TABLES  USEFUL  IN  THE  DETERMINATION 
OF  MINERALS 


THIS  Appendix  contains  a  series  of  tables,  more  or  less  complete,  of  minerals  arranged 
according  to  chemical  composition  or  to  certain  prominent  crystallographic  or  physical 
characters.  These,  it  is  believed,  will  be  of  service  not  only  to  the  student,  but  also  to 
the  skilled  mineralogist. 

The  type  used  in  the  printing  of  the  mineral  names  indicates  their  relative  importance. 
Table  I  is  a  complete  list  of  the  species  named  in  this  book  arranged  first  according  to  the 
prominent  basic  elements  which  they  contain  and  secondly  according  to  their  acid  radicals. 
Table  II  is  of  Minerals  arranged  according  to  their  System  of  Crystallization.  The  other 
tables  make  no  claim  to  completeness,  being  limited  often  to  common  and  important 
species. 

For  an  exhaustive  system  of  Determinative  Tables  based  particularly  upon  blowpipe 
and  chemical  characters,  the  student  is  referred  to  the  work  of  Professors  Brush  and  Pen- 
field,  mentioned  on  p.  330. 

TABLE  I.    MINERALS  ARRANGED  ACCORDING  TO 
CHEMICAL  COMPOSITION 

The  following  lists  include  all  definitely  described  mineral  species  arranged  first  according 
to  their  important  basic  elements  and  secondly  according  to  their  acid  radicals.  If  a 
given  mineral  contains  two  or  more  prominent  bases  its  name  is  repeated  in  all  the  ap- 
propriate sections. 

ALUMINIUM 

NOTE  :  —  Aluminium  is  of  such  common  occurrence  among  the  silicate  minerals  tnat 
it  is  impracticable  to  list  all  of  these  minerals  that  contain  it.  Therefore  only  those  sili- 
cates which  are  essentially  aluminium  minerals  are  included  in  the  following  list. 

Chloralluminit ,  A1C13.6H2O.  GIBBSITE,  A12O3.3H2O. 

CRYOLITE,  Na3AlF6.  Hydrotalcite,  Al(OH)3.3Mg(OH)2.3H2O. 

Koenenite,  Al,Mg,  oxy chloride.  Shanyavskite,  A12O3.4H2O. 

Fluellite,  A1F3.H2O.  Dundasite,  Pb(AlO)2(CO3)2. 

Prosopite,  CaF2.2Al(F,OH)3.  Dawsonite,  Na3Al(CO3)3.2Al(OH)3. 

Pachnolite,  Thomsenolite,   NaF.CaF2.AlF3.  Zunyite,  (Al(OH,F,Cl)2)6Al2Si3Oi2. 

H2O.  Topaz,  [Al(F,OH)]2SiO4. 

Gearksutite,  CaF2.Al(F,OH)3.H2O.  ANDALUSITE,  Al2SiO5. 

Ralstonite,  (Na2,Mg)F2.3Al(F,OH)3.2H2O.  SILLIMANITE,  Al2SiO6. 

Creedite,  2CaF2.2Al(F,OH)3.CaSO4.2H2O.  Cyanite,  Al2SiO5. 

Corundum,  A12O3.  Dumortierite,  8Al2O3.B2O8.6SiO2.H2O. 

Spinel,  MgO.Al2O3.  Staurolite,  (AlO)4(AlOH)Fe(SiO4)2. 

Hercynite,  FeO.Al2O3.  Kaolinite,  H4Al2Si2O9. 

Gahnite,  ZnO.Al2O3.  Faratsihite,  (Al,Fe)2O3.2SiO2.2H2O. 

Chrysoberyl,  BeO.Al2O3.  Halloysite,  H4Al2Si2O9.H2O. 

Uhligite,  Ca(Ti,Zr)O6.Al  (Ti,Al)O6.  Newtonite,  H8Al2Si2On.H2O. 

DIASPORE,  A12O3.H2O.  Cimolite,  2Al2O3.9SiO2.6H2O. 

Bauxite,  A12O3.2H2O.  Montmorillonite,  H2Al2Si4Oi2.nH2O. 

663 


664 


APPENDIX     B 


PYROPHYLLITE,  H2Al2(Si03)4. 
Allophane,  Al2Si06.5H20. 
Melite,  2(Al,Fe)203.S102.8H20. 
Collyrite,  2Al2O3.SiO2.9H2O. 
Schrotterite,  8Al2O3.3SiO2.30H2O. 
Hamlinite,  Al,Sr,  phosphate 
Plumbogummite,  Pb,Al,  phosphate. 
Florencite,  Al,Ce,  phosphate. 
Georceixite,  BaO.2Al2O3.P2O6.5H2O. 
Crandallite,  2CaO.4 A12O3.2P2O5. 10H2O. 
Harttite,  (Sr,Ca)O.2Al2O3.P2O6.SO3.5H2O. 
Durangite,  Na(AlF)AsO4. 
Amblygonite,  Li(AlF)PO4 
Fremontite,  (Na,Li)Al(OH,F)PO4. 
Lazulite,  2AlPO4.(Fe,Mg)(OH)2. 
Tavistockite,  Ca3P2O3.2Al(OH)2. 
Cirrolite,  Ca3Al(PO4)3.Al(OH)3. 
Synadelphite,  2(Al,Mn)AsO4.5Mn(OH)2. 
Hematolite,  (Al,Mn)AsO4.4Mn(OH)2. 
Barrandite,  (Al,Fe)PO4.2H2O. 
Variscite,  A1PO4.2H2O. 
Lucinite,  A1PO4.2H2O. 
Callainite,  A1PO4.2£H2O. 
Zepharovichite,  A1PO4.3H2O. 
Palmerite,  HK2A12(PO4)3.7H2O. 
Rosier6site,  Hydrous,  Al,Pb,Cu,  phosphate. 
WAVELLITE,  4A1PO4.2A1(OH)3.9H2O. 
Fischerite,  AlPO4.Al(OH)3.2iH2O. 
Peganite,  A1PO4.A1(OH)3.HH2O. 
TURQUOIS,  CuO.3Al2O3.2P2O5.9H2O. 
Wardite,  2A12O3.P2O6.4H2O. 
Sphserite,  4A1PO4.6A1(OH)3. 
Liskeardite,  (Al,Fe)AsO4.2(Al,Fe)  (OH)». 

5H2O. 

Evansite,  2A1PO4.4A1(OH)3.12H2O.    ' 
Coeruleolactite,  3 A12O3.2P2O5. 10H2O. 
Angelite,  2Al2O3.P2O6.3H2q. 
Berlinite,Trolleite,  Attacolite  1  Hydrous 
Minasite,  Vashegyite  j  Alphosphates 

Soumansite,  Hydrous,  Al,Na,  fluo-phosphate. 
Childrenite,2AlPO4.2Fe(OH)3.2H2O. 
Eosphorite,  2AlPO4.2(Mn,Fe)  (OH)3.2H2O. 
Egueiite,  Hydrous,  Fe,Al,Ca,  phosphate. 
Liroconite,  Cu6Al(AsO4)5.3CuAl(OH)6. 

20H2O. 

Henwoodite,  Al,Cu,  hydrous  phosphate. 
Ceruleite,  CuO.2Al2O3.As2O5.8H2O. 
Kehoite,  Hydrous,  Al,Zn,  phosphate. 
Goyazite,  Ca3Al10  P2O23.9H2O. 
Rosch6rite,  (Mn,Fe,Ca)2Al(OH)  (PO4)2.2H2O. 
Svanbergite,   Hydrous  Al,  Ca,   phosphate 

and  sulphate. 
Teremejevite,  A1BO3. 
Rhodizite,  A1,K,  borate. 
Millosevichite,  (Fe,Al)2(SO4)3. 
Spangolite,  Cu6AlClSO10.9H2O. 
Alumian,  A12O3.2SO3. 
KaUnite,  KA1(SO4)2.12H2O. 
Tschermigite,  (NH4)A1(SO4)2.12H2O. 
Mendozite,  NaAl(SO4)2.12H2O. 
Pickeringite,  MgSO4.Al2(SO4)3.22H2O. 
Halotrichite,  FeSO4.Al2(SO4)3.24H2O. 
Apjohnite,  MnSO4.Al2(S04)3.24H2O. 


Dietrichite,(Zn,Fe,Mn)SO4.Al2(SO4)H3.222O. 
Alunogen,  A12(SO4)3.18H2O. 
Cyanotrichite,  4CuO.Al2O3.SO3.8H2O. 
Knoxvillite,  Hydrous,  Fe,Al,Cr,  sulphate. 
Cyprusite,  7Fe2O3. A12O3. 10SO3. 14H2O. 
Aluminite,  A12O3.SO3.9H2O. 
Paraluminite,  2A12O3.SO3.10H2O. 
Felsobanyite.  2A12O3.SO3.10H2O. 
Voltaite,  3(K2,Fe)O.2(Al,Fe)2O3.6SO3.9H2O. 
ALUNITE,  K2A16(OH)12.(SO4)4. 
Lowigite,  K2O.3A12O3.4SO3.9H2O. 
Almeriite,Na2SO4.Al2(SO4)3.5Al(OH)3.H2O. 
Ettringite,6CaO.Al2O3.3SO3.33H2O. 
Zincaluminite,  2ZnSO4.4Zn(OH)2.6Al(OH)3. 

5H2O. 
Mellite,  A12C12O12.18H2O. 

ANTIMONY 

NOTE  :  —  The  antimonates  are    not    in- 
cluded in  this  list. 
Allemontite,  SbAs3. 
NATIVE  ANTIMONY,  Sb. 
Stibnite,  Sb2S3. 
Kermesite,  Sb2S2O. 
Senarmontite,  Valentinite,  Sb2O3. 
Cervantite,  Sb2O3.Sb2O6. 
Stibiconite,  H2Sb2O5. 
Stibiotantalite,  (SbO)2(Ta,Nb)2O6. 

ARSENIC 

NOTE  :  —  The  arsenates  are  not  included 
in  this  Ust. 

NATIVE  ARSENIC,  As. 
Allemontite,  SbAs3. 
REALGAR,  AsS. 
ORPIMENT,  As2S3. 
Arsenopyrite,  FeAsS. 
Arsenolite,  Claudetite,  As2O3. 

BARIUM 

Witherite,  BaCO3. 
Bromlite,  (Ba,Ca)CO3. 
Barytocalcite,  BaCO3.CaCO3. 
Hyalophane,  (K2,Ba)Al2(SiO3)4. 
Celsian,  BaAl2Si2O8. 
Cappelenite,  Y,Ba,  boro-silicate. 
Hyalotekite,  (Pb,Ba,Ca)B2(SiO3)12. 
Barylite,  Ba4Al4Si7O24. 
Taramellite,  Ba^e''  Fe4'"  SiidOM. 
Brewsterite,  H4(Sr,Ba,Ca)Al2(SiO3)6.3H2O. 
Wellsite,  (Ba,Ca,K2)Al2Si3Oi0.3H2O. 
Harmotone,  (K2,Ba)Al2Si5Oi4.5H2O. 
Edingtonite,  BaAl2Si3Oi0.3H2O. 
Benitoite,  BaTiSi3O9. 
Leucosphenite,  Na4Ba(TiO)2(Si2O5)5. 
Georceixite,  BaO.2Al2O3.P2O5.5H2O. 
Ferrazite,  3(Ba,Pb)O.2P2O5.8H2O. 
Volborthite,  Cu,Ba,Ca,  vanadate. 
Uranocircite,  Ba(UO2)2P2O8.8H2O. 
Nitrobarite,  Ba(NO3)2. 
Barite,  BaS04. 


APPENDIX     B 


665 


BERYLLIUM 
Chrysoberyl,  BeAl2O4. 
Eudidymite,  Epididymite,  HNaBeS.\3O8. 
Beryl,  Be3Al2(SiO3)6. 


Helvite,  (Be,Mn,Fe)7Si3Oi2S. 
Danalite,  (Be,Fe,Zn,Mn)7Si3Oi2S. 
Phenacite,  Be2SiO4. 
Trimerite,  (Mn,Ca)2SiO4.Be2SiO4. 
Euclase,  HBeAlSiO5. 
Gadolinite,  Be2FeY2Si2O10. 
Bertrandite,  H2Be4Si2O9. 
Beryllonite,  NaBePO4. 
Herderite,  Ca[Be(F,OH)]PO4. 
Hambergite,  Be2(OH)BO3. 

BISMUTH 

NATIVE   BISMUTH,  Bi. 

BlSMUTHINITE,  Bl2S3. 

Guanajuatite,  Bi2Se3. 
Tetradymite,  Bi2(Te,S)3. 
Grunlingite,  Bi4TeS3. 
Joseite,  Wehrlite,  bismuth  tellurides. 
Daubreete,  Bi,  oxychloride. 
Bismite,  Bi2O3. 

Bismutosparite,  Bi2(CO3)3.2Bi2O3. 
Bismutite,  Bi2O3.CO2.H2q. 
Eulytite,  Agricolite,  Bi4Si3Oi2. 
Pucherite,  BiVO4. 
Atelestite,  H2Bi3AsO8. 
Walpurgite,  Bi10(UO2)3(OH)24(AsO4)4. 
Rhagite,  2BiAsO4.3Bi(OH)3. 
Arseno-bismite,  hydrous  Bi  arsenate. 
Mixite,  Hydrous  Cu,  Bi,  arsenate. 
Uranosphaerite,  (BiO)2U2O7.3H2O. 
Montanite,  Bi2p3.Te03.2H2O. 
Koechlinite,  Bi2O3.MoO3. 

BORON 

NOTE  :  —  The  borates  are  not  included  in 
this  list. 

Sassolite,  B(OH)3. 
Cappelenite,  Y,Ba,  boro-silicate. 
Hy  alotekite,  (Pb  .  Ba,  Ca)  B2  (SiO3)  «. 
DANBURITE,  CaB2(SiO4)2. 
Datolite,  HCaBSiO5. 
Homilite,  Ca2FeB2Si2Oi0. 
Axinite,  Ca,Al,  boro-silicate. 
Tourmaline,  complex  boro-silicate. 
Dumortierite,  8AL>O3.B,O3.6SiO2.H2O. 
Serendibite,  10(Ca,Mg)O.5Al2O3.B2O3.6SiO2. 
Manandonite,  H44Li4Ali4B4.Si6O53. 
Bakerite,  Hydrous  Ca,  boro-silicate. 
Searlesite,  NaB(SiO3)2.H2O. 
Luneburgite,  3MgO.B2O3.P2O5.8H2O. 

CADMIUM 

Greenockite,  CdS. 
Cadmiumoxide,  CdO. 
Otavite,  Cd  carbonate. 


CESIUM 

Pollucite,  2Cs2O.2Al2O3.9SiO2.H2O. 
Rhodizite,  Al,K,Cs,  borate. 

CALCIUM 

Oldhamite,  CaS. 

Fluorite,  CaF2. 

Hydrophilite,  CaCl2. 

Yttrofluorite,  (Ca3,Y2)F6. 

Nocerite,  2(Ca,Mg)F2.(Ca.Mg)O. 

Tachhydrite,  CaCl2.2MgCl2.12H2O. 

Prosopite,  CaF2.2Al(F.OH)3. 

Pachnolite,  Thomsenolite,    NaF.CaF2.AlF3. 

H2O. 

Gearksutite.  CaF2.Al(F,OH)3.H2O. 
Creedite,  2CaF2.2Al(F,OH)3.CaSO4.2H2O. 
Yttrocerite,  (Y,Er,Ce)F3.5CaF2.H2O. 
UhUgite,  Ca(Ti,Zr)O5.Al(Ti,Al)O5. 
Calcite,  CaCO3. 
Dolomite,  CaCO3.MgCO3. 
Ankerite,  CaCO3.(Mg,Fe,Mn)CO3. 
Aragonite,  CaCO3. 
Bromlite,  (Ba,Ca)CO3. 
Barytocalcite,  BaCO3.CaCO3 
Parisite,  [(Ce,La,Di)F]2Ca(CO3)2. 
Pirssonite,  CaCO3.Na2CO3.2H2O. 
Gay-Lussite,  CaCO3.Na2CO3.5H2O. 
Gajite,  basic,  hydrous,  Ca,  Mg,  carbonate. 
Uranothallite,  2CaCO3.U(CO3)2. 10H2O. 
Liebigite,  Hydrous  Ca,U,  carbonate. 
Voglite,  Hydrous  U,Ca,Cu,  carbonate. 
Milarite,  HKCa2Al2(Si2O5)6. 
Rivaite,  (Ca,Na2)Si2O6. 

A^desinT       Mixtures  of  NaAlSi308  and 
Labradorite        CaAl2Si2O8. 
Anorthite,  CaAl2Si2O8. 
Anemousite,  Na2O.2CaO.3Al2O3.9SiO2. 
Pyroxene,  Ca,Mg,  etc.,  silicate. 
Wollastonite,  CaSiO3. 
PECTOLITE,  HNaCa2(SiO3)3. 
Schizoh'te,  HNa(Ca,Mn)2(SiO3)3. 
Rosenbuschite,  near  pectolite  with  Zr. 
Wohlerite,  Zr-silicate  and  niobate  of  Ca,Na. 
Lavenite,  Zr-silicate  of  Mn,Ca. 
Babingtonite,     (Ca,Fe,Mn)SiO3    with 

Fe2(SiO3)3. 

Hiortdahlite,  (Na2,Ca)(Si,Zr)O3. 
Amphibole,  Ca,  Mg,  etc.,  silicate. 
Arfvedsonite,  Na,Ca,Fe,  silicate. 
Leucophanite  i  AT    T>    n    a        -i- 
Meliphanite     I  ***&,<&  fluo-sihcate. 

Custerite,  Ca2(OH,F)SiO3. 
Didymolite,  2CaO.3Al2O3.9SiO2. 
Ganomalite,  Pb4(PbOH)2Ca4(Si2O7)3. 
Nasonite,  Pb4(PbCl)2Ca4(Si2O7)3. 
Margarosanite,  Pb(Ca,Mn)2(SiO3)3. 
Hardystonite,  Ca2ZnSi2O7. 
Rocblingite,  5(H2CaSiO4).2(CaPbSO4). 
Haiiynite,  Na2Ca(NaSO4.Al)Al2(SiO4)3. 
Grossularite,  Ca3Al2(SiO4)3. 
Andradite,  Ca3Fe2(SiO4)3. 


566  APPENDIX     B 


UVAROVITE,  Ca3Cr2(SiO4)3. 
Schorlomite,  Ca3(Fe,Ti2)  [(Si,Ti)O«]. 
MonticeUite,  CaMgSiO4. 
Glaucochroite,  CaMnSiO4. 
Trimerite,  (Mn,Ca)2SiO4.Be2SiO4. 
SCAPOLITE  GROUP,      Mixtures  of 
Ca4Al6Si6O25  and  Na4Al3Si9O24Cl. 
Sarcolite,  (Ca,Na2)3Al2(SiO4)3. 
Melilite,  Na2(Ca,Mg)n  (Al,Fe)4(SiO4)9. 


Cebollite, 

Gehlenite, 

Vesuvianite,Ca6[Al(OH,F)]Al2(Si04)6. 

DANBURITE,  CaB2(SiO4)2. 

Guarinite,  2(K,Na)2O.8CaO.5(Al,Fe,Ce)2O3. 

10SiO2. 

Datolite,  HCaBSiO5. 
Homilite,  CazFeB^iAo. 
ZOISITE,  Ca2(AlOH)Al2(SiO4)3. 
Epidote,  Ca2[(Al,Fe)OH](Al,Fe)2(SiO4)3. 
Piedmontite,  Ca2(AlOH)  (Al,Mn)2(SiO4)3. 
Allanite,  (Ca,Fe)2(AlOH)  (Al,Ce,Fe)2(SiO4)3. 
AXINITE,  Ca,Al,  boro-silicate. 
PREHNITE,  HzCa^SiO^. 
Harstigite,  Mn,Ca,  silicate 
Cuspidine,  Ca2Si(O,F2)4. 
ILVAITE,  CaFe3(FeOH)(SiO4)2. 
Clinohedrite,  H2CaZnSiO6. 
Stokesite,  H4CaSnSi3Oii. 
Lawsonite,  Hibschite,  H4CaAl2Si2Oi0. 
Beckelite,  Ca3(Ce,La,Di)4Si3O15. 
Angaralite,2(Ca,Mg)0.5(Al.Fe)2O3.6SiO2. 
Serendibite,  10(Ca,Mg)O.5Al2O3.B2O3.6SiO2. 
Silicomagnesiofluorite,  H2Ca4Mg3Si2O7Fi0. 
Gro  thine,  Ca,Al,  silicate.  , 

Aloisite,  Fe,Ca,Mg,Na,  silicate. 
Inesite,  H2(Mn,Ca)6Si6Oi9.3H2O. 
Hillebrandite,  Ca2SiO4.H2O. 
Crestmoreite,  4H2CaSiO4.3H2O. 
Riversideite,  -2CaSiO5.H2O. 
Lotrite,3(Ca,Mg)0.2(Al,Fe)203.4Si02.2H20 
Okenite,  H2CaSi2O5.H2O. 
Gyre-lite,  H2Ca2Si3O9.H2O. 
APOPHYLLITE,  H7KCa4(SiO3)8.4£H2O. 
Ptilolite.  (Ca,K2,Na,)Al2Si10O24.5H2O. 
Mordemte,  (Ca,K2,Na2)Al2Sii0O24.20H2O. 
HEULANDITE,  H4CaAl2(SiO3)6.3H2O. 
Brewsterite,  H4(Sr,Ba,Ca)Al2(SiO3)6.3H2O. 
Epistilbite,  H4CaAl2  (SiO3)6.3H2O. 
Wellsite,  (Ba,Ca,K2)Al2Si3O10.3H2O. 
Phillipsite,  (K2,Ca)Al2Si4Oi2.4iH2O. 
StUbite,  (Na2,Ca)Al2Si6Oi6.6H2O. 
Flokite,  H8(Ca,Na2)Al2Si9O26.2H2O. 
Gismondite,  CaAl2Si2O8.4H2O. 
Laumontite,  H4CaAl2Si4Oi4.2H2O. 
Laubanite,  Ca2Al2Si5Oi5.6H2O. 
CHABAZITE,  (Ca,Na2)Al2Si4Oi2.6H2O. 
Gmelinite,  (Na2,Ca)Al2Si4Oi2.6H2O. 
Levynite,  CaAl2Si3O10.5H2O. 
Faujasite,  H4Na2CaAl4Si,0O38.  18H2O. 
Scolecite,  Ca(AlOH)3(SiO3)3.2HnO. 

MS5%»  N^^SiaOio^HaO  +2[CaAl2Si3O10 
3H2OJ. 

Gonnardite,  (Ca,Na2)2Al2Si6O15.5^H2O. 


Thomsonite,  (Na2,Ca)Al2Si2O8.2£H2O. 
Hydrpthomsonite;  (H2,Na2,Ca)Ali<Si2O8. 

5H2O. 

Arduinite,  Ca,Na,  zeolite. 
Echellite,  (Ca,Na2)O.2Al2O3.3SiO2.4H2O. 
Epidesmine,  (Na2,Ca)Al2Si6Oi6.6H2O. 
Stellerite,  CaAl2Si7Oi8.7H2O. 
Erionite,  H2CaK2Na2Al2Si6Oi7.5H2O. 
Bavenite,  Ca3Al2(SiO3)6.H2O. 
Bityite,  Hydrous,  Ca,Al,  silicate. 
Margarite,  H2CaAl4Si2Oi2. 
Seybertite,  H3(Mg,Ca)5Al5Si2Oi8. 
Xanthophyllite,  H8(Mg,Ca)i4Al16Si5O62. 
Griffithite,    4(Mg,Fe,Ca)O(Al,Fe)2O3.5SiO2. 

7H2O. 

Cenosite,  H4Ca2(Y,Er)2CSi4Oi7. 
PlazoUte,3CaO.Al2O3.2(SiO2,CO2).2H2O. 
Thaumasite,  CaSiO3.CaCO3.CaSO4. 15H2O. 
Spurrite,  2Ca2SiO4.CaCO3. 
Uranophane,  CaO.2UO3.2SiO2.6H2O. 
Bakerite,  Hydrous  Ca  boro-silicate. 
TINANITE,  CaTiSiO5. 
Molengraafite,  Ca,Na,  titano-silicate. 
Keilhauite,  Ca,Al,Fe,Y,  titano-silicate. 
Joaquinite,  Ca,Fe,  titano-silicate. 
Perovskite,  CaTiO3. 
Dysanalyte,  Ca,Fe,  titano-niobate. 
Pyrochlore,  Ca,Ce,  niobate. 
Koppite,  Ca,Ce,niobate 

Chalcolamprite,  RNb2O6F2.RSiO3. 

Microlite,  Ca2Ta2O7. 

Berzeliite,  (Ca,Mg,Mn,Na1)8A8aO8. 

Graftonite,  (Fe,Mn,Ca)3P2O8. 

Apatite,  Ca4(CaF)(PO4)3. 

Fermorite,  (Ca,Sr)4[Ca(OH,F)][(P,As)O4]3. 

Wilkeite,3Ca3(PO4)2.CaCO3.3Ca3[(SiO4) 

(SO4)].CaO. 
Svabite,  Ca  arsenate. 
Spodiosite,  (CaF)CaPO4. 
AdeHte  (MgOH)CaAsO4. 
Tilasite  (MgF)CaAsO4. 
Herderite,  Ca[Be(F,OH)]PO4. 
Jezekite,  Na4CaAl(AlO)  (F,OH)4(PO4)2. 
Crandallite,  2CaO.4Al2O3.2P2O5. 10H20. 
Lacroixite,  Na4(Ca,Mn)4Al3(F,OH)4P3Oi6. 

2H2O. 
Calciovolborthite,  (Cu,  Ca)  3V2O8.  (Cu,  Ca) 

(OH)2. 

Tavistockite,  Ca3P2O8.2Al(OH)2. 
Cirrolite,  Ca3Al(PO4)3.Al(OH)3. 
Arseniosiderite,  Ca3Fe  (AsO4)  3.3Fe  (OH) 3. 
Retzian,  Y,Mn,Ca,  arsenate. 
Arseniopleite,  (Mn,  Ca)  9 (Mn, Fe)2  (OH)  6 

(AsO4)6. 

Collophanite,  Ca3P2O8.H2O. 
Pyrophosphorite,  Mg2P2O7.4(Ca3P2O8. 

Ca2P207). 

Roselite,  (Ca,Co,Mg)3As2O8.2H2O. 
Brandite,  Ca2MnAs2O8.2H2O. 
Fairfieldite,  Ca2MnP2O8.2H2O. 
Messelite,  (Ca,Fe)3P2O8.2iH2O. 
Anapaite,  (Ca,Fe)3P2O8.4H2O. 


APPENDIX     B 


667 


Picropharmacolite,  (Ca,Mg)As2O8.6H2O. 
Churchite,  Hydrous  Ca,Ce>  phosphate. 
Fernandinite,  CaO.V2O4.5V2O5.14H2O. 
Pascoite,  2CaO.3V2O5.llH2O. 
Pintadoite,  2CaO.V2O5.9H2O. 
Pharmacolite,  HCaAsO4.2H2O. 
Haidingerite,  HCaAsO4.H2O. 
Wapplerite,  HCaAsO4.3£H2O. 
Brushite,  HCaPO4.2H2O. 
Martinite,  H2Ca5(PO4)44H2O. 

Hewettite  \pao  W  O  QTT  O 

Metahewettite  }<-aO.3V2O5.9H2O. 

Isoclasite,  Ca3P2O8.Ca(OH)2.4H2O. 
Conichalcite,   (Cu,Ca)3As2O8.  (Cu,Ca)  (OH)2. 
-  ^H20. 

Volborthite,  Cu,Ba,Ca,  vanadate. 
Mazapilite,  Ca3Fe2(AsO4)4.2FeO(OH).5H2O. 
Yukonite,  (Ca3,Fe2'")(AsO4)2.2Fe(OH)3. 

5H2O. 

Calcioferrite,Ca3Fe2(PO4)4.Fe(OH)3.8H2O. 
Borickite,  Ca3Fe2(PO4)4.12Fe(OH)3.6H2O. 
Egueiite,  Hydrous  Fe,Al,Ca,  phosphate. 
Goyazite,  Ca3Ali0P2O23.9H2O. 
Roscherite,  (Mn,Fe,Ca)2Al(OH)  (PO4)2. 

2H2O. 

Ca(UO2)2P2O,8H2O. 

Uranospinite,  Ca(UO2)2As2O8.8H2O. 
Tyuyamunite,  CaO.2UO3.V2O5.4H2O. 
Romeite,  CaSb2O4. 
Lewisite,  5CaO.2TiO2.3Sb2O5. 
Mauzeliite,  Pb,Ca,  titano-antimonate. 
Podolite,  3Ca3(PO4)2.CaCO3. 
Svanbergite,  Hydrous  Al,Ca,  phosphate  and 

sulphate. 

Nitrocalcite,  Ca(NO3)2.rcH2O. 
Lautarite,  Ca(IO3)2. 
Dietzeite,  Ca  iodo-chroniate. 
Nordenskioldine,  CaSn(BO3)2. 
Howlite,  H5Ca2B5SiOi4. 
COLEMANITE,  Ca2B6On.5H2O. 
Inyoite,  2CaO.3B2O3.13H2O. 
Meyerhofferite,  2CaO.3B2O3.7H2O. 
Ulexite,  NaCaB5O9.8H2O. 
Bechilite,  CaB4O7.4H2O. 
Hydroboracite,  CaMgB6On.6H2O. 
GLAUBERITE,  Na2SO4.CaSO4. 
Anhydrite  \r<oQr» 
Bassanite  |CaSO^ 
Gypsum,  CaSO4.2H2O. 
Syngenite,  CaSO4.K2SO4.H2O. 
Polyhahte,  2CaSO4.MgSO4.K2SO4.2H2O. 
Ettringite,  6CaO.Al2O3.3SO3.33H2O. 
Uranopilite,  CaU8S2O3i.25H2O. 

SCHEELITE,  CaWO4. 

Powellite,  Ca(Mo,W)O4. 
Whewellite,  CaC2O4.H2O. 

CERIUM  EARTHS 

Tysonite,  (Ce,La,Di)F3. 
Fluocerite,  (Ce,La,Di)2OF4. 
Yttrocerite,  (Y,Er,Ce)F3.5CaF2.H2Q. 
Parisite,  [(Ce,La,Di)F]2.CaCO3. 


Bastnasite,  (CeF)CO3. 

Ancylite,  4Ce(OH)CO3.3SrCO3.3H2O. 

Ambatoarinite,  Rare  earths,  Sr,  carbonate. 

Lanthanite,  La2(CO3)3.9H2O. 

Melanocerite 

Caryocerite        Ca,Ce,Y,  fluo-sihcates. 

Steenstrupine 

Tritomite,  Th,Ce,Y,Ca,  fluo-silicate. 

Mackintoshite,  U,Th,Ce,  sihcate. 

Allanite,  Ca,Fe,Ce,Al,  silicate. 

Cerite,  Ce,  etc.,  silicate. 

Beckelite,  Ca3(Ce,La,Di)4Si3O15. 

Hellandite,  Ce,  etc.,  Al,Mn,Ca,  silicate. 

Bazzite,  Sc.,  etc.,  silicate. 

Britholite,  Ce,  etc.,  silicate  and  phosphate. 

Erikite,  Ce,  etc.,  sihcate  and  phosphate. 

Tscheffkinite,  Ce,Fe,  titano-silicate. 

Johnstrupite  ] 

Mosandrite     |Ce,  etc.,  titano-silicates. 

Rinkite 

Knopite,  Ca,Ce,  titanate. 

Pyrochlore,  Ca,Ce,  niobate. 


Y,Ce,U,  niobate- 
titanates. 


Chalcplamprite, 

Koppite,  Ca,Ce,  niobate. 

Fergusonite,  Y,Er,Ce,U,  niobate. 

Sipylite,  Er,Ce,  niobate. 

Yttrotantalite,  Fe,Ca,Y,Er,Ce,  tantalate. 

Samarskite,  Fe,Ca,U,Ce,Y,  niobate. 

Aeschynite,  Ce,  niobate-titanate. 

Polymignite,  Ce,  Fe,  Ca,  niobate-titanate. 

Euxenite 

Polycrase 

Blomstrandine-Priorite 

MONAZITE,  (Ce,La,Di)P'O4. 

Florencite,  Ce,Al,  phosphate. 

Rhabdophanite,  Hydrous  Ce,Y,  phosphate. 

Churchite,  Hydrous  Ce,Ca,  phosphate. 

CHROMIUM 

Daubreelite,  FeS.Cr2S3. 
Chromite,  FeO.Cr2O3. 
Stichtite,  2MgCO3.5Mg(OH)2.2Cr(OH)3. 
Uvarovite,  Ca3Cr2(SiO4)3. 
Furnacite,  Pb,Cu,  chrom-arsenate. 
Dietzite,  Ca  iodo-chromate. 
CROCOITE,  PbCrO4. 
Phcenicochroite,  3PbO.2CrO3. 
Vauquelinite,,  2(Pb,Cu)CrO4.(Pb,Cu)3P2O8. 
Bellite,  Pb,  arseno-chromate. 
Knoxvillite,  Hydrous  Fe,Al,Cr,  sulphate. 
Redingtonite,  Hydrous  Cr  sulphate. 

COBALT 

Sychnodymite,  (Co,Cu)4S5. 


,  Co3S4. 
Carrollite,  CuCo2S4. 
Badenite,  (Co,Ni,Fe)2(As,Bi)3. 
Cobaltnickelpyrite,  (Co,Ni,Fe)S2. 
SMALTITE,  CoAs2. 

COBALTITE,  CoAsS. 

Willyamite,  CoS2.NiS2.CoSb2.NiSb2. 
Villamaninite,  Cu,Ni,Co,Fe,  sulphide. 


668 

Skutterudite,  CoAs3. 
Safflorite,  CoAs2. 
Glaucodot,  (Co,Fe)AsS. 


APPENDIX     B 


iwocuKCj  v««»jv»»)— — 0/5 — * 

Erythrite,  Co3As2O8.8H2O. 
Forbesite,  H2(Ni,Co)2As2O8.8H2O. 
Bieberite,  CoSO4.7H2O. 

COPPER 

Native  Copper,  Cu. 

Horsfordite,  CueSb. 

Domeykite,  Cu3As. 

Mohawkite,  Cu3As. 

Algodonite,  CuoAs. 

Whitneyite,  Cu^As. 

Cocinerite,  Cu4AgS. 

Rickardite,  Cu4Te3. 

Berzelianite,  Cu2Se. 

Eucairite,  Cu2Se.Ag2Se. 

Zorgite,  Pb,Cu,  selenide. 

Crookesite,  Cu,Tl,  selenide. 

Umangite,  CuSe.Cu2Se. 

Chalcocite,  Cu2S. 

Stromeyrite,  (Ag,Cu)2S. 

Chalmersite,  Cu2S.Fe4S6. 

COVELLITE,  CuS. 

Sychnodymite,  (Co,Cu)4S6. 

Boniite,  Cu6FeS4. 

CarroUite,  CuS.Co2S3. 

Chalcopyrite,  CuFeS2. 

Villamaninite,  Cu,Ni,Co,Fe,  sulphide. 

Eichbergite,  (Cu;Fe)2S.3(Bi,Sb)2S3. 

Histrixite,  5CuFeS2.2Sb2S3.7Bi2S3. 

Cuprobismutite,  3Cu2S.4Bi2S3. 

Emplectite,  Cu2S.Bi2S3. 

Chalcostibite,  Cu2S.Sb2S3. 

Hutchinsonite,  (Tl,Ag,Cu)2S.As2S3  +  PbS. 

As2S3? 

Klaprotholite,  3Cu2S.Bi2S3. 
Bournonite,  3(Pb,Cu2)S.Sb2S3. 
Seligmannite,  3(Pb,Cu2)S.As2S3. 
Aikinite,  2PbS.Cu2S.Bi2S3. 
Wittichenite,  3Cu2S.Bi2S3. 
Stylotypite,  3(Cu2,Ag2,Fe)S.Sb2S3. 
Lengenbachite,  7[Pb,  (Ag,Cu)2]S.2As2S3. 
Falkenhaynite,  3Cu2S.Sb2S3. 
Tetrahedrite,  4Cu2S.Sb2S3. 
TENNANTITE,  4Cu2S.As2S3. 
Goldfieldite,  5Cu2S. (Sb, As,Bi)2(S.Te)8. 
Enargite,  3Cu2S.As2S5. 
Famatinite,  3Cu2S.Sb2S5. 
Sulvanite,  3Cu2S.V2S6. 
Epigenite,  4Cu2S.3FeS.As2S6. 
STANNITE,  Cu2S.FeS.SnS2. 
Nantokite,  CuCl. 
Marshite,  Cul. 
Miersite,  4AgI.CuI. 
ATACAMITE,  CuCl2.3Cu(OH)2. 
Percylite,  PbCl2.CuO.H2O. 
Boleite.  9PbCk8CuO.3AgC1.9H2O. 
Pseudoboleite,  5PbCl2.4CuO.6H2O. 


Cumengite,  4PbCl2.4CuO.5H2O. 

Tallingite,  Hydrous  Cu  chloride. 

Cuprite,  Cu2O. 

Tenorite,  Paramelaconite,  CuO. 

Crednerite,  3CuO.2Zn2O3. 

Rosasite,  2CuO.3CuCO3.5ZnCO3? 

Malachite,  CuCO3.Cu(OH)2. 

Azurite,  2CuCO3.Cu(OH)2. 

Aurichalcite,2(Zn,Cu)CO3.3(Zn,Cu)(OH)». 

Voglite,  Hydrous  U,Ca,Cu,  carbonate. 

Dioptase,  H2CuSiO4. 

Plancheite,  H4Cu7(Cu.OH)8(SiO3)12. 

CHRYSOCOLLA,  CuSiO3.2H2O. 

Shattuckite,  2CuSiO3.HiiO. 

Bisbeeite,  CuSiO3.H2O 

Olivenite,  Cu2(OH)AsO4. 

Libethenite,  Cu2(OH)PO4. 

Calciovolborthite,  (Cu,Ca)3V2O8.  ' 

(Cu,Ca)(OH),. 
Turanite,  5CuO.V2O5.2H2O. 


Furncite,  Pb,Cu,  chrom-arsenate. 
Tsumebite,  Pb,Cu,  phosphate. 
CUnoclasite,  Cu3As2O8.3Cu(OH)2. 
Erinite,  Cu3As2O8.2Cu(OH)2. 
Dihydrite,  Cu3P2O8.2Cu(OH)2. 
Pseudomalachite,  Cu3P2O8.3Cu  (OH)2. 
Trichalcite,  Cu3As2O8.5H2O. 
Rosieresite,  Hydrous  Al,Pb,Cu,  phosphate. 
Eucroite,  Cu3As2O8.Cu(OH)2.6H2O. 
Conichalcite,   (Cu,Ca)3As2O8.  (Cu,Ca)  (OH)2. 


Bayldonite,  (Pb,Cu)3As2O8.  (Pb,Cu)  (OH)2. 

Tagihte,  Cu3P2O8.Cu(OH)2.2H2O. 
Leucochalcite,  Cu3As2O8.Cu(OH)2.2H2O. 
Barthite,  3ZnO.CuO.3As2O5.2H2O. 
Volborthite,  Hydrous,  Cu,Ba,Ca,  vanadate. 
Cornwallite,  Cu3As2O8.2Cu(OH)2.H2O. 
Tyrolite,  Cu3As2O8.2Cu(OH)2.7H2O. 
Chalcophyllite,  7CuO.  As2O5.  14H2O. 
Veszelyite,    Hydrous    Cu,Zn,    phospho-ar- 

senate. 

Turquois,  CuO.3Al2O3.2P2O5.9H2O. 
Liroconite,Cu6Al(AsO4)5.3CuAl(OH)5.20H20 
Chenevixite,  Cu2(FeO)2As2O8.3H2O. 
Henwoodite,  Al,Cu,  hydrous  phosphate. 
Ceruleite,  CuO.2Al2O3.As2O6.8H2O. 
Chalcosiderite,  CuO.2Fe2O3.2P2O5.8H2O. 
Torbernite,  Cu(UO2)2P2O8.8H2O. 
Zeunerite,  Cu(UO2)2As2O8.8H2O. 
Mixite,  Hydrous  Cu,Bi,  arsenate. 
Trippkeite,  Cu,  arsenite. 
Lindackerite,  3NiO.6CuO.SO3.2As2O5.7H2O. 
Gerhardtite,  Cu(NO3)2.3Cu(OH)2. 
Hydrocyanite,  CuSO4. 
Vauquehnite,  2(Pb,Cu)CrO4.  (Pb,Cu)3P2O8. 
Connellite,  CuSO4.2CuCl2.  19Cu(OH)2.H2O. 
Spangolite,  Cu6AlClSOi0.9H2O. 
BROCHANTITE,  CuSO4.3Cu(OH)2. 
Dolerophanite,  Cu2SO5. 
Caledonite,  2(Pb,Cu)O.SO3.H2O. 


APPENDIX     B 


669 


Linarite,  (Pb,Cu)SO4.  (Pb,Cu)  (OH)* 
Anthrite,  CuSO4.2Cu(OH)2. 
Pisanite,  (Fe,Cu)SO4.7H2O. 
Boothite,  CuSO4.7H2O. 
Cupromagnesite,  (Cu,Mg)SO4.7H2O. 
CHALCANTHITE,  CuSO4.5H2O. 
Krohnkite,  CuSO4.Na2SO4.2H2O. 
Natrochalcite,Cu4(OH)2(SO4)2.Na2SO4.2H2O 
Phillipite,  CuSO4.Fe2(SO4)3.nH2O. 
Langite,  CuSO4.3Cu(OH)2.H2O. 
Herrengrundite,  2(CuOH)2SO4.Cu(OH)2. 
Vernadskite,  3CuSO4.Cu(OH)2.4H2O. 
Kamarezite,  Hydrous  basic  Cu  sulphate. 
Cyanotrichite,  4CuO.Al?O3.SO3.8H2O. 
Serpierite,  Hydrous  basic  Cu,Zn,  sulphate. 
Beaverite,  CuO.PbO.Fe2O3.2SO3.4H2O. 
Johannite,  Hydrous  Cu,U,  sulphate. 
Gilpinite,  (Cu,Fe,Na2)O.UO3.SO3.4H2O. 
Chalcomenite,  CuSeO3.2H2O. 
Cuprotiungstite,  CuWO4. 

GOLD 

Native  Gold,  Au. 
Petzite,  (Ag,Au)2Te. 
SYLVANITE,  (Au,Ag)Te2. 
Krennerite,  (Au,Ag)Te2. 
CALAVERITE,  AuTe2. 
Muthmannite,  (Ag,Au)Te. 
Nagyagite,  Au,Pb,  sulpho-telluride. 

IRON 

Native  Iron,  Fe. 

Awaruite,  FeNi2. 

Josephinite,  FeNi3. 

Chalmersite,  Cu2S.Fe4S5. 

Sternbergite,  Ag2S.Fe4S6. 

Peritlandite,  (Fe,Ni)S. 

Pyrrhotite,  FeS. 

Troilite,  FeS. 

Daubreelite,  FeS.Cr2S3. 

Badenite,  (Co,Ni,Fe)2(As,Bi)3. 

Chalcopyrite,  CuFeS2. 

Pyrite,  FeS2. 

Bravoite,  (Fe,Ni)S2. 

Cobaltnickelpyrite,  (Fe,Co,Ni)S2. 

Arsenoferrite,  FeAs2. 

Marcasite,  FeS2. 

Lollingite,  FeAs2. 

Arsenopyrite,  FeAsS. 

Eichbergite,  (Cu,Fe)2S.3(Bi,Sb)2S3. 

Histrixite,  5CuFeS2.2Sb2S3.7Bi2S3. 

Berthierite,  FeS.Sb2S3. 

Stylotypite,  3(Cu2,Ag2,Fe)S.Sb2S3. 

Molysite,  FeCl3. 

Lawrencite,  FeCl2. 

Rinneite,  FeCl2.3KCl.NaCl. 

Kremersite,  KCl2.NH4Cl.FeCl2.H2O. 

Erythrosiderite,  2KCl.FeCl3.H2O. 

Hematite,  Fe2O3. 

ILMENITE,  FeTiO3. 

Senaite,  (Fe,Mn,Pb)O.TiO2. 

Arizonite,  Fe2O3.3TiO2. 

Sitaparite,  9Mn2O3.4Fe2O3.MnO2.3CaO. 


Vredenburgite,  3Mn3O4.2Fe2O3. 
Hercynite,  FeO.Al2O3. 
Magnetite,  FeO.Fe2O3. 
FRANKLINITE,     (Fe.Zn.Mn)O. 

(Fe,Mn),Os. 

Magnesioferrite,  MgO.Fe2O3. 
Jacobsite,  (Mn,Mg)O.(Fe,Mn)2Oa. 
Chromite,  FeO.Cr2O3 
Pseudobrookite,  Fe4(TiO4)3. 
Bixbyite,  FeO.MnO2. 
Gothite,  Fe2O3.H2O. 
Lepidocrocite,  Fe2O3.H2O. 
Limonite,  2Fe2O3.3H2O. 
Turgite,  2Fe2O3.H2O. 
Hydrogothite,  3Fe2O3.4H2O. 
Xanthosiderite,  Fe2O3.2H2O. 
Esmeraldaite,  Fe2O3.4H2O. 
Pyroaurite,  Fe(OH)3.3Mg(OH)2.3H2O. 
Skemmatite,  3MnO2.2Fe2O3.6H2O. 
Beldongrite,  6Mn2O3.Fe2O3.8H2O. 
Ankerite,  2CaCO3.MgCO3.FeCO3. 
Mesitite,  2MgCO3.FeCO3. 
Pistomesite,  MgCO3.FeC03. 
Siderite,  FeCO3. 
BrugnateUite,MgCO3.5Mg(OH)2.Fe(OH)3. 

4H2O. 

HYPERSTHENE,  (Fe,Mg)SiO3. 
ACMITE,  NaFe(SiO3)2. 
Pyroxmangite,  Mn,Fe,  pyroxene. 
Babingtonite,    (Ca,Fe,Mn)SiO3,    with 

Fe2(SiO3)3. 

ANTHOPHYLLITE,  (Mg,Fe)SiO3. 
GLAticopHANE,    NaAl(SiO3)2. 

(Fe,Mg)SiO3. 

RIEBECKITE,  2NaFe(SiO3)2.FeSiO3. 
CROCIDOLITE,  NaFe(SiO3)2.FeSiO3. 
ARFVEDSONITE,  Na,Ca,Fe,  silicate. 
^Enigmatite,  Fe,Na,Ti-sihcate. 
Weinbergerite,  NaAlSiO4.3FeSiO3. 
Astrolite,  (Na,K)2Fe(Al,Fe)2(SiO3)6.H20? 
lolite,  H2(Mg,Fe)4Al8Si10O37. 
Taramellite,  Ba4Fe ' 'Fe4 ' ' 'Sii 0O31. 
Helvite,  (Be,Mn,Fe)7Si3Oi2S. 
Almandite,  Fe3Al2(SiO4)3. 
Andradite,  Ca3Fe2(SiO4)3. 
Partschinite,  (Mn,Fe)3Al2Si3Oi2. 
Fayalite,  Fe2SiO4. 
Knebelite,  (Fe,Mn)2SiO4. 
Pyrosmalite,  H7((Fe,Mn)Cl)(Fe,Mn)4Si4O,6. 
Homilite,  (Ca,Fe)3B2Si2O10. 
Allanite,  (Ca,Fe)2(AlOH)  (Al,Ce,Fe)2(SiO4)3. 
ILVAITE,  CaFe2(FeOH)(SiO4)2. 
Melanotekite,  3PbO.2Fe2O3.3SiO2. 
Angaralite,  2(Ca,Mg)O.5(Al,Fe)2O3.6Si02. 
STAUROLITE,  (AlO)4(AlOH)Fe(SiO4)2. 
Grandidierite,  Al,Fe,Mg,  silicate. 
Aloisite,  Fe,Ca,Mg,Na,  silicate. 
Pochite,  Hi6Fe8Mn2Si3O29. 
Lotrite,3(Ca,Mg)0.2(Al,Fe)208.4Si02.2H20. 
Zinnwaldite,  Li-Fe  mica. 
Biotite,  Mg-Fe  mica. 
Lepidomelane,  Iron  mica. 
Chloritoid,  H2(Fe,Mg)Al2Si07. 


670 


APPENDIX     B 


Prochlorite,  Fe,Mg,chlonte. 
Moravite,  2Fe0.2(Al,Fe)203.7Si02.2H20. 
Cronstedtite,  4FeO.2Fe2O3.3SiO2.4H2O. 
Thuringite,  8FeO.4(Al,Fe)2O3.6SiO2.9H2O. 
Brunsvigite,  9(FeM^O.2A\f)^O2m,O. 
Griffithite,  4(Mg,Fe,Ca)0.(Al,Fe)203.5Si02. 

7H2O. 

Chamosite,  Fe,Mg,  silicate. 
Stilpnomelane  \  Fe  silicates. 
Mmgu6tite       / 
Strigovite,  H4Fe2(Al,Fe)2Si2Oii. 
Spodiophyllite,    (Na2,K2)2(Mg,Fe)3(Fe,Al)2 

(SiO3)8. 

Celadonite,  Fe,Mg,K,  silicate. 
Glauconite,  Hydrous  Fe,K,  silicate. 
Pholidolite,    K20.12(Fe,Mg)O.A}203.13Si02. 

5H2O. 

Faratsihite,  (Al,Fe)2O3.2Si02.2H2O. 
Melite,  2(Al,Fe)203.Si02.8H20. 
Chloropal,  H6Fe2(SiO4)2.2H2O. 
Mullerite,  Fe2Si3O9.2H2O. 
Hisingerite  \  Hydrous  ferric  silicates. 
Morencite    /     J 

Astrophyllite,     Na,  K,  Fe,  Mn,     titano-sil- 
icate. 

Narsarsukite,  Fe,Na,  titaim-silicate. 
Neptunite,  Fe,Mn,Na,K,  titano-silicate. 
Joaquinite,  Ca,Fe,  titano-silicate. 
Dysanalyte,  Ca,Fe,  titano-niobate. 
Geikielite,  (Mg,Fe)Ti03. 
Delorenzite,  Fe,U,Y,  titanate. 
Neotantalite,  Fe  tantalate. 
COLUMBITE,    TANTALITE,     (Fe,Mn) 

(Nb,Ta)206. 

Tapiolite,  Fe(Ta,Nb)2O6. 
Yttrotantalite,  Fe,Ca,Y,Er,Ce,  tantalate. 
Samarskite,  Fe,U,Y,  etc.,  niobate-tantalate. 
Hielmite,  Y,Fe,Mn,Ca,  stanno-tantalate. 
Monimolite,  Pb,Fe,  antimonate. 
TRIPHYLITE,  Li(Fe,Mn)PO4. 
Graftonite,  (Fe,Mn,Ca)3P2O8. 
Triplite.  (RF)RPO4;  R  =  Fe,Mn. 
Triploidite  (ROH)RPO4;  R  =  Fe,Mn. 
Dufrenite,  FePO4.Fe(OH)3. 
LazuUte,  2AlPO4.(Fe,Mg)(OH)2. 
Arseniosiderite,  Ca3Fe(AsO4)3.3Fe(OH)3. 
Dickinsonite  i  Hydrous  Mn,Fe,Na, 
Fillowite         /     phosphate. 
Messelite  (Ca,Fe)3P2O8.2§H2O. 
Anapaite,  (Ca,Fe)3P2O8.4H2O. 
Vivianite,  Fe3P2O8.8H2O. 
Symplesite,  Fe3As->O8.8H2O. 
Scorodite,  FeAsO4.2H2O. 
Vilateite,  Hydrous  Fe,  Mn,  phosphate. 
Purpurite,  2(Fe,Mn)PO4.H2O. 
Strengite,  FePO4.2H2O. 
Phosphosiderite,  2FePO4.3^H2O. 
Barrandite,  (Al,Fe)PO4.2H2O. 
Koninckite,  FePO4.3H2O. 
Sicklerite,  Fe2O3.6MnO.4P2O5.3(Li,H)2O. 
Salmonsite,  Fe2O3.9MnO.4P2O5. 14H,O. 
Liskeardite,  (Al,Fe) AsO4.2(Al,Fe) (OH)3. 

5H2O. 


Pharmacosiderite,6FeAs04.2Fe(OH)3. 

12H20. 

Ludlamite,  2Fe3P2O8.Fe(OH)2.8H2O. 
Cacoxenite,  FePO4.Fe(OH)3.4^H2O. 
Beraunite,  2FePO4.Fe(OH)3.2|H2O. 
Childrenite,  2AlPO4.2Fe(OH)2.2H2O. 
Mazapilite,  Ca3Fe2(AsO4)4.2FeO(OH).5H2O. 
Yukonite,  (Ca3,Fe2'/')  (AsO4)2.2Fe(OH)3. 

5H2O. 

Calciof  errite,  Ca3Fe2  (PO4)  4.  Fe  (OH  )  3.  8H2O. 
Borickite,  Ca3Fe2(PO4)4.  12Fe(OH)3.6H2O. 
Egueiite,  Hydrous  Fe,Al,Ca,  phosphate. 
Richelite,  4FeP2O8.Fe2OF2(OH)2.36H2O. 
Chenevixite,  Cu2(FeO)2As2O8.3H2O. 
Chalcosiderite,  CuO.3Fe2O3.2P2O5.8H2O. 
Roscherite,  (Mn,Fe,Ca)2Al(OH)  (PO4)2. 

2H20. 

Tripuhyite,  2FeO.Sb2O5. 
Flajolotite,  4FeSbO4.3H2O. 
Catoptrite,    14(Mn,Fe)O.2(Al,Fe)2O3.2SiO2. 


Derbylite,  Fe  antimo-titanate. 
Diadochite,    Hydrous    Fe   phosphate    and 

sulphate. 
Pitticite,    Hydrous   Fe   arsenate   and   sul- 

phate. 

Beudantite,  3Fe2O3.2PbO.2SO3.As2O8.6H2O. 
Hinsdalite,  3Fe2O3.2PbO.2SO3.P2O5.6H2O. 
Lossenite,    Hydrous    Fe,Pb,    arsenate   and 

sulphate. 

Ludwigite,  3MgO.B2O3.FeO.Fe2O3. 
Vonsenite,  3(Fe,Mg)O.B2O3.FeO.Fe2O3. 
Magnesioludwigite,  3MgO.B2O3.MgO.Fe2O3. 
Warwickite,  (Mg,Fe)3TiB2O8. 
Lagonite,  Fe2O3.3B2O3.3H2O. 
Hulsite,  12(Fe,Mg)O.2Fe2O3.lSnO2.3B2O3. 
Millosevichite,  (Fe,Al)2(SO4)3. 
Szomolnokite,  FeSO4.H2O. 
Ilesite,  (Mn,Zn,Fe)SO4.4H2O. 
Melanterite,  FeSO4.7H2O. 
Pisanite;  (Fe,Cu)SO4.7H2O. 
Halotrichite,  FeSO4.Al2(SO4)3.24H2O. 
Bilinite,  FeSO4.Fe2(SO4)3.24H2O. 
Dietrichite,  (Zn,Fe,Mn)SO4.Al2(SO4)3. 

22H2O. 

Coquimbite,  Fe2(SO4)3.9H2O. 
Quenstedtite,  Fe2(SO4)8.10H2O. 
Ihleite,  Fe2(SO4)3.12H2O. 
Phillipite,  CuSO4.Fe2(SO4)3.nH2O. 
Ferronatrite,3Na2SO4.Fe2(SO4)3.6H2O. 
Romerite,  FeSO4.Fe2(SO4)3.14H2O. 
Beaverite,  CuO.PbO.Fe2O3.2SO3.4H2O. 
Vegasite,  PbO.3Fe2O3.3SO3.6H2O. 
Copiapite,  2Fe2O3.5SO3.18H2O. 
Castanite,  Fe2O3.2SO3.8H2O. 
Utahite,  3Fe2O3.2SO3.7H2O. 
Amaranthite,  Fe2O3.2SO3.7H2O. 
Fibrof  errite,  Fe2O3.2SO3.10H2O. 
Raimondite,  2Fe2O3.3SO3.7H2O. 
Carphosiderite,  3Fe2O3.4SO3.7H2O. 
Planoferrite,  Fe2O3.SO3.15H2O. 
Glockerite,  2Fe2O3.SO3.6H2O. 
Knoxvillite,  Hydrous  Fe,Al,Cr,  sulphate. 


APPENDIX     B 


671 


Cyprusite,  7Fe2O3. A12O3. 10SO3. 14H2O. 
Botryogen,  MgO.FeO.Fe2O3.4SO3. 18H2O. 
Sideronatrite,  2Na2O.Fe2O3.4SO3.7H2O. 
Voltaite,  3(K2,Fe)O.2(Al,Fe)2O3.6SO3.9H2O. 
Metavoltine,    5(K2,Na2,Fe)O.3Fe2O3.12SO3. 

18H2O. 

Jarosite,  K2Fe6(OH)2(SO4)4. 
Natrojarosite,  Na2Fe6(OH)12(SO4)4. 
Plumbo jarosite,  PbFe«(OH)ij(SO4)4. 
Quetenite,  MgO.FeoO3.3SO3.13H2O. 
Rhomboclase,  Fe2O3.4SO3.9H2O. 
Emmonsite,  Hydrous  Fe  tellurate. 
Durdenite,  Fe2(TeO3)3.4H2O. 
WOLFRAMITE,  (Fe,Mn)WO4. 
Reinite,  FeWO4. 
Ferritungstite,  Fe2O3.WO3.6H2O. 
Humboltine,  FeC204.2H20. 

LEAD 

Native  Lead,  Pb 

Galena,  PbS. 

Altaite,  Pb,Te. 

Clausthalite,  PbSe. 

Naumannite,  (Ag2,Pb)Se. 

Zorgite,  Pb,Cu,  selenide. 

Chiviatite,  2PbS.3Bi2S3. 

Rezbanyite,  4PbS.5Bi2S3. 

Zinkenite,  PbS.Sb2S3. 

Andorite,  Ag2S.2PbS.3Sb2S3. 

Sartorite,  PbS.As2S3. 

Platynite,  PbS.Bi2Se3. 

Galenobismutite,  PbS.Bi2S3. 

Hutchinsonite,     (Tl,Ag,Cu)2S.As2S3  +  PbS. 

As2S3? 

Baumhauerite,  4PbS.3As2S3. 
Schirmerite,  3(Ag2,Pb)S.2Bi2S3. 
Rathite,  3PbS.2As2S3. 
Jamesonite,  2PbS.Sb2S3. 
Dufrenoysite,  2PbS.As2S3. 
Cosalite,  2PbS.Bi2S3. 
Kobellite,  2PbS.(Bi,Sb)2S3. 
Plagionite,  Heteromorphite,  Semseyite,  Pb, 

Sb,  sulphides. 

Freieslebenite,  5(Pb,Ag2)S.2Sb2S3. 
Diaphorite,  5(Pb,Ag2)S.2Sb2S3. 
Boulangerite  5PbS.2Sb2S3. 
Mullanite,  5PbS.2Sb2S3. 
Bournonite,  3(Pb,Cu2)S.Sb2S3. 
Seligmanite,  3(Pb,Cu2)S.As2S3. 
Aikinite,  2PbS.Cu2S.Bi2S3. 
Lillianite,  3PbS.(Bi,Sb)2S3. 
Guitermanite,  3PbS.As2S3. 
Lengenbachite,  7[Pb,  (Ag,Cu)2]S.2As2S3. 
Jordanite,  4PbS.As2S3. 
Meneghinite,  4PbS.Sb2S3 
Geocronite,  5PbS.Sb2S3. 
Beegerite,  6PbS.Bi2S3. 
Epiboulangerite,  3PbS.Sb2S3. 
Teallite,  PbSnS2. 
Franckeite,  Pb5Sn3FeSb2Su. 
Cylindrite,  Pb3Sn4FeSb2Si4. 
Cotunnite,  PbCl2. 


Percylite,  PbCl2.CuO.H2O. 
Boleite,  9PbCl2.8CuO.3AgC1.9HoO. 
Pseudo-boleite,  5PbCl2.4CuO.6H2O. 
Cumengite,  4PbCl2.4CuO.5H2O. 
Matlockite,  PbCl2.PbO. 
Mendipite,  PbCl2.2PbO. 
Lorettoite,  PbCl2.6PbO. 
Laurionite,  PbCl2.Pb(OH)2. 
Penfieldite,  2PbCl2.PbO. 
Daviesite,  Pb  oxychloride. 
Schwartzenbergite,  Pb(I,Cl)2.2PbO. 
Massicot,  PbO. 
Senaite,  (Fe,Mn,Pb)O.TiO2. 
Qoronadite,  (Mn,Pb)Mn3O7. 
Minium,  2PbO.PbO2. 
Plattnerite,  PbO2. 
Cerussite,  PbCO3. 
PHOSGENITE,  PbCO3.PbCl2. 
Hydrocerussite,  2PbCO3.Pb(OH)2. 
Dundasite,  Pb(AlO)2(CO3)2. 
Alamosite,  PbSiO3. 
Barysilite,  Pb3Si2O7. 
Molybdophyllite,  (Pb,Mg)SiO4.H2O. 
Ganomalite,  Pb4(PbOH)2Ca4(Si2O7)3. 
Nasonite,  Pb4(PbCl)2Ca4(Si2O7)3. 
Margarosanite,  Pb(Ca,Mn)2(SiO3)3. 
Hy alotekite,  (Pb, Ba, Ca) B2  (SiO3) , 2. 
Roeblingite,  5(H2CaSiO4).2(CaPbSO4) 
Hancockite,  Pb,Mn,Ca,Al,  etc.,  silicate. 
Kentrolite,  3PbO.2Mn2O3.3SiO2. 
Melanotekite,  3PbO.2Fe2O3.3SiO2. 
Plumboniobite,  Y,U,Pb,Fe,  niobate 
Monimolite,  Pb,Fe,  antimonate. 
Carminite,  Pb3As2O8.10FeAsO4. 
Georgiadesite,  Pb3(AsO4)2.3PbCl2. 
PYROMORPHITE,  Pb4(PbCl)(PO4)3. 
Mimetite,  Pb4(PbCl)(AsO4)3. 
Vanadinite,  Pb4(PbCl)(VO4)3. 
Trigonite,  Pb3MnH(AsO3)3. 
Plumbogummite,  Pb,Al,  phosphate. 
Descloizite,  (Pb,Zn)2(OH)VO4. 
Pyrobelonite,  4PbO.7MnO.2V2O5.3H2O. 
Dechenite,  PbV2O6. 
Psittacinite     \  T^I  ^  ,„  !„, 

Mottramite    )  Pb,Cu,  vanadates. 

Furnacite,  Pb,Cu,  chrom-arsenate. 
Tsumebite,  Pb,Cu,  phosphate. 
Rosiere"site,  Hydrous  Al,Pb,Cu,  phosphate. 
Ferrazite,  3(Ba,Pb)O.2P2O5.8H2O. 
Bayldonite,     (Pb,Cu)3As2O8.  (Pb,Cu)  (OH)2. 

Hiigelite,  Hydrous  Pb,Zn,  vanadate. 
Bindheimite,  Hydrous  Pb  antimonate. 
Nadorite,  PbClSbO2. 
Ecdemite,  Pb4As2O7.2PbCl2. 
OchroUte,  Pb4Sb2O7.2PbCl2. 
Mauzeliite,  Pb,Ca,titano-antimonate. 
Beudantite,  3Fe2O3.2PbO.2SO3.As2O6.6H2O. 
Hinsdalite,  3Fe2O3.2PbO.2SO3.P2O6.6H2O. 
Lossenite,  Hyclrous  Fe,  Pb,  arsenate  and 

sulphate. 
Anglesite,  PbSO4. 
CROCOITE,  PbCrO4 


672 


APPENDIX     B 


Phcenicochroite,  3PbO.2Cr03. 
Vauquelinite,  2(Pb,Cu)CrO4.  (Pb,Cu)3P2Os 
Bellite,  Pb  arseno-chromate. 
Leadhillite,  PbSO4.2PbCO3.Pb(OH)2. 
Caracolite,  Pb(OH)Cl.Na2SO4. 
Lanarkite,  Pb2SO6. 

Caledonite,  (Pb,Cu)S04.  (Pb,Cu)  (OH)2. 
Linarite,  (Pb,Cu)SO4.  (Pb,Cu)  (OH)2. 
Beaverite,  CuO.PbO.Fe2O3.2SO3.4H2O. 
Vegasite,  PbO.3Fe2O3.3SO3.6H2O. 
Plumbojarosite,  PbFe6(OH)i2(SO4)4. 
Palmierite,  3(K,Na)2SO4.4PbSO4. 


Chillagite,  3PbW04.PbMo04. 

WULFENITE,  PbMoO4. 

LITHIUM 

Petalite,  LiAl(Si2O5)2. 
Spodumene,  LiAl(SiO3)2. 
Eucryptite,  LiAlSiO4. 
LEPIDOLITE,  Lithium  mica. 
Zinnwaldite,  Lithium-iron  mica. 
Manandonite,  H24Li4Ali4B4Si6()53. 
TRIPHYLITE,  Li(Fe,Mn)PO4. 
Lithiophilite,  Li(Mn,Fe)PO. 
AMBLYGGNITE,  Li(AlF)PO4. 
Fremontite,  (Na,Li)Al(OH,F)PO4. 
Sicklerite,  Fe2O3.6MnO.4P2O5.3(Li,H)2O. 

MAGNESIUM 
Chloromagnesite,  MgCl2. 
Sellaite,  MgF2. 

Nocerite,  2(Ca,Mg)F2(Ca,Mg)O. 
Koenenite,  Al,Mg,  oxy  chloride. 
Carnallite,  KCl.MgCl2.6H2O. 
Bischofite,  Mi  " 


,  _.-0Jl2.6H20. 

Tachhydrite,  CaCl2.2MgCl2.12HoO 
Ralstonite,  (Na2,Mg)F2.3Al(F.OH)3.2H2O. 
Periclase,  MgO. 
Spinel,  MgO.Al2O3. 
Magnesioferrite,  MgO.Fe2O3. 
Jacobsite,  (Mn,Mg)O.(Fe,Mn)2O3. 
BRUCITE,  Mg(OH)2. 

Hydrotalcite,  Al(OH)3.3Mg(OH)2.3H2O. 
Pyroaurite,  Fe(OH)3.3Mg(OH)2.3H20. 
Dolomite,  CaCO3.MgCO3. 
Ankerite,  CaCO3.(Mg,Fe,Mn)CO3. 
Magnesite,  MgCO3. 
Mesitite,  2MgCO3.FeCO3. 
Pistomesite,  MgCO3.FeCO3. 
Northupite,  MgCO3.Na2CO3.NaCl. 
Tychite,  2MgCO3.2Na2CO3.Na2SO4. 
Nesquehonite,  MgCO3.3H2O. 
Hydromagnesite,  3MgCO3.Mg(OH)2.3H2O. 
Hydrogiobertite,MgC03.Mg(OH)2.2H20. 
Artimte,  MgCO3.Mg(OH)2.3H2O. 
Lansfordite,  3MgC03.Mg(OH)2.21H20. 
Brugnatelhte,    MgCO3.5Mg(OH)2.Fe(OH)3. 

4ji2v-J« 

Gajite   basic,  hydrous  Ca,Mg,  carbonate. 
Stichtite,2MgC03.5Mg(OH)2.2Cr(OH)3. 
ENSTATITE,  MgSiOs. 


HYPERSTHENE,  (Fe,Mg)Si03. 
Pyroxene,  Ca,Mg,  etc.,  silicate. 
ANTHOPHYLLITE,  (Mg,Fe)SiO3. 
Amphibole,  Ca,Mg,  etc.,  silicate. 
GLAUCOPHANE,    NaAl  (SiO3)2.  (Fe,Mg)SiO8  , 
IOLITE,  H2(Mg,Fe)4Al8SiioO37. 
Molybdophyllite,  (Pb,Mg)SiO4.H2O. 
Pyrope,  Mg3Al2(SiO4)3. 
Chrysolite,  (Mg,Fe)2SiO4. 
Monticellite,  CaMgSiO4. 
Fosterite,  Mg2SiO4. 
Hortonolite,  (Fe,Mg,Mn)2SiO4. 
CHONDRODITE,  [Mg(F,OH)]2Mg3(SiO4)2. 
Humite,  [Mg(F,OH)]2Mg5(Si04)3. 
Clinohumite,  [Mg(F,OH)]2Mg7(SiO4)4. 
Kornerupine,  MgAl2SiO6. 
Sapphirine,  Mg5Ali2Si2O27. 
Serendibite,  10(Ca,Mg)O.5Al2O3.B2O3.6SiO2. 
Silicomagnesiofluorite,  H2Ca4Mg3Si2O7Fi0 
Lptrite,3(Ca,Mg)O.2(Al,Fe)2O3.4SiO2.2H2O. 
Biotite,  Magnesium-iron  mica. 
Phlogopite,  Magnesium  mica. 
Ta3niolite,  K,  Mg,  silicate. 
Seybertite,  H3(Mg,Ca)6Al5Si2Oi8. 
Xanthophyllite,  H8(Mg,Ca)14Al16Si6O52. 
Chloritoid,  H2(Fe,Mg)Al2SiO7. 
Clinochlore,  Penninite,  H8Mg5Al,Si3O18. 
Prochlorite,  Fe,Mg,  chlorite. 
Brunsvigite,  9(Fe,Mg)O.2Al2O3.6SiO2.8H2O. 
Griffithite,  4(Mg,Fe,Ca)O.  (Al,Fe)2O3.5SiO2. 

7H2O. 
Spodiophyllite,   (Na2,K2)2(Mg,Fe)3(Fe,Al)2 


. 

Serpentine,  H4Mg3Si2O9. 
Deweylite,  4MgO.3SiO2.6H2O. 
Genthite,  2NiO.2MgO.3SiO2.6H2O. 
Nepouite,  3(Ni,Mg)O.2SiO2.2H2O. 
Garnierite,  H2(Ni,Mg)SiO4  +  water. 
Talc,  H2Mg3(Si03)4. 
SEPIOLITE,  H4Mg2Si3Oi0. 
Spadaite,  5MgO.6SiO2.4H2O. 
Saponite,  Hydrous  Mg,Al,  silicate. 
Celadonite,  Fe,Mg,K,  silicate. 
Pholidolite,    K20.  12(Fe,Mg)0.  A1203.  13SiO2 

5H2O. 

Colerainite,  4MgO.Al2O3.2SiO2.5H2O. 
Tartarkaite,  Al,Mg,  hydrous  silicate. 
Geikielite,  (Mg,Fe)TiO3. 
Berzeliite,  (Ca,Mg,Mn,Na2)3As2O8. 
Wagnerite,  (MgF)MgPO4. 
Adelite,  (MgOH)CaAsO4. 
Tilasite,  (MgF)CaAs04. 
Lazulite,  2AlPO4.(Fe,Mg)(OH)2 
Struvite,  Hydrous,  NH4,Mg,  phosphate. 
Pyrophosphorite,  Mg2P2O7.4(Ca3P2O8. 

Ca2P2O7). 

Roselite,  (Ca,Co,Mg)3As2O8.2H2O. 
Bobierrite,  Mg3P2O8.8H2O. 
Hcernesite,  Mg3As2O8.8H2O. 
Cabrerite,  (Ni,Mg)3As2O8.8H2O. 
Newberyite,  HMgPO4.3H2O. 
Hannayite    i  Hydrous,  NH4,Mg, 
Schertelite   /     phosphates. 


APPENDIX     B 


673 


Liineburgite,  3MgO.B2O3.P2O6.8H2O. 
Nitromagnesite,  Mg(NO3)2.nH2O. 
Sussexite,  H(Mn,Zn,Mg)BO3. 
Ludwigite.  3MgO.B2O3.FeO.Fe2O3. 
Vonsenite,  3(Fe,Mg)O.B2O3.FeO.Fe2O3. 
Magnesioludwigite,  3MgO.B2O3.MgO.Fe2O3. 
Pinakiolite,  3MgO.B2O3.MnO.Mn2O3. 
Szaibelyite,  2Mg5B4Oi,.3H2O. 
BORACITE,  Mg7Cl2Bi6O30. 
Ascharite,  Hydrous  Mg,  borate. 
Warwickite,  (Mg,Fe)3TiB2O8. 
Pinnoite,  MgB2O4.3H2O. 
Heintzite,  Hydrous  Mg,K,  borate. 
Hulsite,  12(Fe,Mg)O.2Fe2O3.  !SnO2.3B2O3. 

2H2O. 

Hydroboracite,  CaMgB6On.6H2O. 
Sulphoborite,  2MgSO4.4MgHBO3.7H2O. 
Langbeinite,  K2Mg2(SO4)3. 
Vanthoffite,  3Na2SQ4.MgSO4. 
Kainite,  MgSO4.KC1.3H2O. 
Kieserite,  MgSO4.H2O. 
Epsomite,  MgSO4.7H2O. 
Cupromagnesite,  (Cu,Mg)SO4.7H2O. 
Loweite,  MgSO4.Na2SO4.2£H2O. 
Blodite,  MgSO4.Na2SO4.4H2O. 
Leonite,  MgSO4.K2SO4.4H2O. 
Boussingaulite,  (NH4)2SO4.MgSO4.6H2O. 
Picromerite,  MgSO4.K2SO4.6H2O. 
Polyhalite,  2CaSO4.MgSO4.K2SO4.2H2O. 
Hexahydrite,  MgSO4.6H2O. 
Pickeringite,  MgSO4.Al2(SO4)3.22H2O. 
Botryogen,  MgO.FeO.Fe2O3.4SO3. 18H,O. 
Quetenite,  MgO.Fe2O3.3SO3.13H2O. 

.  MANGANESE 

Alabandite,  MnS. 
Hauerite,  MnS2. 
Samsonite,  2Ag2S.MnS.Sb2S3. 
Sacchite,  MnCl2. 

Chlormanganokalite,  4KCl.MnCl2. 
Manganosite,  MnO. 
Senaite,  (Fe,Mn,Pb)O.TiO2. 
Pyrophanite,  MhTiO3. 
Sitaparite,  9Mn2O3.4Fe2O3.MnO2.3CaO. 
Vredenburgite,  3Mn3O4.2Fe2O3. 
FRANKLINITE,  (Fe,Zn,Mn)O. (Fe,Mn)2O3. 
Jacobsite,  (Mn,Mg)O.(Fe,  Mn)2O3. 
Hausmannite,  MnO.Mn2O3. 
Coronadite,  (Mn,Pb)Mn3O7. 
Crednerite,  3CuO.2Mn2O3. 
BRAUNITE,  3Mn2O3.MnSiO3. 
Bixbyite,  FeO.MnO2. 
Polianite,  MnO2. 
Pyrolusite,  MnO2. 
Manganite,  Mn2O3.H2O. 
Pyrochroite,  Mn(OH)2. 
Backstromite,  Mn(OH)2. 
Chalcophanite,  (Mn,Zn)O.2MnO2.2H2O 
Heta3roHte,  2ZnO.2Mn2O3.lH2O. 
Psilomelane,  Hydrous    Mn    manganate. 
Wad,  Mn  oxides. 
Skemmatite,  3MnO2.2Fe2O3.6H2O. 
Beldongrite,  6Mn3O5.Fe2O8.8H2O. 


Rhodochrosite,  MnCO3. 

Schizolite,  HNa(Ca,Mn)2(SiO3)3 

Lavenite,  Zr-silicate  of  Mn,  Ca. 

Rhodonite,  MnSiO3. 

Pyroxmangite,  Mn,Fe  pyroxene. 

Babingtonite,  (Ca,Fe,Mn)SiO3  with 
Fe2(SiO3)3. 

Margarosanite,  Pb(Ca,Mn)2(SiO3)3. 

Helvite,  (Be,Mn,Fe)7Si3O12S. 

Danalite,  (Be,Fe,Zn,Mn)7Si3O12S. 

Spessartite,  Mn3Al2(SiO4)3. 

Partschinite,  (Mn,Fe)3Al2Si3Oi2. 

Glaucochroite,  CaMnSiO4. 

Knebelite,  (Fe,Mn)2SiO4. 

Tephrdite,  Mn2SiO4. 

Trimerite,  (Mn,Ca)2SiO4.Be2SiO4. 

Friedelite,  H7(MnCl)Mn4Si4Oi6. 

Pyrosmahte,  H7((Fe,Mn)Cl)(Fe,Mn)4Si4Oi6 

Piedmontite,  Mn  epidote. 

Hancockite,  Pb,Mn,Ca,Al,  etc.,  silicate. 

Harstigite,  Mn,Ca,  silicate. 

Leucophoenicite,  Mn5(MnOH)2(SiO4)3. 

Ardennite,  Al,Mn,V,  silicate. 

Langbanite,  Mn  silicate  with   Fe   antimon- 
ate. 

Kentrolite,  3PbO.2Mn2O3.3SiO2. 

Carpholite,  H4MnAl2Si2O10. 

Pochite,  Hi6Fe8Mn2Si3O29. 

Inesite,  H2(Mn,Ca)6Si6Oi9.3H2O. 

Ganophyllite,  7MnO.Al2O3.8SiO2.6H2O. 

Alurgite,  Manganese  mica. 

Dixenite,  MnSiO3.2Mn2(OH)AsO3. 

Bementite,  H6Mn5(SiO4)4. 

Ectropite,  Mn2Si8O28.7H2O. 

Agnolite,  H2Mn3(SiO3)4.H2O. 

Hodgkinsonite,  3(Zn,Mn)O.SiO2.H2O. 

Gageite,  Hydrous,  Mn,Mg,Zn,  silicate. 

Caryopilite,  4MnO.3SiO2.3H2O. 

Neotocite,  Hydrous,  Mn,  Fe,  silicate. 
Astrophyllite,  Na,K,Fe,Mn,Ti-silicate. 

Neptunite,  Fe,Mn,K,Na,  titano-silicate. 
COLUMBITE-TANTALITE,  (Fe,Mn) 

(Nb,Ta)2O6. 

Hielmite,  Y,Fe,Mn,Ca,  stanno-tantalate. 
Berzeliite,  (Ca,Mg,Mn,Na2)3As2O8. 
Lithiophilite,  Li(Mn,Fe)PO4. 
Natrophilite,  NaMnPO4. 
Graftonite,  (Fe,Mn,Ca)3P2O8. 
Triplite,  (RF)RPO4;  R  =  Fe,Mn. 
Triploidite  (ROH)RPO4;  R  =  Mn.Fe. 
Sarkinite,  (MnOH)MnAsO4. 
Trigonite,  Pb3MnH(AsO3)3. 
Lacroixite,  Na4(Ca,Mn)4Al3(F,OH)4P3Oi0. 

2H20. 

Pyrobelonite,  4PbO.7MnO.2V2O6.3H2O. 
Allactite,  Mn3As2O8.4Mn(OH)2. 
Synadelphite,  2(Al,Mn)AsO4.5Mn(OH)2. 
Flinkite,  MnAsO4.2Mn(OH)2. 
HematoHte,  (Al,Mn)AsO4.4Mn(OH)2. 
Retzian,  Y,Mn,Ca,  phosphate. 
Arseniopleite,  (Mn,Ca)9(Mn,Fe)2(OH)« 

(AsO4)6. 
Manganostibiite,  Mn  antimonate. 


674 


APPENDIX     B 


Dickinsonite   l  Hydrous  Mn,Fe,Na, 
Fillowite         I     phosphates. 
Brandite,  Ca2MnAs2O8.2H2O. 
Fairfieldite,  Ca3MnP2O8.2H2O. 
Reddingite,  Mn3P2O8.3H2O. 
Palaite,  5MnO.2P2O6.4H2O. 
Stewartite,  3MnO.P2O5.4H2O. 
Purpurite,  2(Fe,Mn)PO4.H2O. 
Sicklerite,  Fe2O3.6MnO.4P2O5.3(Li,H)2O. 
Salmonsite,  Fe2O3.9MnO.4P2O6.  14H2O. 
Hureaulite,  H2Mn6(PO4)4.4H2O. 
Hemafibrite,  Mn3As2O8.3Mn  (OH)2.2H2O. 
Eosphorite,  2AlPO4.2(Mn,Fe)  (OH)2.2H2O. 
Rosche-rite,  (Mn,Fe,Ca)2Al(OH)  (PO4)o.2H,O 
Catoptrite,    14(Mn,Fe)O.2(Al,Fe)2O3.2SiO2. 


Sussexite,  H(Mn,Zn,Mg)BO3. 
Pinakiolite,  3MgO.B2O3.MnO.Mn2O3. 
Szmikite,  MnSO4.H2O. 
Ilesite,  (Mn,Zn,Fe)SOi.4H2O. 
Mallardite,  MnSO4.7H2O. 
Apjohnite,  MnSO4.Al2(SO4)3.24H2O. 
Dietrichite,     (Zn,Fe,Mn)S04.Al2(SO4)3. 

22H.O. 
Hiibnerite,  MnWO4. 

MERCURY 
Native  Mercury,  Hg. 
Amalgam,  (Ag,Hg). 
Metacinnabarite,  HgS. 
Tiemannite,  HgSe. 
Onofrite,  Hg(S,Se). 
Cotoradoite,  HgTe. 
Cinnabar,  HgS. 
Livingstonite,  HgS.2Sb2S3. 
Calomel,  HgCl. 
Kleinite,  Hg,NH4,  chloride. 
Eglestonite,  Hg4Cl2O. 
Terlinguaite,  HgClO. 
Mosesite,  Hydrous  Hg,NH4,  chloride. 
Montroydite,  HgO. 
Ammiolite,  Hg  antimonite. 

MOLYBDENUM 
Molybdenite,  MoS2. 
Molybdite,  MoO3. 
Powellite,  Ca(Mo,W)O4. 
Chillagite,  3PbWO4.PbMoO4. 

WULFENITE,  PbMoO4. 

Koechlinite,  Bi2O3.Mo03. 

NICKEL 

Awaruite,  FeNi2. 
Jbsephinite,  FeNi3. 
Maucherite,  Ni3As2. 
PENTLANDITE,  (Fe,Ni)S. 
Millerite,NiS 
Beyrichite,  NiS. 
Hauchecornite,  Ni(Bi,Sb,S)? 
Niccolite,  NiAs. 
Breithauptite,  NiSb 
Polydymite,  Ni4S6. 
Badenite,  (Co,Ni,Fe)2(As,Bi)8. 


Bravoite,  (Fe,Ni)S2. 

Cobaltnickelpyrite,  (Co,Ni,Fe)S2. 

CHLOANTHITE,  NiAs2. 

Gersdorffite,  NiAsS. 

Willyamite,  CoS2.NiS2.CoSb2.NiSb2. 

Villamaninite,  Cu,Ni,Co,Fe,  sulphide. 

Ullmanite,  NiSbS. 

Kallilite,  Ni(Sb,Bi)S. 

Rammelsbergite,  NiAs2. 

Wolfachite,  Ni(As,Sb)S. 

Melonite,  NiTe2. 

Bunsenite,  NiO. 

Zaratite,  NiCO3.2Ni(OH)2.4H2O. 

Genthite,  2NiO.2MgO.3SiO2.6H2O. 

Nepouite,  3(Ni,Mg)O.2SiO2.2H2O. 

Garnierite,  H2(Ni,Mg)SiO4  +  water. 

Connarite,  H4Ni2Si3Oi0. 

Annabergite,  Ni3As2O8.8H2O. 

Cabrerite,  (Ni,Mg)3As2O8.8H2O. 

Forbesite,  H2(Ni,Co)2As2O8.8H2O. 

Lindackerite,  3NiO.6CuO.SO3.2As2O6. 7H20. 

Morenosite,  NiSO4.7H2O. 

PLATINUM 
Native  Platinum,  Pt. 
Sperrylite,  PtAs2. 

POTASSIUM 
SYLVITE,  KC1. 

Chlormanganokalite,  4KCl.MnCl2. 
Rinneite,  FeCl2.3KCl.NaCl. 
Hieratite,  K,Si,  fluoride. 
CARNALLITE,  KCl.MgCl2.6HoO. 
Kremersite,  KCl,NH4Cl.FeCl2.H2O. 
Erythrosiderite,  2KCl.FeCl3.H2O. 
Milarite,  HKCa2Al2(Si2O5)6. 
Orthoclase,  Microcline,  KAlSi3O8. 
Hyalophane,  (K2,Ba)Al2(SiO3)4. 
Anorthoclase,  (Na,K)AlSi3O8. 
Leucite,  KAl(SiO3)2. 
Kaliophilite,  KAlSiO4. 
ApophylUte,  H7KCa4(SiO3)8.4|H2O. 
PtiloHte,  (Ca,K2,Na2)Al2Si10O24.5H2O. 
Mordenite,  (Ca,K2,Na2)Al2SiioO24.20H20.    - 
Wellsite,  (Ba,Ca,K2)Al2Si3O10.3H20. 
Phillipsite,  (K2,Ca)Al2Si4O,2.4iH2O. 
Harmotone,  (K2, Ba) Al2Si6Oi4. 5H2O . 
Offretite,  Potash  zeolite. 
Muscovite,  H2KAl3(SiO4)3. 
TaBniolite,  K,Mg,  silicate. 

Sppdiophyllite,  (Na2K2)2(Mg,Fe)3(Fe,Al)2 

(SiO3)8. 

Celadonite,  Fe,Mg,K,  silicate. 
Glauconite,  Hydrous  Fe,  K,  silicate. 
Astrophyllite,  Na,K,Mn,Fe,  titano-sih'cate. 
Palmerite,  HK2Al2(PO4)3.7HoO. 
Carnotite,  K2O.2U2O3.V2O5.3H2O. 
Niter,  KNOs. 
Rhpdizite,  A1,K,  borate. 
Heintzite,  Hydrous  Mg,K,  borate. 
Taylorite,  5K2SO4.  (NH4)2S04. 
Aphthitalite,  (K,Na)2SO4. 
Langbeinite,  K2Mg2(SO4)3. 


APPENDIX     B 


675 


Kainite,  MgSO4.KC1.3H2O. 

Hanksite,  9Na2SO4.2Na2CO3.KCl. 

Misenite,  HKSO4. 

Lecontite,  (Na,NH4,K)SO4.2H2O. 

Syngenite,  CaSO4.K2SO4.H2O. 

Leonite,  MgSO4.K2SO4.4H2O. 

Picromerite,  MgSO4.K2SO4.6H2O. 

Polyhalite,  2CaSO4.MgSO4.K2SO4.2H2O. 

Kalinite,  KA1(SO4)2.12H2O. 

Voltaite,  3(K2,Fe)O.2(Al,Fe)2O3.6SO3.9H2O. 

Metavoltine,  5(K2,Na2,Fe)O.3Fe2O3.12SO8. 

18H2O. 

ALUNITE,  K2A16(OH)12(SO4)4. 
Jarosite,  K2Fe6(OH)12(SO4)4. 
Palmierite,  3(K,Na)2SO4.4PbSO4, 
Lowigite,  K2O.3A12O3.4SO3.9H2O. 

SILVER 

Native  Silver,  Ag. 

Amalgam,  (Ag,Hg). 

Dyscrasite,  Ag3Sb. 

Chilenite,  Ag6Bi. 

Cocinerite,  Cu4AgS. 

Stutzite,  Ag4Te. 

Naumannite,  (Ag2,Pb)Se 

Argentite,  Ag2S. 

Hessite,  Ag2Te.  «, 

Petzite,  (Ag,Au)2Te. 

Aquilarite,  Ag2(S,Se). 

Eucairite,  Cu2Se.Ag«Se. 

Crookesite,  (Cu,Tl,Ag)2Se. : 

Stromeyrite,  (Ag,Cu)2S. 

Acanthite,  Ag2S. 

Sternbergite,  Ag2S.Fe4S5. 

Sylvanite,  (Au,Ag)Te2. 

Krennerite,  (Au,Ag)Te2. 

Muthmannite,  (Ag,Au)Te. 

Andorite,  Ag2S.2PbS.3Sb2S3. 

Matildite,  Ag2S.Bi2S3. 

Miargyrite,  Ag2S.Sb2S3. 

Smithite,  Ag2S.Sb2S3. 

Trechmanite,  Ag2S.As2S3. 

Hutchinsonite,     (Tl,Ag,Cu)2S.As2S3  +  PbS. 

As2S3(?). 

Schirmerite,  3(Ag2.Pb)S.2Bi2S3. 
Freieslebenite,  5(Pb,Ag2)S.2Sb2S3. 
Diaphorite,  5(Pb,Ag2)S.2Sb2S3. 
Stylotypite,  3(Cu2,Ag2,Fe)S.Sb2S3. 
Lengenbachite,  7[Pb,  (Ag,Cu)2]S.2As2S8. 
PYRARGYRITE,  3Ag2S.Sb2S3. 
PROUSTITE,  3Ag2S.As2S3. 
Pyrostilpnite,  3Ag2S.Sb2S3. 
Samsonite,  2Ag2S.MnS.Sb2S3. 
STEPHANITE,  5Ag2S.Sb2S3. 

POLYBASITE,  9Ag2S.Sb2S3. 

Pearceite,  9Ag2S.As2S3. 
Polyargyrite,  12Ag2S.Sb2S3. 
Xanthoconite,  3Ag2S.As2Ss. 
Argyrodite,  4Ag2S.GeS2. 
Canfieldite,  4Ag2S.SnS2. 
Cerargyrite,  AgCl. 
Embolite,  Ag(Br,Cl). 
Bromyrite,  AgBr. 


lodobromite,  2AgCl.2AgBr.AgI. 
Miersite,  4AgI.CuI. 
lodyrite,  Agl. 

SODIUM 
Halite,  NaCl. 
Villiaumite,  NaF. 
Huantajayite,  20NaCl.AgCl. 
Rinneite,  FeCl3.3KCl.NaCl. 
CRYOLITE,  Na3AlF6. 
ChioUte,  5NaF.3AlF3. 
Ralstonite,  (Na2,Mg)F2.3Al(F,OH)3.2H2O. 
Northupite,  MgCO3.Na2CO3.NaCl. 
Tychite,  2MgCO3.2Na2CO3.Na2SO4. 
Dawsonite,  Na3Al(CO3)3.2Al(OH)3. 
Thermonatrite,  Na2CO3.H2O. 
Natron,  Na2CO3. 10H2O. 
Pirssonite,  CaCO3.Na2CO3.2H2O. 
Gay-Lussite,  CaCO3.Na2CO3.5H2O. 
Trona,  Na2CO3.HNaCO3.2H2O. 
Eudidymite,  Epididymite,  HNaBeSi3O8. 
Rivaite,  (Ca,Na2)Si2O6. 
Anorthoclase,  (Na,K)AlSi3O8. 
Albite,  NaAlSi3O8. 
Oligoclase       Mixtures  of 

CaAl2Si2O8, 


and 


Andesine 

Labradorite 

Anemousite,  NaO.2CaO.3Al2O3.9SiO2. 

Ussingite,  HNa2Al'(SiO3)3. 

ACMITE,  NaFe(SiO3)2. 

JADEITE,  NaAl(SiO3)2. 

PECTOLITE,  HNaCa2(SiO3)3. 

Schizolite,  HNa(Ca,Mn)2(SiO3)3. 

Rosenbuschite,  near  pectolite  with  Zr. 

Wohlerite,  Zr-silicate  and  niobate  of  Ca,Na. 

Hiortdahlite,  (Na2.Ca)  (Si,Zr)O3. 

GLAUCOPHANE,  NaAl(SiO3)2.(Fe,Mg) 

Si03. 

RIEBECKITE,  2NaFe(SiO3)o.FeSiO3. 
CROCIDOLITE,  NaFe(SiO3)2.FeSiO3. 
Arfyedsonite,  Na^a^e"  silicate. 
jiEnigmatite,  Fe,Na,Ti-silicate. 
Weinbergerite,  NaAlSiO4.3FeSiO3. 
Elpidite,  Na2O.ZrO2.6SiO2.3H2O. 
Catapleiite,  H4  (Na2,  Ca)  ZrSi3On  . 


Nephelite,  NaAlSiO4. 

CANCRINITE,     H6Na6Ca(NaCO3)2Al8 

(Si04)9. 

Microsommite,  Davyne,  near  cancrimte. 
SODALITE,  Na4(AlCl)Al2(SiO4)3 
Hackmanite,  near  sodalite. 
HAITTNITE,  (Na2,Ca)2(NaSO4.Al)Al2 

(SiO4)3. 

Noselite,  Na4(NaSO4.Al)Al2(SiO4)3. 
LAZURITE,  Na4(NaS3.Al)Al2(SiO4)3. 
SCAPOLITE  GROUP,  Mixtures  of 

Ca4Al6Si6O26  and  Na4Al3Si9O24Cl. 
Sarcolite,  (Ca,Na2)3Al2(SiO4)3. 
Melilite,  Na2(Ca,Mg)n(Al,Fe)4(SiO4)9. 
Mordenite,  (Ca,K2,Na2)Al2Si,0O24.20H2O. 
Stilbite,  (Na2,Ca)Al2Si6Oi6.6H2O. 


676 


APPENDIX     B 


Flokite,  H8(Ca,Na2)Al2Si9O26.2H2O. 

CHABAZITE,  (Ca,Na2)Al2Si4Oi2.6H2O. 

Gmelinite,  (Na2Ca)Al2Si4OI2.6H2O. 

Analcite,  NaAlSi2O6.H2O. 

Faujasite,  H4Na2CaAl4Si10O38. 

Natrolite,  Na2Al2Si3Oi0.2H2O. 

Mesolite,   Na2Al2Si3Oi0.2H2O  +  2[CaAl2Si3 

Oi0.3H2O]. 

Gonnardite,  (Ca,Na2)2Al2Si6O,5.5|H2O. 
Thomsomte,  (Na2,Ca)Al2Si2O8.2£H2O. 
Hydrothomsonite,  (H2,Na2,Ca)Al2Si2O8. 

5H2q. 

Arduinite,  Ca,Na,  zeolite. 
Echellite,  (Ca,Na2)O.2Al2O3.3SiO2.4H2O. 
Epidesmine,  (Na2,Ca)Al2Si6Oi6.6H2O. 
Erionite,  H2CaK2Na2Al2Si6O17.5H2O. 
Hydronephelite,  HNa2Al3Si3Oi2.3H2O. 
Paragonite,  H2NaAl3(SiO4)3. 
Spodiophyllite,   (Na2,K2)2(Mg,Fe)3(Fe,Al)2 

(Si03)8. 

Searlesite,  NaB(SiO3)2.H2O. 
Molengraafite,  Ca,Na,  titano-silicate. 
Astrophyllite,  Na,K,Mn,Fe,titano-silicate. 
Narsarsukite,  Fe,Na,  titano-silicate. 
Leucosphenite,  Na4Ba(TiO)2(Si2O5)5. 
Lorenzenite,  Na2(TiO)2Si2O7. 
Epistolite,  Ti,Na,etc.,  niobate. 
Berzeliite,  (Ca,Mg,Mn,Na2)3As2O8. 
Natrophilite,  NaMnPO4. 
Beryllonite,  NaBePO4. 
Jezekite,  Na4CaAl(AlO)  (F,OH)4(PO4)2. 
Lacroixite,    Na4(Ca,Mn)4Al3(F,OH)4P3O16. 

2H2O. 

Durangite,  Na(AlF)AsO4. 
Fremontite,  (Na,Li)Al(OH,F)PO4. 

raiowite11^  }3(Mn,Fe,Na2)3P208.H20. 
Stercorite,  HNa(NH4)PO4.4H2O. 
Soumansite,  Hydrous  Al,Na,  fluophosphate. 
SODA  NITER,  NaNO3. 
Darapskite,  NaNO3.Na2SO4.H2O. 
Nitroglauberite,  6NaNO3.2Na2SO4.3H2O 
Borax,  Na2B4O7.10H2O. 
Ulexite,  NaCaB5O9.8H2O. 
Thenardite,  Na2SO4. 
Aphthitalite,  (K,Na)2SO4. 
GLAUBERITE,  Na2SO4.CaSO4. 
Vanthoffite,  3Na2SO4.MgSO4. 
Sulphohalite,  3Na2SO4.NaCl.NaF. 
Caracolite,  Pb(OH)Cl.Na2SO4. 
Hanksite,  9Na2SO4.2Na2CO3.KCl 
Lecontite,  (Na,NH4,K)2SO4.2H2O. 
Mirabikte,  Na2SO4.  10H2O. 
Loweite,  MgSO4.Na2SO4.2iH2O. 
Blodite,  MgSO4.Na2SO4.4H2O. 
Mendozite,  NaAI(SO4)2.12H2O. 
Krohnkite,  CuSO4.Na2SO4.2H2O. 
NatrochalciteCu4(OH)2(S04)2.Na2S04.2H20. 
Ferronatnte,  3Na2S04.Fe2(S04)3.6H26 
Sideronatrite,  2Na20.Fe203.4S03.7H20 

3.  12S03. 


Palmierite,  3(K,Na)2SO4.4PbSO4. 
Almeriite,  Na2SO4.Al2(SO4)3.5Al(OH)3.H2O. 

STRONTIUM 
Strontianite,  SrCO3. 
Ancylite,  4Ce(OH)CO3.3SrCO3.3H2O. 
Ambatoarinite.  Rare  earths,  Sr,  carbonate. 
Brewsterite,  H4(Sr,Ba,Ca)Al2(SiO3)6.3H2O. 
Fermorite,  (Ca,Sr)4[Ca(OH,F)][(P,As)O4]3. 
Hamlinite,  Sr,Al,  phosphate. 
Harttite,  Sr.Al.  phosphate  and  sulphate. 
Celestite,  SrSO4. 

THORIUM 

Trftomfte  &  /Ca,Ce,Y,Th,  fluo-silicates. 
Thorite,  ThSiO4. 
Auerlite,  Th  silico-phosphate. 
Yttrialite,  Th,Y,  silicate. 
Mackintoshite,  U,Th,Ce,  silicate. 
Yttrocrasite,  Hydrous  Y,Th,  titanate. 
Pyrochlore,  RNb2O6.R(Ti,Th)O3. 
MONAZITE,  (Ce,La,Di)PO4  with  ThO2. 
Thorianite,  Th  and  U  oxides. 

TIN 

Stannite,  Cu2S.FeS.SnS2. 
Canfieldite,  4Ag2"S.SnS2. 
Teallite,  PbSnS2. 
Franckeite,  Pb5Sn3FeSb2S14. 
Cylindrite,  Pb3Sn4FeSb2Si4. 
Cassiterite,  SnO2. 
Stokesite,  H.CaSnSisOu. 
Hielmite,  Y,Fe,Mn,Ca,  stanno-niobate. 
Nordenskioldine,  CaSn(BO3)2. 
Hulsite,    12(Fe,Mg)0.2Fe203.  !SnO2.3B2O3. 
2H2O. 

TITANIUM 
ILMENITE,  FeTiO3. 
Senaite,  (Fe,Mn,Pb)O.TiO2. 
Arizonite,  Fe2O3.3TiO2. 
Pyrophanite,  MnTiO3. 
Pseudobrookite,  Fe4(TiO4)3. 
Rutite,  Ti02. 

Octahedrite,  Brookite,  TiO2. 
Uhligite,  Ca(Ti,Zr)O5.Al(Ti,Al)O6. 


Natrojarosite,  Na2Fe6(OH)12(S04)4 


Molengraafite,  Ca,Na,  titano-silicate. 

Keilhauite,  Ca,Al,Fe,Y,  titano-silicate. 

Ischeffkmite,  Ce,  etc.,  titano-silicate 

Astrophyllite,  Na,K,Fe,Mn,  titano-silicate. 

Johnstrupite 

Mosandrite         Ce,  etc.,  titano-silicates 

Rmkite 

Narsarsukite,  Fe,Na,  titano-silicate. 

Neptunite,  Fe,Mn,Na,K,  titano-silicate. 

Benitoite,  BaTiSi3O9. 

Leucosphenite,  Na4Ba(TiO)2(Si2O6)6. 

Lorenzenite,  Na2(TiO)2Si2O7. 

Joaquinite,  Ca,Fe,  titano-sih'cate. 

PEROVSKITE,  CaTiO3. 

Knopite,  Ca,Ce,  titanate. 


APPENDIX     B 


677 


Dysanalyte,  Ca,Fe,  titano-silicate. 
Geikielite,  Mg,Fe,  titanate. 
Delorenzite,  Fe,U,Y,  titanate. 
Yttrocrasite,  Hydrous  Y,  Th,  titanate. 
Brannerite,  (UO,TiO,UO2)TiO3. 
Pyrochlore,  RNb2p6.R(Ti,Th)O3. 
Aeschynite,  Ce,  niobate-titanate. 
Polymignite,  Ce,Fe,Ca,  niobate-titanate. 
Euxenite  1  ^r  ^   TT     •  i_  j 

Polvcrase  Y  Ce,U  mobate- 

Blomstrandine-Priorite  j      tltanates- 
Betafite,  U,  etc.,  niobate-titanate. 
Epistolite,  Na,Ti,  etc.,  mobate. 
Lewisite,  5CaO.2Tiq2.3Sb2O5. 
Mauzeliite,  Pb,Ca,  titano-antimonate. 
Warwickite,  (Mg,Fe)3TiB2O8. 

TUNGSTEN 

Tungstenite,  WS2. 
Tungstite,  WO3. 
WOLFRAMITE,  (Fe,Mn)WO4. 
Hubnerite,  MnWO4. 

SCHEELITE,   CaWO4. 

Cuprotungstite,  CuWO4. 
Powellite,  Ca(Mo,W)O4. 


Chillagite,  3PbWO4.PbMoO4. 
Reinite,  FeWO4. 
Ferritungstite,  Fe2O3.WO3.6H2O. 

URANIUM 
Rutherfordine,  UO2CO3. 
Uranothallite,  2CaCO3.U(CO3)2.10H2O. 
Liebigite,  Hydrous,  U,Ca,  carbonate. 
Voglite,  Hydrous,  U,  Ca,  Cu,  carbonate. 
Mackintoshite,  U,Th,Ce,  silicate. 
Uranophane,  CaO.2UO3.2SiO2.6H2O. 
Delorenzite,  Fe,U,Y,  titanate. 
Brannerite,  (UO,TiO,UO2)TiO3. 
Hatchettolite,  U,  tantalo-niobate. 
Samiresite,  U,  etc.,  niobate. 
Fergusonite,  Y,Er;U,  niobate. 
Samarskite,  Fe,Ca,U,Ce,Y,  niobate. 
Ampangabeite,  U,  etc.,  niobate. 

Annerodite,  U,Y,  niobate. 
Euxenite  1  v  n^  TT      •  u  ^ 

Polvcrase  \  Y>Ce>U'  mobate- 

Blomstrandine-Priorite  j      tltanates- 
Betafite,  U,  niobate-titanate. 
Plumboniobite,  Y,U,Pb,  niobate. 
Uvanite,  2UO3.3V2O6.15H2O. 
Ferganite,  U3(VO4)2.6H2O. 
Torbernite,  Cu(UO2)2P2O8.8H3O. 
Zeunerite,  Cu(UO2)2As2O8.8H2O. 

Bas'sTtfte  }Ca(UO2)2P2O8.8H2O. 
Uranospinite,  Ca(UO2)2As2O8.8H2O. 
Uranocircite,  Ba(UO2)2P2O8.8H2O. 
CARNOTITE,  K2O.2U2O.V2O6.3H2O. 
Tyuyamunite,  CaO.2UO3.V2O5.4H2O. 
Uranospathite,  Hydrous  uranyl  phosphate. 


Phosphuranylite,  (UO2)3P2O8.6H2O. 
Trogerite,  (UO2)3As2O8.12H2O. 
Walpurgite,  Bi10(UO2)3(OH)24(AsO4)4. 
.URANINITE,  Uranyl,  etc.,  uranate. 
Gummite,  alteration  of  uraninite. 
Thorianite,  Th  and  U  oxides. 
Uranosphaerite,  (BiO)2U2O7.3H2O. 
Johannite,  Hydrous  Cu,U,  sulphate. 
Gilpinite,  (Cu,Fe,Na2)O.UO3.SO3.4H2O. 
Uranopilite,  CaU8S2O3i.25H2O. 

VANADIUM     fcS 

PATRONITE,  VS4. 

Sulvanite,  3Cu2S.V2S5. 

Alaite,  V2O5.H2O. 

Ardennite,  Al,Mn,V,  silicate. 

Roscoelite,  Vanadium  mica. 

Pucherite,  BiVO4. 

Vanadinite,  Pb4(PbCl)(VO4)3. 

Descloizite,  (Pb,Zn)2(OH)VO4. 

Pyrobelonite,  4PbO.7MnO.2V2O5.3H2O. 

Dechenite,  PbV2O6. 

Calciovolborthite,     (Cu,Ca)3V2O8.  (Cu,Ca) 

(OH)2. 
Turanite,  5CuO.V2O5.2HoO. 

}Pb,Cu,™nadates. 

Uvanite,  2UO3.3V2O5.15H2O. 
Ferganite,  U3(VO4)2.6H2O. 
Fernandinite,  CaO. V2O4.5V2O5. 14H2O. 
Pascoite,  2CaO.3V2O5.llH2O. 
Pintadoite,  2CaO.V2O6.9H2O. 

MeUhewettite  }  CaO.3V!O,9H2O. 
Volborthite,  Hydrous,  Cu,Ba,Ca,  vanadate. 
Hiigelite,  Hydrous,  Pb,Zn,  vanadate. 
CARNOTITE,  K2O.2U2O3.V2O5.3H2O. 
Tyuyamunite,  CaO.2UO3.V2O5.4H2O. 
Minasragrite,  (V2O2)H2(SO4)3. 15H2O. 

YTTRIUM,  Etc. 

Yttrofluorite,  (Ca3,Y2)F6. 

Yttrocerite,  (Y,Er,Ce)F3.5CaF2.H2O. 

Tengerite,  Y  carbonate. 

Cappelenite,  Y,Ba,  boro-silicate. 

Melanocerite    \ 

Caryocerite      [Ca,Y,Ce,  fluo-silicates. 

Steenstrupine  J 

Tritomite,  Th,Ce,Y,Ca,  fluo-silicate. 

Gadolinite,  Be2FeY2Si2Oi0. 

Yttriah'te,  Th,Y,  silicate. 

Rowlandite,  Y  sih'cate.  . 

Thalenite,  Y  silicate 

Thortveitite,  (Sc,Y)2Si2O7. 

Cenosite,  H4Ca2(Y,Er)2CSiOi7. 

Keilhauite,  Ca,Al,Fe,Y,  titano-silicate. 

Delorenzite,  Fe,U,Y,  titanate. 

Yttrocrasite,  Hydrous  Y,Th,  titanate. 

Risorite,  Y  niobate. 

Fergusonite,  Y,Err  niobate. 

Sipylite,  Er  niobate. 

Yttrotantalite,  Y,  etc.,  tantalate-niobate. 


678 


APPENDIX     B 


Samarskite,   Fe,Ca,U,Ce,Y,   niobate-tanta- 

late. 

Annerodite,  U,Y,  niobate. 
Hielmite,  Y,Fe,Mn,Ca,  stanno-tantalate. 
Euxenite  !  Y,Ce,U,  niobate- 


Plumboniobite,  Y,U,Pb,Fe,  niobate. 
XENOTIME,  YPO4. 
Retzian,  Y,Mn,Ca,  arsenate. 
Rhabdophanite,  Hydrous  Ce,Y,  phosphate. 

ZINC 

Sphalerite,  ZnS. 
Wurtzite,  ZnS. 
Voltzite,  Zn^O. 
ZINCITE,  ZnO. 
Gahnite,  ZnO.A]2O3. 

FRANKLINITE,  (Fe,Zn,Mn)O.  (Fe,Mn)203. 
Chalcophanite,  (Mn,Zn)O.2MnO2.2H2O. 
Hetserolite,  2ZnO.2Mn2O3.lH2O. 
Smithsonite,  ZnCO3. 
Rosasite,  2CuO.CuCO3.5ZnCO3? 
Aurichalcite,    2(Zn,Cu)CO3,3(Zn,Cu)(OH)2. 
Hydrozincite,  ZnCO3.2Zn(OH)2. 
Hardystonite,  Ca2ZnSi2O7. 
Danalite,  (Be,Fe,Zn,Mn)7Si3Oi2S. 
Willemite,  Zn2SiO4. 
Calamine,  H2ZnSiO5. 
Clinohedrite,  H2CaZnSiO5. 
Hodgkinsonite,  3(Zn,Mn)O.SiO2.H20. 
Gageite,  Hydrous,  Mn,  MR,  Zn,  silicate. 
Tarbuttite,  Zn3P2O8.Zn(OH)2. 


Adamite,  Zn2(OH)AsO4. 
Descloizite,  (Pb,Zn)2(OH)VO4. 

Par^peite  }  ^P2O8.4H!O. 
Kottigite,  Zn3As2O8.8H2O. 
Barthite,  3ZnO.CuO.3As2O5.2H2O. 
Hugelite,  Hydrous,  Pb,  Zn,  vanadate 
Spencerite,  Zn3(PO4)2.Zn (OH)2.3H2O. 
Hibbenite,  2Zn3(PO4)2.Zn(OH)2.6iH2O. 
Veszelyite,     Hydrous,    Cu,  Zn,      phospho- 

arsenate. 

Kehoeite,  Hydrous,  Al,  Zn,  phosphate. 
Sussexite,  H(Mn,Zn,Mg)BO3. 
Zinkosite,  ZnSO4. 
Ilesite,  (Mn,Zn,Fe)SO4.4H2O. 
Goslarite,  ZnSO4.7H2O. 
Dietrichite,  (Zn,Fe,Mn)SO4.Al2(SO4)3. 

22H2O. 

Serpierite,  Hydrous,  Cu,  Zn,  sulphate. 
Zincaluminite,  2ZnSO4.4Zn(OH)2.6Al(OH)3. 

5H2O. 

ZIRCONIUM 
Baddeleyite,  ZrO2. 
Uhligite,  Ca(Ti,Zr)O6.Al(Ti,Al)O6. 
Rosenbuschite,  Na,Ca,Zr,  silicate. 
Wohlerite,  Na,Ca,Zr,  silicate  and  niobate. 
Lavenite,  Mn,Ca,Zr,  silicate. 
Hiortdahlite,  (Na2,  Ca)  (Si, Zr)  O3. 
Eudialyte,  Zr,Fe,Ca,Na,  silicate. 
Elpidite,  Na2O.ZrO2.6SiO2.3H2O. 
Catapleiite,  H4(Na2,Ca)ZrSi3On. 
Zircon,  Zr  SiO4. 
Chalcolamprite,  R ' 'Nb  .O6. R ' 'SiO3. 


APPENDIX   B 


679 


TABLE    II.     MINERALS    ARRANGED    ACCORDING    TO    THEIR 
SYSTEM    OF    CRYSTALLIZATION. 

The  following  lists  are  intended  to  include  all  well-recognized  species,  whose  crystalliz- 
ation is  known,  arranged  according  to  the  system  to  which  they  belong,  and  further  classi- 
fied by  their  luster  and  specific  gravity;  the  hardness  is  also  given  in  each  case. 

»  I.     CRYSTALLIZATION     ISOMETRIC.* 

A.   LUSTER  NONMETALLIC. 


Specific 
Gravity. 

Hard- 
ness. 

Specific 
Gravity. 

Hard- 
ness. 

Sal  Ammoniac  (p.  397)  . 
Kalinite  (p.  637)  
Faujasite  (p.  555)  
Sylvite  (p.  396)  

1-53 
175 
1-92 
1-98 

1-5-2 
2-2-5 
5 
2 

Arsenolite  (p.  409)  
Schorlomite  (p.  510)  .  .  . 
Betafite  (p.  591)  
Hercynite  (p.  420). 

3-7 

3-81-3-88 
3-75-4-17 
3-9-3-95 

1-5 

7-7-5 

7-5-8 

Halite  (p.  395) 

2-14 

2-5 

Sphalerite  (p  367) 

3-9-4-1 

3'5-4 

Hydrophilite  (p.  399)  .  . 
Sodalite  (p.  502)  
Analcite  (p.  554)  
Noselite  (p.  503)  
Northupite  (p.  450)  
Haiiynite  (p.  503)  

2-2 
2-14-2-30 
2-2-2-3 
2-25-2-4 
2-38 
2-4-2-5 

5-5-6 
5-5-5 
5-5 
3-5-4 
5-5-6 

Nantokite  (p.  395)  
Marshite  (p.  395)  
Alabandite  (p.  369)  
Perovskite  (p.  586)  .... 
Berzeliite  (p.  593)  
Gahnite  (p.  420) 

3-93 
5-6? 
3-95-4-04 
4-03 
4-08 
4-0-4-6 

2-2-5 

3-5-4 
5-5 
5 

7-5-8 

Leucite  (p.  469) 

2-45-2-50 

5-5-6 

Pyrochlore  (p  587) 

4-2-4-36 

5-5-5 

Lazurite  (p.  503)  
Sulphohalite  (p.  631)... 
Tychite  (p.  450)  
Ralstonite  (p.  402)  .... 

2-38-2-45 
2-49 
2-5 

2-58 

5-5-5 
3-5 
3-5 
4-5 

Koppite  (p.  587)  
Zirkelite  (p.  428)  
Hatchettolite  (p.  587).. 
Lewisite  (p.  618) 

4-45-4-56 
471 
4-8-4-9 
4-95 

5-5 
5 
5-5 

Voltaite  (p.  639)  

2-79 

3^ 

Atopite  (p.  618)  . 

5-03 

5-5-6 

Villiaumite  (p.  396)  
Langbeinite  (p.  625) 

2-81 
2-83 

Percylite,  Boleite 
(p.  401). 

5-08 

2-5 

Zunyite  (p.  505)  ...  
Pollucite  (p.  470)  
Boracite  (p.  620)  

2-87 
2-90 
2-9-3 

7 
6-5 

7 

Mauzeliite  (p.  618)  
Manganosite  (p.  411)  .  . 
Neotantalite  (p.  587) 

5-11 
5-18 
5-2 

6-6-5 
5-6 
3-8 

Pharmacosiderite, 
(p.  614)   .     . 

2-9-3 

2-5 

•lenarmontite  (p.  409)  .  . 
Samiresite  (p.  587) 

5-2-5-3 
5-24 

2-2-5 

Plazolite  (p.  580)  . 

3-13 

6-5 

Embolite  (p.  397) 

5-3-54 

1-1-5 

Nitrobarite  (p  619)  .... 
Fluorite  (p.  398)  
Helvite  (p.  504)  
Garnet  (p.  505) 

3-2 
3-2 
3-16-3-36 
3-3-4-3 

4 
6-6-5 
6-5-7-5 

Cerargyrite  (p.  397).... 
Miersite  (p.  598)  
Vlicrolite  (p.  587)  
lodobromite  (p.  397) 

5-55 
5-6 
5-5-6-1 
571 

1-1-5 

5-5 
1-1-5 

Rhodizite  (p.  621) 

3-4 

8 

Bromyrite  (p.  397) 

5-8-6 

2-3 

Danalite  (p.  504)  .  . 

3-43 

5'5-6 

Cuprite  (p.  410)  . 

5-85-6-15 

3-5-4 

Hauerite  (p.  378)  
Diamond  (p.  345)  
Yttrofluorite  (p.  399)  .  . 
Spinel  (p.  419)  
Periclase  CD.  411)  .. 

3-46 
3-52 
3-55 
3-5-4-1 
3-67 

4 
10 
4-5 

8 
6 

Eulytite  (p.  504)  
Bunsenite  (p.  411)  
Monimolite  (p.  593)  .  .  . 
Sglestonite  (p.  401)  
Mosesite  CD.  402)  .  . 

6-11 
64 
6-58;7'29 
8-3 

4-5 
5-5 
5-6 
2-3 
3 

*  Some  pseudo-isometric  species  are  here  included, 
some  species  are  included  in  both  lists. 


Species  with  submetallic  luster  are  placed  under  B,  but 


680 


APPENDIX  B 


B.  LUSTER  METALLIC  (AND  SUBMETALLIC)  . 


Specific 
Gravity. 

Hard- 
ness. 

Specific 
Gravity. 

Hard- 
ness. 

Hauerite  (p.  378)  

3-46 

4 

Canfieldite  (p.  394)  

6-28 

2-5-3 

Sphalerite  (p.  367)  
Alabandite  (p.  369)  
Cubanite  (p.  374) 

3-9-4-1 
3-95-4-04 
4-0-4-1 

3-5-4 
3-5-4 
4 

Ullmannite  (p.  379)  
Smaltite,  Chloanthite 
(p.  378) 

6-2-6-7 
6-4-6-6 

5-5-5 
5  '5-6 

Dysanaly  te  (p.  586)  .... 
Chromite  (p.  423)  
Villamaninite  (p.  379)  .  . 
Tennantite  (p.  391)  

4-13 
4-3^-57 
4-4 
44^-49 

5-6 
5-5 
4-5 
3-4 

Skutterudite(p.380)... 
Willyamite  (p.  379)  
Polyargyrite  (p.  562)  .  .  . 
Laurite  (p.  379) 

6-7-6-86 
6-87 
6-97 
7-0 

6 
5-5 
2-5 
7-5 

Tetrahedrite  (p.  390)  .  .  . 
Magnesioferrite  (p.  420) 

4-4-5-1 
4-57-4-65 

3-4 
6-6-5 

Argentite  (p.  364)  
IRON  (p.  356)  

7-2-7-36 
7-3-7-8 

2-2-5 
4-5 

Polydymite  (p.  373)  .  .  . 

4-5-4-8 

4-5 

Galena  (p.  363)  

7-4-7-6 

2-5-3 

Cobaltnickelpyrite 
(p.   378)  

4-71 

5 

Eucairite  (p.  365)  
Vletacinnabarite  (p  369) 

7-5 

7-8 

2-5- 

Q 

Jacobsite  (p.  421)  .  .  . 

475 

6 

Clausthalite  (p  364) 

7'6  8"8 

2>p>  *3 

Sychnodymite  (p.  373)  . 

LlNN^EITE  (p.  374)  

4-76 
4-8-5 

5-5 

S"aumannite  (p.  364)  .  .  . 
Altaite  (p.  364)  

8-0 
8-16 

2-5 
3 

Carrollite  (p.  374)  
Bixbyite  (p.  425) 

4-85 
4-95 

5-5 
6-6-5 

Tiemannite  (p.  369)  

Hp«?«?itp  (n  36^ 

8-2-8-5 

0.0     Q.K 

2-5 

O.C     0 

PENTLANDITE 
(p.  369)  

5-0 

3-5-4 

Copper  (p.  353)  
Uraninitf*  fr>  fi£^ 

8-8-8-9 

Q   Q-7 

2-5-3 

5.K 

Pyrite  (p.  377)  .... 
Franklinite  (p.  420)  .  . 

4-95-5-10 
5-07-5-22 

6-6-5 
6-6-5 

Thorianite  (p.  624). 
Silver  (p.  352)  

9-3 
10-1-11-1 

2-5-3 

Magnetite  (p.  420)  
Bornite  (p.  374)  . 
Gersdorffite  (p.  379) 
Cuprite  (p.  410)  
Brongniardite  (p.  387)  .  .  ' 

5-18 
4-9-5-4 
5-6-6-2 
5-85-6-15 
5-95 

6-6-5 
3 
5-5 
3-5^ 
3-5 

Sperrylite  (p.  379)  
Lead  (p.  354)  
Palladium  (p.  355)  .... 
AMALGAM  (p.  354)  
Platinum  (p.  355)  

10-6 
11-4 
11-3-11-8 
137-14-1 
14-19 

6-7 
1-5 
4-5-5 
3-3-5 
4-4-5 

Corymte  (p.  379)  
Argyrodite  (p.  391).  .  . 

5-95-6-03 
6-1-3-2 

4-5-5 
2-5 

Gold  (p.  350)  
Iridium  (p.  355)  .... 

15-6-19-3 
22-6-22-8 

2-5-3 
6-7 

Cobaltite  (p.  379)  

6-6-3 

5-5 

APPENDIX   B 


681 


II.     CRYSTALLIZATION  TETRAGONAL. 
A.     LUSTER  NONMETALLIC. 


Specific 
Gravity. 

Hard- 
ness. 

Specific 
Gravity. 

Hard- 
ness. 

Mellite  (p.  645)  
Darapskite  (p.  619)  
Pinnoite  (p.  622)  
Apophyllite  (p.  546)  
Loweite  (p.  637)  

1-64 

2-29 
2-3-2-4 

2-38 

2-2-5 

4-5-5 
2-5-3 

Hardystonite  (p.  498).. 
Torbernite  (p.  648)  
Trippkeite  (p.  618)  
Octahedrite  (p.  428)  ... 
Rutile  (p.  427) 

3-4 
3-4-3-6 

3-8-3-95 
4-18-4-25 

3-4 
2-2-5 

5-5-6 
6-6-5 

Ecdemite  (p.  618)  

6-9-7-1 

2-5-3 

Xenotime  (p.  592) 

445-4-56 

4-5 

Sarcolite  (p.  518)  
Marialite  (p.  518)  

2-54-2-93 
2-57 

6 
5-5-6 

Powellite  (p.  643)  
Thorite  (p.  522) 

4-53 
4-4-54 

3-5 
4-5-5 

Mizzonite  (Dipyre), 
(p.  517)  

2-62 

5-5-6 

Fergusonite  (p.  588)  
Zircon  (p.  520)  

4-4-5-8 
4-68^-7 

5-5-6 
7-5 

Wernerite  (Scapolite), 
(p.  516) 

2-66-2-73 

5-5-6 

Romeite  (p.  618)  
Sipylite  (p.  588) 

471 
4-89 

5-5-6 
6 

Meionite  (p.  516) 

2-70-2-74 

5-5-6 

Nasonite  (p.  498) 

54 

4 

Edingtonite  (p.  555)  .... 
Narsarsukite  (p.  585)  .  .  . 
Chiolite  (p.  400)  
Soumansite  (p.  614).  .  .  . 

270 
2-7 

2-84-2-99 

2-87 

4-4-5 
7-0 
3-5-4 
4-5 

Ganomalite  (p.  498)  
Scheelite  (p.  642)  
Phosgenite  (p.  450)  
Calomel  (p.  395)  

5-74 
5-9-6-1 
6-6-09 
6-48 

3 

4-5-5 
2-75-3 
1-2 

Melilite  (p  518) 

2-9-3-1 

5 

Wulfenite  (p.  643) 

67-7-0 

275-3 

Gehlenite  (p.  518)  
Meliphanite  (p.  496)  .  .  . 
Sellaite  (p  399) 

2-9-3-1 
3-01 
2'97-3'15 

5-5-6 
5-5-5 
5 

Cassiterite  (p.  425)  
Matlockite  (p.  401)  .... 
Tapiolite  (p.  590) 

6-8-7-1 
7-2 
7-36-7-5 

6-7 
2-5-3 
6 

Zeunerite  (p.  616)  

3-2 

2-2-5 

Larettoite  (p.  401)  

7-6 

3 

Pinnoite  (p  622) 

3-27-3-37 

3-4 

Stolzite  (p.  643)  

7*87-8-13 

2-75-3 

Vesuvianite(p.519).... 

3-35-3-45 

6-5 

B.  LUSTER  METALLIC  (AND  SUBMETALLIC). 


Chalcopyrite  (p  374) 

4-1-4-3 

3-5-4 

Polianite  (p.  427)  

4-84-5-0 

6-6-5 

STANNITE  (p.  394)  

4-3-4-5 

4 

Reinite  (p.  644)  

6-64 

4 

Rutile  (p  427) 

4-18-4-25-5-2 

6-6-5 

Hauchecornite  (p.  372)  . 

64 

5 

Fergusonite  (p.  588)  
Hausmannite  (p,  424)  .  . 

4-4-5-8 
47^-86 

5-5-6 
5-5-5 

Tapiolite  (p.  590)  
Maucherite  (p.  362)  

7-36-7-5 

7-83 

6 
5 

Braunite  (p.  425)1  

4-75-4-82 

6-6-5 

Plattnerite  (p.  428)  

8-5 

5-5-5 

682 


APPENDIX  B 

III.   CRYSTALLIZATION  HEXAGONAL.* 

Rhombohedral  species  are  distinguished  by  a  letter  R. 

A.   LUSTER  NONMETALLIC. 


Specific 

Hard- 

Specific           Hard- 

Gravity. 

ness. 

Gravity. 

ness. 

Ice  (p  411) 

0-9 

1-5 

Hamlinite  (p.  601)  R.  . 

3-23 

4-5 

Cyprusite?(p.639)... 
Ettringite  (p.  640)  .  .  . 
Thaumasite  (p.  581)  . 
Koenenite  (p.  401)R  . 
Gmelinite  (p.  554)  R. 
Pyroaurite  (p.  455)  R 
Coquimbite  (p.  637)  R. 

1-75 
1-75 

1-88 
2-0 
2-04-2-17 
2-07 
2-09 

2 
2-2-5 
3-5 
2-0 
4-5 
2-3 
2-2-5 

Pyrochroite  (p.  435)  R. 
Jeremejevite  (p.  620)  .  . 
Dioptase  (p.  515)  R  — 
Svanbergite  (p.  618)  R. 
Cronstedtite  (p.  571)  R 
Hematolite  (p.  606)  R. 
Connellite  (p.  631)  

3-26 
3-28 
3-28-3-35 
3-30 
3-35 
3-35 
3-36 

2-5 
6-5 
5 
5 
3-5 
3-5 
3 

Utahite  (p.  639)  R  

Mesitite  (p.  443)  R.  .  .  . 

3-33-3-42 

3-5-4 

Chabazite(p.552)R... 

2-08-2-16 
2-09-2'16 

4-5 
4-4-5 

Rhodochrosite  (444)  R. 

Svabite  (p.  598)  

3-45-3-60 
3-52 

3-5-4-5 
5 

Hydronephelite?  (p.  558) 

2-26 

4-5-6 

Fermorite  (p.  597)  

3-52 

5 

Soda  niter  (p.  619)  R   .. 

2-26 

1-5-2 

Florencite  (p.  601)  R.  .  . 

3-58 

5 

TriHvmitp  (rt   4-07} 

2-28-2-33 

7 

Benitoite  (p.  585) 

3-6 

6-2-6-5 

_L  riLiy  1111  tt?  \p»  A^'  /  .  >     «  • 

Rinneite  (p.  399)  R.  . 

2-3 

3 

Siderite  (p.  443)  R  

3-83-3-88 

3-5-4 

Brucite  (p.  434)  R  

2-38-2-4 

2-5 

Rhabdophanite  (p.  609) 

Cancrinite  (p.  501) 

2-42-2-5 

5-6 

R  

3-94-4-01 

3-5 

Microsommite  (p.  501) 

2-44 

6 

Wurtzite  (p.  371).  ... 

3-98 

3-5-4 

Kaliophilite  (p.  501).... 

2-49 

6 

Corundum  (p.  413)  R.. 

3-95-4-10 

9 

Carphosiderite? 

Willemite(p.513)R.... 

3-94-4-19 

5-5 

(p.  539)  R. 

2-50 

4-4-5 

Geikielite  (p.  586)  R.  .  .  . 

4-0 

6-0 

Colerainite  (p.  583)  .... 

2-51 

2-5-3 

Sphserocobaltite  (446)  R 

4-02-4-13 

4 

Metavoltine  (p.  639)  .  .  . 

2-53 

2-5 

Melanocerite  (p.  406)  R. 

413 

5-6 

Chalcophyllite(p.612)R 

2-44-2-66 

2 

Tritomite  (p.  496)  R  

4-20 

5-5 

Nephelite  (p.  499) 

2-55-2-65 

5-5-6 

Nordenskioldine  (620)  R 

4-20 

5-5-6 

Hanksite(p.  631)  
Ferronatrite  (p.  638)  R. 
Milarite  (p.  455)  

2-56 
2-56 
2-57 

3-3-5 

2 
5-5-6 

Caryocerite  (p.  496)  R. 
Parisite  (p.  621)  
Smithsonite(p.445)R.. 

4-29 
4-36 
4-30-4-45 

5-6 
4-5 
5 

Spodiophyllite  (p.  572)  . 

2-6 

3-3-2 

Beudantite  (p.  618)  R.  . 

4-4-3 

3-5-4-5 

Aphthitalite  (p.  624)  R. 

2-64 

3-3-5 

Plumbogummite? 

Quartz  (p.  403)  R.  .  .  . 

2-65 

7 

(p.  601). 

4^-9 

4-5 

Beryl  (p.  495)  

2'  64-2'  7  ;2'  80 

7-5-8 

Britholite  (p.  580)    .... 

4-4 

5-5 

Eucryptite  (p.  500)  

2-67 

Cappelenite  (p.  496)  .  .  . 

4-41 

6-6-5 

Alunite  (p.  639)  R  

2-67 

3-5^ 

Pyrophanite  (p.  418)  .  .  . 

4-5 

5 

Penninite  (pseu.) 

Hinsdalite  (p.  618)  

4-65 

4-5 

(p.  570)  R. 

2-6-2-85 
2-71 

2-25 
3 

Molybdophyllite  (p.498) 
Bastnasite  (p.  449)  

47 
4-9 

3-4      . 
4-5 

Calcite  (p.  438)  R  

Nepouite  (p.  515)  

2-5-3-2 

2-2-5 

GrREENOCKITE  (p.  371)  . 

4-9-5-0 

3-3-5 

Alumian  (p.  632)  

2-74 

2-3 

Hematite  (p.  415)  R  

4-9-5-3 

5-5-6-5 

Catapleiite(p.496).... 

2-8 

6 

Xanthoconite  (p.  393)  R 

5-5-2 

2 

Dolomite  (p.  442)  R.  .  .  . 

2-8-2-9 

3-5-4 

Zincite  (p.  411)  . 

5-4-5-7 

4-4-5 

Martinite  (p.  611)  R. 

2-89 

Bellite  (p.  631)  

5-5 

2-5 

Eudialyte(p.496)R... 

2.91-2-93 

5-5-5 

PROUSTITE,  (p.  389)  R 

5-6 

2-2-5 

Ankerite  (p.  443)  R  

2-95-3-1 

3-5-4 

lodyrite  (p.  397)  

5-6-57 

1-1-5 

Phenacite  (p.  514)  R. 

2-97-3-0 

7-5-8 

Fluocerite  (p.  399)  

5-7-5-9 

4 

Tourmaline  (p.  540)  R. 

2-98-3-20 

7-7-5 

PYRARGYRITE  (p.  389)  R 

5-85 

2-5 

Bityite  (p.  558)  
Magnesite  (p.  443)  R.  .  . 
Pyrosmalite  (p.  515)R  . 
Friedelite  (p.  515)  R. 
Podolite  (p.  618)  
Spangolite  (p.  631)R.  . 

3-0 
3-0-3-12 
3-06-3-19 
3-07 
3-1 
3-14 

5-5 
3-5-4-5 
4-4-5 
4-5 

2 

Penfieldite  (p.  401)  
Barysilite  (p.  498)  
Tysonite  (p.  399)  
Pyromorphite  (p.  597)  .  . 
Vanadinite  (p.  598)  
Mimetite  (p.  598)  

6-11 
6-13 
6-5-7-1 
6-66-6-86 
7-0-7-25 

3 
4-5-5 
3-5-4 
3 
3'5 

Apatite  (p.  595)  
Harttite  (p.  601)  
Jarosite(p.  640)  R...!! 

3-17-3-23 
3-2 
3-20 

5 
4-5-5 

Kleinite  (p.  395)  .  . 

8-0 

8-08-8-2 

3-5 

2-2-5 

Cinnabar  (p.  370)  R.  .  .  . 

Raimondite  (p.  639)  .  .  . 

3-20 

3 

Wilkeite  (p.  597)    . 

3-23 

5 

Some  pseudo-hexagonal  species  are  included. 


APPENDIX  B 

B.  LUSTER  METALLIC   (AND  SUB  METALLIC). 


683 


Specific 
Gravity. 

Hard- 
ness. 

Specific 
Gravity. 

Hard- 
ness. 

Graphite  (p.  347)  R  
Chalcophanite  'p.  435)  R 
Ilmenite  (p  417)  R. 

2-1-2-2 
3-91 
4-5-5 

1-1-5 
2-5 

5-6 

Pyrargyrite  (p.  389)  R.  . 
Tellurium  (p.  349)  R.... 
Allemontite  (p  349)  R 

5-85 
6-1-6-3 
6'2 

2-5 
2-2-5 
3'5 

COVELLITE  (p.  371)  
Pyrrhotite  (p.  373)  
Molybdenite  (p.  360)  .  .  . 
Langbanite  (p.  539)  .  .  . 
Xanthoconite  (p.  393)  .  . 
Hematite  (p.  415)  R.  ... 
Senaite  (p.  418)  R  
Millerite  (p.  372)  R. 

4-6 
4-6 
47-4-8 
4-92 
5 
5-2-5-3 
5-3 
5-3-5-65 

1-5-2 
3-5^-5 
1-1-5 
6-5 

5-5-6-5 
6 
3-3-5 

ANTIMONY  (p.  349)  R  .  . 
Tetradymite  (p.  360)  R. 
Niccolite  (p.  372)  
Breithauptite  (p.  372)  .. 
Platynite  (p.  385)  R.  .  .  . 
Cinnabar  (p.  370)  R.  .  .  . 
BISMUTH  (p.  349)  R.  .  .  . 
Iridosmine  (p  355)  R 

67 
7-2-7-6 
7-3-7-67 
7-54 
8 
8-0-8-2 
9-7-9-8 
19-3-21-1 

3-3-5 
1-5-2 
5-5-5 
5-5 
2-3 
2-2-5 
2-2-5 
6-7 

ARSENIC  (p.  348)  R  

56^57 

3-5 

IV.   CRYSTALLIZATION  ORTHORHOMBIC. 
A.   LUSTER  NONMETALLIC. 


Teschemacherite  (p.450) 
Thermonatrite  (p.  452)  . 
Carnallite  (p.  401)  
Struvite  (p.  606)  
Epsomite  (p.  635)  .  . 

1-45 
1-5-1-6 
1-6 
1-65-17 
175 

1-5 
1-1-5 
1-1-5 
2 
2-2-5 

Edingtonite  (p.  555)  .  .  . 
Hillebrandite  (p.  546) 
Hopeite  (p.  607)  
Phosphosiderite  (p.610) 
Talc  (p.  575)  

2-69 

27 
276 
276 

2-7-2-8 

4-4-5 
5-5 
2-5-3 
375 
1-1-5 

Mascagnite  (p.  624)  .... 
Nesquehonite  (p.  452)  .  . 
Goslarite  (p.  635)  

177 
1-84 
2'0 

2-2-5 
2-5 
2-2-25 

Beryllonite  (p.  595)  .... 
Haidingerite  (p.  610)  .  .  . 
Strengite  (p.  610)  

2-84 
2-85 
2-87 

5-5-S 
1-5-2-5 
3-4 

Erionite  (p.  558)  

1-99 

Prehnite  (p.  534)  

2-8-2-95 

6-6-5 

Morenosite  (p.  635)  .... 
Sulphur  (p.  347) 

1-9-2-1 
2-07 

2-2-5 
1-5-2-5 

Guarinite  (p.  525)  
Anhydrite  (p.  629)  

2-9-3-3 
2-90-2-98 

6-5 
3-3-5 

Lindackerite  (p.  618).  .  . 
Newberyite  (p.  611).... 
Stellerite  (p.  558)  
Niter  (p.  619)  

2-0-2-5 
2-10 
2-12 
2-09-2-14 

2-2-5 
3-3-5 
3-5-4 
2 

Aragonite  (p.  446)  
Spodiosite?  (p.  600)  
Leucophanite  (p.  496)  .  . 
Cebollite  (p.  518)  

2-94 
2-94 
2-96 
2-96 

3-5-4 
4 
5 
5-0 

Sideronatrite  (p.  639)  .  . 
Epidesmine  (p.  558)  .... 
Fluellite  (p.  402) 

2-15 
2-16 
2-17 

2-2-5 
3 

Danburite  (p.  522)  
Bementite  (p.  582)  
Hopeite  (p.  607)  

2-97-3-02 
2-98 
3-0-3-1 

7-7-25 
3-2 

Natrolite  (p.  556)  
Okenite?  (p.  546)  
Fels6banyiteQ..639)..  . 
Thomsonite  (p.  557)  .... 
Wavellite  (p.  612) 

2-20-2-25 
2-28 
2-33 
2-3-2-4 
2-33 

5-5-5 
4-5-5 
1-5 
5-5-5 
3-5-4 

Tyrolite  (p.  612)  
Harstigite  (p.  535)  
Reddingite  (p.  607)  .... 
Lawsonite  (p.  540)  
Grothine  (p.  545)  

3-0-31 
3-05 
3-10 
3-08 
3-09 

1-5 
5-5 
3-3-5 

7-5-8 

Hambergite  (p  620) 

2-35 

7-5 

Humite  (p.  536) 

3-1-3-2 

6-6-5 

Pirssonite  (p.  452)  .  .  .  .  : 
Sulfoborite  (p.  623)  
Dawsonite  (p  452) 

2-35 
2-38-2-45 
2-40 

3-35 
4 

Anthophyllite  (p.  486)  .  . 
Andalusite  (p.  524)  
Enstatite  (p.  472)  

3-1-3-2 
3-16-3-2 
3-15-3-3 

5-5-6 
7-5 
5-5 

Fischerite  (p.  613) 

2-46 

5 

Autunite  (p.  616)  

3-05-3-19 

2-2-5 

Peganite  (p.  613)  
Variscite  (p.  610)  
Lucinite  (p.  610)  
Elpidite  (p.  496)  
Howlite?  (p.  621)  
Bertrandite  (p.  539)  
Lanthanite  (p.  453)  .... 
lolite  (p.  497)  
Thenardite  (p.  624)  .... 

2-50 

2-52 
2-52-2-59 
2-55 
2-6 
2-6 
2-6-2-66 
2-68-2-69 

3-3-5 
4 
5 
6-5-7 
3-5 
6-7 
2-5-3 
7-7-5 
2-3 

Monticellite  (p.  513)  .  .  . 
Eosphorite  (p.  615)  
Childrenite  (p.  615)  
Sillimanite  (p.  526)  .... 
Scorodite  (p.  609)  
Lossenite  (p.  619)  
?orsterite  (p.  513)  
Dumortierite  (p.  543)  .  . 
Kornerupine  (p.  544)  .  .  . 

3-03-3-25 
3-11-3-15 
3-18-3-24 
3-24 
3-1-3-3 

3-2-3-33 
3-26 
3-27 

5-5-5 
5 
4-5-5 
6-7 
3-5-4 

6-7 
7' 
6-5 

684 


APPENDIX   B 
A.  LUSTER  NONMETALLIC 


Specific 
Gravity. 

Hard- 
ness. 

Specific 
Gravity. 

Hard- 
ness. 

Zoisite  (p.  530)  

3-25-3-37 

6-6-5 

Barylite  (p.  498)  

4-03 

7 

Dufrenite  (p  605) 

3-23-3-4 

3-5-4 

Tephroite  (p.  513) 

4-4-12 

5-5-6 

Chrysolite  (p.  511)  
Warwickite  (p.  621)... 
Euchroite  (p  611) 

3-27-3-37 
3-35 
3-39 

6-5-7 
3-4 
3-5-4 

Carminite  (p.  594)  .... 
Ampangabeite  (p.  591) 
Fayalite  (p.  513) 

4-105 
3-97-4-29 
4-4-14 

2-5 
4-0 
6-5 

Astrophyllite  (p.  585)  . 
Diaspore(p.431)  
Lorenzenite  (p.  586)  .  .  . 
Purpurite  (p.  610)  
Natrophilite  (p.  594)  .  . 
Cenosite  (p.  580) 

3-3-3-4 
3-3-3-5 
3-4 
3-4 
3-41 
3-41 

3 
6-5-7 
6-0 
4-4-5 
4-5-5 
5-5 

Retzian  (p.  606)  
Olivenite  (p.  603)  
Hulsite  (p.  622)  
Witherite  (p.  447)  
Adamite  (p.  604)  
Pseudobrookite  (p  424) 

4-15 
4-1-44 
4-3 
4-3-4-35 
4-34-4-35 
44-5 

4 
3 
3 
3-3-75 
3-5 

Gerhardtite  (p.  619)  . 

3-43 

2 

Barite  (p.  625) 

4-5 

2-5-3-5 

Hypersthene(p.473).. 
Uranospinite  (p.  617)  . 
Guarinite  (p.  525)  .... 
Calamine  (p.  539)  

3-4-3-5 
3-45 
3-49 
3-4-3-5 

5-5 
2-3 
6 
4-5-5 

Derbylite  (p.  618)  
Euxenite  (p.  591)  
Yttrocrasite  (p.  586)  .. 
Cerite(p.  540). 

4-53 
4-6-5 

4-8 
4'86 

5 
6-5 
5-5-6 
5-5 

Lithiophilite  (p.  594).. 
Topaz  (p.  523) 

3-42-3-56 
3-4-3-65 

4-5-5 

8 

Blomstrandine  (p.  591)  . 
iEschynite  (p  591) 

4-8-4-9 

4-QQ.C.17 

r;  fi 

Langite  (p.  638) 

3-49 

2-5-3 

Poly  erase  (p  591) 

4'97  5  -04 

K.  a 

Erikite  (p.  580)  
Uranocircite  (p.  617) 
Triphylite  (p.  594)  
Epididymite  (p.  455)  .  .  . 
Mazapilite  (p.  615). 

3-5 
3-53 
3-52-3-55 
3-55 
3-57 

5-5 

4-5-5 
5-5 
4-5 

Cotunnite  (p.  399)  ..... 
Pyrobelonite  (p.  604)  .  .  . 
Valentinite  (p.  410)  ... 
Samarskite  (p.  59$  .... 
Yttrotantalite  (p  590) 

5-24-5-8 
5-38 
5-57 
5-6-5-8 

^•^    'vQ 

2 
3-5 
2-5-3 
5-6 

K     K..K. 

Thortveite  (p.  529).. 
Hemafibrite  (p.  611)  .  . 
Chrysoberyl  (p.  423)  .  .  . 
Aurichalcite  (p.  451) 

3-57 
3-50-3-65 
3-5-3-8 
3-54-3-64 

6-7 
3 

8-5 

Melanotekite  (p.  539).  .  '. 
Annerodite  (p.  591)  ..    . 
Phcenicochroite? 
(p.  630)  

5-7 
5-7 

5-75 

6-5 
6 

3-3-5 

Ardenmte  (p.  539)  ..  . 
Libethenite  (p.  603).... 
Staurolite  (p.  543) 

3-62 
3-6-3-8 
3-65-3-75 

6-7 
4 
7-7-5 

Tellurite  (p.  410)  
Descloizite  (p.  604)  .... 
Tsumebite  (p  604) 

5-9 
5-9-6-2 
A.I 

2 
3-5 

Q.C 

Strontianite  (p.  447) 

3-68-3-71 

3-5-4 

Kentrolite  (p.  539)... 

6-19 

5 

Bromlite  (p.  447) 

3-72 

4-4-5 

Anglesite  (p  628) 

6'12-fV3Q 

2-7^  ^ 

ATACAMITE  (p.  400)  .... 
Uranophane  (p.  581) 
Flinkite  (p.  606)  '. 
Serpierite  (p.  638).... 
Brochantite  (p.  632) 
Brookite  (p.  429) 

376 
3-81-3-9 
3-87 

3-91 
3-87-4-07 

3-3-5 
2-3 
4-4-5 

3-5-4 
5-5-6 

Pucherite  (p.  594)  
Saledonite  (p.  632)  
Daviesite  (p.  401)  
Laurionite  (p.  401)  
Cerussite  (p.  448)  
Nadorite  (p  618) 

6-25 
6'4 

6-46-6-57 
7-09 

4 
2-5-3 

3-3-5 
3-3-5 

Q.C_4 

Pmakiolite  (p.  620)  

3-88 

6 

Ochrolite  (p.  618)  

Ancylite  (p.  449)  

3-9 

4-5 

Vlendipite  (p.  401)  

7-7-1 

2-5-3 

Celestite  (p.  627)  .  .  . 
Ludwigite  (p.  620)  .  . 
Knebelite(p.513). 

3-95-3-97 
3-91^-02 
3-9-4-1 

3-3-5 
5 
6-5 

Georgiadesite  (p.  594)  . 
Stibiotantalite  (p.  590) 
Montroydite  (p.  412)  .  .  . 

7-1 

6-0-74 

3-5 
5-5 
1-5-2 

Brookite  (p.  429) . 
IlvaiteKp.  538) .  . 
Gothite  (p.  431) ... 
Sternbergite  (p.  367) 
Manganite  (p.  432) 
Enargite(p.393)...: 
Wittichenite  (p.  388) 


B.  LUSTER  METALLIC   (AND  SUBMETALLIC). 

Stibnite  (p.  358) . . 
Famatinite  (p.  393) .  .  . 
Klaprotholite  (p.  386) . 
Hutchinsonite  (p.  386) 

Euxenite  (p.  591) 

Chalmersite  (p.  366) 
Chalcostibite  (p.  386)  . 


3-87-4-07 
4-0-4-05 
4-0-44 
4-1-4-2 
4-2-44 

4-43-4-45 
4-5 


5-5-6 
5-5-6 
5-5-5 
1-1-5 

4 

3 


4-5^-6 
4-57 
4-6 
4-6 
4-6-5 
47 

4-75-5 


2 

3-5 
2-5 
1-5-2 
6-5 
3-5 
3-4 


APPENDIX   B 
B.  LUSTER  METALLIC  (AND  SUBMETALLIC)  . 


685 


Specific 

Hard- 

Specific 

Hard- 

Gravity. 

ness. 

Gravity. 

ness. 

Pyrolusite  (p.  430)  

473-4-86 

2-2-5 

Kentrolite  (p.  539)  . 

6'19 

5 

Polymignite  (p.  591)  .  .  . 
Stylotypite  (p.  388)  
Marcasite  (p.  380)  
^Eschynite  (p.  591)  
Urbanite  (p.  477)  

ZlNKENITE  (p.  385)    .... 

Andorite  (p.  385)  

4-77-4-85 
4-8 
4-85-4-9 
4-93;  5-17 
5-3 
5-3-5-35 
5-34 

6-5 
3 
6-6-5 
5-6 
3-5 
3-3-5 

Aikinite  (p.  388)  
Stromeyerite  (p.  366)  .  .  . 
STEPHANITE  (p.  392) 
Guanajuatite  (p.  359)  .  . 
Mullanite  (p.  388)  
Geocronite  (p.  392)  .  . 
Wolfachite  (p.  382)  .  .  . 

6-1-6-8 
6-15-6-3 
6-2-6-3 
6-25-6-6 
6-3 
6-3-6-45 
6-37 

2-2-5 
2-5-3 
2-2-5 
2-5-3-5 
3-5 
2-5 
4-5-5 

Sartonte  (p.  385)  

5-39 

3 

Emplectite  (p.  386)  

6-3-6-5 

2 

Columbite  (p.  588)  
Rathite  (p.  386)  

DUFRENOYSITE 

5-36-6-0 
5-4 
i 

6 
3 

Teallite  (p.  394)  .  .  .-  
Meneghinite  (p.  391).  .. 

BlSMUTHINITE 

6-4 
6-4 

1-2 
2-5 

(p.  387)  

5-55 

3 

(p  359) 

6-4-fi-^ 

2 

Chalcocite  (p.  366)  
Yttrotantalite  (p.  590)  . 

5-5-5-8 
5.5-5-9 

2-5-3 
5-5-5 

Schapbachite  (p.  387)  .  . 
Alloclasite  (p.  382)  .  . 

6-43 
6-6 

3-5 
4-5 

Annerodite  (p.  591)..  .  . 

57 

6 

Cosalite  (p.  387)  

6-4-6-75 

2-5-3 

Melanotekite  (p.  539)..  . 
Bournonite  (p.  388)  .... 

5-7 
5-7-5-9 

6-5 
2-5-3 

Nagyagite  (p.  383)  
Rammelsbergite 

6-85-7-2 

1-1-5 

Seligmanite  (p.  388)...  . 

3 

(p.  382)  

6-9-7-2 

5-5-6 

BOULANGERITE 

Safflorite  (p.  382)  . 

6-9-7-3 

4'5-5 

(p.  387) 

575-6-0 

2-5-3 

Tantalite  (r>   ttR} 

7  7-^i 

Hielmite  (p.  591)  

5-82 

5 

Lolling!  te  (p  381) 

7-0-7-4 

K     K.C 

Diaphorite  (p.  387)  

5-9 

2-5-3 

Acanthite  (p.  367)  

7-2-7-3 

2-2-5 

Glaucodot  (p.  382) 

5-9-6-0 

5 

Krennerite  (p  383) 

Q.OC 

Arsenopyrite  (p.  381)  .  . 

5-9-6-2 

5-5-6 

Dyscrasite  (p.  361)  

9-4-9-8 

3-5-4 

\ 

Natron  (p.  452) 

r.   CRYST, 
A. 

1-44 
1-48 

1-615 
1-66 
1-6-1-8 
1-69-1-72 
1-70 
1-78 
1-84 
1-87 
1-90 
1-9-2-0 

1-9-2-0 
1-94 
1-98 
2:0 
2-035 
2-04-2-14 
2-08 
2-07-2-19 
2-08-2-14 
2-10 
2-10 

\LLIZA1 

LUSTER  . 

1-1-5 
1-5-2 
2-5 
2 
1-2 
1-5-2 
2-2-5 

1-5 
2-2-5 
2-0 

2 

2 
2-3 
2-5 
2-0 
3 
2-2-5 
3-4 
2-5-3 
3 
2-5 
5 

TON  MONOCLINIC. 

SONMETALLIC. 

Trona  (p  453) 

2-12 
2-1-2-2 
2-12 
2-12 
2-13 
2-16 
2-16-2-20 
2-16-24 
2-21 
2-18-2-22 
2-20 
2-2 
2-2-2-4 
2-25 
2-25 
2-26 
2-25-2-36 
2-29 
2-28-2-37 
2-3 
2-31 
2-31-2-33 
2-3-2-4 
2-39-2-46 
242 

2-5-3 

3 
2-5 
4-5 
3-5 
3-5-4 
5-5-5 
2-2-5 
3-5-4 
2-3 
4^-5 
5 
2-5 
4-4-5 
4-5 
3-5-4 
2-5-3 
4^-5 
4-5 
1-0 
1-5-2 
2-5-3-5 
6-6-5 
4-4-5 

Mirabilite  (p.  632)  
Whewellite  (p.  641)  
Stercorite  (p.  611)  
Aluminite  (p.  639)  
Alunogen  (p.  638)  
Borax  (p.  622)  
Boussingaultite  (p.  637)  . 
Apjohnite?  (p.  637)  
Fibroferrite?  (p.  639).  .  . 
Inyoite  (p.  622) 

Picromerite  (p.  637)  
Castanite  (p.  639)  
Quenstedtite  (p.  637)  .  .  . 
Heintzite  (p.  622)  
Hydromagnesite  (p.  452) 
Stilbite  (p.  551)  

Scolecite  (p.  557) 

Brushite  (p.  611)  
Heulandite  (p.  548)  
Darapskite  (p.  619)  
Phillipsite  (p.  550)  
Mesolite  (p.  557)  
Blodite  (p.  637)  

Melanterite  (p.  636)  .  .  . 
Halotrichite?  (p.  637)  .  . 
Pickeringite  (p.  637)  .  . 
Hydroboracite  (p.  623)  . 
Gay-Lussite  (p.  452)  .  .  . 
Krohnkite  (p.  638) 

Epistilbite  (p.  549)  
Gismondite  (p.  552)  .... 
Laumontite  (p.  552)  .... 
Metabrushite  (p.  611)  .  . 
Wellsite  (p.  549)  
Natrochalcite  (p.  638)  .  . 
Griffithite  (p.  572) 

Artinite  (p.  453) 

Diadochite  (p.  618).  .  .  . 
Botryogen  (p.  639)  
Mordenite  (p.  548)  
Kainite  (p.  631)  
8uetenite?.(p.  640)  
opiapite  (p.  638)  
Flokite  (p.  552)  . 

Gypsum  (p.  633). 

Gibbsite  (p.  435)  
Petalite  (p.  455)  
Colemanite  (p.  621).  .  .  . 

686 


APPENDIX   B 
A.   LUSTER  NONMETALLIC. 


Specific 
Gravity 

Hard- 
ness. 

Specific 
Gravity 

Hard- 
ness. 

Hautefeuillite  (p.  608)  . 
Brewsterite  (p.  549)  .  .  . 
Harmotome  (p.  550)  .  . 
Pascoite  (p.  609)  
Ectropite  (p.  582)  
Hoernesite  (p.  608).... 
Wapplerite?  (p.  611)  .  . 
Serpentine  (p.  573)  .  .  . 
Calcioferrite  (p.  615)  .  . 
Eudidymite(p.455)... 
Orthoclase  (p.  457)  .  .  . 
Kieserite  (p.  633)  
Vivianite  (p.  608)  
Syngenite  (p.  636)  
Kaolinite  (p.  578)  
Pharmacolite  (p.  610) 
Clinochlore  (p.  569)  .  .  . 
Pectolite  (p.  483)  
Augelite  (p.  614)  
Bavenite  (p.  558) 

2435 
245 
2-44-2 
246 
246 
247 
248 
2-50-2-6 
2-52-2-5 
2-55 
2-57 
2-57 
2-58-2-6 
2-60 
2-6-2-6 
2-64-2-7 
2-65-2-7 
2-68-2-7 
2-7 
27 
2-71 
273 
2-7-2-8 
2-75 
2-77 
2-76-3 
2-8-2-9 
27-3-1 
2-78-2-85 
2-78-2-96 
2-805 
2-84 
2-82-3-20 
2-86 
2-86 
2-88 
2-8-2-9 
2-8-2-9 
2-89 
2-9 
2-90 
2-77-2:96 
2-9 
2-91 
2-92 
2-92-2-94 
2-93 
2-9-3-0 
2-93-3 
2-93-3 
2-95-3 
2-93-3 
2-94 
2-95 
2-96 

2-5 
5 
4-5 
2-5 
4 
1 
2-2-5 
2-5-4 
2-5 
6 
6 
3-3-5 
1-5-2 
2-5 
2-2-5 
2-2-5 
2-2-5 
5 
4-5-5 
5-5 
4-5 
3-5 
2-5-3 
3-4 
2-5-3 
2-2-5 
2-5-4 

2-5-3 
1-2 
6-6-5 
4-4-5 
2-5-3 
5-6 

2-2-5 
4-5-5 
1-2 
4-5 
1-1-5 
2-5 
34 
2-5-3 
5-0 
1-5 

5-5-5 
5-5-5 
3 
2-3 
2-5 
4 
4-5 
1-5-2-5 
2-5 

Cabrerite  (p.  609)  
Beraunite  (p.  615)  .... 
Herderite  (p.  601)  
Margarite  (p.  566)  
Amphibole  (p.  487)  .... 
Leucosphenite  (p.  585) 
Fremontite  (p.  602)  .  .  . 
Lazulite  (p.  605)  
Wagnerite(p.  600).... 
Szomolnokite  (p.  633)  . 
Xanthophyllite  (p.  567) 
Seybertite  (p.  566)  
Lepidomelane  (p.  565). 
Bassetite(p.  617)  
Kottigite  (p.  609)  
Euclase  (p.  529)  
Glaucophane  (p.  492)  .  . 
Ludlamite  (p.  614)  
Spencerite  (p.  612)  
Lacroixite  (p.  601)  
Herrengrundite  (p.  638) 
Churchite?  (p.  609)  
Chondrodite  (p.  536)  .  .  . 
Clinohumite  (p.  536)  .  .  . 
Prolectite  (p.  538) 

2-96 
2-98. 
2-99-3-0 
2-99-3-0 
2-9-34 
3-0 
3-04 
3-06 
3-07 
3-08 
3-09 
3-3-1 
3-0-3-2 
3-10 
3-1 
3-10 
3-10-3-1 
3-12 
3-12 
3-13 
3-13 
3-14 
3-1-3-2 
3-1-3-2 

3-13-3-2 
3-185 
3-199 
3-2 
3-21 
3-3-3-6 
3-23 
3-29 
3-25-3-5 
3-3 
3-3 
3-3 
73-3 
3-33 
•33-3-35 
3-37 
3-38 
3-34 
340 
41-344 
•42-3-48 
343 
343 
344-3-8 
34-3-5 
346 
44-3-45 
45-3-50 
34-3-65 
5-3-55 

2 

5 
3-5-4-5 
5-6 
6-5 
5-5 
5-6 
5-5-5 

4-6 
4-5 
3 

2-5-3 
7-5 
6-6-5 
3-4 
27 
4-1 
2-5 
o  —  o  *o 
6-6-5 
6-6-5 

6-5-7 
5 

3-7 
5-6 
5-6 

6-7 
5-6 

6-7 
2 
5-5 
6-5-7 
6-6-5 
5 
3-5-4 
6-5 
5-5-6 
7-5 

4-5 
4-5-5 
1-5-2 
5 
6 
4-5 
5-5-5 
6-6-5 

Didymolite  (p.  497) 
Creedite  (p.  402)  

Glauberite  (p.  625).... 
Vilateite  (p.  610)  
Polyhalite?  (p.  637) 
Muscovite  (p.  560)  .  .  . 
Lepidolite  (p.  562)  
Biotite  (p.  563)  .  .  . 

Spodumene  (p.  480)  .... 
Eureaulite  (p.  611)  

3alaite(p.  607).  / 
Hibbenite  (p.  612)  
Pyroxene  (p.  474)  .  . 

Phlogopite  (p.  565).... 
Prochlorite  (p.  571)  
Hyalophane  (p.  460)  .  . 
Ganophyllite  (p.  546)  .  . 
Zinnwaldite  (p.  563)  .... 
Cuspidine  (p.  535)  .  .  . 

Neptunite  (p.  585)  
Johnstrupite  (p.  585)  .  .  . 
Epidote  (p  531) 

Mmguetite  (p.  572)  
Liroconite  (p.  615)  
Wollastonite  (p.  482) 
Pyrophyllite  (p.  579)  .  .  . 
Prosopite  (p.  402)  

Rosenbuschite  (p.  483)  . 
Trogerite  (p.  617) 

Ottrelite?  (p.  567) 

ailpinite  (p.  640)  
Clinohedrite  (p.  540) 
Jadeite  (p.  479)  ! 
Celsian  (p.  460)  .  .  . 

Epistolite(p.592). 

Corundophilite  (p.  571) 
Stilpnomelane  (p.  572) 
Tamiolite  (p.  565)  
Custerite  (p.  497)  .  .  . 

lomilite  (p.  529)  
Dickinsonite  (p.  607) 
Piedmontite  (p.  532)  .  . 
Wohlerite  (p.  484)  
apphirine  (p.  544)  .... 
liebeckite  (p.  493) 
Fillowite  (p.  607) 

Isoclasite?  (p.  611)  
Roscoelite  (p.  565)  ..... 
Carpholite  (p.  540)... 
Datolite(p.527).... 

Pachnolite  (p.  402)  
Thomsenolite  (p.  402) 
Cryolite  (p.  399)  .' 
Mosandrite  (p.  585)  
Jezekite  (p.  601) 
Erythrite(p.608).. 

Yiplite  (p.  600)  . 

ORPIMENT  (p.  357) 
Rinkite  (p.  585)  ... 

Arfvedsonite  (p.  494)  .  .  .  j 
ynadelphite  (p.  606) 
itanite  (p.  583)  .             j 

Symplesite  (p.  608)  

cmite(p.  479)..  .           ! 

APPENDIX  B 


687 


A.  LUSTER  NONMETALLIC. 


Specific 
Gravity. 

Hard- 
ness. 

Specific 
Gravity. 

Hard- 
ness. 

Veszelyite  (p.  612)  
Lavenite  (p.  484)  
Chloritoid?  (p.  567)  
Keilhauite  (p.  585)  
Graf  tonite  (p.  594)  

3-53 
3-51-3-55 
3-52-3-57 
3-52-3-77 
37 

3-5-4 
6 
6-5 
6-5 
5 

Dihydrite  (p.  605)  
Sarkinite  (p.  601)  
Pyrostilpnite  (p.  390)  .  . 
Thalenite  (p.  529)  
Clinoclasite  (p.  604) 

.  4-4-4 
4-18 
4-2 
4-2 
4-19-4-36 

4-5-5 
4-5 
2 
6-5 
2-5-3 

Dietzeite  (p.  619)  

3-70 

3-4 

Kermesite  (p.  383) 

4-5-4-6 

1-1-5 

Triploidite  (p.  601)  
REALGAR  (p.  357)  

37 
3-6 

4-5-5 
1-5-2 

Catoptrite  (p.  618)  
Lautarite  (p.  619)  

4-5 
4-59 

5-5 

Barytocalcite  (p.  449)  .  . 
Adelite,  Tilasite  (p.  601) 

3-65 
3-74 

4 
5 

Monazite  (p.  593)  
Linarite  (p.  632)  

4-9-5-3 
5-3-545 

5-5-5 
2-5 

Chalcomenite  (p.  641)  .  . 

3-76 

Lorandite  (p.  386)  

5-53 

2-2-5 

Azurite  (p.  451)  

3-77-3-83- 

3-5-4 

Baddeleyite  (p.  428)  .... 

5-5;6-025 

6-5 

Leucophoenicite  (p.  538) 
Allactite  (p  606) 

3-8 
3-83-3-85 

5-5-6 
4-5 

Vauquelinite  (p.  630)  .  .  . 
Crocoite  (p.  630)  

5-8-6-1 
5-9-6-1 

2-5-3 
2-5-3 

Allanite  (p.  533)  

3  -5-1  -2 

5-5-6 

Agricolite  (p.  510)  

6-0? 

Claudetite  (p.  409)  
Hodgkinsonite  (p.  582) 

3-85HL-15 
3-91 

2-5 
4-5-5 

Tenorite  (p.  412)  
Leadhillite  (p.  631)  

5-8-6-25 
6-26-6-44 

3-4 
2-5 

Malachite  (p.  450) 

3-9-4-03 

3-5-4 

Lanarkite  (p.  632)  

6-3-64 

2-2-5 

Durangite  (p.  601) 

3-94-4-07 

5 

A.telestite  (p.  606)  

6-4 

3-1-5 

Hancockite  (p.  533)  
Partschinite  (p.  510)  .  .  . 
Gadolinite  (p  529) 

4-0 
4-0 
4-0-4-5 

6-7 
6-5-7 
6-5-7 

Alamosite  (p.  483)  
Fiedlerite  (p.  401)  
Hiibnerite  (p.  642)  

6-5 

7-2-7-5 

4-5 
5-5-5 

Barylite  (p.  498)  
Tagilite  (p.  612)  

4-03 
4-08 

7 
3-4 

Raspite  (p.  643)  
Terlinguaite  (p.  401)  .  .  . 

8-7 

2-3 

Barthite  (p.  612)  

4-19 

3 

B.  LUSTER  METALLIC  (AND  SUBMETALLIC). 


YVmrnHmioritp  fn  ^Sfi^l 

3'3 

3 

Semseyite  (p.  387) 

5-95 

2-3 

Allanite  (p.  533)  
Arizonite  (p.  418)  
Crednerite  (p.  424)  

^mitViitfk  (n  ^Sfi^ 

3-5-4-2 
4-25 
4-9-5-1 
4*9 

5-5-6 
5-5 
4-5 
T5-2 

POLYBASITE  (p.  392).  .  .  . 

Pearceite  (p.  393)  
FREIESLEBENITE 
(p  387) 

6-0-6-2 
6-15 

6-2-6-4 

2-3 
3 

2-2-5 

MlARGYRITE  (p.  386)  .  . 

PLAGIONITE  (p.  387)  .  .  . 
JAMESONITE  (p.  386)  .  .  . 
Rittingerite(p.393).... 

5-1-5-3 
54 
5-5-6-0 
5-63 

2-2-5 
2-5 
2-3 
2-2-5 

Jordanite  (p.  391)  
Wolframite  (p.  641).... 
SYLVANITE  (p.  382)  
CALAVERITE  (p.  383)... 

6-39 
7-2-7-5 
7-9-8-3 
9 

3 
5-5-5 
1-5-2 
2-5 

688 


APPENDIX  B 


VI.  CRYSTALLIZATION  TRICLINIC. 
A.   LUSTER  NONMETALLIC. 


Specific 
Gravity. 

Hard- 
ness. 

Specific 
Gravity. 

Hard- 
ness. 

Sassolite  (p.  435)      

1-48 
1-54 
1-89 
2-11 
2-12 
2-12-2-30 
2-17 
2-5 
2-54-2-57 
2-57-2-60 
2-62-2-65 
2-65-2-67 
2-68 
2-68-2-69 
2-70-2-72 
2-74-2-76 
2-6-2-83 
275 
2-8 
2-94 
3-0-31 

1 
2-5 

2-5 
2 
2-5 
3-3-5 
6-7 
6-6-5 
6 
6-6-5 
6-6-5 

6-6-5 
6-6-5 
6-6-5 
5-6 
3-5 
3-5 

5-5-5 

Inesite  (p.  546)  
Amblygonite  (p.  602)  .  .  . 
Fairfieldite  (p.  607)  
Messelite  (p.  607)  
Chalcosiderite  (p.  616)  . 
Axinite  (p.  534)  

3-03 
3-01-3-09 
3-10 

3-11 
3-27 
3-27 
3-3 
3-35-3-37 
3-37 
3-4-3-68 
3-47 
3-52-3-57 
3-5-3-6 
3-56-3-67 
3-67 
.     3-8 
3-85 
3-99 
4-1 
576 

6 

6 
3-5 
3-5 
4-5 
6-5-7 
5-5-6 
37 
5-5-6 
6-6-5 
5-5-6-5 
6-7 
6-5 
3-5 
5-7-25 
5-5-5 
5-5-6 

2-5-3 
37 
3-5 

Lansfordite(P-453).... 
Hannavite  (p.  611)  
Amarantite  (p.  639)  
(I    Meyerhofferite  (p.  622)  . 
Ml    Chalcanthite(p.636)... 
1   Romerite  (p.  638)  
Ussingite  (p.  470)  

Hiortdahlite  (p.  485)  .  .  . 
Parahopeite  (p.  607)  .  .  . 
Babingtonite  (p.  485)  .  . 
Celsian  (p.  460)  
Rhodonite  (p.  484)  
Trimerite  (p.  515) 

—  —  Microcline  (p.  460)  
Anorthoclase  (p.  461)  .  . 
_^-Albite  (p.  464)  
—  .—Oligoclase  (p.  466)  

Anemousite  (p.  468)  
«—  —  Andesine  (p.  466)  
.^Jabradorite  (p.  466)  
«•..  Anorthite  (p.  467)  
^        Turquois  (p.  613)  

Chloritoid?  (p.  567)  
Roselite  (p.  607)  

Cyanite  (p.  526)  
Brandtite  (p.  607)  
Pyroxmangite  (p.  485)  .  . 
^Enigmatite  (p.  494)  
Margarosanite  (p.  498)  . 
Tarbuttite  (p.  604)  
Walpurgite?  (p.  617)  ... 

Monetite  (p.  606)  

Anapaite  (p.  607) 

Stewartite  (p.  607)  
Schizolite  (p.  483)  

APPENDIX     B  689 

TABLE  III.   CRYSTALLINE  HABIT. 
I.   ISOMETRIC   SYSTEM. 

In  the  following  lists  some  species  are  enumerated  whose  crystalline  habit  is  often  so 
marked  as  to  be  a  distinctive  character. 

Cubes.  —  METALLIC  LUSTER:  Galem^  !  Pyrite. 

NONMETALLIC  LUSTER:  FluonTe  :  Cuprite  (at  times  elongated  into  capillary  forms) 
Cerargyrite;  Halitej  Sylvite;  Boracite;  Pharmacosiderite.  Also  Percy  lite;  Perovskite. 

Cube-like  forms  occur  with  the  following:  Apophyllite  (tetragonal);  Cryolite  (mono- 
clinic).  Also  with  the  rhombohedral  species:  Chabazite:  Alunite;  Calcite;  rarely  Quartz 
and  Hematite. 

Octahedrons.  —  METALLIC  AND  SUBMETALLIC  LUSTER:  Magnetite:  Franklinite;  Chro- 
mite;  Uraninite.  Also  sometimes,  Galena;  Pvrite;  Linnaeite;  Dysanalyte. 

NONMETALLIC  LUSTER:  Spinel  (incl."Hercynite  and  Gahnite)  ;  Cuprite;  Diamond;  Pyro- 
chlore  and  Microlite;  Ralstonite;  Periclase;  Alum. 

Forms  somewhat  resembling  regular  octahedrons  occur  with  some  tetragonal  species,  as 
Braunite;  Hausmannite;  Chalcopyrite;  Zircon,-  etc.;  also  with  some  rhombohedral  species, 
as  Dolomite. 

Dodecahedrons.  —  METALLIC  LUSTER:  Magnetite;  Amslgam. 

NONMETALLIC  LUSTER:  Garnet;  Cuprite;  SoH^lif^ 

Tetrahexahedrons.  —  Native  Copper;  Fluorite. 

Trapezohedrons.  —  NONMETALLIC  LUSTER:   Garnet;  Leucite;  Analcite. 

Also  Gersd 


Pyritohedrons.  —  METALLIC  LUSTER:  JPyrite^  (Jobaltite.  Also  Gersdorffite;  Hauerite 
(submetallic). 

Tetrahedrons.  —  METALLIC  LUSTER:  Tetrahedrite. 

NONMETALLIC  LUSTER:   Sphalerite;  Boracite;  Helvite;  Eulytite;  Diamond;  Zunyite. 
The  tetragonal  sphenoids  of  Chalcopyrite  sometimes  closely  resemble  tetrahedrons. 

II.  TETRAGONAL  SYSTEM. 

Square  Pyramids.  —  SUBMETALLIC  LUSTER:     Braunite;  Hausmannite. 

NONMETALLIC  LUSTER:  Zircon;  Wulfenite;  Vesuvianite;  Octahedrite;  Xenotime. 

Square  Prisms.  —  NONMETALLIC  LUSTER:  zircon:  vesuvianite.:  Scapolites;  Apophyllite; 
Phosgenite.  """" 

Square  tabular  crystals  occur  with  Apophyllite;  Wulfenite;  Torbernite. 

Prisms  nearly  square  are  noted  with  a  itiuritDer  of  orthorhombic  species,  e.g.,  Topaz; 
Andalusite;  Danburite:  also  with  the  monoclinic  Pyroxene  (100  A  010  =  90°, 
110  A  110  =  87°) 

III.  HEXAGONAL  SYSTEM. 

Hexagonal  Prisms.  —  NONMETALLIC  LUSTER:  Bervl:  Apatite:  Pyromprphite;  Vanadi- 
nite;  Mimetite  (usually  indistinct  rounded  forms).  Also  Nephelite;  Milarite:  Tysonite, 
and  others. 

Hexagonal  prisms  are  also  common  with  the  rhombohedral  species:  Quartz;  Calcitej 

the  Micas,  efc.  Numef^ 


Tourmaline  L  Willemite;  Phenacite;  Dioptass,  etc.     Again,  with 
ous  rare  specit    could  be  included  here.    - 

Many  orthorhombic  (or  monoclinic)  species  having  a  prismatic  angle  of  about  60°  (and 
120°)  simulate  this  form  both  in  simple  crystals  and  still  more  as  the  result  of  twinning. 
Thus,  Aragonite;  Strontianite;  Leadhillite;  lolite.  It  is  also  to  be  noted  that  the  isometric 
dodecahedron,  e.g.,  of  Garnet,  has  often  the  form  of  a  hexagonal  pyramid  with  trihedral 
terminations  (cf.  Fig.  470,  p.  175). 

Tabular  hexagonal  prisms  are  noted  with  various  species.  Thus,  METALLIC  LUSTER: 
Graphite;  Molybdenite;  Hematite;  Ilmenjte;  Pyrrhotite.  NONMETALLIC  LUSTER:  Tri^ 

Hexagonal  Pyramids.  —  Apatite:  Corundum, (rhombohedral);  Quartz  (rhombohedral- 
trapezohedral) :  Hanksite. 

This  form  is  often  simulated  by  various  orthorhombic  species,  in  part  as  the  result  of 
twinning.  For  example,  METALLIC  LUSTER:  Chalcocite;  Stephanite;  Polybasite;  Jor- 
danite;  etc.  Also  Brookite. 

NONMETALLIC  LUSTER:  Witherite;  Bromlite;  Cerussite;  lolite. 

Trigonal  Prisms.  —  Tourmaline. 

Rhombohedrons.  —  Angle  ?5u(and  105°):  Calcite ; :  JDolomitej.  Siderite :  PJiodochrosite. 
Angle  not  far  from  90°:  Chabazite;  Alunite ; Talciter'also  Quartz ; Hematite. 

Scalenohedrons.  —  Calcite  and  allied  Carbonates^  ProustifE7~~ 


690  APPENDIX     B 

IV.  ORTHORHOMBIC,   MONOCLINIC  AND  TRICLINIC  SYSTEMS. 
Prismatic  Crystals.  —  METALLIC  LUSTER:  Stibnite;  Arsenopyrite;  Bournonite;  Manga- 

m  NONMETALLIC  LUSTER:    (orthorhombic)  Tojmz;   Sj^ijrolite;   Andalusite;   £arite:    Celes- 

tite;   Danburite.     Also  (monoclinic)  Pyroxene;  Amphibole;  Qrthoclase,  and  many  others. 
Epidote  crystals  are  often  prismatic  in  aspect  (Fig.  894,  p.  531JT 
Tabular  Crystals.  —  Barite;  Cerussite;  Calamine;  Diasppre;  Wollastonite;  4lhl'te, 
Acicular  Crystals.  —  METALLIC   LUSTER:     Stibnite;    BismutEimtej    Miflente;    Jame- 

sonite;  Aikinite,  and  other  species. 
NONMETALLIC  LUSTER:     gectolite;  Natrolite:  Scolecite;  Thomsonite,  and  other  Zeolites. 

Also  Aragonjie;  Strontianite;  lesd  '  6f  ten  Calcite.     Also  many  other  species. 

TwinTrystals.  —  The  habit  of  the  twins  occurring  with  many  species  is  very  character- 

istic.    Reference  is  made  to  pp.  165  to  172  and  the  accompanying  figures  for  a  presentation 

of  this  subject. 

TABLE  IV.  STRUCTURE  OF  MASSIVE  MINERALS 

Fibrous.  —  Fibers  separable:  Asbestus  (amphibole);  also  the  similar  asbestiform  va- 
riety of  serpentine  (chrysotile)  ;  Crocidolite  (color  blue). 

Fibers  not  separable,  chiefly  straight:  Anthophyllite;  Calcite;  Gypsum.  Also  Aragonite; 
Barite;  Celestite;  Anhydrite;  Brucite;  Enstatite;  Wollastonite;  Dufrenite;  Vivianite. 
See  also  Columnar  below. 

Fibrous-Radiated.  —  Wavellite;  Pectolite;  Thomsonite;  Natrolite;  Stilbite,  Scolecite; 
and  other  Zeolites;  Gothite;  Malachit  . 

Columnar.  —  METALLIC  LUSTER:     Stibnite;  Hematite;  Jamesonite;  Zinkenite,  etc. 

NONMETALLIC  LUSTER:  Limonite;  Gothite;  Aragonite;  Amphibole  (tremolite,  actino- 
lite,  etc.);  Epidote;  Zoisite;  Tourmaline;  Sillimanite;  Natrolite  and  other  Zeolites:  Stron- 
tianite; Witherite;  Topaz. 

Cyanite  has  often  a  bladed  ,  tructure. 

Fibrous  and  columnar  varieties  pass  into  one  another. 

Lamellar-Stellate.  —  Gypsum;  Pyrophyllite;  Talc. 

Foliated.  —  METALLIC  LUSTER:  Graphite;  Molybdenite;  Tetradymite;  Sternbergite- 
Nagyagite. 

NONMETALLIC  LUSTER:  Talc;  Orpiment;  Gypsum;  Pyrophyllite;  Serpentine;  Gypsum 

Micaceous.  —  The  Micas,  p.  559:  also  the  Brittle  Micas,  p.  566,  and  the  Chlorites,  p.  568 
Also  Brucite;  Orpiment;  Talc;  Torber^ite;  Autunite. 

Granular.  —  METALLIC  LUSTER:  Galena;  Hematite;  Magnetite.  Many  sulphides, 
sulpharsemtes;  etc.,  have  varieties  which  are  fine-granular  to  compact  and  impalpable 

NONMETALLIC  LUSTER:     Pyroxene  (coccolite);  Garnet;  Calcite;  Barite,  etc 

Botryoidal,  Mammillary,  Reniform,  etc.  —  METALLIC  LUSTER:  Hematite;  Arsenic- 
Allemontite. 


Malachite;   Prehnite;   Smithsonite;   Calamine;   Chalcedony; 

Stalactitic.  —  METALLIC  LUSTER:  Limonite;  Psilomelane;  Marcasite. 

NONMETALLIC  LUSTER:  Calcite;  Aragonite;  Gibbsite;  Chalcedony. 

Granular  Cleavable.— METALLIC  LUSTER:  Galena. 

NONMETALLIC  LUSTER:  Calcite;  Dolomite;  Sphalerite;  Fluorite. 

Oolitic.  —  Calcite;  Aragonite;  Hematite. 

fcartny.  —  NONMETALLIC  LUSTER:  Magnesite;  piolite 

TABLE  V.  PHYSICAL  CHARACTERS. 

I.   CLEAVAGE. 
Cubic.  —  METALLIC  LUSTER:     Galena. 

STER:    Halite:    Sylvite.     The  cleavage  of  Anhydrite  (also  of  Cyro- 
Ui.  also  Corundum,  p.  413. 

Diamond.     Magnetite   (also  Franklinite)   has  often  distinct 


l  ^  Sodalite;  Hauynite. 

75          105!  >dral'~  °alcite  and  other  sPecies  of  th^  wine  group  (pp.  437-445)  angles 
Square  Prismatic  (90°).  -  Scapolite;  Rutile;  Xenotime. 


APPENDIX     B 


691 


Prismatic.  —  Barite  (78  °i,  101°^);  Celestite;  Amphibole  (54°  and  126°),  etc. 

Basal.  —  METALLIC  LUSTER:   Graphite;   Molybdenite. 

NONMETALLIC  LUSTER:  Apophyllitej  Topaz;  Talc;  the  Micas  and  Chlorites;  Chalco- 
phyllite,  etc.  Pyroxene  often  shows  marked  basal  parting. 

Pinacoidal.  —  METALLIC  LUSTER:  Stibnite. 

NONMETALLIC  LUSTER:  Gypsum;  Orpiment;  Euclase;  Diaspore;  Sillimanite;  Cyanite; 
Feldspars. 

II.   HARDNESS. 

1.  Soft  Minerals.  —  The  following  minerals  are  conspicuously  Soft,  that  is,  H  =  2 
or  less;  they  hence  have  a  greasy  feel.     (See  further  the  Tables,  pp.  679  to  688.) 

METALLIC  LUSTER:  Graphite;  Molybdenite;  Tetradymite;  Sternbergite;  Argentite; 
Nagyagite;  some  of  the  Native  Metals  (Lead,  etc.). 

NONMETALLIC  LUSTER:  Talc;  Pyrophyllite;  Brucite;  Tyrolite;  Orpiment;  Cerargyrite; 
Cinnabar;  Sulphur;  Gypsum. 

Also  Calomel,  Arsenolite,  and  many  hydrous  sulphates,  phosphats,  etc. 

2.  Hard  Minerals.  —  Minerals  whose  hardness  is  equal  to  or  greater  than  7  (Quartz  =  7). 
The  following  minerals  are  here  included: 

LUSTER  NONMETALLIC 


QUARTZ  (p.  403) 7 

Tridymite  (p.  407) 7 

Barylite  (p.  498).- 7 

Dumortierite  (p.  543) 7 

Danburite  (p.  522) 7-7'25 

BORACITE  (p.  620) 7 

Zunyite  (p.  505) 7 

CYANITE  (p.  526) 5-7'25 

TOURMALINE  (p.  540) 7-7*5 

GARNET  (p.  505) 6'5-7'5 

IOLITE  (p.  497) 7-7-5 

STAUROLITE  (p.  543) 7-7 "5 

Schorlpmite  (p.  510) 7-7*5 

Sapphirine  (p.  544) 7'5 

Euclase  (p.  529) 7'5 


Hambergite  (p.  620) 7'5 

ZIRCON  (p.  520) 7'5 

ANDALUSITE  (p.  524) 7'5 

BERYL  (p.  495) 7'5-8 

Lawsonite  (p.  540) 7'5-8 

Phenacite  (p.  514) 7'5-8 

Gahnite  (p.  420) 7'5-8 

Hercynite  (p.  420) 7 '5-8 

SPINEL  (p.  419) 8 

TOPAZ  (p.  523) 8 

Rhodizite  (p.  621) 8 

CHRYSOBERYL  (p.  423) 8'5 

CORUNDUM  (p.  413) 9 

DIAMOND  (p.  345) 10 


The  following  minerals  have  hardness  equal  to  6  to  7,  or  6 '5  —  7. 

LUSTER  METALLIC:    Iridosmine  (p.  355);  Iridium  (p.  355);  Sperrylite  (p.  379). 

LUSTER  NONMETALLIC:  Ardennite  (p.  539);  Axinite  (p.  534);  Bertrandite  (p.  539); 
Cassiterite  (p.  425);  Chrysolite  (p.  511);  Diaspore  (p.  431);  Elpidite  (p.  496);  Epidote 
(p.  531);  Forsterite  (p.  513);  Gadolinite  (p.  529);  Jadeite  (p.  479);  Partschinite  (p.  510); 
Sillimanite  (p.  526);  Spodumene  (p.  480);  Trimerite  (p.  515). 

III.   SPECIFIC   GRAVITY. 

Attention  is  called  to  the  remarks  in  Art.  302  (p.  199),  on  the  relation  of  specific  gravity  to 
chemical  composition.  Also  to  the  statements  in  Art.  303  as  to  the  average  specific  gravity 
among  minerals  of  metallic  and  norimetallic  luster  respectively.  The  species  in  each  of  the 
separate  lists  of  Table  II  of  minerals  classified  with  reference  to  crystallization  are  arranged 
according  to  ascending  specific  gravities.  Hence  the  lists  give  at  a  glance  minerals  dis- 
tinguished by  both  low  and  high  density. 

IV.    LUSTER.     (See  Art.  364,  p.  249) 

Metallic.  —  Native  metals;  most  Sulphides;  some  Oxides,  those  containing  iron,  man- 
ganese, lead,  etc. 

Submetallic.  —  Here  belong  chiefly  certain  iron  and  manganese  compounds,  as  Ilmenite; 
Ilvaite;  Columbite;  Tantalite  (and  allied  species);  Wolframite;  Braunite;  Hausmannite. 
Also  Brookite;  Uraninite,  etc. 

Adamantine.  —  Here  belong  minerals  of  high  refractive  index:  (a)  Some  hard  minerals: 
Diamond;  Corundum;  Cassiterite;  Zircon;  Rutile.  (6)  Many  species  of  high  density,  as 
compounds  of  lead,  also  of  silver,  copper,  mercury.  Thus,  Cerussite,  Anglesite,  Phos- 
genite,  etc.;  Cerargyrite;  Cuprite;  some  Cinnabar,  etc.  (c)  Also  certain  varieties  of  Sphal- 
erite, Tjtanite  and  Octahedrite. 


(592  APPENDIX     B 

Metallic-Adamantine.  —  Pyrargyrite;  some  varieties  of  the  following:  Cuprite,  Cerus- 
site, Octahedrite,  Rutile,  Brookite. 

Resinous  or  Waxy.  —  Sphalerite;  Sulphur;  Elseohte;  Serpentine;  many  Phosphates. 

Vitreous.  —  Quartz  and  many  Silicates,  as  Garnet,  Beryl,  etc. 

Pearly  —The  foliated  species:  Talc,  Brucite,  Pyrpphylhte.  Also  (on  cleavage  sur- 
faces) conspicuously  the  following:  Apophyllite,  Stilbite,  Heulandite.  Also,  less  promi- 
nent: Barite;  Celestite;  Diaspore;  some  Feldspar,  and  others. 

Silky.  —  Some  fibrous  minerals,  as  Gypsum,  Calcite;  also  Asbestus;  Malachite. 

V.   COLOR. 

The  following  lists  may  be  of  some  use  in  the  way  of  suggestion.  It  is  to  be  noted,  how- 
ever, that  especially  in  the  case  of  metallic  minerals  a  slight  surface  change  may  alter  the 
effect  of  color.  Further,  among  minerals  of  nonmetallic  luster  particularly,  no  sharp 
line  can  be  drawn  between  colors  slightly  different,  and  many  variations  of  shade  occur 
in  the  case  of  a  single  species.  For  these  reasons  no  lists,  unless  inconveniently  extended, 
could  make  any  claim  to  completeness. 

(a)  METALLIC  LUSTER. 

Silver-white,  Tin-white.  —  Native  silver;  Native  Antimony,  Arsenic  and  Tellurium; 
Amalgam;  Arsenopyrite  and  Lollingite;  several  sulphides,  arsenides,  etc.,  of  cobalt  or 
nickel,  as  Cobaltite  (reddish);  some  Tellurides;  (Bismuth  (reddish).)  No  sharp  line  can 
be  drawn  between  these  and  the  following  group. 

Steel-gray.  —  Platinum;  Manganite;  Chalcocite;  Sylvanite;   Bournonite. 

Blue-gray.  —  Molybdenite;  Galena. 

Lead-gray.  —  Many  sulphides,  as  Galena  (bluish);  Stibnite;  many  Sulpharsenites,  etc., 
as  Jamesonite,  Dufrenoysite,  etc. 

Iron-black.  —  Graphite;  Tetrahedrite;  Polybasite;  Stephanite;  Enargite;  Pyrolusite; 
Magnetite;  Hematite;  Franklinite. 

Black  (with  submetallic  luster).  —  Ilmenite;  Limonite;  Columbite;  Tantalite,  etc.; 
Wolframite;  Ilvaite;  Uraninite,  etc.  The  following  are  usually  brownish  black:  Braunite; 
Hausmannite. 

Copper-red.  —  Native  copper. 

Bronze-red.  —  Bornite  (quickly  tarnished  giving  purplish  tints) ;  Niccolite. 

Bronze-yellow.  —  Pyrrhotite;  Pentlandite;  Breithauptite. 

Brass-yellow.  —  Chalcopyrite;  Millerite  (bronze).  Pale  brass-yellow:  Pyrite;  Mar- 
casite  (whiter  than  Pyrite). 

Gold-yellow.  —  Native  gold;  chalcopyrite  and  pyrite  sometimes  are  mistaken  for  gold. 

Streak.  —  The  following  minerals  of  metallic  luster  are  notable  for  the  color  of  their 
streak: 

Cochineal-red:  Pyrargyrite. 

Cherry-red:  Miargyrite. 

Dull  Red:  Hematite;  Cuprite;  some  cinnabar. 

Scarlet:  Cinnabar  (usually  nonmetallic). 

Dark  Brown:  Manganite;  Franklinite;  Chromite. 

Yellow:  Limonite. 

Tarnish.  — The  following  are  conspicuous  for  their  bright  or  variegated  tarnish:  Chal- 
copyrite; Bornite  (purplish  tints);  Tetrahedrite;  some  Limonite. 

(6)  NONMETALLIC  LUSTER. 

Colorless.  —  IN  CRYSTALS:  Quartz;  Calcite;  Aragonite;  Gypsum;  Cerussite;  Angles- 
ite;  Albite;  Barite;  Adulana;  Topaz;  Apophyllite;  Natrolite  and  other  Zeolites;  Ce- 
lestite; Diaspore;  Nephelite;  Meionite;  Calamine;  Cryolite;  Phenacite,  etc 

MASSIVE:  Quartz;  Calcite;  Gypsum;  Hyalite  (botryoidal) 

White.  -  CRYSTALS:  Amphibole  (tremolite);  Pyroxene  (diopside,  usually  greenish). 
lit^T  lIVEiCr  i^;  Mllk7  Quartz5  Felspars,  especially  Albite;  Barite;  Cerussite,  Scapo- 
lite;  Talc;  Meerschaum;  Magnesite;  Kaolinite;  Amblygonite,  etc. 

Blue.  —  BLACKISH  BLUE:  Azurite;  Crocidolite. 

INDIGO-BLUE:  Indicolite  (Tourmaline);  Vivianite. 

AZURE-BLUE:  Lazulite;  Azurite;  Lapis  Lazuli;  Turquois 

mIN"BLUE:    Sapphire;  Cyanite;  Mite;  Azurite;  Chalcanthite  and  many  copper 


APPENDIX  693 

SKY-BLUE,  MOUNTAIN-BLUE:  Beryl;  Celestite. 

VIOLET-BLUE:  Amethyst;  Fluorite. 

GREENISH  BLUE:  Amazon-stone;  Chrysocolla;  Calamine;  Smithsonite;  some  Turquois; 
Beryl. 

Green.  —  BLACKISH  GREEN:  Epidote;  Serpentine;  Pyroxene;  Amphibole. 

EMERALD-GREEN:  Beryl  (Emerald);  Malachite;  Dioptase;  Atacamite;  and  many  other 
copper  compounds;  Spodumene  (hiddenite);  Pyroxene  (rare);  Gahnite;  Jadeite  and  Jade. 

BLUISH  GREEN:  Beryl;  Apatite;  Fluorite;  Amazon-stone;  Prehnite;  Calamine;  Smith- 
sonite; Chrysocolla;  Chlorite;  some  Turquois. 

MOUNTAIN  GREEN:   Beryl  (aquamarine);  Euclase. 

APPLE-GREEN:  Talc;  Garnet;  Chrysoprase;  Willemite;  Garnierite;  Pyrophyllite:  some 
Muscovite;  Jadeite  and  Jade,  Pyrophyllite. 

PISTACHIO-GREEN:  Epidote. 

GRASS-GREEN:  Pyromorphite;  Wavellite;  Variscite;  Chrysoberyl. 

GRAYISH  GREEN:  Amphibole  and  Pyroxene,  many  common  kinds;  Jasper;  Jade. 

YELLOW-GREEN  to  OLIVE-GREEN:  Beryl;  Apatite;  Chrysoberyl;  Chrysolite  (olive- 
green);  Chlorite;  Serpentine;  Titanite  Datolite;  Olivenite;  Vesuvianite. 

Yellow.  —  SULPHUR-YELLOW:  Sulphur;  some  Vesuvianite. 

ORANGE-YELLOW:  Orpiment;  Wulfenite;  Mimetite. 

STRAW-YELLOW,  also  WINE-YELLOW,  WAX- YELLOW:  Topaz;  Sulphur;  Fluorite;  Can- 
crinite;  Wulfenite;  Vanadinite;  Willemite;  Calcite;  Barite;  Chrysolite;  Chondrodite; 
Titanite;  Datolite,  etc. 

BROWNISH  YELLOW:   Much  Sphalerite;  Siderite;  Gothite. 

OCHER- YELLOW:   Gothite:  Yellow  ocher  (limonite). 

Red.  —  RUBY-RED:  Ruby  (corundum);  Ruby  spinel;  much  Garnet;  Proustite;  Vana- 
dinite; Sphalerite;  Chondrodite. 

COCHINEAL-RED:  Cuprite;  Cinnabar. 

HYACINTH-RED.  —  Zircon;  Crocoite. 

ORANGE-RED.  —  Zincite;  Realgar;  Wulfenite. 

CRIMSON-RED:  Tourmaline  (rubellite);  Spinel,  Fluorite. 

SCARLET-RED:  Cinnabar. 

BRICK-RED:  Some  Hematite  (red  ocher). 

ROSE-RED  to  PINK:  Rose  quartz;  Rhodonite;  Rhodochrosite;  Erythrite;  some  Scapo- 
lite.  Apophyllite  and  Zoisite;  Eudialyte;  Petalite;  Margarite. 

PEACH-BLOSSOM  RED  to  LILAC:  Lepidolite;  Rubellite. 

FLESH-RED:  Some  Orthoclase;  Willemite  (the  variety  troostite);  some  Chabazite; 
Stilbite  and  Heulandite;  Apatite;  rarely  Calcite;  Polyhalite.. 

BROWNISH  RED:  Jasper;  Limonite;  Garnet;  Sphalerite;  Siderite;  Rutile. 

Brown.  —  REDDISH  BROWN:  Some  Garnet;  some  Sphalerite;  S  aurolite;  Cassiterite; 
Rutile. 

CLOVE-BROWN:  Axinite;  Zircon;  Pyromorphite. 

YELLOWISH  BROWN:  Siderite  and  related  carbonates;  Sphalerite;  Jasper;  Limonite; 
Gothite;  Tourmaline;  Vesuvianite;  Chrondrodite;  Staurolite. 

BLACKISH  BROWN:  Titanite;  some  Siderite;  Sphalerite. 

SMOKY  BROWN:  Quartz. 

Black:  Tourmaline;  black  Garnet  (melanite);  some  Mica  (especially  biotite):  also 
some  Amphibole,  Pyroxene  and  Epidote  (these  are  mos'ly  greenish  or  brownish  back); 
further,  some  Sphalerite  and  some  kinds  of  Quartz  (varying  from  smoky  brown  to  black); 
also  Allanite;  Samarskite.  Some  black  minerals  with  submetalhc  luster  are  mentioned 
on  p.  692. 

Streak.  —  The  streak  is  to  be  noted  in  the  case  of  some  minerals  with  nonmetallic  luster. 
By  far  the  majority  have,  even  when  deeply  colored  in  the  mass  (e.g.  Tourmaline),  a  streak 
differing  but  little  from  white.  The  following  may  be  mentioned: 

ORANGE-YELLOW:  Zincite,  Crocoite. 

COCHINEAL-RED:   Pyrargyrite  and  Proustite. 

SCARLET  RED:  Cinnabar. 

BROWNISH  RED:  Cuprite;  Hematite. 

BROWN:  Limonite.  ,.  ,    ,  .,      A 

The  streak  of  the  various  copper,  green  and  blue  minerals,  as  Malachite,  Azunte,  etc., 
is  about  the  same  as  the  color  of  the  mineral  itself,  though  often  a  little  paler. 


GENERAL  INDEX 


Abbreviations,  5 
Absorption  of  light,  222 

biaxial  crystals,  287 
uniaxial  crystals,  268 
Acicular  structure,  183 
Acid  salts,  319 
Acids,  318 

Adamantine  luster,  209 
Aggregate  polarization,  300 
Aggregates,  crystalline,  182 

optical  properties,  300 
Airy's  spirals,  270 
Albite  law  (twinning),  172 
Alkalies,  test  for,  319 
Alkaline  taste,  310 
Alliaceous  odor,  310 
Aluminium  (aluminum),  tests  for,  338 
Amorphous  structure,  8,  183 
Amplitude  of  vibration,  203 
Amygdaloidal  structure,  183 
Analyzer,  229 
Analysis,  blowpipe,  331 
chemical,  326 
microchemical,  326 
Angle,  critical,  210 

of  extinction,  278 
Angles,  measurement  of,  152 

of  isometric  forms,  63,  66,  70 
Anisometric  crystals,  252 
Anisotropic  crystals,  252 
Anomalies,  optical,  301 
Anorthic  system,  143 
Antimony,  test.-  for,  338 
Aborescent  structure,  see  Dendritic,  183 
Argillaceous  odor,  310 
Arsenic,  tests  for,  338 
Artificial  minerals,  1,  326 
Asterism,  250 
Astringent  taste,  310 
Asymmetric  class,  147 
Atom,  311 
Atomic  weight,  311 
Axes,  crystallographic,  15 

of  symmetry,  11 

optic,  276,  285 

dispersion  of,  289,  292 
Axial  angle,  optic,  277 
\  measurement  of,  284 

plane,  26 

ratio,  26 


B 

Barium,  tests  for,  338 

Basal  pinacbid,  78,  95,  122,  134 

Bases,  chemical,  318 

Basic  salts,  319 

Baveno  twins,  171 

Becke  test,  216 

Belonite,  180 

Betrand  ocular,  279 

Berylloid,  98 

Bevel,  Bevelment,  57 

Biaxial  crystals,  behavior  of  light  in,  270 

positive  and  negative,  277 
Biaxial  indicatrix,  274 

interference  figure,  281 

optic  axes,  281 
Binary  symmetry,  11 
Bi-quartz  wedge  plate,  280 
Birefringence,  determination  of,  237 
Bisectrix,  acute,  277 
obtuse,  277 

Bismuth,  tests  for,  338 
Bitter  taste,  310 
Bituminous  odor,  310 
Bivalent  element,  317 
Bladed  structure,  182 
Blebby  bead,  332 
Blowpipe,  330 

flame,  331 

Borax  bead  tests,  336 
Boron,  tests  for,  338 
Botryoidal  structure,  183 
Brachy-axis,  121 
Brachydome,  123 
Brachypinacoid,  122 
Brachyprism,  123 
Brachypyramid,  124 
Brazil  law  (twin).  168,  404 
Brewster's  law,  227 
Bri; 


Cadmium 


7,  73,  91,  116,  130, 

s 

formula,  321 


>r,  338 


696 


GENERAL   INDEX 


Carlsbad  twin,  170 
Center  of  symmetry,  12 
Charcoal  tests,  334 
Chemical  compound,  318 

composition    and    optical    char- 
acters, 298 
elements,  311,  312 
formula,  312 
mineralogy,  311 
radicals,  317 
reactions,  317 
symbol,  312 
tests,  328,  338 
Chlorides,  tests  for,  338 
Chromium,  tests  for,  339  . 

Circular  polarization,  240,  270 

imitated  by  mica  sec- 
tions, 300 

Classification  of  minerals,  343 
Cleavage,  186 

basal,  187 
cubic,  187 
dodecahedral,  187 
octahedral,  187 
prismatic,  187 
rhombohedral,  187 
Clino-axis,  133 
Clinodome,  135 
Clinohedral  class,  138 
Clinopinacoid,  134 
Clinoprism,  135 
Clinopyramid,  135 
Closed  tube  tests,  333 
Cobalt,  tests  for,  339 

nitrate,  use  of,  332 
Cohesion,  186 
Colloid  structure,  183 
Colloidal  minerals,  324 
Color,  204,  247,  248 

complementary,  205 
Columnar  structure,  182 
Complementary  colors,  205 
Composition-plane,  161 
Compound  crystals,  160 
Concentric  structure,  182 
Conchoidal  fracture,  191 
Conductivity,  for  electricity,  306 

for  heat,  304 
Conical  refraction,  276 

Conoscope,  243 ,, - 

Contact  •goniometer 
Contact-twin,  162 
Cooling  taste,  310 
Copper,  tests  for,  389^ 
Coralloidal  struetur 
Corrosion  forms,  191^. 
Cotangent  relation,;  Jlffi 
Critical  angle,  210  h 
Crossed  dispersion, 
Crypto-crystalline,  H 
Crystal,  definition,  H 
distorted 
form,  30 


Crystalline  aggregate,  8,  182 

structure,  8 
Crystallites,  180 
Crystallization,  systems  of,  15 
Crystallography,  7 

literature  of,  2 
Cube,  54 
Cubic  system,  52 
Curved  crystals  and  faces,  177 

D 

Decrepitation,  332,  333 

Deltoid  dodecahedron,  69 

Dendritic  structure,  173,  183 

Density,  195 

Description  of  species,  343 

Determination  of  minerals,  341 

Diamagnetic  minerals,  309 

Diamagnetism,  309 

Diametral  prism,  monoclinic  system,  134 

orthorhombic  system,  122 
Diaphaneity,  247 
Diathermancy,  305 
Dibasic  acid,  318 
Dichroism,  247,  268 
Dichroscope,  269 
Diffration,  223 

Dihexagonal  bipyramidal  class,  95 
Dihexagonal  pyrism,  96 
Dihexagonal  pyramid,  98 
Dihexagonal  pyramidal  class,  98 
Dimorphism,  325 
Diploid,  65 
Dispersion,  221 

crossed,  294 
horizontal,  293 
inclined,  292 
of  bisectrices,  293,  294 
of  optic  axes,  289 
Distorted  crystals,  13,  174 
Ditetragonal  bipyramidal  class,  77 
Ditetragonal  prism,  79 

pyramid,  82 

Ditetragonal  pyramidal  class,  84 
Ditrigonal  bipyramidal  class,  103 
Ditrigonal  prism,  103 

pyramid,  103 

Ditrigonal  pyramidal  class,  109 
Ditrigonal  scalenohedral  class,  104 
J. Divergent  structure,  182 
Dodecahedron,  54 

deltoid,  69 
dyakis,  65 
pentagonal,  64 

tetrahedral,  72 
rhombic,  54 
Domatic  class,  138 
Domes,  31,  123,  135,  145 
Double  refraction,  223 
Drusy,  183 

Dyakis-dodecahedron,  65 
Dyakisdodecahedral  class,  63 


GENERAL   INDEX 


697 


E 

Earthy  fracture,  191 
Effervescence,  328 
Eightling,  164 
Elasticity,  186,  194 
Elastic  minerals,  194 
Electrical  conductivity  in  minerals,  306 
Electro-negative  elements,  313 
-positive  elements,  313 
Elements,  angular,  128,  139,  148 
axial,  128,  139,  148 
chemical,  312 

Elliptically  polarized  light,  240 
Elongation,  negative  or  positive,  280 
Enantimorphous  forms,  71,  113 
Epoptic  figures,  288 
Etching  figures,  189 
Exfoliation,  332 
Expansion  by  heat,  304 
Exterior  conical  refraction,  276 
Extinction,  230 

directions,  character  of,  239 

inclined,  260,  278 

parallel,  260,  278 
Extinction-angle,  278 
Extraordinary  ray,  254 


Feel,  310 

Fetid  odor,  310 

Fibrous  structure,  182 

Filiform,  183 

First  order  prisms,  79,  95 

pyramids,  80,  97 
Fiveling,  164 
Flame  coloration,  332 

oxidizing,  331 

reducing,  331 
Flexible,  194 
Fluorescence,  251 
Fluorides,  test  for,  339 
Fluxes,  336 

Foliated  structure,  182 
Forceps,  330 
Form,  30 
Formula,  chemical,  312,  320 

calculation  of,  321 
Fracture,  191 

Frictional  electricity  in  minerals,  306 
Fundamental  form,  30 
Fusibility,  304,  332 

scale  of,  332 


Gels,  324 

General  mineralogy,  literature  of,  3 

Gladstone  law,  210 

Glass,  optical  characters  of,  252,  300 

Glass  tubes,  331,  use  of,  333 

Gliding  planes,  187 

Glimmering  luster,  250 


Glistening  luster,  250 
Globular  structure,  183 
Globulites,  180 
Glowing,  332,  333 
Gnomonic  projection,  40 
Gnomonic  projection  of  isometric  forms,  62 
hexagonal  forms,  99, 

109 

tetragonal  forms,  84 

triclinic   forms,  147 

•  monoclinic      forms, 

137 
orthorhombic  forms, 

127 

Goniometer,  contact  or  hand,  152 
horizontal,  155 
reflecting,  154 
theodolite,  157 
two-circle,  157 
Granular  structure,  182 
Greasy  luster,  249 
Grouping,  molecular,  22 

parallel,  172,  173 
Gyroidal  forms,  71 

H 

Habit,  crystal,  10 
Hackly  fracture,  191 
Hand  goniometer,  152 
Hard  minerals,  193 
Hardness,  191 
Heat,  303 

effect  on  optical  properties,  296 
Heavy  solutions,  198 
Hemihedral  forms,  21 
Hemimorphic  class,  hexagonal  system,  98 
monoclinic      system, 

138 
orthorhombic     system, 

126 

tetragonal  system,  84 
Hexagonal  axes,  94 

bipyramidal  class,  100 

prisms,  95,  96 

prism  of  third  order,  111 

pyramidal  class,  101 

pyramids,  97,  98 

symmetry,  11 

system,  17,  94 

trapezohedral  class,  102 

trapezohedron,  102 
Hexakistetrahedron,  70 
Hexoctahedral  class,  52 
Hexoctahedron,  59 
Hextetrahedral  class,  66 
Hextetrahedron,  70 
Holohedral  forms,  21 
Horizontal  dispersion,  292 

goniometer,  155 
Horse-radish  odor,  310,  334 
Houppes,  288 
Hour-glass  structure,  478 
Hydroxides,  318 


698 


GENERAL   INDEX 


Icosahedron,  65,  67 
Icositetrahedron,  58 
Impalpable  structure,  182 
Indicatrix,  biaxial,  274 

uniaxial,  257 
Indices,  crystallographic,  Dana,  29 

Goldschmidt,  29 
Naumann,  29 
Weiss,  29 
rational,  29 
refractive,  207 

determination  of,  280, 

213,  216 

Incidence,  angle  of,  206 
Inclined  dispersion,  292 

hemihedrons,  67 
Inclusions,  179 
Inelastic  minerals,  194 
Insoluble  minerals,  329 
Interference  of  light,  224,  230 
colors,  236 

biaxial  crystals,  260 
uniaxial  crystals, 

278 
figures,  biaxial,  281 

inclined,  267,  283 
uniaxial,  260 

Interior  conical  refraction,  276 
Intumescence,  332 
Iridescence,  250 
Iron,  test  for,  339 
Iron  cross,  166 
Isodiametric  crystals,  252 
Isodimorphism,  325 
Isometric  crystals,  optical  properties  252 

system,  16,  52 
Isomorphism,  322 
Isomorphous  group,  322 

mixtures,  323 
Isotropic  crystals,  252 


Jolly  balance,  196 


Klein  solution,  198 


K 


Lamellar  polarization,  302 

.    structure,  182 
Lamp  for  blowpipe,  330 
Law  of  rational  indices,  29 
Lead,  test  for,  339 
Left-handed  crystal,  114,  403 
polarization,  241 
Light,  nature  of,  200 
Light-ray,  204 
Light  velocity,  relation  to  refractive  index, 


Light-waves,  202 

Liquids  with  high  refractive  indices,  213 

Lithium,  test  for,  339 

Lorentz  law,  210 

Lorenz  law,  210 

Luster,  249 

M 

Macro-axis,  121,  144 

Macrodome,  123,  145 

Macropinacoid,  122,  145 

Macroprism,  123 

Macropyramid,  124 

Magnesium,  test  for,  339 

Magnetic  minerals,  308 

Magnetism,  308 

Magnets,  natural,  308 

Malleable  minerals,  193 

Mammillary  structure,  183 

Manganese,  test  for,  339 

Manebach  twin,  171,  457 

Margarites,  180 

Measurement  of  crystal  angles,  152 

Mercury,  test  for,  339 

Meta-colloids,  325 

Metagenetic  twins,  163 

Metallic-adamantine  luster,  249 

Metallic  luster,  249 

Metallic  pearly  luster,  249 

Metals,  313 

Mica  plate,  use  of,  264 

Mica  sections  superposed,  300 

Micaceous  structure,  182 

Microchemical  analysis,  326 

Microcosmic  salt,  v.  Salt  of  Phosporus,  336 

Microlites,  180 

Microscope,  245 

Miller  hexagonal  axes,  117 

indices,  117 
indices,  28 
Mimetic  crystals,  14 
Mineral,  artificial,  326 

literature  of,  4 
definition  of,  1 
synthesis,  326 
Mineral  kingdom,  1 
Mineralogical  journals,  4 
Mineralogy,  chemical    and    determinative, 

literature  of,  4 
science  of,  1,  2 
Models  of  crystals,  21 
Mohs  scale  of  hardness,  191 
Molecular  networks,  22,  25 
structure,  7 
weight,  316 
Molecule,  311 
Molybdenum,  test  for,  339 
Monobasic  acid,  318 
Monoclinic  axes,  133 

crystals,  134 

optical  characters,  291 
system,  17,  133 
Mossy  structure,  183 


GENERAL   INDEX 


699 


N 

Natural  magnets,  308 

Naumann's  indices,  29 

Negative  crystal,  biaxial,  277,  286 

uniaxial,  254,  258,  264 
element,  313 
elongation,  280 
Network,  molecular,  22 
Neutral  salt,  319 
Newton's  rings,  225 
Nickel,  test  for,  339 
Nicol  prism,  228 
Niobium,  test  for,  339 
Nitrates,  test  for,  339 
Nodular  structure,  183 
Non-metallic  luster,  249 
Non-metals,  313 
Normal  angles,  44 

class,  isometric  system,  52 
hexagonal  system,  95 
monoclinic  system,  133 
orthorhombic  system,  121 
tetragonal  system,  77 
triclinic  system,  144 
salt,  319 


Oblique  system,  133 
Octahedron,  54 
Ocular,  Bertrand,  279 
Odor,  310 
Opalescence,  250 
Opaque,  247 
Open  tube  tests,  334 

form,  30 

Optic  axes,  273,  276 
axial  angle,  277 
axis,  254 
Optical  anomalies,  301 

characters  of  crystalline  aggregates, 

300 

twin  crystals,  298 
effect  of  heat  upon,  296 
pressure  on,  300 
relation    to    chemical 

composition,  298 
tests,  methods  and  order  of,  295 
Ordinary  ray,  254 
Ortho-axis,  133 
Orthodome,  135 
Orthopinacoid,  134 
Orthoprism,  135 


Orthopyramid,  135 
Orthorhombi 


ombic  axes,  121 

bipyramidal  class,  121 
bisphenoidal  class,  128 
crystals,  121 

optical     characters, 

288 

dispersion,  289 
pyramidal  class,  126 
system,  17,  121 


Oscillatory  combination,  176 
Oxides,  318 
Oxidizing  flame,  331 


Paragenetic  twins,  163 
Parallel  extinction,  260,  278 
grouping,  172 
hemihedrons,  64 
Paramagnetic  minerals,  309 
Paramagnetism,  309 
Parameter,  27 
Paramorph,  27' 
Paramorphism,  27 
Parting,  188 
Pearly  luster,  249 
Penetration-twin,  162 
Penfield  beam  balance,  197 
Pentagonal  dodecahedron,  64 

tetrahedral,  72 

hemihedral  class,  63 

icositetrahedral  class,  71 

icositetrahedron,  71 
Pentavalent  element,  317 
Percussion  figure,  188 
Pericline  law  (twinning),  172,  462 
Periodic  law,  314,  315 
Phanero-crystaUine,  182 
Phosphates,  test  for,  339 
Phosphorescence,  251 
Phosphoric  acid,  test  for,  339 
Photo-electricity,  307 
Physical  characters,  185 

mineralogy,  literature  of,  2 
Piezo-electricity,  307 
Pinacoid,  31 
Pinacoidal  class,  144 
Plagiohedral  class,  71 
Plagiohedral  hemihedral  class,  71 
Plane-polarized  light,  226 
Plane  of  polarization,  226 
Planes  of  symmetry,  10 
Platinum  wire,  330,  336 
Play  of  colors,  250 
Pleochroic  halos,  288 
Pleochroism,  247,  287 
Pleomorphism,  325 
Point  system,  23 
Polariscope,  229,  243 
Polarization,  226 
Polarization-brushes,  288 

-microscope,  245 
Polarized  light,  226 
Polarizer,  229 

Polysynthetic  twinning,  163 
Positive  crvstal,  biaxial,  277,  286 

uniaxial,  254,  258,  264 
element,  313 
elongation,  280 
Potassium,  test  for,  340 
Pressure,  effect    upon    optical    characters, 

300 
figures,  189 


700 


GENERAL   INDEX 


Primary  optic  axes,  276 
Prism,  30 

hexagonal  system,  dihexagonal,  96 
first  order,  95 
second  order,  96 
third  order,  100 
monoclinic  system,  135 
orthorhombic  system,  123 
tetragonal  system,  ditetragonal,  79 
first  order,  79 
second  order,  79 
third  order,  85 
triclinic  system,  145 
Prismatic  class,  133 
Projection,  gnomonic,  40 

literature  of,  44 
horizontal,  31 
spherical,  31 
stereographic,  32 

literature  of,  44 
Pseudo-hexagonal  crystals,  14,  169,  437 

-isometric  crystals,  301 
Pseudomorph,  183,  326 
Pseudomorphism,  326 
Pseudosymmetry,  14,  60,  164,  174,  297 
Pycnometer,  197 
Pyramid,  31 

hexagonal  system,  dihexagonal,  98 
first  order,  97 
second  order,  97 
third  order,  100 
monoclinic  system,  135 
orthorhombic  system,  124 
tetragonal  system,  ditetragonal,  79 
first  order,  79 
second  order,  79 
third  order,  85 
triclinic  system,  145 
Pyramidal  hemihedral  hemimorphic  class, 

101 

Pyramidal-hemimorphic    class,     hexagonal 
system,  101 

tetragonal 
system,  86 

Pyritohedral  class,  63 
Pyritohedron,  64 
Pyro-electricity,  306 
Pyrognostics,  338 

Q 

Quarter-undulation  mica  plate,  264 
Quartz  wedge,  231 

use  of,  286 


Radiated  structure,  182 
Radical,  chemical,  317 
Rational  indices,  law  of,  29 
Reaction,  chemical,  317 
Reagents,  chemical,  328 
Reducing  flame,  331 
Reduction  of  metals,  334 


Reflecting  goniometer,  154 
Reflection  of  light,  205 
angle  of,  205 
Refraction,  206 

double,  223 

strength  of,  224 
Refractive  index,  207 

determination  of,   213. 

216,  180 
relation  to  light  velocitv, 

208 

indices,  principal,  209 
Refractometer,  241 
Regular  system,  52 
Relief,  high  or  low,  212 
Reniform  structure,  183 
Resinous  luster,  249 
Reticulated  structure,  182 
Rhombic  section,  462 

sphenoid,  128 

Rhombohedral  class,  104,  110 
Rhombohedral  division,  103 
Rhombohedral  hemihedral  class,  104 
hemimorphic  class,  109 
tetartohedral  class,  110 
Rhombohedron,  positive  and  negative, 

104,  105 

second  order,  110 
third  order,  110 
Right-handed  crystal,  114,  403 
polarization,  241 
Roasting,  334 
Rontgen  rays,  25 


Saccharoidal  structure,  182 
Saline  taste,  310 
Salt  of  phosporus,  337 
Salts,  319 
Scalenohedron,  106 

tetragonal,  88 
Scalenohedral  class,  87 
Scale  of  fusibility,  332 
Scale  of  hardness,  191 
Schiller,  251 
Schillerization,  251 
Sclerometer,  192 
Second  order  prism,  hexagonal  system,  96 

tetragonal    system,  79 
pyramid,    hexagonal   system, 
97 

tetragonal    system,  79- 
rhombohedron,  110 
Secondary  optic  axes,  276 

twinning,  165,  188 
Sectile,  193 

Selenite-plate,  236,  266 
Selenium,  test  for,  340 
Semi-metals,  313 
Semi-transparent,  247 
Sensitive  tint,  236 

use  of,  266 


GENERAL   INDEX 


701 


Separable,  182 
Shining  luster,  250 
Silica,  test  for,  340 
Silky  luster,  249 
Silver,  test  for,  340 
Soda,  use  of,  330,  336 
Sodium,  test  for,  340 
Soft  minerals,  193 
Solid  solution,  323 
Solubility  in  minerals,  328 
Solution  planes,  189 
Sonstadt  solution,  198 
Sound  waves,  201 
Specific  gravity,  195 

determination  of,  196 
Spectroscope,  221 
Sphenoid,  87 

rhombic,  128 

Sphenoidal  class,  monoclinic  system,  138 
orthorhombic   system, 

128 

tetragonal  system,  87 
hemihedral  class,  87 
tetartohedraj  class,  89 
Spherical  projections,  31 
Spherulites,  300,  459 
Splendent  luster,  250 
Splintery  fracture,  191 
Stalactitic  structure,  183 
Stellated  structure,  182 
Stereographic  circles  and  scales,  36 
projection,  32 

literature  of,  44 
hexagonal    forms, 

99,  108 
isometric     forms, 

61 
tetragonal  forms, 

83 
triclinic       forms, 

146 
monoclinic  forms, 

137 

orthorhombic 
forms,  126 
protractor,  35,  39 
Streak,  247 

Strength  of  double  refraction,  224 
Striations,  176 

Strike-figure,  v.  Percussion-figure,  188 
Strontium,  test  for,  340 
Structure  of  minerals,  182 
Sublimate,  333,  334 
Subtranslucent,  247 
Subtransparent,  247 
Subvitreous,  249 
Sulphates,  test  for,  340 
Sulphides,  test  for,  340 
Sulpho-salts,  320 
Sulphur,  test  for,  340 
Sulphurous  odor,  310 
Swelling  up,  332 
Symbol,  chemical,  312 

crystallographic,  27 


Symmetry,  10 

axis  of,  11 
center  of,  12 
classes,  15 

exhibited  by  Stereographic  pro- 
jection, 45 
of  systems,  18,  19 
planes  of,  10 
Synthesis,  mineral,  326 
System,  hexagonal,  94 
isometric,  52 
monoclinic,  133 
.    orthorhombic,  121 
tetragonal,  77 
triclinic,  143 
Systems  of  crystallization,  15 


Tangent  relation ,  49 

Tarnish,  250 

Taste,  310 

Tautozonal  faces,  45 

Tellurium,  test  for,  340 

Tenacity,  193 

Test  paper,  330 

Tetartohedral  class,  isometric  system,  72 

tetragonal  system,  89 
forms,  22 
Tetragonal  bipyramidal  class,  85 

bisphenoidal  class,  89 

crystals,  77 

pyramidal  class,  86 

scalenohedron,  88 

sphenoidal  class,  87 

symmetry,  11 

system,  16,  77 

trapezohedral  class,  89 

trapezohedron,  89 

trisoctahedron,  58 

tristetrahedron,  69 
Tetrahedral  class,  66 

hemihedral  class,  66 

pentagonal  dodecahedral 

class,  72 

s/      pentagonal  dodecahedron,  72 
Tetrahedron,  67 
Tetrahexahedron,  56 
Tetravalent  element,  317 
Theodolite  goniometer,  157 
Thermo-electricity,  307 
Third-order  prism,  hexagonal  system,  100 
tetragonal  system,  85 

pyramid,  hexagonal  system,  TOO 
tetragonal  system  85 

rhombohedron,  110 
Thoulet  solution,  198 
Tin,  test  for,  340 
Titanium,  test  for,  340 
Total  reflection,  210 

refractometer,  219,  241 
Tourmaline  tongs,  243 
Translucent,  247 
Transparency,  247 


702 


GENERAL  INDEX 


Transparent,  247 

Trapezohedral    class,     hexagonal    system, 

102,  112 

tetragonal  system,  89 
hemihedral  class,  102 
tetratohedral  class,  112 
Trapezohedron,  58 

hexagonal,  102 
tetragonal,  89 
trigonal,  113 
Tribasic  acid,  318 
Trichite,  180 
Triclinic  axes,  143 

crystals,  143 

optical  characters  of,  295 
system,  17,  143 
symmetry,  115 

Trigonal  bipyramidal  class,  114 
class,  103 
division,  103 
hemihedral  class,  103 

hemimorphic  class,  109 
prism,  103 
pyramid,  103 
pyramidal  class,  114 
symmetry,  11 
system,  103 
tetartohedral  class,  114 

hemimorphic  class,  114 
trapezohedral  class,  112 
trapezohedron,  113 
trisoctahedron,  57 
trictetrahedron,  69 
Trigondodecahedron,  69 
Trigonotype  class,  103 
Trilling,  164 
Trimorphous,  325 
Tripyramidal  class,  hexagonal   system,  100 

tetragonal  system,  85 
Trisoctahedron,  57 
Trirhombohedral  class,  110 
Tristetrahedrons,  69 
Trivalent  element,  317 
Truncate,  truncation,  56 
Tungsten,  test  for,  340 
Twin  crystals,  160 

optical  characters  of,  298 
Twinning,  artificial,  188 
axis,  161 
plane,  161 
polysynthetic,  163 
repeated,  163 
secondary,  165 
symmetrical,  163 
Twins,  isometric,  165 
hexagonal,  167 
monoclinic,  170 
orthorhombic,  169 
spinel,  419 
tetragonal,  166  ' 
triclinic,  172 
Two-circle  goniometer,  157 


U 

Ultra-blue,  521 
Uneven  fracture,  191 
Uniaxial  crystals,  253 

behavior    of    light    in, 

253 

determination   of   refrac- 
tive indices,  254 
examination    in    conver- 
gent    polarized    light, 

examination  in  polarized 

light,  259 

interference  colors,  260 
optical  characters,  270 
positive  and  negative, 

254 

indicatrix,  257 
wave  surface,  255 
Unit  form,  30 
Univalent  element,  317 
Uranium,  test  for,  340 
Uralitization,  490 


Valence,  317 
Vanadium,  test  for,  340 
Velocity  of  light,  203 

relation  to  refractive  in- 
dex, 208 

Vicinal  forms,  24 
Vitreous  luster,  209 

W 

Water  of  crystallization,  320 

Water-waves,  201 

Wave-front,  203 

Wave-length,  204 

Wave-motion,  201 

Wave-surface,  biaxial  crystals,  273 

uniaxial  crystals,  255 
Waxy  luster,  249 
Westphal  balance,  199 
White  light,  204 
Widmanstatten  lines,  356 


X-rays  and  crystal  structure,  25 


Zinc,  test  for,  340 
Zirconium,  test  for,  341 
Zirconoid,  82 
Zonal  equations,  46 
Zone,  31 
Zone-axis,  31 


INDEX  TO   SPECIES 


Aarite,  v.  Arite,  372 
Abriachanite,  493 
Acadialite,  552 
Acanthite,  367 
Acerdese,  v.  Manganite 
Achmatite,  532 
Achroite,  542 
Acmite,  479 

Actinolite,  Actinote,  489 
Adamantine  spar,  413 
Adamine,  604 
Adamite,  604 
Adelite,  601 

Adipocire,  v.  Hatchettite 
Adular,  Adularia,  458 
^Edelite,  535 
^Egirine,  419 
^girite,  479 
^Egirite-augite,  477 
jEnigmatite,  494 
JEschynite,  591 
Agalite,  576 
Agalmatolite,  562 
Agaric  mineral,  440 
Agate,  405 
Agate-jasper,  406 
Agnolite,  582 
Agricolite,  510 
Aguilarite,  365 
Aikinite,  388 
Akermanite,  519 
Alabandin,  369 
Alabandite,  369 
Alabaster,  634 

Oriental,  440 
Alaite,  436 
Alalite,  476 
Alamosite,  483 
Alaskaite,  386 
Alaun,  v.  Alum, 
Alaunstein,  v.  Alunite 
Albertite,  647 
Albite,  464 
Alexandrite,  424 
Algodonite,  362 
Alisonite,  364 
Allactite,  Allaktit,  606 
Allagite,  485 
Allanite,  533 
Allemontite,  349 


Allochroite,  508 
Alloclasite,  Alloklas,  382 
Allopalladium,  356 
Allophane,  580 
Almandine,  Almandite,  507, 

419 

Almeriite,  640 
Aloisiite,  545 
Alpha-quartz,  403 
Alshedite,  584 
Alstonite,  v.  Bromlite,  447 
Altaite,  364 
Alum,  637 
Alumian,  632 
Alumina,  413,  418 
ACUMINATES,  418  et  seq. 
Aluminite,  639 
Aluminium  borate,  620 

carbonate,  452 

chloride,  399 

fluorides,  399,  400 

hydrates,  431,  435 

mellate,  645 

oxide,  413,  431,  435 

phosphates,  605,  610,  etc. 

silicates,   523,   524,   5?6, 
578,  579,  580,  etc. 

sulphates,  632,  637,  639 
Aluminium  ore,  433 
Alumstone,  639 
Alundum,  414 
Alunite,  639 
Alunogel,  434 
Alunogen,  638 
Alurgite,  565 
Amalgam,  354 
Amarantite,  639 
Amazonite,  461 
Amazonstone,  461 
Ambatoarinite,  449 
Amber,  276,  645 
Amblygonite,  602 
Amblystegite,  473 
Amesite,  571 
Amethyst,  405 

Oriental,  410 
Amianthus,  490.  573 
Ammiolite,  618 
Ammonium,  carbonate,  450 

chloride,  397 

oxalate,  644 

phosphates,  610,  etc. 

703 


Ammonium,  sulphates,  624, 

etc. 

Ampangabeite,  591 
Amphibole,  487 
AMPHIBOLE  Group,  485 
Amphibole-anthophyllite, 

489 

Amphigene,  469 
Amphodelite,  468 
Analcime,  554 
Analcite,  554 
Anapaite,  607 
Anatase,  428 
Ancylite,  449 
Andalusite,  524 
Andesine,  466 
Andorite,  385 
Andradite,  507 
Andrewsite,  616 
Anemousite,  468 
Angaralite,  540 
Anglesite,  628 
Anhydrite,  629 
Animikite,  362 
Ankerite,  443 
Annabergite,  609 
Annerodite,  591     . 
Annite,  565 
Anomite,  564 
Anorthite,  467 
Anorthoclase,  461 
Anthophyllite,  486 
Hydrous,  487 
Anthracite,  648 
Antigorite,  573 
Antimonarsen,  v.  Allemontite 
ANTIMONATES,  618 
Antimonblende,  v.  Kermes- 

ite 

Antimonglanz,  v.  Stibnite 
ANTIMONIDES,  372,  etc. 
Antimonite,  358 
ANTIMONITES,  618 
Antimonnickel,  v.  Breithaup- 

tite 
Antimonsilber.    v.    Dyscras- 

ite 
Antimonsilberblende,  v.   Py- 

rargyrite 
Antimony,  349 
Gray,  358 
Native,  349 


704 


INDEX   TO   SPECIES 


Antimony,  Red,  v.  Kermesite 
White,  409 

Antimony  oxides,  409 
oxysulphide,  383 
sulphide,  358 

Antimony  glance,  358 

Antlerite,  632 

Apatite,  595 

Aphanese,  Aphanesite,  604 

Aphrite,  440 

Aphrizite,  542 

Aphrosiderite,  571 

Aphthalose,  624 

Aphthitalite,  624 

Apjohnite,  637 

Aplome,  508 

Apophyllite,  546 

Apotome,  627 

Aquamarine,  495 

Araeoxene,  604 

Aragonite,  446 

Arcanite,  624 
Ardennite,  539 
Arduinite,  558 
Arendalite,  531 
Arfvedsonite,  494 
Argentine,  440 
Argentite,  364 
Argentobismutite,   v.    Matil- 

dite 

Argyrodite,  394 
Arite,  372 
Arizonite,  418 
Arkansite,  430 
Arquerite,  354 
Armangite,  594 
Arragonite,     v.     Aragonite, 

44  O 

ARSENATES,  592 
Arsenic,  348 

White,  409 

Arsenical  antimony,  349 
Arsenic  oxide,  409" 
sulphide,  357 
ARSENIDES,  361 
Arsenikalkies,    v.    Arsenopy- 

nte 
Arsenikkies,   y.   Arsenopy- 

rite 

Arseniopleite,  606 
Arseniosiderite,  606 
Arsenkies,  v.  Arsenopyrite 
Arsenobismite,  617 
Arsenoferrite,  378 
Arsenolite,  409 
Arsenopyrite,  381 
Arsensilberblende,   v.   Prous- 

tite 

Artinite,  453 
Asbestos,    Asbestus,    489, 

573 

,  Blue,  493 
Asbolan,  436 
Asbolite,  436 


Ascharite,  621 

Asmanite,  408 
Asparagus-stone,  596 
Aspasiolite,  498 
Asphaltum,  647 
Asteria,  413 
Asteriated  quartz,  405 

sapphire,  413 
Astrakanite,  637 
Astrolite,  496 
Astrophyllite,  585 
Atacamite,  400 
Atelestite,  606 
Atopite,  618 
Attacolite,  614 
Auerlite,  522 
Augelite,  614 
Augite,  477 
Auralite,  498 
Aurichalcite,  451 
Auripigmentum,  357 
Automolite,  420 
Autunite,  616 
Aventurine  feldspar,  465 

quartz.  405 
Ax-stone,  482 
Axinite,  534 
Awaruite,  356 
Azurite,  451 

B 


Bababudanite,  493 

Babingtonite,  485 

Backstromite,  435 

Saddeckite,  562 

Jaddeleyite,  428 

Jadenite,  374 

Sagrationite,  533 

Saikalite,  477 

Jakerite,  581 

Salas  ruby,  419 

Saltimorite,  573 

Samlite,  526 

Sarbierite,  458 

3aricalcite,  440 

iarite,  625 

Barium     carbonate,     447, 
449 

nitrate,  619 
silicate,    460,    498,    549, 

550,  555,  etc. 
sulphate,  625 

ariumuranit,  617 

arkevikite,  494 
Barrandite,  610 
Barsowite,  523 
Barthite,  612 
Barylite,  498 
Barysilite,  498 
Baryt,  Barytes,  625 
Baryta,  v.  Barium 
Baryta-feldspar,  460 
Baryta-orthoclase,  460 


I  Barytocalcite,  449 
1  Baryturanit,  617 
Basanite,  406 
Bassanite,  630 
1  Bassetite,  617 
Bastite,  474,  573 
Bastnasite,  449 
I  Batchelorite,  579 
Bathvillite,  646 
Batrachite,  512 
Baumhauerite,  386 
Bauxite,  433 
Bavenite,  558 
Bayldonite,  612 
Bazzite,  540 
Beaumontite,  549 
Beauxite,  433 
Beaverite,  638 
Bechilite,  623 
Beckelite,  540 
Beegerite,  392 
|  Beilstein,  v.  Nephrite 
Beldongrite,  436 
Bellite,  631 
|  Bell-metal  ore,  394 
Belonesite,  399 
Bementite,  582 
I  Benitoite,  585 
Beraunite,  615 
Bergamaskite,  491 
Bergblau,  v.  Azurite 
Bergkrystall,  v.  Quartz 
Bergmannite,  556 
Bergsalz,  v.  Halite 
Bergseife,  579 
Bergtheer,  v.  Pittasphalt 
|  Berlinite,  614 
Bernstein,  v.  Amber 
Berthierite,  386 
Bertrandite,  539 
Beryl,  495 

Beryllium  aluminate,  423 
borate,  620 
phosphate,  601 
silicate,    495,    496,    514, 

529,  539 
Beryllonite,  595 
Berzelianite,  365 
Berzeliite,  593 
Betafite,  591 
Beta-quartz,  403 
Beudantite,  618 
'  Beyrichite,  372 
Bieberite,  636 
Bildstein,  v.  Agalmatolite 
Bilinite,  637 
Bindheimite,  617 
Binnite,  391 
Biotina,  Biotine,  468 
Biotite,  563 
Bisbeeite,  581 
Bischofite,  402 
Bismite,  410 
I  Bismuth,  349 


INDEX   TO   SPECIES 


705 


Bismuth  arsenate,  606 

carbonate,  449,  454 

oxide,  410 

oxychloride,  401 

selenide,  359 

silicate,  504 

sulphide,  359 

tellurate,  641 

telluride,  360 

uranate,  617 

vanadate,  594 
Bismuth  glance,  359 
Bismuth  gold,  350 
Bismuth  ocher,  410 
Bismuthinite,  359 
Bismutite,  454 
Bismutoplagionite,  387 
Bismutosmaltite,  380 
Bismutosphaerite,  449 
Bittersalz,  v.  Epsomite 
Bitter   spar,    Bitterspath,   v. 

Dolomite 
Bitumen,  646,  647 
Bituminous  coal,  648 
Bityite,  558 
Bixbyite,  425 
Bjelkite,  387 
Black  jack,  367 
Black  lead,  347 
Blanfordite,  477 
Blatter tellur,  v.  Nagyagite 
Blaueisenerde,  v.  Vivianite 
Bleiantimonglanz,  v.  Zinken- 

ite 

Bleiglanz,  v.  Galena 
Bleiniere,  Bleinierite,  v.  Bind- 

heimite 

Bleischweif,  363 
Bleivitrol,  v.  Anglesite 
Blende,  367 
Blodite,  637 
Bloedite,  Bloedite,  637 
Blomstrandine,  591 
Bloodstone,  405 
Blue  asbestus.  493 

iron  earth,  608 

John,  398 

malachite,  v.  Azurite 

vitriol,  636 
Bobierrite,  608 
Bccumlerite,  399 
Boghead  cannel,  648 
Bog-iron  ore,  433 

manganese,  436 
Bole,  579 
Boleite,  401 
Bologna  stone,  626 
Boltonite,  513 
Bone-phosphate,  597 

turquoise,  613 
Bonsdorffite,  498 
Boort,  345 
Boothite,  636 
Boracite,  620 


BORATES,  619 
Borax,  622 
Borickite,  615 
Boric  acid,  435 
Bomite,  374 
Boron  hydrate,  435 

silicate,  522,  527 
Boronatrocalcite,  622 
Bort,  345 
Bostonite,  575 
Botryogen,  639 
Botryolite,  528 
Boulangerite,  387 
Bournonite,  388 
Boussingaultite,  637 
Bowenite,  572 
Bowmannite,  601 
Brackebuschite,  604 
Bragite,  588 
Brandisite,  566 
Brandtite,  607 
Brannerite,  586 
Brauneisenstein,    v.    Limon- 

ite 

Braunile,  425 
Braunstein,  Grauer,  v.  Pyro- 

lusite 

Bravoite,  378 
Brazilian  pebble,  325 

emerald,  542 

sapphire,  542 
Brazilite,  428  ' 
Bredbergite,  508 
Breislakite,  490 
Breithauptite,  372 
Breunerite,  443 
Breunnerite,  443 
Brevicite,  556 
Brewsterite,  549 
Britholite,  580 
Brittle  silver  ore,  392 
Brochantite,  632 
Broggerite,  623 
Bromargyrite,  397 
BROMIDES,  397 
Bromlite,  447 
Bromyrite,  397 
Brongnartine,  632 
Brongniardite,  387 
Bronzite,  472 
Brookite,  429 
Brown  coal,  648 

iron  ore,  432 

iron  stone,  432 

hematite,  432 

ocher,  432 

spar,  443 
Brucite,  434 
Brugnatellite,  453 
Brunsvigite,  572 
Brushite,  611 
Bucholzitef526 
Bucklandite,  532,  533 
Buhrstone,  406 


Bunsenite,  411 
Buntkupfererz,  v.  Bornite 
Burrstone,  406 
Bushmanite,  637 
Bustamite,  484 
Buttermilcherz,    v.    Cerargy- 

rite 

Byssolite,  490 
Bytownite,  467 


Cabrerite,  609 
Cacholong,  408 
Cacoxenite,  614 
Cadmia,  540 
Cadmium  sulphide,  371 
Cadmium  blende,  v.  Green- 

ockite,  371 
Cadmium  oxide,  411 
Caesium  silicate,  470 
Cainosite,  v.  Cenosite,  580 
Cairngorm  stone,  405 
Caking  coal,  648 
Calamine,  539,  445 
Calaverite,  383 
Calc  sinter,  440 

spar,  438 

tufa,  440 
Calcioferrite,  615 
Calciostrontianite,  448 
Calciovolborthite,  604 
Calcite,  438 
Calcium  arsenate,  610,  etc. 

antimonate,  618 

borate,  620,  621,  etc. 

carbonate,  438,  446 

chloride,  399 

flouride,  398 

iodate,  619 

molybdate,  643 

niobate,  587,  etc. 

nitrate,  619 

oxalate,  644 

oxyfluoride,  401 

phosphate,  595,  606, 
611,  etc. 

silicate,  483,  467,  etc. 

sulphate,  629,  633,  etc. 

sulphide,  369 
Calcium  tantalate,  587 

titanate,  583,  586 

tungstate,  642 
Caledonite,  632 
Californite,  520 
Callainite,  610 
Calomel,  395 
Campylite,  598 
Canaanite,  476 
Cancrinite,  501 

sulphatic,  501 
Canfieldite,  394 
Cannel  coal,  648 
Caoutchouc,  Mineral,  647 


706 

Capillary  pyrites,  372 
Caporcianite,  552 
Cappelenite,  496 
Caracolite,  631 
Carbon,  345 
Carbonado,  345 
CARBONATES,  436 
Carlosite,  585 
Carminite,  594 
Carnallite,  401 
Carnegieite,  468 
Carnelian,  405 
Carneol,  v.  Carhelian 
Caraotite,  617 
Carpholite,  540 
Carphosiderite,  639 
Carrollite,  374 
Caryinite,  593 
Caryocerite,  496 
Caryopilite,  582 
Cassiterite,  425 
Castanite,  639 
Castor,  CastorHe,  455 
Caswellite,  565 
Catapleiite,  496 
Cataspilite,  498 
Catlinite,  580 
Catoptrite,  618 
Cat's  eye,  405,  424 
Cauk,  Cawk,  626 
Cebollite,  518 
Celadonite,  577 
Celestine,  627 
Celestite,  627 
Celsian,  460 
Cenosite,  580 
Cerargyrite,  397 
Cerite,  540 
Cerium  carbonate,  449 

fluoride,  399 

niobates,  587 

phosphates,  593,  609,  etc. 

silicates,  533, 540, 585,  etc. 
Ceruleite,  616 
Cerussite,  448 
Cervantite,  410 
Cesarolite,  424 
Ceylanite,  Ceylonite,  410 
Chabazite,  552 
Chalcanthite,  636 
Chalcedony,  405 
Chalcocite,  366 
Chalcodite,  572 
Chalcolamprite,  587 
Chalcomenite,  641 
Chalcophanite,  435 
Chalcophyllite,  612 
Chalcopyrite,  374 
Chalcosiderite,  616 
Chalcosine,  366 
Chalcostibite,  386 
Chalcotrichite,  411 
Cfcalk,  440 

French,  575 


INDEX   TO   SPECIES 

Chalmersite,  366 

Chalybite,  443 

Chamoisite,  Chamosite,  572 

Chathamite,  378 

Chemawinite,  645 

Chenevixite,  616 

Chert,  406 

Chessy  copper,  451 

Chessylite,  451 

Chesterlite,  461 

Chiastolite,  525 

Childrenite,  615 

Chilenite,  362 

Chillagite,  643 

Chiolite,  400 

Chiviatite,  385 

Chladnite,  472 

Chloanthite,  378 

Chloralluminite,  399 

Chlor-apatite,  595 

Chlorargyrite,  397 

Chlorblei,  v.  Cotunnite 

CHLORIDES,  395 

Chlorite,  568 

CHLORITE  Group,  568 

Chloritoid,  567 

Chloritspath,  v.  Chloritoid 

Chlormanganokalite,  399 

Chlorocalcite,  399 

Chloromagnesite,  399 

Chloromelanite,  482 

Chloropal,  582   ' 

Chlorophseite,  571 

Chlorophane,  398 

Chlorophyllite,  498 

Chlorquecksilber,     v      Calo- 
mel 

Chlorospinel,  419 

Chlorsilber  v.  Cerargyrite 

Chondrarsenite,  601 

Chondrodite,  536 

Chrismatine,    Chrismatite, 
645 

Christianite,  468 

Christobalite,  408 

Christophite,  368 

CHROMATES,  630,  etc. 

Chrome  diopside,  476 

Chrome  spinel,  419 

Chromeisenstein,   v.   Chrom- 
ite 

Chromic  iron,  423 

Chromite,  423 

Chromitite,  423 

Chromium  oxide,  423 
sulphate,  639 
sulphide,  374 

Chrysoberyl,  423 

Chrysocolla,  581 

Chrysolite,  511 

CHRYSOLITE  Group,  510 

Chrysoprase,  405 

Chrysotile,  573 

Churchite,  609 


Cimolite,  579 
Cinnabar,  370 

Inflammable,  646 
Cinnamon-stone,  507 
Cirrolite,  606 
Citrine,  405 
Clarite,  393 
Claudetite,  409 
Clausthalite,  364 
Clay,  et  seq.  578 
Clay  iron-stone,  416 

Brown,  433 
Cleavlandite,  465 
Cleiophane,  368 
Cleveite,  623 
Cliachite,  434 
Cliftonite,  347 
Clinochlore,  569 
Ch'noclase,  604 
Clinoclasite,  604 
Clinoenstatite,  477 
Clinohedrite,  540 
Clinohumite,  536 
Clinozoisite,  532 
Clintonite,  566 
CLINTONITE  Group,  566 
Coal,  Mineral,  647,  648 
Cobalt  arsenate,  607,  608 

carbonate,  446,  453 

arsenide,  378,  379,  380, 
381 

selenite,  641 

sulph-arsenide,  378 

sulphate,  636 

sulphide,  378 
Cobalt  bloom,  608 
Cobalt  glance,  v.  Cobaltite 
Cobaltine,  379 
Cobaltite,  379 
Cobaltnickelpyrite,  378 
Cobaltoadamite,  604 
Cobaltocalcite,  441 
Cobaltomenite,  641 
Coccolite,  477 
Cocinerite,  362 
Cockscomb  Pyrite,  380 
Crelestine,  627 
Coeruleolactite,  614 
Cohenite,  356 
Coke,  648 
Colemanite,  621 
Colerainite,  583 
Cb'lestine,  v.  Celestite 
Collbranite,  620 
Collophanite,  606 
Collyrite,  580 
Colophonite,  508,  520 
Coloradoite,  369 

COLUMBATES      V.      NlOBATES. 

587 

Columbite,  588 
Comptonite,  558 
Confolensite,  579 
Conichalcite,  612 


INDEX   TO   SPECIES 


707 


Connarite,  577 
Connellite,  631 
Cookeite,  563 
Copal,  Fossil,  645 
Copaline,  Copalite,  645 
Copiapite,  638 
Copper,  353 

Emerald,     v.     Dioptase 
515 

Gray,  390 

Indigo,    v.    Covellite, 
371 

Native,  353 

Red,  v.  Cuprite,  410 
Copper,  Vitreous,  v.  Chalco- 
cite,  366 

Yellow,  374 

Copper   arsenate,    603,    604, 
612,  etc. 

arsenide,  362 

carbonate,  450,  451 

chloride,  395,  400 

manganate,  424 

iodide,  395 

nitrate,  619 

oxides,  410,  412 

oxychlorides,  400 

phosphates,  603,  612, 
etc. 

selenides,  365 

selenite,  641 

silicates,  515,  581 

sulphantimonate,  393 

sulphantimonites,  386  et 
seq. 

sulpharsenates,  393 

sulpharsemte,  386 

sulphates,  630,  632;  hy- 
drous, 636  et  seq. 

sulphides,  366,  371,  374 
et  seq. 

sulpho-bismuthites,  386 

tungstate,  643 

vanadates,  604 
Copper  glance,  366 
Copper  mica,  616 
Copper  nickel,  372 
Copper  pyrites,  374 
Copper  uranite,  616 
Copper  vitriol,  636 
Copperas,  636 
Coprolites,  597 
Coquimbite,  637 
Cordierite,  497 
Cordylite,  449 
Gorki te,  618 
Cornwallite,  612 
Coronadite,  424 
Corundophilite,  571 
Corundum,  413 
Corynite,  379 
Cosalite,  387 
Cossyri'te,  494 
Cotunnite,  399 


Couseranite,  517 
Covellite,  371 
Crandallite,  601 
Creedite,  402 
Crednerite,  424 
Crestmoreite,  546 
Crichtonite,  417 
Cristobalite,  408 
Crocalite,  556 
Crocidolite,  493 
Crocoite,  630 

Cromfordite,  v.  Phosgenite 
Cronstedtite,  571 
Crookesite,  365 
Crossite,  493 
Cryolite,  399 
Cryolithionite,  400 
Cryophyllite,  363 
Cryptolite,  593 
Cryptoperthite,  460 
Cuban,  374 
Cubanite,  374 
Cube  ore,  v.  Pharmacosider- 

ite 

Cube  spar,  v.  Anhydrite 
Culsageeite,  572 
Cumengite,  401 
Cummingtonite,  489 
Cuprite,  410 
Cuproadamite,  604 
Cuprobismutite,  385 
Cuprodescloizite,  604 
Cuprogoslarite,  635 
Cupromagnesite,  636 
Cuproplumbite,  364 
Cuproscheelite,  643 
Cuprotungstite,  643 
Cuspidine,  535 
Custerite,  497 
Cyanite,  526 
Cyanochroite,  637 
Cyanotrichite,  638 
Cyclopite,  468 
Cylindrite,  394 
Cymatolite,  481 
Cymophane,  423 
Cyprine,  519 
Cyprusite,  639 
Cyrtolite,  522 

D 

Dahllite,  597 
Damourite,  561 
Danaite,  382 
Danalite,  504 
Danburite,  522 
Dannemorite,  489 
Darapskite,  619 
Datholite,  527 
Datolite,  527 

Daubreeite,  Daubreite,  401 
Daubreelite,  374 
Davidsonite,  496 


Lake 


Daviesite,  401 
Davyne,  501 
Dawsonite,  452 
Dechenite,  604 
Deeckeite,  518 
Delessite,  571 
Delatynite,  645 
Delorenzite,  586 
Delphinite,  531 
Delvauxite,  615 
Demant,  v.  Diamond,  345 
Demantoid,  508 
Derbylite,  618 
Derbyshire  spar,  398 
Descioizite,  604 
Desmine,  551 
Destinezite,  618 
Dewalquite,  539 
Deweylite,  575 
Diabantite,  571 
Diadochite,  618 
Diallage,  477 
Dialogite,  444 
Diamant,  345 
Diamond,  345 
Diamond,     Bristol, 

George,  405 
Dianite,  589 
Diaphorite,  387 
Diaspore,  431 
Diasporogelite,  434 
Diatomite,  409 
Dichroite,.497 
Dickinsonite,  607 
Didymolite,  497 
Dietrichite,  637 
Dietzeite,  619 
Dihydrite,  605 
Diopside,  476 
Dioptase,  515 
Dipyre,  517 
Disterrite,  566 
Disthene,  526 
Dixenite,  581 
Dog-tooth  spar,  439 
Dolerophanite,  632 
Dolomite,  442 
Domeykite,  362 
Domingite,  387 
Doppelspath,  v.  Calcite 
Dopplerite,  646 
Double-refracting  spar, 
Doughtyite,  638 
Douglasite,  402 
Dreelite,  626 
Dry-bone,  445 
Dudleyite,  572 
Dufreniberaunite,  605 
Dufrenite,  605 
Dufrenoysite,  387 
Dumortierite,  543 
Dundasite,  452 
Durangite,  601 
Durdenite,  641 


708 

Dysanalyte,  586 
Dyscrasite,  361 
Dysluite,  420 
Dysodile,  646 
Dyssnite,  485 
Dysyntribite,  500,  562 

E 

Ecdemite,  618 
Echellite,  558 
Ectropite,  582 
ficume  de  Mer,  576 
Edelite,  535 
Edenite,  490 
Edingtonite,  555 
Egeran,  520 
Eglestonite,  401 
Egueiite,  615 
Ehrenwerthite,  432 
Ehlite,  605 
Eichbergite,  385 
Eichwaldite,  620 
Eisen,  v.  Iron 
Eisenblau,  v.  Vivianite 
Eisenbliithe,  v.  Flos  ferri 
Eiaenglanz,  v.  Hematite 
Eisenglimmer,  v.  Hematite 
Eisenkies,  v.  Pyrite 
Eisenniekelkies,  v.  Pentland- 

ite 

Eisenrahm,  v.  Hematite 
Eisenrosen,  v.  Hematite 
Eisenspath,  v.  Siderite 
Eisenstassfurtite,  621 
Eisspath,  v.  Rhyacolite 
Eisstein.  v.  Cryolite 
Ekdemite,  618 
Elseolite,  499 
Elaterite,  647 
Electrum,  350 
Elements,  344  et  seq. 
Eleolite,  499 
Eleonorite,  615 
Elpidite,  496 
Embolite,  397 
Embrithite,  387 
Emerald,  495 
Oriental,  413 
Uralian,  508 
Emerald  copper,  v.  Dioptase, 

515 

Emerald  nickel,  453 
Emery,  410 
Emmonsite,  641 
Emplectite,  386 
Empressite,  383 
Enargite,  393 
Endeiolite,  587 
Endellionite,   v.   Bournonite 

388 

Endlichite,  598 
Enstatite,  472 
Eosphorite,  615 


INDEX   TO   SPECIES 

Epiboulangerite,  394 
Epichlorite,  571 
Epidesmine,  558 
Epididymite,  455 
EPIDOTE  Group,  530 
Epidote,  531 
Epigenite,  394 
Epistilbite,  549 
Epistolite,  592 
Epsom  salt,  635 
Epsomite,  635 
Erbium  niobate,,  588,  591 
Erbsenstein,  v.  Pisolite 
Erdkobalt,  v.  Asbolite 
Erikite,  580 
Erinite,  605 
Erionite,  558 
Erubescite,  374 
Erythrite,  608 
Erythrosiderite,  402 
Esmarkite,  498 
Esmeraldaite,  433 
Essonite,  507 
Ettringite,  640 
Eucairite,  365 
Euchroite,  611 
Euclase,  529 
Eucolite,  496 
Eucolite-titanite,  584 
Eucryptite,  500 
Eudialyte,  496 
Eudidymite,  455 
Eudyalite,  496 
Eugenglanz,  v.  Polvbasite 
Eukairite,  365 
Euklas,  529 
Eulytine,  504 
Eulytite,  504 
Eupyrchroite,  596 
Euralite,  571 
Eusynchite,  604 
Euxenite,  591 
Evansite,  614 


Facellite,  501 
Fahlerz,  390 
Fahlunite,  498 

Fairfieldite,  607 

Palkenhaynite,  390 

False  Galena.  367 
Famatinite,  393 
Faratsihite,  578 

?argite,  556 

?aserkiesel,  v.  Fibrolite 

?aserzeolith,  v.  Natrolite 

?assaite,  477 
Faujasite,  555 
"ava,  428 
Fayalite,  513 

^eather-alum,   v.   Halotrich- 
ite 

feather-ore,  387 

^edererz,  v.  Jamesonite 


FELDSPAR  Group,  456 
Feldspar,  Baryta,  460 

Blue  v.  Lazulite 

Common,  457 

Glassy,  458 

Labrador,  466 

Lime,  467 

Potash,  457,  460 

Soda,  464 
Felsobanyite,  639 
Felspar,  v.  Feldspar 
Ferganite,  609 
Fergusonite,  588 
Fermorite,  597 
Fernandinite,  609 
FERRATES,  418 
Ferrazite,  611 
Ferritungstite,  644 
Ferroanthophyllite,  487 
Ferrobrucite,  434 
Ferrocalcite,  441 
Ferrocobaltite,  379 
Ferrogoslarite,  635 
Ferronatrite,  638 
Ferropallidite,  633 
Feuerblende  v.  Pyrostilpnite, 
Fibroferrite,  639 
Fibrolite,  526 
Fichtelite,  645 
Fiedlerite,  401 
Fillowite,  607 
Fiorite,  409 
Fire  opal,  408 

marble,  356 
Fireblende,  v.    Pyrostilpnite, 

390 

Fischerite,  613 
Flagstaffite,  646 
Flajolotite,  618 
Fleches  d' amour,  427 
Flinkite,  606 
Flint,  406 
Float-stone,  409 
Flokite,  552 
Florencite,  601 
Flos  ferri,  446 
Fluellite,  402 
Fluocerite,  399 
Fluor  v.  Fluorite, 
Fluor-apatite,  595 
Fluor  spar,  398 
FLUORIDES,  398  et  seq. 
Fluorite,  398 
Flusspath,  v.  Fluorite 
Foliated    tellurium   v.    Nag- 

yagite,  383 

Pontainebleau  limestone,  439 
Footeite,  631 
?orbesite,  611 
?orstereite,  513 
Fossil  copal,  645 

wood,  405,  408 
^oucherite,  615 
Fouqueite.  532 


INDEX   TO    SPECIES 


709 


Fowlerite,  484 
Franckeite,  394 
Francolite,  596 
Franklinite,  420 
Fraueneis,  v.  Selenite 
Frauenglas,  v.  Mica 
Fredricite,  391 
Freibergite,  390 
Freieslebenite,  387 
Fremontite,  602 
French  chalk,  576 
Frenzelite,  359 
Friedelite,  515 
Frieseite,  367 
Fuchsite,  561 
Fuggerite,  518 
Furaacite,  604 


Gadolinite,  529 
Gageite,  582 
Gahnite,  420 
Gajite,  453 
Galactite,  556 
Galapectite,  579 
Galena,  Galenite,  363 
Galena,  False,  367 
Galenobismutite,  386 
Galmei,  v.  Calamine 
Ganomalite,  498 
Ganophyllite,  546 
Garnet,  505 

Cinnamon,  507 

Chrome,  417 

Grossalur,  507 

Oriental,  507 

Precious,  507 

Tetrahedral,  v.  Helvite 

White,  v.  Leucite 
Garni  erite,  575 
Gastaldite,  493 
Gavite,  576 
Gay-Lussite,  452 
Gearksutite,  402 
Gedanite,  645 
Gedrite,  487 
Gehlenite,  518 
Geikielite,  586 
Gekrosstein,  v.  Tripe  stone 
Gelbbleierz,  v.  Wulfenite 
Gelbeisenerz,  v.  Jarosite 
Gelbeisenstein,     v.     Xantho- 

siderite 
Genthite,  575 
Geocerellite,  646 
Geocerite,  646 
Georceixite,  601 
Geocronite,  392 
Geomyricite,  646 
Georgiadesite,  594 
Geraesite,  601 
Gerhardtite,  619** 


GERMANATES,  394 
Gersdorffite,  379 
Geyerite,  381 
Geyserite,  409 
Gibbsite,  435 
Gieseckite,  500,  562 
Gigantolite,  498,  562 
Gilbertite,  561 
Gilpinite,  640 
Gilsonite,  647 
Giorgiosite,"  453 
Gips,  v.  Gypsum 
Girasol,  408 
Gismondine,  552 
Gismondite,  552 
Glance  coal,  648 

Cobalt,  v.  Colbaltite 

Copper,  v.  Chalcocite 
Glanzeisenerz,  v.  Hematite 
Glaserite,  v.  Aphthitalite 
Glaskopf,  Brauner,  v.  Limon- 
ite 

Rother,  v.  Hematite 
Glassy  Feldspar,  458 
Glauber  salt,  632 
Glauberite,  625 
Glaucochroite,  513 
Glaucodot,  382 
Glaucolite,  517 
Glauconite,  577 
Glaucophane,  492 
Glaukodot,  382 
Glessite,  645 
Glimmer,  v.  Mica 
Globosite,  615 
Glockerite,  639 
Glucinum,  v.  Beryllium 
Gmelinite,  554 
Goethite,  431 
Gold,  350 
Goldfieldite,  391 
Gold  tellurides,  382,  383 
Gonnardite,  557 
Goshenite,  496 
Goslarite,  635 
Gothite,  431 
Goyazite,  616 
Graftonite,  594 
Grahamite,  647 
Gramenite,  Graminite,  582 
Grammatite,  489 
Granat,  v.  Garnet 
Grandiderite,  544 
Graphic  tellurium.  382 
Graphite,  347 
Gray  antimony,  358 

copper,  390 
Greenalite,  577 
Green  lead  ore,  597 
Greenockite,  371 
Greenovite,  584 
Grenat,  v.  Garnet 
Griffithite,  572 
Griphite,  500 


Grossular,  Grossularite,  507 
Grothine,  545 
Grothite,  584 
Griinbleierz,     v.     Pyromor- 

phite 

Griineisenerde,  v,  Dufrenite 
Griinerite,  490 
Griinlingite,  360 
Guadalcazarite,  369 
Guanajuatite,  359 
Guano,  597 
Guarinite,  525 
Guejarite,  386 
Guitermanite,  388 
Gummierz,  v.  Gummite 
Gummite,  624 
Gymnite,  575 
Gypsum,  633 
Gyrolite,  546 


Haarkies,  v.  Millerite 
Haarsalz,  v.  Epsomite 
Hackmanite,  502 
Hematite,  v.  Hematite 
Haidingerite,  610 
Hair  salt,  635 
Halite,  395 
Hallerite,  562 
Hallite,  572 
Halloysite,  578 
Halotrichite,  637 
Hamartite,  449 
Hambergite,  620 
Hamlinite,  601 
Hancockite,  533 
Hanks! 
Hannaite,  611 


HaMfouite,  498 

Harl. 

Harmotomc 
Harstigite,  535 
Hartite,  645 
Harttite,  601 
Hastingsite,  491 
Hatchettine,    Hatchettite, 

645 

Hatchettolite,  587 
Hauchecornite,  372 
Hauerite,  378 
Haughtonite,  564 
Hausmannite,  424 
Hautefeuillite,  608 
Hauyne,  503 
Haiiynite,  503 
Haydenite,  552 
Heavy  spar,  625 
Hebronite,  602 
Hedenbergite,  476 
Hedyphane,  598 
Heiiitzite,  622 
Heliodor,  495 


710 

Heliophyllite,  618 
Heliotrope,  405 
Hellandite,  540 
Helvite,  Helvine,  504 
Hemafibrite,  611 
Hematite,  415 

Brown,  432 
Hematogel,  434 
Hematolite,  606 
Hematostibiite,  606 
Hemimorphite,  539 
Henwoodite,  616 
Hepatic  cinnabar,  370 
Hercynite,  420 
Herderite,  601 
Herrengrundite,  638 
Herschelite,  552 
Hessite,  365 
Hessonite,  507 
Hetaerolite,  435 
Heterocline,  425 
Heteromorphite,  387 
Heulandite,  548 
Hewattite,  611 
Hexahydrite,  637 
Hibbenite,  612 
Hibschite,  540 
Hielmite,  Hjelmit,  591 
Hieratite,  400 
Hiddenite,  481 
Highgate  resin,  645 
Hipgensite,  604 
Hillebrandite,  546 
Himbeerspath,  v.  Rhodochro- 

site 

Hinsdalite,  618 
^jabzeitc,  622 
Hiortdah'.u 


Hoernesite,  608 
Hohmannite,  639 
Hokutolite,  630 
Hollandite,  424 
Holmquistite,  493 
Holzopal,  v.  Wood-opal 
Holzzinnerz,  v.  Wood- tin 
Homilite,  529 
Honey-stone,    Honigstein,   v. 

Mellite 
Hopeite,  607 
Horn  quicksilver,  395 
Horn  silver,  397 
Hornblei,  v.  Phosgenite 
Hornblende,  490 
Hornesit,  Hornsilber,  397 
Hornstone,  406 
Horse-flesh  ore,  374 
Horsfordite,  362 
Hortonolite,  513 
Howlite,  621 


INDEX   TO   SPECIES 

Huantajayite,  396 
Hiibnerite,  642 
Hiigelite,  612 
Hudsonite,  492 
Hullite,  571      ' 
Hulsite,  622 
Humboltine,  645 
Humboldtilite,  518 
Humboldtite,  528 
Humite,  536 
Huntilite,  362 
Hutchinsonite,  386 
Hureaulite,  611 
Hussakite,  592 
Hyacinth,- 521,  507 
Hyalite,  409 
Hyalophane,  460 
Hyalosiderite,  511 
Hyalotekite,  498 
Hydrargillite,  435 
Hydraulic  limestone,  440 
Hydroboracite,  623 
HYDROCARBONS,  645 
Hydrocerussite,  452 
Hydroclinohumite,  538 
Hydrocyanite,  630 
Hydrofranklinite,  435 
Hydrogothite,  433 
Hydrogiobertite,  453 
Hydrohematite,  433 
Hydromagnesite,  452 
Hydromica,  561 
Hydromuscovite,  561 
Hydronephelite,  558  ' 
Hydrophane,  408 
Hydrophilite,  399 
Hydrotalcite,  435 
Hydrothomsonite,  558 
Hydroxyapatite,  596 
Hydrozincite,  451 
Hypersthene,  473 
Hypostiibite,  551 


Iberite,  498 
Ice,  411 

Ice  spar,  v.  Rhyacolite 
Iceland  spar,  439 
Iddingsite,  512 
Idocrase,  519 
Idrialite,  646 
Igelstromite,  435 
Ihleite,  638 
Ilesite,  634 
Illmenite,  417 
Ilmenorutile,  427 
Hvaite,  538 
Imerinite,  490 
Impsonite,  647 
Indianaite,  579 
Indianite.  467 
Indicolite,  542 
Indigolite.  .542 


Inesite,  546 

Inflammable  cinnabar,  646 

Infusorial  earth,  409 

Inyoite,  622 

lodate  of  calcium,  619 

lodembolite,  397 

IODIDES,  397 

lodobromite,  397 

lodyrite,  397 

lolite,  497 

Hydrous,  498 
Iridium,  355 
Iridosmine,  355 
Iron,  Chromic,  v.  Chromite 

Magnetic,  420 

Meteoric,  356 

Native,  356 

Oligist,  v.  Hematite 
Iron  aluminate,  420 

arsenates,  608,  609,  etc.  • 

arsenides,  381 

carbide,  356 

carbonate,  443 

chlorides,  399 

chromate,  423 

columbate,  588 

ferrate,  420 

hydrates,  431,  432 

niobate,  588 

oxalate,  528 

oxide,     415,     420;     hy- 
drated,  431,  432 

phosphates,     605,     608, 
610  etc. 

silicates,   513,  538,  571, 
572 

sulphantimonite,  386 

sulpharsenide,  381 

sulphates,  636,  637,  638, 
etc. 

sulphides,  369,  373,  377, 
381 

magnetic,  373 

tantalates,  588 

tellurite,.641 

titanates,  417,  424 

tungstates,  641,  644 
Iron  alum,  637 
Iron  natrolite,  556 
Iron  pyrites,  377 

Magnetic,  373 

White,  380 
Irvingite,  563 
Iserine,  427 
Isoclasite,  611 
Isothose,  458 
Itabirite,  417 
Itacolumite,  406 
Ixiolitc 


J 


Jacobsite, 
Jade,  482:  489 


B 


• 


INDEX   TO   SPECIES 


711 


Jade  tenace,  482 
Jadeite,  479-^-7 
Jalpaite,  365 
Jamesonite,  386 
Janosite,  638 
Jargon,  521 
Jarosite,  640 
Jasper,  406 
Jaspopal,  409 
Jefferisite,  572 
Jeffersonite,  477 
Jeremejevite,  620 
Jet,  648 
Jezekite,  601 
Joaquinite,  586 
Johannite,  640 
Johnstrupite,  585 
Jordanite,  391 
Joseite,  360 
Josephinite,  356 
Jurupaite,  498 


K 

Kaersutite,  491 
Kainite,  631 
Kakoxen,  614 
Kaliborite,  622 
Kalifeldspath,  v.  Orthoclase 
Kaligliinmer,  v.  Muscovite 
Kalinite,  637 
Kaliophilite,  501 
Kalisalpeter,  v.  Niter 
Kalgoorlite,  369 
Kalkglimmer,  470 
Kalkspath,  v.  Calcite 
Kalkuranit,  v.  Autunite 
Kallait,  v.  Turquois 
Kallfflte,  379 
Kalomei,  395 
Kaluszite,  636 
Kamacite,  356 
Kammererite,  570 
Kamarezite,  638 
Kammkies,  v.  Marcasite 
Kampylite,  598 
Kaolin,  578 
Kaolinite,  578 
Karminspath,  v.  Carminite 
Karneol,  v.  Carnelian 
Karstenite,  v.  Anhydrite 
Karyinite,  593 
Kataforite,  491 
Katzenauge,  v.  Cat's-eye 
Kehoeite,  616 
Keilhauite,  585 
Kelyphite,  509 
Kentrolite,  539 
Kermes,  383 
Kermesite,  383 
Kerosene,  646 
Kerrite,  572 
Kertschinite,  615 


Kibdelophan,  418 
Kidney  ore,  416 

stone,  489 

Kieselwismuth,  v.  Euytite 
Kieselzinkerz,  v.  Calamine 
Kieserite,  633 
Kilbrickenite,  392 
Killinite,  562  . 
Kjerulfine,  600 
Klaprotholite,  386 
Kleinite,  395 
Klinoklas,  604 
Klinozoisit,  532 
Knebelite,  513 
Knopite,  586 
Knoxvillite,  639 
Kobaltbliithe,  v.  Erythrite 
Kobaltglanz,  v.  Cobaltite 
Kobaltkies,  v.  Linnaeite 
Kobaltspath,  v.  Sphaerocobal- 

tite 

Kobellite,  387 
Kochsalz,  v.  Halite 
Koechlinite,  644 
Koenenite,  401 
Kohlenspath,  v.  Whewellite 
Koksharovite,  491 
Kongsbergite,  354 
Konigite,  632 
Koninckite,  610 
Koppite,  587 
Kornerupine,  544 
Korund,  v.  Corundum 
Kotschubeite,  569 
Kottigite,  609 
Krantzite,  645 
Kraurite,  605 
Kreittonite,  420 
Kremersite,  402 
Krennerite,  383 
Kreuzbergite,  615 
Krisuvigite,  632 
Krohnkite,  638 
Kronkite,  Kronnkite,  638 
Kryptoperthit,  460 
Ktypeite,  447 
Kunzite,  481 
Kupfer,  v.  Copper 
Kupferantimonglanz,  v.  Chal- 

costibite 
Kupferblende,  v.  Sandberger- 

ite 

Kupferglanz,  v.  Chalcocite 
Kupferglimmer,    v.    Chalco- 

phyllite 

Kupferindig,  v.  Covellite 
Kupferkies,  v.  Chalcopyrite 
Kupferlasur,  v.  Azurite 
Kupfernickel,  v.  Niccolite 
Kupferschaum,  v.  Tyrolite 
Kupferuranit,   v.    Torbernite 
Kupfervitriol,     v.     Chalcan- 

thite 
Kupfferite,  491 


Kyanite,  526 
Kylindrite,  394 


Labrador  feldspar,  466 

Labradorite,  466 

Lacroixite,  601 

Lagonite,  621 

Lampadite,  436 

Lanarkite,  632 

Landerite,  509 

Langbanite,  539 

Langbeinite,  625 

Langite,  638 

Lansfordite,  453    . 

Lanthanite,  453 

Lanthanum  carbonate,  453 

Lapis-lazuli,  503 

Larderellite,  621 

Lassalite,  577 

Lasurapatite,  596 

Lasurite,  503 

Latrobite,  468 

Laubanite,  552 

Laumonite,  552 

Laumontite,  552 

Laurionite,  401 

Laurite,  380 

Lautarite,  619 

Lavenite,  484 

Lavrovite,  476 

Lawrencite,  399 

Lawsonite,  540 

Lazulite,  605 

Lazurite,  503 

Lead,  354 

Black,  347 
Native,  354 
White,  v.  Cerussite 

Lead  antimonate,  617 
arsenates,  598 
carbonates,  448,  452 
chloride,  399,  401 
chloro-carbonates,  450 
chromates,  630 
dioxide,  428 
molybdate,  643 
oxides,  412,  '424,  428 
oxychlorides,  401 
phosphate,  597 
selenides,  364,  365 
silicates,  498,  539 
sulphantimonate,  394 
sulphantimonites,      385, 

etc. 

sulpharsenites,  385  etc. 
sulphates,  628  etc. 
sulphate-carbonate,  631 
sulphide,  363 
sulphobismuthites,     386 

etc. 
telluride,  364 


712 


INDEX   TO   SPECIES 


Lead  tungstate,  643 

vanadates,  598,  604 
Lead  glance,  363 
Lead  vitriol,  v.  Anglesite 
Leadhillite,  631 
Lecontite,  632 
Ledererite,  554 
Lederite,  584 
Ledouxite,  362 
Lehrbachite,  365 
Lengenbachite,  388 
Lennilite,  572 
Leonhardite,  552 
Leonite,  637 
Leopoldite,  397 
Lepidocrocite,  432 
Lepidolite,.562 
Lepidomelane,  565 
Lepolite,  468 
Lettsomite,,  638 
Leucaugite,  477 
Leuchtenbergite,  569 
Leucite,  469 
Leucochalcite,  612 
Leucomanganite,  607 
Leucopetrite,  646 
Leucophanite,  496 
Leucophoenicite,  538 
Leucopyrite,  381 
Leucosphenite,  585 
Leucoxene,  418 
Levynite,  554 
Lewisite,  618 
Libethenite,  603 
Liebenerite,  500,  562 
Liebigite,  454 
Lievrite,  538 
Lignite,  648 
Ligurite,  584 
Lillianite,  388 
Lime,  v.  Calcium 
Lime-mesotype,  557 
Lime  uranite,  515 
Limestone,  440 

Hydraulic,  440 

Magnesian,  442 
Limonite,  432 
Linarite,  632 
Lindackerite,  618 
Linnaeite,  374 
Linsenkupfer,  v.  Liroconite 
Lintonite,  557 
Liroconite,  615 
Liskeardite,  614 
Lithia  mica,  562 
Lithionglimmer,    v.    Lepido- 

lite 

Lithiophilite,  594 
Lithium    phosphates,    594. 
602 

silicates  480,  500,  562 
Lithographic  stone,  440 
Lithomarge,  578 
Liveingite,  387 


Livingstonite,  385 
Lodestone,  421 
Loeweite,  637 
Loewigite,  640 
Lollingite,  381 
Lorandite,  386 
Loranskite,  591 
Lorenzenite,  586 
Lorettoite,  401 
Lossenite,  619 
Lotrite,  546 
Loweite,  637 
Lowigite,  640 
Loxoclase,  458 
Lublinite,  439 
Lucinite,  610 
Luckite,  636 
Ludlamite,  614 
Ludwigite,  620 
Luigite,  545 
Lumachelle,  440 
Liineburgite,  619 
Lussatite,  405 
Lutecite,  407 
Luzonite,  393 
Lydian  stone,  406 

M 

Mackintoshite,  529 
Made,  525 
Maconite,  572 
Magnesioferrite,  420 
Magnesioludwigite,  620 
Magnesite,  443 
Magnesium  aluminate,  419 

arsenate,  608 

borate,  621,  622 

carbonates,    443,    452, 
453 

ferrate,  420 

fluoride,  399 

hydrate,  434 

oxides,  411,  434 

phosphates,     600,     608, 
611 

silicates,  472,  473,  etc.; 
513,  536,  573,  576 

sulphates,  633,  635 

titanate,  586 
Magnetic  iron  ore,  420 
Magnetic  pyrites,  373 
Magnetite,  420 
Magnetkies,  v.  Pyrrhotite 
Magnoferrite,  420 
Malachite,  450 

Blue,  v.  Azurite 

Green,  450 
Malacolite,  476 
Malacon,  522 
Maldonite,  350 
Malinowskite,  391 
Mallardite,  636 
Maltha,  646 


Manandonite,  563 

MANGANATES,  418 
Manganandalusite,  524 
Manganapatite,  596 
Manganblende,  v.  Alabandite 
Manganbrucite,  434 
Manganchlorite,  569 
Manganepidote,  v.  Piedmon- 

tite 
Manganese  antimonate,  606 

arsenates,  601,  606 

carbonate,  444 

disulphide,  378 

hydrates,  432,  435 

niobate,  588 

oxides,    411,    424,    425, 
v     427,  430,  432,  435 

phosphates,     594,     600, 

silicates,  484,  513,  582, 
etc. 

sulphates,  633,  636 

sulphide,  369,  378 

tantalate,  588 

titanate,  418 

tungstate,  642 
Manganfayalite,  513 
Manganglanz  v.  Alabandite 
Mangangranat,    v.    Spessar- 

tite 

Manganhedenbergite,  476 
Manganite,  432 
Manganmagnetite,  420 
Manganocalcite,  441,  444 
Manganocolumbite,  589 
Manganophyllite,  564 
Manganosiderite,  444 
Manganosite,  411 
Manganospherite,  444 
Manganostibiite,  606 
Manganotantalite,  589 
Manganpectolite,  483 
Manganspath)  v.  Rhodochrc 

site 

Mangantantalite,  588 
Mangan-vesuvianite,  520 
Marble,  440 

Verd-antique,  573 
Marcasite,  380' 
Marceline,  425,  485 
Margarite,  566 
Margarodite,  561 
Margarosanite,  498 
Marialite,  518 
Marignacite,  587 
Mariposite,  565 
Marmatite,  368 
Marmolite,  573 
Marshite,  395 
Marsjakskite,  577 
Martinite,  611 
Martite,  417 
Mascagnite,  624 
Maskelynite,  467 


INDEX   TO    SPECIES 


713 


Masonite,  567 
Massicot,  412 
Matildite,  386 
Matlockite,  401 
Maucherite,  362 
Mauzeliite,  618 
Maxite,  631 
Mazapilite,  615. 
Meerschaum,  576 
Meionite,  516 
Melaconite,  412 
Melanglanz,  v.  Stephanite 
Melanite,  508 
Melanocerite,  496 
Melanophlogite,  408 
Melanotekite,  539 
Melanterite,  636 
Melilite,  518 
Melinophane,    v.    Meliphan- 

ite 

Meliphanite,  496 
Melite,  580 

Mellate  of  aluminium,  645 
Mellite,  645 
Meionite,  382 
Menaccanite,  417 
Mendipite,  401 
Mendozite,  637 
Meneghinite,  391 
Menilite,  408 
Mennige,  v.  Minium 
Mercurammonite,  395 
Mercury,  354 

Horn,  395 

Native,  354 
Mercury  antimonite,  618 

chloride,  3Q5 

selenides,  369 

sulphides,  369,  370 

sulpho-selenide,  369 

telluride,  369 
Mercury  amalgam,  354 
Meroxene,  564 
Mesitite,  443 
Mesitinspath,  v.  Mesitite 
Mesole,  v.  Thorn sonite 
Mesolite,  557 
Mesotype,  556 
Messelite,  607 
Metabrushite,  611 
Metachinabarite,  369 
Metahewettite,  611 
Metastibnite,  359 
Meta-torbernite  I,  616 
Metavoltine,  639 
Metaxite,  575 
Meteoric  iron,  356 
Mexican  onyx,  440 
Meyerhofferite,  622 
Miargyrite,  386 
MICA  Group,  559 
Mica,  Iron,  563,  565 

Lime,  566 

Lithia,  562 


Mica,  Magnesia,  563,  565 

Potash,  560 

Soda,  562 

Vanadium,  565 
Micaceous  iron  ore,  415 
Michei-levyte,  626 
Microcline,  460 
Microcosmic  salt,  611 
Microlite,  587 
Microsonunite,  501 
Microperthite,  460 
Microphyllite,  467 
Microplakite,  467 
Miersite,  397 
Miesite,  598 
Mikroklin,  460 
Milarite,  455 
Milky  quartz,  405 
Millerite,  372 
Millosevichite,  630 
Mimetene,  Mimetesite,  598 
Mimetite,  598 
Minasite,  614 
Minasragrite,  641 
Mineral  caoutchouc,  647 
Mineral  coal,  647 

oil,  646 

pitch,  647- 

resin,  645 

tallow,  645 

tar,  v.  Pittasphalt 

wax,  645 
Minguetite,  572 
Minium,  424 
Mirabilite,  632 
Misenite,  631 
Mispickel,  381 
Misy,  638 
Mitchellite,  423 
Mixite,  617 
Mizzonite,  517 
Mocha  stone,  v.  Moss  agate 
Mock  lead,  291 
Moissanite,  356 
Mohawkite,  362 
Molengraaffite,  585 
Molybdanbleispath,  v,  Wul- 

fenite 

Molybdanglanz,    v.    Molyb- 
denite 

MOLYBDATES,  641 

Molybdenum  sulphide,  360 

trioxide,  410 
Molybdenite,  360 
Molybdic  ocher,  410 
Molybdite,  410 
Molybdomenite,  641 
Molybdophyllite,  498 
Molybdosodalite,  502 
Molysite,  399 
Monazite,  593 
Monetite,  606 
Monheimite,  445 
Monimolite,  593 


Monite,  606 
Monrolite,  526 
Montanite,  641 
Monticellite,  513 
Montmorillonite,  579 
Montroydite,  412 
Moonstone,  458,  465 
Moravite,  571 
Mordenite,  548 
Morencite,  582 
Morenosite,  635 
Morganite,  495 
Morion,  405 
Moroxite,  596 
Mosandrite,  585 
Mosesite,  402 
Moss  agate,  405 
Mossite,  590 
Mottramite,  604 
Mountain  cork,  490 

leather,  490 

soap,  578 

tallow,  645 

wood,  490 
Miillerite,  582 
Mullanite,  388 
Muller's  glass,  409 
Mullicite,  608 
Mundic,  v.  Pyrite 
Murchisonite,  458 
Muscovite,  560 
Muscovy  glass,  562 
Mussite,  478 
Muthmannite,  383 

•    N 

Nadeleisenerz,  v.  Gothite 
Nadelerz,  v.  Aikinite 
Nadelzeolith,  v.  Natrolite 
Nadorite,  618 
Naegite,  522 
Nagyagite,  383 
Nailhead  spar,  439 
Nantokite,  395 
Napalite,  645 
Naphtha,  646 
Narsarsukite,  585 
Nasonite,  498 
NATIVE  ELEMENTS,  344 
Natramblygonite,  602 
Natrium,  v.  Sodium 
Natroborocalcite,  622 
Natrochalcite,  638 
Natrolite,  556 
Natrojarosite,  640 
Natromontebrasite,  602 
Natron,  452 
Natrophilite,  594 
Naumannite,  364 
Needle  ironstone,  432 
Needle  ore,  v.  Aikinite 
Needle  zeolite,    v.    Natrolite, 
556 


714 


INDEX   TO    SPECIES 


Nemalite,  434 
Neocolemanite,  621 
Neotantalite,  587 
Neotocite,  485,  582 
Nepheline,  499 
Nephelite,  499 
Nephrite,  489 
Nepouite,  575 
Neptunite,  585 
Nesquehonite,  452 
Nevyanskite,  355 
Newberyite,  611 
Newtonite,  579 
Niccolite,  372 
Nicholsonite,  446 
Nickel  antimonide,  372 

arsenates,  609 

arsenides,  372,  378,  382 

carbonate,  453 

oxides,  411 

silicate,  575 

sulphantimonide,  379 

sulpharsenide,  379,  382 

sulphate,  635 

sulphides,  369,  372, 373 

telluride,  382 
Nickelantimonglanz,    v.    Ull- 

maimite 
Nickelarsenikglanz,   v.   Gers- 

dorffite 

Nickel-gymnite,  575 
Nickel-skutterudite,  380 
Nigrine,  427 
Nigrite,  647 
NIOBATES,  587 
Niter,  619 
Niter,  Soda,  619 
NITRATES,  619 
Nitrobarite,  619 
Nitrocalcite,  619 
Nitroglauberite,  619 
Nitromagnesite,  619 
Nivenite,  623 
Nocerite,  401 
Nontronite,  582 
Nordenskipldine,  620 
Nordmarkite,  544 
Northupite,  450 
Nosean,'  503 
Noselite,  503 
Noumeite,  575 
Nussierite,  598 


Ocher,  Brown,  432 

Red,  415 
Ochrolite,  618 
Octahedrite,  428 
Odontolite  613 
(Eil  de  chat,  424 
(Ellacherite,  561 
Offretite,  554 
Oil,  Mineral  646 


Oisanite,  532 
Okenite,  546 
Oldhamite,  369 
Oligist  iron  v.  Hematite 
Oligoclase,  466 
Oligonite,  444 
Olivenerz,  v.  Olivenite 
Olivenite,  603 
Olivine,  511 
Omphacite,  477 
Oncosin,  561 
Onofrite,  369 
Onyx,  406 

Mexican,  440 
Onyx  marble,  440 
Oolite,  440 
Opal,  408 
Opal  jasper,  409 
Ophicalcite,  573 
Ophiolite,  573 
Ophite,  575 
Orangite,  522 
Oriental  alabaster,  440 

amethyst,  413 

emerald,  413 

ruby,  413 

topaz,  413 
Orientite,  582 
Orpiment,  357 
Orthite,  533 
Orthoclase,  457 
Orthose,  v.  Orthoclase 
Oruetite,  360 
Osannite,  494 
Osmelite,  483 
Osmiridium,  355 
Osmium  sulphide,  379 
Osteolite,  596 
Otavite,  452 
Ottrelite,  567 
Ouvarovite,  508 
Owenite,  572 

3XALATES,  644 

Oxammite,  644 
3xiDEs,  402 

3XYCHLORJDES,  400 
3XYFLUORIDES,  400 

Dxykertschenite,  61 
DXYSULPHIDES,  383 
3zarkite,  557 
Ozocerite,  645 


Pachnolite,  402 
Pagodite,  562 
Paigeite,  622 
Paisbergite,  484 
Palaite,  607 
Palladium,  355 
Palmerite,  610 
Palmierite,  640 
Panabase,  v.  Tetrahedrite 
Pandermite,  621 


Paposite,  639 

Paracelsian,  460 

Paraffin,  645 

Paragonite,  562 

Parahopeite,  607 

Paralaurionite,  401 

Paraluminite,  639 

Paramelaconite,  412 

Parasite,  621  • 

Paravivianite,  608 

Paredrite,  428 

Pargasite,  490 

Parisite,  449 

Parophite,  562 

Parrot  coal,  648 

Partschinite,  510 

Pascoite,  609 

Passauite,  517 

Paternoite.  621 

Patronite,  361 

Peacock  Ore,  374 

Pearceite,  393 

Pearl  sinter,  409 

Pearl-spar,  441 

Peat,  648 

Pebble,  Brazilian,  405 
Pechblende,    Percherz,    v. 
Uraninite 

Peckhamite,  474 

Pectolite,  483 

Peganite,  613 

Pencil-stone,  579 
Penfieldite,  401 
Pennine,  570 
Penninite,  570 
Pentlandite,  369 
Peplolite,  498 

Percylite,  401 

Periclase,  411 
Pericline,  465 
Peridot,  511 
Peristerite,  465 

Perthite,  460 
Perofskite,  586 
Perovskite,  586 
Perowskit,  586 
Petalite,  455 
Petrified  wood,  406 
Petroleum,  646 
Petzite,  365 

Phacelite,  Phacellite,  501 
hacolite,  553 

Pharmacolite,  610 

Pharmacosiderite,  614 

Phenacite,  514 
Phengite,  561 
Philadelphite,  572 
Philipstadite,  491 
Phillipite,  638 
Phillipsite,  550 
Phlogopite,  565 

3hoenicite,  630 

Phcenicochroite,  630 
Pholerite,  578 


INDEX   TO    SPECIES 


715 


Pholidolite  577 
Phosgenite,  450 
PHOSPHATES,  592 
Phosphoferrite,  601 
Phosphorite,  596 
Phosphophyllite,  618 
Phosphorsalz,  v.  Stercorite 
Phosphosiderite,  610 
Phosphuranylite,  617 
Photicite,  485 
Phyllite,  567 
Physalite,  523 
Picite,  615 
Pickeringite,  637 
Picotite,  419 
Picroepidote,  532 
Picrolite,  573 
Picromerite,  637 
Picropharmacolite,  607 
Picrotitanite,  417 
Piedmontite,  532 
Pigeonite,  479 
Pinakiolite,  620 
Pinguite,  582 
Pinite,  562,  498 
Pinnoite,  622 
Pintadoite,  609 
Piotine,  576 
Pirssonite,  452 
Pisanite,  636 
Pisolite,  440 
Pistacite,  531 
Pistomesite,  443 
Pitchblende,  623 
Pittasphalt,  646 
Pitticite,  618 
Placodine,  3r>2 
Plagioclase,  374 
Plagionite,  38T7 
Plancheite,  515 
Planoferrite,  639 
Plasma,  405 
Plaster  of  Paris,  634 
Platina,  355 
Platiniridium,  355 
Platinum,  35 r 
Platinum,  arsenide,  379 
Plattnerite,  428 
Platynite,  385 
Plazolite,  580 
Plenargyrite,  386 
Pleonaste,  419 
Plessite,  356 
Plumbago,  347 
Plumbogummite,  601 
Plombocalcite,  441 
Plumbojarosite,  640 
Plumboniobite,  592 
Plumbostib,  387 
Plumosite,  387 
Podolite,  618 
Pochite,  545 
Polianite,  427 
Pollucite,  470 


Polyadelphite,  508 
Polyargite,  562 
Polyargyrite,  393 
Polyarsenite,  601 
Polybasite,  392 
Polycrase,  591 
Polychroilite,  498 
Polydymite,  373 
Polyhalite,  637 
Polylithionite,  563 
Polymignite,  591 
Polysphaerite,  598 
Ponite,  445 

Poonahlite,  v.  Scolecite 
Porpezite,  350 
Posepnyte,  646 
Potash  alum,  637 
Potassium  borate,  622 

chloride,  396 

nitrate,  619 

silicate,    457,    460,    469, 
560,  etc. 

sulphate,  624 
Potstone,  576 
Powellite,  643 
Prase,  405 
Praseolite,  498 
Prehnite,  534 
Preslite,  604 
Pfibramite,  368 
Priceite,  621 
Priorite,  591 
Prismatine,  544 
Przibramite,  368 
Prochlorite,  571 
Prolectite,  538 
Prosopite,  402 
Protobastite,  473 
Proustite,  389 
Prussian  blue,  Native,  608 
Przibramite,  432 
Pseudoboleite,  401 
Pseudobrookite,  424 
Pseudocampylite,  598 
Pseudoleucite,  470 
Pseudomalachite,  605 
Pseudomeionite,  516 
Pseudomesqlite,  557 
Pseudophillipsite,  550 
Pseudophite,  570 
Pseudosteatite,  579 
Pseudowollastonite,  483 
Psilomelane,  436 
Psittacimite,  604 
Ptilolite,  548 
Pucherite,  594 
Puflerite,  551 
Punamu,  482 
Purple  copper  ore,  374 
Purpurite,  610 
Puschkinite,  532 
Pycnite,  523 
Pycnochlorite,  571 
Pyrargillite,  498 


Pyrargyrite,  389 
Pyreneite,  508 
Pyrgom,  477 
Pyrite,  377 

.Pyrites,  Arsenical,  v.  Arseno- 
pyrite,  381 

Capillary,  372 

Cockscomb,  380 

Copper,  374 

Iron,  377 

Magnetic,  373 

Radiated,  380 

Spear,  380 

Tin,  394 

White  iron,  380 
Pyroaurite,  435 
Pyrobelonite,  604 
Pyrochlore,  587 
Pyrochroite,  435 
Pyrolusite,  430 
Pyromorphite,  597 
Pyrope,  507 
Pyrophanite,  418 
Pyrophosphorite,  606 
Pyrophyllite,  579 
Pyrophysalite,  523 
Pyroretinite,  646 
Pyrosclerite,  572 
Pyrosmalite,  515 
Pyrostilpnite,  390 
Pyroxene,  474 
PYROXENE  Group,  470 
Pyroxmangite,  485 
Pyrrharsenite,  593 
Pyrrhite,  588 
Pyrrhotine,  373 
Pyrrhotite,  373 

Q 

Quartz,  403 
Quartzine,  407 
Quartzite,  406 
Quecksilber,     Gediegen,     v. 

Cinnabar 
Quecksilberhornerz,  v.  Calo- 
mel 

(uenstedtite,  637 
luetenite,  640 
uicksilver,  354 
uisqueite,  347 

R 

Radelerz,  v.  Bournonite 
Radiated  pyrite,  380 
Radiotine,  573 
Rafaelite,  401 
Raimondite,  639 
Ralstonite,  402 
Ramirite,  604 
Rammelsbergite,  382 
Ranite,  558 
Raspite,  643 


716 


INDEX   TO    SPECIES 


Rathite,  386 
Rauchquarz,     v.     Smoky 

Quartz 
Raumite,  498 
Realgar,  357 
Red  antimony,  v.  Kermesite 

chalk,  416 

copper  ore,  410 

hematite,  415 

iron  ore,  416 

lead  ore,  630 

ocher,  416 

silver  ore,  389 

zinc  ore,  411 
Reddingite,  607 
Reddle,  416 
Redingtonite,  639 
Redruthite,  366 
Reinite,  644 
Reissite,  549 
Remingtonite,  453 
Rensselaerite,  576 
Resin,  Mineral,  645 
Retinalite,  573 
Retinite,  645 
Retzbanyite,  385 
Retzian,  606 
Rezbanyite,  385 
Rhabdophanite,  609 
Rhaetizite,  527 
Rhagite,  617 
Rhodalose,  v.  Bieberite 
Rhodizite,  621 
Rhodochrome,  570 
Rhodochrosite,  444 
Rhodolite,  507 
Rhodonite,  484 
Rhodophyllite,  570 
Rhodotilite,  546 
Rhodusite,  493 
Rhonite,  494 
Rhomboclase,  641 
Rhyacolite,  458 
Riband  jasper,  406 
Richellite,  615 
Richterite,  489 
Rickardite,  362 
Ricolite,  573 
Riebeckite,  493 
Rinkite,  585 
Rinneite,  399 
Ripidolite,  569 
Risorite,  588 
Rittingerite,  393 
Rivaite,  455 
Riversideite,  546 
Rizopatronite,  361 
Rock  crystal,  405 

meal,  440 

milk,  440 

salt,  395 
Roeblingite,  498 
Romerite,  638 
Roepperite,  513 


Romanzovite,  507 

Romeite,  618 

Romerite,  638 

Rosasite,  449 

Roscherite,  616 

Roscoelite,  565 

Rose  quartz,  405 

Roselite,  607 

Rosenbuschite,  483 

Rosieresite,  610 

Rosite,  562 

Rosolite,  509 

Rothbleierz,  v.  Crocoite 

Rotheisenerz,  Rotheisenstein, 
v.  Hematite 

Rothgiiltigerz,     v.     Pyrargy- 
rite 

Rothkupfererz,  v.  Cuprite 

Rothnickelkies,  v.  Niccolite 

Rothoffite,  508 

Rothspiessglanzerz,    v.    Ker- 
mesite 

Rothzinkerz,  v.  Zincite 

Rowlandite,  529 

Rubellite,  542 

Rubicelle,  419 

Rubin,  419 

Ruby,  Almandine,  419 
Balas,  419 
Oriental,  413 
Spinel,  419 

Ruby  blende,  368 

Ruby  copper,  410 

Ruby  silver,  389 

Ruby  zinc,  368 

Ruin  marble,  440 

Rumanite,  645 

Rumpfite,  572 

Ruthenium  sulphide,  302 

Rutherfordine,  449 

Rutile,  427 


Safflorite,  382 
Sagenite,  405,  427 
Sahlite,  477 
Sal  Ammoniac,  397 
Salite,  477 
Salmiak,  397 
Salmite,  567 
Salmonsite,  610 
Salt,  Rock,  395 
Saltpeter,  v.  Niter 
Salvadorite,  636 
Samarskite,  590 
Samiresite,  587 
Sammetblende,  432 
Samsonite,  390 
Sandbergerite,  391 
Sanguinite,  390 
Sanidine,  458 
Saphir  d'eau,  498 


Saponite,  576,  579 

Sapphire,  413 

Sapphirine,  544 

Sarcolite,  518 

Sard,  405 

Sardonyx,  406 

Sarkinite,  601 

Sartorite,  385 

Sassolite,  435 

Satin  spar,  439,  634 

Saualpite,  530 

Saussurite,  350 

Scacchite,  399 

Scapolite,  516 

SCAPOLITE  Group,  515 

Schafarzikite,  618 

Schalenblende,  368 

Schapbachite,  387 

Schaumerde,  v.  Aphrite 

Schaumopal,  409 

Schaumspath,  v.  Aphrite 

Scheelbleispath,  v.  Stolzite 

Scheelite,  642 

Scheelspath,  v.  Scheelite 

Scheererite,  645 

Schefferite,  477 

Schertelite,  611 

Schiller-spar,  474 

Schirmerite,  386 

Schizolite,  483 

Schlangenalabaster,  v.  Tripe- 
stone 

Schmirgel,  v.  Emery 

Schneiderite,  552 

Schoenite,  637 

Schorlomite,  510 

Schorza,  531 

Schreibersite,  356 

Schrifterz,  Schrifttellur,  v. 
Sylvanite 

Schrotterite,  580 

Schuppenstein,  v.  Lepidolite 

Schwartzembergite,  401 

Schwatzite,  391 

Schwefel  v.  Sulphur 

Schwefelkies,  v.  Pyrite 

Schwefelquecksilber,  v.  Cin- 
nabar 

Schwerbleierz,  v.  Plattnerite 

•Jchwerspath,  v.  Barite 

Scleroclase,  v.  Sartorite 

Scolecite,  Scolezite,  557 

Scorodite,  609 

Scorza,  531 

Scovillite,  609 

Searlesite,  583 

Seebachite,  552 

SELENIDES,  364,  365 

Selenite,  634 

SELENITES,  641 

Selenium,  344 

Selenquecksilber,  v.  Tieman- 
nite 

Selensulphur,  348 


INDEX    TO    SPECIES 


717 


Selenwismuthglanz,  v.  Guan- 
juatite 

Seligmannite,  388 

Sellaite,  399 

Semeline,  584 

Semi-opal,  408 

Semseyite,  387 

Senaite,  418 

Senarmontite,  409 

Sepiolite,  576 

Serendibite,  545 

Sericite,  561 

Serpentine,  573 

Serpeirite,  638 

Seybertite,  566 

Shanyavskite,  436 

Shattuckite,  581 

Shepardite,  472 

Sheridanite,  571 

Shell  marble,  440 

Siberite,  542 

Sicklerite,  610 

Siderite,  443 

Sideronatrite,  639 

Siderophyllite,  564 

Siegenite,  374 

Silber,  v.  Silver 

Silberamalgam,  v.  Amalgam 

Silberglanz,  v.  Argentite 

Silber  hornerz,    v.    Cerargy- 
rite 

Silex,  Silica,  403 

SILICATES,  454 

Siliceous  sinter,  409 

Silicified  wood,  404 

Silicomagnesiofluorite,  545 

Silicon  oxido,  403,  407,  408 

Sillimanite,  526 

Silver,  352 

Silver  antimonide,  361 
arsenide,  362 
bismuthide,  362 
bromide,  397 
chlorides,  397 
iodide,  397 
selenide,  364 
.     sulphantimonites,    386, 

389 

sulpharsenite,  389 
sulphide,  364,  367 
sulpho-bismuthite,  386 
sulpho-germanate,  394 
telluride,  362,  365,  382 

Silver  glance,  364 

Simetite,  645 

Simonyite,  637 

Sinopite,  580 

Sinter,  Siliceous,  409 

Sipylite,  588 

Siserskite,  355 

Sismondine,  Sismondite,  567 

Sisserskite,  355 

Sitaparite,  418 

Skapolith,  516 


Skemmatite,  436 
Skleroklas,  v.  Sartorite 
Skogbolite,  590 
Skutterudite,  380 
Smaltite,  378. 
Smaragd,  v.  Emerald 
Smaragdite,  490 
Smectite,  579,  580 
Smegmatite,  579 
Smirgel,  v.  Emery 
Smithite,  386 
Smithsonite,  445,  539 
Smoky  quartz,  405 
Soapstone,  576 
Sobralite,  485 
Soda  alum,  637 
Soda-mesotype,  557 
Soda  microcline,  461 
Soda  niter,  619 
Soda  orthoclase,  458 
Soda-sarcolite,  518 
Sodalite,  502 
Sodium  borate,  622 

carbonate,  452,  453 
hloride,  395 

fluoride,  399,  etc. 

nitrate,  619 

phosphate,  594,  etc. 

silicate,  464,  502,  554, 
556 

sulphate,    625:    hydrous 

632,  etc. 

Somervillite,  518 
Sonnenstein,  v.  Sunstone 
Soretite,  491 
Souesite,  356 
Soumansite,  614 
Spadaite,  577 
Spaerocobaltite,  446 
Spangolite,  631 
Spargelstein,     v.     Asparagus 

stone 

Spathic  iron,  443 
Spatheisenstein,  v.  Siderite 
Spear  pyrites,  380 
Speckstein,  v.  Steatite 
Specular  iron,  415 
Speerkies,  v.  Marcasite 
Speiskobalt,  v.  Smaltite 
Spencerite,  612 
Spessartine,  Spessartite,  507 
Speziaite,  491 
Sperrylite,  379 . 
Sphaerite,  614 
Sphaerocobaltite,  446 
Sphalerite,  367 
Sphene,  583 
Sphenomanganite,  432 
Spiauterite,  v.  Wurtzite 
Spinel,  419 
Spinel  ruby,  419 
Spinthere,  584 
Spodiophyllite,  572 
Spodiosite,  600 


Spodumene,  480 
Sporogelite,  434 
Spreustein,  556 
Sprodglanzerz,  v.  Polybasite 
Sprodglaserz,  v.  Polybasite 
Sprudelstein,  446 
Spurrite,  581 
Staffelite,  596,  597 
Stalactite,  440 
Stalagmite,  440 
Stannite,  394 
Stassfurtite,  621 
Star-quartz,  405 

sapphire,  410 
Staurolite,  543 
Staurotide,  543 
Steatite,  576 
Steenstrupine,  496 
Steinheilite,  498 
Steinmannite,  363 
Steinmark,  v.  Lithomarge 
Steinsalz,  v.  Halite 
Stellerite,  558 
Stelznerite,  632 
Stephanite,  392 
Stercorite,  611 
Sternbergite,  367 
Stewartite,  607 
Stibiconite,  410 
Stibiotantalite,  590 
Stibnite,  358 
Stichtite,  453 
Stilbite,  551,  548 
Stilpnochloran,  572 
Stilpnomelane,  572 
Stoffertite,  611 
Stokesite,  540 
Stolpenite,  579 
Stolzite,  643      • 
Strahlerz,  v.  Clinoclasite 
Strahlkies,  v.  Marcasite 
Strahlstein,  489 
Stratopeite,  485 
Stream  tin,  426 
Strengite,  610 
Strigovite,  572 
Stromeyerite,  366 
Strontianite,  447 
Strontianocalcite,  440 
Strontium  carbonate,  447 

silicate,  549 

sulphate,  627 
Struvite,  606 
Striiverite,  427 
Stiitzite,  362 
Stylotypite,  388 
Succinic  acid,  645 
Succinite,  645,  507 
Sulfoborite,  623 
SULPHANTIMONATES,  393 
SULPHANTIMONITES,  383 
SULPHARSENATES,  393 
SULPHARSENITES,  383 
SULPHATES,  624 


718 


INDEX    TO    SPECIES 


SULPHIDES,  357 
SULPHOBISMUTHITES,  383 
Sulphoborite,  623 
Sulphohalite,  631 

SULPHOSTANNATES,  315 

Sulphur,  347 
Sulvanite,  393 
Sundtite,  385 
Sunstone,  466 
Susannite,  631 
Sussexite,  619 
Svabite,  598 
Svanbergite,  618 
Sychnodymite,  373 
Sylvanite,  382 
Sylvite,  396 
Symplesite,  608 
Synadelphite,  606 
Synchisite,  449 
Syngenite,  636 
Syntagmatite,  489 
Szaboite,  474 
Szaibelyite,  620 
Szechenyiite,  489 
Szmikite,  633 
Szomolnokite,  633 

T 

Tabular  spar,  482 
Tachhydrite,  402 
Tachyhydrite,     Tachydrite, 

402 

Taeniolite,  565 
Taenite,  356 

Tafelspath,  v.  Wollastonite 
Tagilite,  612 
Talc,  575 

Talkeisenerz,  v.  Magnetite 
Talktriplite,  600 
Tallingite,  402 
Tallow,  Mineral,  645 
Tamanite,  607 
TANTALATES,  587 
Tantalite,  588 
Tantalum,  349 
Tapalpite,  389 
Tapiolite,  590 
Taramellite,  498 
Tarbuttite,  604 
Tarnowitzite,  446 
Tartarkaite,  583 
Tasmanite,  646 
Tavistockite,  606 
Tawmanite,  532 
Taylorite,  624 
Teallite,  394 
Tellur,  v.  Tellurium 
TELLURATES,  641 
Tellurbismuth,  360 
Tellurblei,  v.  Altaite 
TELLURIDES,  364  et  sea 
Tellurite,  410 
TELLURITES,  641 
Tellurium,  349 


Tellurium  oxide,  410 
Tellurnickel,  v.  Melonite 
Tellursilber,  v.  Hessite 
Tellurwismuth,    v.    Tetrady 

mite 

Temiskamite,  372 
Tengerite,  454 
Tennantite,  391 
Tenorite,  412 
Tephroite,  513 
Terlinguaite,  401 
Termierite,  579 
Teschemacherite,  450 
Tesseralkies,  v.  Skutterudite 
Tetradymite,  360 
Tetrahedrite,  390 
Thalenite,  529 
Thallite,  531 
Thallium  selenide,  365 
Thaumasite,  581 
Thenardite,  624 
Thennonatrite,  452 
ThermophyUite,  575 
Thinolite,  441 
Thiorsauite,  468 
Thomsenplite,  402 
Thomsonite,  557 
Thonerde,  v.  Aluminium 
Thorianite,  624 
Thorite,  522 

Thorium  silicate,  522,  540 
Thortveitite,  529 
Thorogummite,  624 
Thulite,  530 
Thuringite,  571 
Tiemannite,  369 
Tiger-eye,  405 
Tilasite,  601 
Tile  ore,  410 
Tilkerodite,  364 
Tin,  Native,  354 
Tin  borate,  620 

oxide,  425 

sulphide,  394 
Tin  ore,  Tin  stone,  425 
Tin  pyrites,  394 
Tincal,  622 
Tinkal,  622 
Tirolite,  612 

TlTANATES,  583 

Titaneisen,  v.  Ilmenite 
Titanic  iron  ore,  417 
Titanite,  583 
Titaniumoxide,  427,  428,  429 

ritanomorphite,  584 
Toernebohnite,  540 
Topaz,  523 
False,  405 
Oriental,  413 

Topazolite,  508 

Porbanite,  648 

Torberaite,  616 

Touchstone,  406 
Tourmaline.  540 


Traversellite,  476 
Travertine,  440 
Trechmanite,  386 
Tremolite,  489 
Trichalcite,  607 
Tridymite,  407 
Trigonite,  601 
Trimerite,  515 
Tripestone,  629 
Triphane,  480 
Triphyline,  594 
Triphylite,  594 
Triplite,  600 
Triploidite,  601 
Triploite,  409 
Trippkeite,  618 
Tripuhyite,  618 
Tritochorite,  604 
Tritomite,  496 
Trogerite,  617 
Troilite,  373 
Trolleite,  614 
Trona,  453 
Troostite,  514 
Tscheffkinite,    Tschewkinit, 

585 

Tschermigite,  637 
Tsumebite,  604 
Tufa,  Calcareous,  440 
Tungsten  trioxide,  410 
Tungstenite,  361 
Tungstite,  410 
Turanite,  604 
Turgite,  433 
Tiirkis,  613 
Turmalin,  540 
Turnerite,  593 
Turquois,  Turquoise,  613 
Tychite,  450 
Tyrite,  588 
Tyrolite,  612 
Tysonite,  399 
Tyuyamunite,  617 

U 

Uhligite,  428 
Uintahite,  Uintaite,  647 
Ulexite,  622 
Ullmannite,  379 
Jltrabasite,  392 
Jltramarine,  503 
Umangite,  365 
Jnionite,  530 
Jraconite,  641 
Jralite,  490 
JRANATES,  623 
Jraninite,  623 
Jranite,  616 
Jranium  arsenate,  617 

carbonates,  454 

niobates,  590,  591 

phosphates,  616 

silicates,  581 

sulphate,  641 


INDEX   TO   SPECIES 


719 


Uranmica,  616 
Uranocircite,  617 
Uranniobite,  623 
Uranophane,  581 
Uranopilite,  641 
Uranosphaerite,  624 
Uranospathite,  617 
Uranospinite,  617 
Uranothallite,  454 
Uranotil,  581 
Uranpecherz,  v.  Uraninite 
Urao,  453 
Urbanite,  477 
Urpethite,  645 
Urusite,  639 
Ussingite,  470 
Utahite,  639 
Utahlite,  610 
Uvanite,  609 
Uvarovite,  Uwarowit,  508 


Vaalite,  487,  572 

Valencianite,  458 

Valentinite,  410 

Vanadinbleirerz,  v.  Vanadin- 
ite 

Vanadinite,  598 

Vanadium  silicate,  565 

Vanthoffite,  625 

Variegated  copper  ore,  374 

Variscite,  610 

Vashegyite,  614 

Vauquelinite,  630 

Vegasite,  638 

Velardenite,  518 

Velvet  copper  ore,  v.  Lett- 
somite 

Venasquite,  568 

Venus-hairstone,  427 

Verd-antique,  573 

VERMICULITES,  572 

Vermilion,  v.  Cinnabar 

Vernadskite,  638. 

Vesuvianite,  51i> 

Veszelyite,  612 

Victorite,  472 

Vilateite,  610 

Villamaninite,  379 

Villiaumite,  396 

Viluite,  519 

Violan,  476 

Viridine,  525 

Vitreous  copper,  v.  Chalcocite 
silver,  v.  Argentite 

Vitriol,  Blue,  636 

Vitriolbleierz,  v.  Anglesite 

Vivianite,  608 

Voelckerite,  596 

Voglianite,  641 

Voglite,  454 

Volborthite,  612 

Voltaite,  639 


Voltzite,  Voltzine,  383 
Vonsenite,  620 . 
Vorobyevite,  495 
Vrbaite,  386 
Vredenburgite,  418 
Vulpinite,  629 

W 

Wad,  436 
Wagnerite,  600 
Walkerite,  483 
Walpurgite,  617 
Waluewite,  567 
Wapplerite,  611 
Wardite,  614 
Waringtonite,  632 
Warrenite,  387 
Warwickite,  621 
Washingtonite,  418 
Wassersapphir,  v.  lolite 
Wavellite,  612 
Webnerite,  385 
Websterite,  639 
Wehrlite,  360 
Weibullite,  386 
Weibyeite,  449 
Weinbergerite,  494 
Weissbleierz,  v.  Cerussite 
Weissgiiltigerz,  v.  Freibergite 
Wellsite,  549 
Wernerite,  516 
Wheel  ore,  388 
Whewellite,  644 
White  antimony,  409 
White  arsenic,  409 

garnet,  v.  Leucite 

iron  pyrites,  380 

lead  ore,  448 
Whitneyite,  362 
Wiikite,  591 
Wilkeite,  597 
Willemite,  513 
Williamsite,  575 
Willyamite,  379 
Wilsonite,  562 
Wiltshireite,  386 
Wiluite,  507,  520 
Winchite,  489 
Wiserine,  428 
Wismuth,  v.  Bismuth 
Wismuthantimonnickel- 

glanz,  v.  Kallilite 
Wismuthblende,  v.  Eulytite 
Wismuthglanz,  v.  Bismuthin- 

ite 

Wismuthspath,  v.  Bismutite 
Withamite,  532     . 
Witherite,  447 
Wittichenite,  388 
Wocheinite,  434 
Wohlerite,  484 
Wolfachite,  382 
Wolframite,  641 
Wolfsbergite,  386 


Wolftonite,  435 

Wollastonite,  482 

Wolnyn,  626 

Wood,  Fossil,  Petrified,  406 

Wood  copper,  603 

Wood  opal,  409 

Wood  tin,  426 

Worthite,  526 

Wulfenite,  643 

Wiirfelerz,  v.  Pharmacosider- 

ite 
Wurtzite,  371 


Xalostocite,  509 
Xantharsenite,  601 
Xanthoconite,  393 
Xanthophyllite,  567 
Xanthosiderite,  433 
Xanthoxenite,  614 
Xenolite,  526 
Xenotime,  592 


Yellow  copper  ore,  374 

lead  ore,  643 
Yenite,  538 
Yttergranat,  508 
Yttrialite,  529 
Yttrium  carbonate,  454 
Yttrium  niobates,  588,  etc. 

phosphates,  592,  601 

silicates,  529 
Yttrocerite,  402 
Yttrocolumbite,  v.  Yttrotan- 

talite,  590 
Yttrocrasite,  586 
Yttrofluorite,  399 
Yttrogummite,  624 
Yttrotantalite,  590 
Yukonite,  615 


Zamboninite,  582 
Zaratite,  453 
ZEOLITES,  547 
Zepharovichite,  610 
Zeunerite,  616 
Zeigelerz,  v.  Tile  ore 
Zeophyllite,  546 
Zeyringite,  446 
Zietrisikite,  645 
Zinc,  349 

Red  Oxide  of,  411 
Zinc  aluminate,  420 

arsenates,  604,  609 

carbonates,  445 

oxide,  411,  420 

oxysulphide,  383 

phosphate,  607 

silicates,  513,  539,  540 


720 

Zinc,  sulphates,  630,  635 
sulphides,  367,  371 
vanadate,  604 

Zinc  blende,  367 

Zinc  ore,  Red,  441 

Zincorodochrosite,  445 

Zincaluminite,  640 

Zincite,  411 

Zinckenite,  385 

Zincocalcite,  441 


INDEX   TO   SPECIES 

Zinkblende,  v.  Sphalerite 
Zinkenite,  385. 
Zinkosite,  630 
Zinkspath,  v.  Smithsonite 
Zinnerz,  425 
Zinnkies,  v,  Stannite 
Zinnober,  v.  Cinnabar 
Zinnstein,  425 
Zinnwaldite,  563 
Zippeite,  641 


Zircon,  520 
Zirconium  dioxide,  428 

silicate,  520,  484 
Zirkelite,  428 
Zoisite,  530 
Zorgite,  365 
Zunyite,  505 
Zurlite,  518 
Zwieselite,  500 


c 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

^ARTH  SCIENC 

This  book  is  due  on  the  last 

on  the  date  to  which  renewed. 
Renewed  books  are  subject  to  immediate  recall. 


LD  21-50m-6,'60 
(B1321slO)476 


General  Library 

University  of  California 

Berkeley 


